1	# HTTP/1.1 and HTTP/2 client, with an HTTP/1.1 server. Source: https://github.com/paymog/bend-kit/tree/main/http
2	import Base
3	# By hash: bend-kit-url@0.4.1.0, -encoding@0.3.0.0, -json@0.5.0.1, -bytes@0.3.0.0, -zlib@0.2.0.0.
4	import bend-kit-wire@0.4.2.0/wire.bend as Wire
5	import bend-kit-http2@0.1.2.0/http2.bend as H2
6	import bend-kit-http2@0.1.2.0/hpack.bend as Hpack
7	import bend-kit-bytes@0.3.1.0/bytes.bend as HBytes
8	import bend-kit-time@0.1.0.0/time.bend as Time
9	import bend-kit-int@0.2.0.0/int.bend as Int
10	import bend-kit-concurrency@0.1.0.0/concurrency.bend as Conc
11	import 0x1f2d80f53f971b16c6de6a65cb1918ae/url.bend as Url
12	import 0xcfc8be7b076f41f95c8e118383892d55/encoding.bend as Enc
13	import 0x584fc27920487ceab242392391418d7f/json.bend as Json
14	import 0x49814d83de8f70993a43e1002be29ecd/bytes.bend as Bytes
15	import bend-kit-dns@0.5.0.0/dns.bend as Dns
16	import 0xaca98ab7f724003ea421c18792cafe52/zlib.bend as Zlib
17	
18	# HTTP/1.1 codec and client (RFC 9112) for http:// and https:// (OpenSSL 3 at run time).
19	# parse: start-line → field lines → blank → body length (§6.3); chunked (§7.1).
20	# Bodies are Bytes. The String parsers below are the spec: one Char per octet.
21	# fetch reads until frame() says the response is whole. It returns Result, not Maybe.
22	# Build with -o for big bodies: the `bend file.bend` runner overflows on ~30 KB strings; native binaries do not.
23	#   import bend-kit-http@0.22.0.0/http.bend as Http
24	
25	type Req is Type:
26	  Req{method: String, path: String, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes}
27	
28	type Res is Type:
29	  Res{status: U32, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes}
30	
31	# The body type and its conversions, so a caller needs no bytes import.
32	def Body() -> Type:
33	  Bytes.Bytes
34	
35	# A byte string (one Char per octet) to a body, and back.
36	def from_string(+s: String) -> Bytes.Bytes:
37	  Bytes.from_string(s)
38	
39	def to_string(b: Bytes.Bytes) -> String:
40	  Bytes.to_string(b)
41	
42	def length(b: Bytes.Bytes) -> Bytes.Bytes & U32:
43	  Bytes.length(b)
44	
45	# Why fetch failed. Wire errors keep the errno and the text the effect already had.
46	# ponytail: 60 and 110 are ETIMEDOUT on macOS and Linux. Windows is out of scope.
47	type Err is Data:
48	  ErrUrl{}
49	  ErrDns{}
50	  ErrConnect{code: U32, why: String}
51	  ErrTls{code: U32, why: String}
52	  ErrRead{code: U32, why: String}
53	  ErrWrite{code: U32, why: String}
54	  ErrTimeout{}
55	  ErrRedirect{}
56	  ErrBad{}
57	
58	def err.late(+code: U32) -> Bool:
59	  Bool.or(U32.is_eq(code, 60), U32.is_eq(code, 110))
60	
61	def err.pick(e: Err, late: Bool) -> Err:
62	  match late:
63	    case True{}:
64	      ErrTimeout{}
65	    case False{}:
66	      e
67	
68	def err.or_late(code: U32, e: Err) -> Err:
69	  err.pick(e, err.late(code))
70	
71	type Fields is Data:
72	  FieldsBad{}
73	  FieldsOk{m: Map<&2, List<&2, String>>}
74	
75	# One list per field name, in arrival order. header() is the first value.
76	# Set-Cookie is never joined. Encode writes one line per value.
77	def empty() -> Map<&2, List<&2, String>>:
78	  Map.new(&2, List<&2, String>)
79	
80	def fields.of(r: Map<&2, List<&2, String>> & List<&2, String>) -> List<&2, String>:
81	  (h, xs) = r
82	  xs
83	
84	def fields(+h: Map<&2, List<&2, String>>, k: String) -> List<&2, String>:
85	  fields.of(Map.get(List<&2, String>, Nil{}, h, k))
86	
87	def header.first(xs: List<&2, String>) -> String:
88	  match xs:
89	    case Nil{}:
90	      ""
91	    case Con{v, t}:
92	      v
93	
94	def header(+h: Map<&2, List<&2, String>>, k: String) -> String:
95	  header.first(fields(h, k))
96	
97	def field.last(xs: List<&2, String>) -> String:
98	  match xs:
99	    case Nil{}:
100	      ""
101	    case Con{v, Nil{}}:
102	      v
103	    case Con{v, t}:
104	      field.last(t)
105	
106	# Transfer-Encoding is a list; chunked, when present, is the last coding.
107	def header.last(+h: Map<&2, List<&2, String>>, k: String) -> String:
108	  field.last(fields(h, k))
109	
110	def snoc(xs: List<&2, String>, v: String) -> List<&2, String>:
111	  match xs:
112	    case Nil{}:
113	      [v]
114	    case Con{h, t}:
115	      Con{h, snoc(t, v)}
116	
117	def set(m: Map<&2, List<&2, String>>, k: String, v: String) -> Map<&2, List<&2, String>>:
118	  Map.set(&2, List<&2, String>, m, k, [v])
119	
120	def add(+m: Map<&2, List<&2, String>>, +k: String, v: String) -> Map<&2, List<&2, String>>:
121	  Map.set(&2, List<&2, String>, m, k, snoc(fields(m, k), v))
122	
123	def sanitize.cons(ch: Char, rest: String, drop: Bool) -> String:
124	  match drop:
125	    case True{}:
126	      rest
127	    case False{}:
128	      SCon{ch, rest}
129	
130	def sanitize(s: String) -> String:
131	  match s:
132	    case SNil{}:
133	      SNil{}
134	    case SCon{Chr{+c}, t}:
135	      sanitize.cons(Chr{c}, sanitize(t), Bool.or(U32.is_eq(c, 13), U32.is_eq(c, 10)))
136	
137	def drop_cr.last.if(cr: Bool, c: U32) -> String:
138	  match cr:
139	    case True{}:
140	      SNil{}
141	    case False{}:
142	      SCon{Chr{c}, SNil{}}
143	
144	def drop_cr.last(+c: U32) -> String:
145	  drop_cr.last.if(U32.is_eq(c, 13), c)
146	
147	# prev is the char before s; it is kept unless it is a final CR.
148	def drop_cr.go(s: String, prev: U32) -> String:
149	  match s:
150	    case SNil{}:
151	      drop_cr.last(prev)
152	    case SCon{Chr{c}, t}:
153	      SCon{Chr{prev}, drop_cr.go(t, c)}
154	
155	def drop_cr(s: String) -> String:
156	  match s:
157	    case SNil{}:
158	      SNil{}
159	    case SCon{Chr{c}, t}:
160	      drop_cr.go(t, c)
161	
162	# w holds the last four octets; a char past 255 clears it.
163	def blank_end.go(s: String, w: U32) -> Bool:
164	  match s:
165	    case SNil{}:
166	      U32.is_eq(w, 218762506)
167	    case SCon{Chr{+c}, t}:
168	      blank_end.go(t, Bool.pick(U32, U32.is_lt(c, 256), (w * 256 + c : U32), 0))
169	
170	# String.ends_with(s, "\r\n\r\n") in one pass, with no reversed copy.
171	def blank_end(s: String) -> Bool:
172	  blank_end.go(s, 0)
173	
174	def trim_end.cons(h: Char, r: String, space: Bool) -> String:
175	  match r:
176	    case SNil{}:
177	      match space:
178	        case True{}:
179	          SNil{}
180	        case False{}:
181	          SCon{h, SNil{}}
182	    case SCon{a, t}:
183	      SCon{h, SCon{a, t}}
184	
185	# String.trim_end without the two reversed copies.
186	def trim_end(s: String) -> String:
187	  match s:
188	    case SNil{}:
189	      SNil{}
190	    case SCon{+h, t}:
191	      trim_end.cons(h, trim_end(t), Char.is_space(h))
192	
193	def trim(s: String) -> String:
194	  trim_end(String.trim_start(s))
195	
196	# Bool.pick evaluates both arms; a split that recursed inside it would reverse acc at every byte.
197	def take.cut(acc: String, rest: String) -> String & String:
198	  (String.reverse(String.drop(acc, 1n)), rest)
199	
200	# hit: the last char pushed onto acc was the stop char.
201	def take_sp.go(s: String, acc: String, hit: Bool) -> String & String:
202	  match s:
203	    case SNil{}:
204	      match hit:
205	        case True{}:
206	          take.cut(acc, SNil{})
207	        case False{}:
208	          (String.reverse(acc), SNil{})
209	    case SCon{Chr{+c}, t}:
210	      match hit:
211	        case True{}:
212	          take.cut(acc, SCon{Chr{c}, t})
213	        case False{}:
214	          take_sp.go(t, SCon{Chr{c}, acc}, U32.is_eq(c, 32))
215	
216	def take_sp(s: String) -> String & String:
217	  take_sp.go(s, SNil{}, False{})
218	
219	def start_line.ver(m: String, pv: String & String) -> String & String & String:
220	  (p, v) = pv
221	  (m, p, drop_cr(v))
222	
223	def start_line.rest(mr: String & String) -> String & String & String:
224	  (m, r) = mr
225	  start_line.ver(m, take_sp(r))
226	
227	def start_line(s: String) -> String & String & String:
228	  start_line.rest(take_sp(s))
229	
230	def split_at_blank.go(s: String, e: Bool, w: U32, acc: String) -> String & String:
231	  match s:
232	    case SNil{}:
233	      (String.reverse(acc), SNil{})
234	    case SCon{Chr{+a}, t}:
235	      match e:
236	        case True{}:
237	          (String.reverse(acc), SCon{Chr{a}, t})
238	        case False{}:
239	          +w2 = (w * 256 + a : U32)
240	          split_at_blank.go(t, U32.is_eq(w2, 218762506), w2, SCon{Chr{a}, acc})
241	
242	# split_at_blank, plus whether the head ends in the blank line.
243	def split_at_blank.flag.go(+raw: String, s: String, off: Nat, w: U32, e: Bool) -> String & String & Bool:
244	  match s:
245	    case SNil{}:
246	      (String.take(raw, off), SNil{}, e)
247	    case SCon{Chr{+a}, t}:
248	      match e:
249	        case True{}:
250	          (String.take(raw, off), SCon{Chr{a}, t}, True{})
251	        case False{}:
252	          +w2 = (w * 256 + a : U32)
253	          +off1 = (1n + off : Nat)
254	          split_at_blank.flag.go(raw, t, off1, w2, U32.is_eq(w2, 218762506))
255	
256	def split_at_blank.pair(r: String & String & Bool) -> String & String:
257	  (head, rest, whole) = r
258	  (head, rest)
259	
260	def split_at_blank(+s: String) -> String & String:
261	  split_at_blank.pair(split_at_blank.flag.go(s, s, 0n, 0, False{}))
262	
263	def split_colon.go(s: String, acc: String, hit: Bool) -> String & String:
264	  match s:
265	    case SNil{}:
266	      match hit:
267	        case True{}:
268	          take.cut(acc, SNil{})
269	        case False{}:
270	          (String.reverse(acc), SNil{})
271	    case SCon{Chr{+c}, t}:
272	      match hit:
273	        case True{}:
274	          take.cut(acc, SCon{Chr{c}, t})
275	        case False{}:
276	          split_colon.go(t, SCon{Char.to_lower(Chr{c}), acc}, U32.is_eq(c, 58))
277	
278	def split_colon(+s: String) -> String & String:
279	  split_colon.go(s, SNil{}, False{})
280	
281	def has_header.of(r: Map<&2, List<&2, String>> & Bool) -> Bool:
282	  (h, b) = r
283	  b
284	
285	def has_header(+h: Map<&2, List<&2, String>>, k: String) -> Bool:
286	  has_header.of(Map.has(&2, List<&2, String>, h, k))
287	
288	def folded(+line: String) -> Bool:
289	  Bool.or(String.starts_with(line, " "), String.starts_with(line, "\t"))
290	
291	def tracked(+k: String) -> Bool:
292	  Bool.or(String.eq(k, "host"), String.eq(k, "content-length"))
293	
294	def fields_put.dup(m: Map<&2, List<&2, String>>, k: String, v: String, bad: Bool) -> Fields:
295	  match bad:
296	    case True{}:
297	      FieldsBad{}
298	    case False{}:
299	      FieldsOk{add(m, k, v)}
300	
301	def fields_put.tracked(+m: Map<&2, List<&2, String>>, +k: String, v: String, t: Bool) -> Fields:
302	  match t:
303	    case True{}:
304	      fields_put.dup(m, k, v, has_header(m, k))
305	    case False{}:
306	      FieldsOk{add(m, k, v)}
307	
308	def fields_put.key(+m: Map<&2, List<&2, String>>, +k: String, v: String) -> Fields:
309	  fields_put.tracked(m, k, v, tracked(k))
310	
311	def fields_put.kv(m: Map<&2, List<&2, String>>, kv: String & String) -> Fields:
312	  (k, v) = kv
313	  fields_put.key(m, k, trim(v))
314	
315	def fields_put.fold(m: Map<&2, List<&2, String>>, line: String, fold: Bool) -> Fields:
316	  match fold:
317	    case True{}:
318	      FieldsBad{}
319	    case False{}:
320	      fields_put.kv(m, split_colon(line))
321	
322	def fields_put.empty(m: Map<&2, List<&2, String>>, +line: String, e: Bool) -> Fields:
323	  match e:
324	    case True{}:
325	      FieldsOk{m}
326	    case False{}:
327	      fields_put.fold(m, line, folded(line))
328	
329	def fields_put.ok(m: Map<&2, List<&2, String>>, +line: String) -> Fields:
330	  fields_put.empty(m, line, String.is_empty(line))
331	
332	def fields_put(acc: Fields, line: String) -> Fields:
333	  match acc:
334	    case FieldsBad{}:
335	      FieldsBad{}
336	    case FieldsOk{m}:
337	      fields_put.ok(m, line)
338	
339	def parse.headers.done(acc: Fields) -> Maybe<&2, Map<&2, List<&2, String>>>:
340	  match acc:
341	    case FieldsBad{}:
342	      None{}
343	    case FieldsOk{m}:
344	      Some{m}
345	
346	
347	def parse.headers.scan.line(acc: String, fields: Fields) -> Fields:
348	  match acc:
349	    case SCon{Chr{13}, t}:
350	      fields_put(fields, String.reverse(t))
351	    case other:
352	      fields_put(fields, String.reverse(other))
353	
354	def parse.headers.scan(s: String, acc: String, fields: Fields) -> Fields:
355	  match s:
356	    case SNil{}:
357	      parse.headers.scan.line(acc, fields)
358	    case SCon{Chr{10}, t}:
359	      parse.headers.scan(t, SNil{}, parse.headers.scan.line(acc, fields))
360	    case SCon{c, t}:
361	      parse.headers.scan(t, SCon{c, acc}, fields)
362	
363	def parse.headers.raw(s: String) -> Maybe<&2, Map<&2, List<&2, String>>>:
364	  parse.headers.done(parse.headers.scan(s, SNil{}, FieldsOk{empty()}))
365	
366	def parse.first(s: String, acc: String) -> String & String:
367	  match s:
368	    case SNil{}:
369	      (String.reverse(acc), SNil{})
370	    case SCon{Chr{10}, t}:
371	      (String.reverse(acc), t)
372	    case SCon{c, t}:
373	      parse.first(t, SCon{c, acc})
374	
375	def parse_u32.digit(+c: U32) -> Bool:
376	  Bool.and(U32.is_le(48, c), U32.is_le(c, 57))
377	
378	def parse_u32.add(acc: U32, c: U32) -> U32:
379	  (acc * 10 + (c - 48 : U32) : U32)
380	
381	def parse_u32.done(acc: U32, bad: Bool) -> Maybe<&2, U32>:
382	  match bad:
383	    case True{}:
384	      None{}
385	    case False{}:
386	      Some{acc}
387	
388	def parse_u32.go(s: String, acc: U32, bad: Bool) -> Maybe<&2, U32>:
389	  match s:
390	    case SNil{}:
391	      parse_u32.done(acc, bad)
392	    case SCon{Chr{+c}, t}:
393	      parse_u32.go(t, parse_u32.add(acc, c), Bool.or(bad, Bool.not(parse_u32.digit(c))))
394	
395	def parse_u32(s: String) -> Maybe<&2, U32>:
396	  match s:
397	    case SNil{}:
398	      None{}
399	    case SCon{Chr{+c}, t}:
400	      parse_u32.go(t, parse_u32.add(0, c), Bool.not(parse_u32.digit(c)))
401	
402	# More: a valid prefix. Bad: cannot become a body. Body: a whole chunked body.
403	type Hold is Data:
404	  HoldMore{}
405	  HoldBad{}
406	  HoldBody{b: String}
407	  HoldUntil{b: String}
408	
409	def is_hex(+c: U32) -> Bool:
410	  Bool.or(parse_u32.digit(c), Bool.or(Bool.and(U32.is_le(97, c), U32.is_le(c, 102)), Bool.and(U32.is_le(65, c), U32.is_le(c, 70))))
411	
412	def hexv(+c: U32) -> U32:
413	  Bool.pick(U32, parse_u32.digit(c), (c - 48 : U32), Bool.pick(U32, U32.is_le(c, 70), (c - 55 : U32), (c - 87 : U32)))
414	
415	# A chunked body decoder that reads each byte once, so a body fed in pieces
416	# costs O(bytes) in total. Tr{j}: j bytes of the closing CRLF CRLF matched.
417	type Dc is Data:
418	  DcSize{acc: U32, seen: Bool}
419	  DcExt{n: U32}
420	  DcSizeLf{n: U32}
421	  DcData{k: U32}
422	  DcDataCr{}
423	  DcDataLf{}
424	  DcTr{j: U32}
425	  DcDone{}
426	  DcBad{}
427	
428	# st: where the decoder is. racc: the body so far, reversed. rest: bytes after a Done body.
429	type Dco is Data:
430	  Dco{st: Dc, racc: String, rest: String}
431	
432	def dc.start() -> Dc:
433	  DcSize{0, False{}}
434	
435	def dc.size.semi(+n: U32, semi: Bool) -> Dc:
436	  match semi:
437	    case True{}:
438	      DcExt{n}
439	    case False{}:
440	      DcBad{}
441	
442	def dc.size.cr(+n: U32, +c: U32, cr: Bool) -> Dc:
443	  match cr:
444	    case True{}:
445	      DcSizeLf{n}
446	    case False{}:
447	      dc.size.semi(n, U32.is_eq(c, 59))
448	
449	def dc.size.end(+n: U32, +c: U32, seen: Bool) -> Dc:
450	  match seen:
451	    case False{}:
452	      DcBad{}
453	    case True{}:
454	      dc.size.cr(n, c, U32.is_eq(c, 13))
455	
456	# A size that would overflow 32 bits ends the digits, and size.end then refuses it.
457	def dc.size(+acc: U32, seen: Bool, +c: U32, digit: Bool) -> Dc:
458	  match digit:
459	    case True{}:
460	      DcSize{(acc * 16 + hexv(c) : U32), True{}}
461	    case False{}:
462	      dc.size.end(acc, c, seen)
463	
464	# RFC 9112 §7.1.1: recipients ignore unknown chunk extensions; a bare LF is not CRLF.
465	def dc.ext.lf(+n: U32, lf: Bool) -> Dc:
466	  match lf:
467	    case True{}:
468	      DcBad{}
469	    case False{}:
470	      DcExt{n}
471	
472	def dc.ext(+n: U32, +c: U32, cr: Bool) -> Dc:
473	  match cr:
474	    case True{}:
475	      DcSizeLf{n}
476	    case False{}:
477	      dc.ext.lf(n, U32.is_eq(c, 10))
478	
479	def dc.sized(+n: U32, zero: Bool) -> Dc:
480	  match zero:
481	    case True{}:
482	      DcTr{2}
483	    case False{}:
484	      DcData{n}
485	
486	def dc.size.lf(+n: U32, lf: Bool) -> Dc:
487	  match lf:
488	    case True{}:
489	      dc.sized(n, U32.is_eq(n, 0))
490	    case False{}:
491	      DcBad{}
492	
493	# k data bytes are left and m of them were just read.
494	def dc.data(+k: U32, +m: U32) -> Dc:
495	  Bool.pick(Dc, U32.is_le(k, m), DcDataCr{}, DcData{(k - m : U32)})
496	
497	def dc.pick(ok: Bool, next: Dc) -> Dc:
498	  match ok:
499	    case True{}:
500	      next
501	    case False{}:
502	      DcBad{}
503	
504	# ponytail: trailer fields are dropped unparsed (§7.1.2 allows discarding)
505	def dc.tr.hit(+j: U32) -> Dc:
506	  Bool.pick(Dc, U32.is_eq(j, 3), DcDone{}, DcTr{(j + 1 : U32)})
507	
508	def dc.tr(+j: U32, +c: U32, hit: Bool) -> Dc:
509	  match hit:
510	    case True{}:
511	      dc.tr.hit(j)
512	    case False{}:
513	      Bool.pick(Dc, U32.is_eq(c, 13), DcTr{1}, DcTr{0})
514	
515	def dc.tr.want(+j: U32) -> U32:
516	  Bool.pick(U32, U32.is_eq(U32.mod(j, 2), 0), 13, 10)
517	
518	def dc.byte(h: Char) -> U32:
519	  Chr{c} = h
520	  c
521	
522	# One byte c. Done and Bad never look at it, and a data byte is not inspected.
523	def dc.step(st: Dc, +c: U32) -> Dc:
524	  match st:
525	    case DcBad{}:
526	      DcBad{}
527	    case DcSize{+acc, seen}:
528	      dc.size(acc, seen, c, Bool.and(is_hex(c), U32.is_le(acc, 268435455)))
529	    case DcExt{+n}:
530	      dc.ext(n, c, U32.is_eq(c, 13))
531	    case DcSizeLf{+n}:
532	      dc.size.lf(n, U32.is_eq(c, 10))
533	    case DcDataCr{}:
534	      dc.pick(U32.is_eq(c, 13), DcDataLf{})
535	    case DcDataLf{}:
536	      dc.pick(U32.is_eq(c, 10), dc.start())
537	    case DcTr{+j}:
538	      dc.tr(j, c, U32.is_eq(c, dc.tr.want(j)))
539	    case DcData{+k}:
540	      dc.data(k, 1)
541	    case DcDone{}:
542	      DcDone{}
543	
544	def dc.live(st: Dc) -> Bool:
545	  match st:
546	    case DcDone{}:
547	      False{}
548	    case DcBad{}:
549	      False{}
550	    case DcSize{a, b}:
551	      True{}
552	    case DcExt{n}:
553	      True{}
554	    case DcSizeLf{n}:
555	      True{}
556	    case DcData{k}:
557	      True{}
558	    case DcDataCr{}:
559	      True{}
560	    case DcDataLf{}:
561	      True{}
562	    case DcTr{j}:
563	      True{}
564	
565	def dc.feed(s: String, st: Dc, racc: String) -> Dco:
566	  match s:
567	    case SNil{}:
568	      Dco{st, racc, ""}
569	    case SCon{h, t}:
570	      match st:
571	        case DcBad{}:
572	          Dco{DcBad{}, racc, ""}
573	        case DcDone{}:
574	          Dco{DcDone{}, racc, SCon{h, t}}
575	        case DcData{+k}:
576	          dc.feed(t, dc.data(k, 1), SCon{h, racc})
577	        case DcSize{+acc, seen}:
578	          dc.feed(t, dc.step(DcSize{acc, seen}, dc.byte(h)), racc)
579	        case DcExt{+n}:
580	          dc.feed(t, dc.step(DcExt{n}, dc.byte(h)), racc)
581	        case DcSizeLf{+n}:
582	          dc.feed(t, dc.step(DcSizeLf{n}, dc.byte(h)), racc)
583	        case DcDataCr{}:
584	          dc.feed(t, dc.step(DcDataCr{}, dc.byte(h)), racc)
585	        case DcDataLf{}:
586	          dc.feed(t, dc.step(DcDataLf{}, dc.byte(h)), racc)
587	        case DcTr{+j}:
588	          dc.feed(t, dc.step(DcTr{j}, dc.byte(h)), racc)
589	
590	def chunk.hold(o: Dco) -> Hold:
591	  Dco{st, racc, rest} = o
592	  match st:
593	    case DcDone{}:
594	      HoldBody{String.reverse(racc)}
595	    case DcBad{}:
596	      HoldBad{}
597	    case DcSize{a, b}:
598	      HoldMore{}
599	    case DcExt{n}:
600	      HoldMore{}
601	    case DcSizeLf{n}:
602	      HoldMore{}
603	    case DcData{k}:
604	      HoldMore{}
605	    case DcDataCr{}:
606	      HoldMore{}
607	    case DcDataLf{}:
608	      HoldMore{}
609	    case DcTr{j}:
610	      HoldMore{}
611	
612	def chunk.live(s: String) -> Hold:
613	  chunk.hold(dc.feed(s, dc.start(), ""))
614	
615	def chunk.rest(o: Dco) -> Maybe<&2, String>:
616	  Dco{st, racc, rest} = o
617	  match st:
618	    case DcDone{}:
619	      Some{rest}
620	    case DcBad{}:
621	      None{}
622	    case DcSize{a, b}:
623	      None{}
624	    case DcExt{n}:
625	      None{}
626	    case DcSizeLf{n}:
627	      None{}
628	    case DcData{k}:
629	      None{}
630	    case DcDataCr{}:
631	      None{}
632	    case DcDataLf{}:
633	      None{}
634	    case DcTr{j}:
635	      None{}
636	
637	def chunk.suffix(s: String) -> Maybe<&2, String>:
638	  chunk.rest(dc.feed(s, dc.start(), ""))
639	
640	def chunk.decode.hold(h: Hold) -> Maybe<&2, String>:
641	  match h:
642	    case HoldMore{}:
643	      None{}
644	    case HoldBad{}:
645	      None{}
646	    case HoldUntil{b}:
647	      None{}
648	    case HoldBody{b}:
649	      Some{b}
650	
651	def chunk.decode(s: String) -> Maybe<&2, String>:
652	  chunk.decode.hold(chunk.live(s))
653	
654	def bytes.snd(r: Bytes.Bytes & Bytes.Bytes) -> Bytes.Bytes:
655	  (a, b) = r
656	  b
657	
658	def found.at(+from: U32, m: Maybe<&2, U32>) -> Maybe<&2, U32>:
659	  match m:
660	    case None{}:
661	      None{}
662	    case Some{+j}:
663	      Some{(from + j : U32)}
664	
665	# A chunked body decoded from piece[i..]: a data run is sliced whole, and every other byte steps dc.
666	type Cs is Type:
667	  Cs{piece: Bytes.Bytes, i: U32, st: Dc, parts: List<&1, Bytes.Bytes>}
668	
669	# st: where the decoder stopped. parts: the data so far, newest first. rest: the bytes after a Done body.
670	type Ck is Type:
671	  Ck{st: Dc, parts: List<&1, Bytes.Bytes>, rest: Bytes.Bytes}
672	
673	def ck.next(+len: U32, +i: U32, +st: Dc, piece: Bytes.Bytes, parts: List<&1, Bytes.Bytes>) -> Bool & Cs:
674	  (Bool.and(U32.is_lt(i, len), dc.live(st)), Cs{piece, i, st, parts})
675	
676	def ck.data(+len: U32, +i: U32, +k: U32, +m: U32, parts: List<&1, Bytes.Bytes>, r: Bytes.Bytes & Bytes.Bytes) -> Bool & Cs:
677	  (piece, run) = r
678	  ck.next(len, (i + m : U32), dc.data(k, m), piece, Con{run, parts})
679	
680	def ck.byte(+len: U32, +i: U32, st: Dc, parts: List<&1, Bytes.Bytes>, r: Bytes.Bytes & Maybe<&2, U32>) -> Bool & Cs:
681	  (piece, m) = r
682	  match m:
683	    case None{}:
684	      ck.next(len, i, DcBad{}, piece, parts)
685	    case Some{+c}:
686	      ck.next(len, (i + 1 : U32), dc.step(st, c), piece, parts)
687	
688	def ck.step(+len: U32, cs: Cs) -> Bool & Cs:
689	  Cs{piece, +i, st, parts} = cs
690	  match st:
691	    case DcData{+k}:
692	      +m = U32.min(k, (len - i : U32))
693	      ck.data(len, i, k, m, parts, Bytes.slice(piece, i, m))
694	    case DcDone{}:
695	      (False{}, Cs{piece, i, DcDone{}, parts})
696	    case DcBad{}:
697	      (False{}, Cs{piece, i, DcBad{}, parts})
698	    case DcSize{+acc, seen}:
699	      ck.byte(len, i, DcSize{acc, seen}, parts, Bytes.get(piece, i))
700	    case DcExt{+n}:
701	      ck.byte(len, i, DcExt{n}, parts, Bytes.get(piece, i))
702	    case DcSizeLf{+n}:
703	      ck.byte(len, i, DcSizeLf{n}, parts, Bytes.get(piece, i))
704	    case DcDataCr{}:
705	      ck.byte(len, i, DcDataCr{}, parts, Bytes.get(piece, i))
706	    case DcDataLf{}:
707	      ck.byte(len, i, DcDataLf{}, parts, Bytes.get(piece, i))
708	    case DcTr{+j}:
709	      ck.byte(len, i, DcTr{j}, parts, Bytes.get(piece, i))
710	
711	def ck.rest(st: Dc, parts: List<&1, Bytes.Bytes>, r: Bytes.Bytes & Bytes.Bytes) -> Ck:
712	  (piece, rest) = r
713	  Ck{st, parts, rest}
714	
715	def ck.end(+len: U32, cs: Cs) -> Ck:
716	  Cs{piece, +i, st, parts} = cs
717	  ck.rest(st, parts, Bytes.slice(piece, i, (len - i : U32)))
718	
719	# Each step reads at least one byte, so len steps are enough.
720	def ck.feed(f: Nat, +len: U32, r: Bool & Cs) -> Ck:
721	  match f:
722	    case 0n:
723	      (go, cs) = r
724	      ck.end(len, cs)
725	    case 1n+p:
726	      (go, cs) = r
727	      match go:
728	        case False{}:
729	          ck.end(len, cs)
730	        case True{}:
731	          ck.feed(p, len, ck.step(len, cs))
732	
733	def ck(piece: Bytes.Bytes, +st: Dc, parts: List<&1, Bytes.Bytes>) -> Ck:
734	  Bytes.Bytes{+len, buf} = piece
735	  ck.feed(U32.to_nat(len), len, ck.next(len, 0, st, Bytes.Bytes{len, buf}, parts))
736	
737	def parse.res.cl.have(+rest: String, +k: Nat, short: Bool) -> Hold:
738	  match short:
739	    case True{}:
740	      HoldMore{}
741	    case False{}:
742	      HoldBody{String.take(rest, k)}
743	
744	def parse.res.cl.k(+rest: String, +k: Nat) -> Hold:
745	  parse.res.cl.have(rest, k, Nat.is_lt(String.length(rest), k))
746	
747	def parse.res.cl.n(rest: String, n: Maybe<&2, U32>) -> Hold:
748	  match n:
749	    case None{}:
750	      HoldBad{}
751	    case Some{k}:
752	      parse.res.cl.k(rest, U32.to_nat(k))
753	
754	def parse.body.cl(+h: Map<&2, List<&2, String>>, rest: String, hascl: Bool) -> Hold:
755	  match hascl:
756	    case False{}:
757	      HoldBody{""}
758	    case True{}:
759	      parse.res.cl.n(rest, parse_u32(header(h, "content-length")))
760	
761	# RFC 9112 §6.3 (4): a request coding other than chunked cannot be framed.
762	def parse.body.chunked.eq(rest: String, ok: Bool) -> Hold:
763	  match ok:
764	    case False{}:
765	      HoldBad{}
766	    case True{}:
767	      chunk.live(rest)
768	
769	def parse.body.chunked.val(te: String, rest: String) -> Hold:
770	  parse.body.chunked.eq(rest, String.eq(String.to_lower(te), "chunked"))
771	
772	def parse.body.chunked(+h: Map<&2, List<&2, String>>, rest: String, hascl: Bool) -> Hold:
773	  match hascl:
774	    case True{}:
775	      HoldBad{}
776	    case False{}:
777	      parse.body.chunked.val(header.last(h, "transfer-encoding"), rest)
778	
779	def parse.body.te(+h: Map<&2, List<&2, String>>, rest: String, te: Bool) -> Hold:
780	  match te:
781	    case True{}:
782	      parse.body.chunked(h, rest, has_header(h, "content-length"))
783	    case False{}:
784	      parse.body.cl(h, rest, has_header(h, "content-length"))
785	
786	def parse.body(+h: Map<&2, List<&2, String>>, rest: String) -> Hold:
787	  parse.body.te(h, rest, has_header(h, "transfer-encoding"))
788	
789	# Bad: never a request. More: the head is not whole; read on. Head: the head is whole
790	# and valid, and the body is still coming (req.body is empty). Req: a whole request.
791	type Got is Type:
792	  GotBad{}
793	  GotMore{}
794	  GotHead{req: Req}
795	  GotReq{req: Req}
796	
797	def parse.finish(method: String, path: String, h: Map<&2, List<&2, String>>, body: Hold) -> Got:
798	  match body:
799	    case HoldBad{}:
800	      GotBad{}
801	    case HoldMore{}:
802	      GotHead{Req{method, path, h, Bytes.new(0)}}
803	    case HoldUntil{b}:
804	      GotBad{}
805	    case HoldBody{b}:
806	      GotReq{Req{method, path, h, Bytes.from_string(b)}}
807	
808	def parse.host(method: String, path: String, +h: Map<&2, List<&2, String>>, rest: String, has: Bool) -> Got:
809	  match has:
810	    case False{}:
811	      GotBad{}
812	    case True{}:
813	      parse.finish(method, path, h, parse.body(h, rest))
814	
815	# RFC 9112 §3.2: only HTTP/1.1 requires Host.
816	def parse.fields(method: String, path: String, rest: String, v11: Bool, fs: Maybe<&2, Map<&2, List<&2, String>>>) -> Got:
817	  match fs:
818	    case None{}:
819	      GotBad{}
820	    case Some{+h}:
821	      parse.host(method, path, h, rest, Bool.or(Bool.not(v11), has_header(h, "host")))
822	
823	def target_ok(+p: String) -> Bool:
824	  Bool.or(String.starts_with(p, "/"), Bool.or(String.eq(p, "*"), String.starts_with(p, "http://")))
825	
826	def parse.target(method: String, +path: String, headers: String, rest: String, v11: Bool, ok: Bool) -> Got:
827	  match ok:
828	    case False{}:
829	      GotBad{}
830	    case True{}:
831	      parse.fields(method, path, rest, v11, parse.headers.raw(headers))
832	
833	def parse.ver(method: String, +path: String, +v: String, headers: String, rest: String, ok: Bool) -> Got:
834	  match ok:
835	    case False{}:
836	      GotBad{}
837	    case True{}:
838	      parse.target(method, path, headers, rest, String.eq(v, "HTTP/1.1"), target_ok(path))
839	
840	def parse.empty_method(method: String, path: String, +v: String, headers: String, rest: String, empty: Bool) -> Got:
841	  match empty:
842	    case True{}:
843	      GotBad{}
844	    case False{}:
845	      parse.ver(method, path, v, headers, rest, Bool.or(String.eq(v, "HTTP/1.1"), String.eq(v, "HTTP/1.0")))
846	
847	def parse.start3(mpv: String & String & String, headers: String, rest: String) -> Got:
848	  (+method, path, v) = mpv
849	  parse.empty_method(method, path, v, headers, rest, String.is_empty(method))
850	
851	def parse.lines(lr: String & String, rest: String) -> Got:
852	  (line, headers) = lr
853	  parse.start3(start_line(line), headers, rest)
854	
855	
856	def parse.head(+head: String, rest: String, whole: Bool) -> Got:
857	  match whole:
858	    case False{}:
859	      GotMore{}
860	    case True{}:
861	      parse.lines(parse.first(head, SNil{}), rest)
862	
863	def parse.of(hb: String & String & Bool) -> Got:
864	  (head, rest, whole) = hb
865	  parse.head(head, rest, whole)
866	
867	# serve reads until this is not GotMore.
868	def parse.got(+raw: String) -> Got:
869	  parse.of(split_at_blank.flag.go(raw, raw, 0n, 0, False{}))
870	
871	
872	def parse.req(g: Got) -> Maybe<&1, Req>:
873	  match g:
874	    case GotReq{req}:
875	      Some{req}
876	    case GotBad{}:
877	      None{}
878	    case GotMore{}:
879	      None{}
880	    case GotHead{req}:
881	      None{}
882	
883	def parse(raw: String) -> Maybe<&1, Req>:
884	  parse.req(parse.got(raw))
885	
886	def parse.res.cl(+h: Map<&2, List<&2, String>>, rest: String, hascl: Bool) -> Hold:
887	  match hascl:
888	    case False{}:
889	      HoldBody{rest}
890	    case True{}:
891	      parse.res.cl.n(rest, parse_u32(header(h, "content-length")))
892	
893	def parse.res.chunked.eq(rest: String, ok: Bool) -> Hold:
894	  match ok:
895	    case False{}:
896	      HoldUntil{rest}
897	    case True{}:
898	      chunk.live(rest)
899	
900	def parse.res.chunked.val(te: String, rest: String) -> Hold:
901	  parse.res.chunked.eq(rest, String.eq(String.to_lower(te), "chunked"))
902	
903	def parse.res.chunked(+h: Map<&2, List<&2, String>>, rest: String, hascl: Bool) -> Hold:
904	  match hascl:
905	    case True{}:
906	      HoldBad{}
907	    case False{}:
908	      parse.res.chunked.val(header.last(h, "transfer-encoding"), rest)
909	
910	def parse.res.te(+h: Map<&2, List<&2, String>>, rest: String, te: Bool) -> Hold:
911	  match te:
912	    case True{}:
913	      parse.res.chunked(h, rest, has_header(h, "content-length"))
914	    case False{}:
915	      parse.res.cl(h, rest, has_header(h, "content-length"))
916	
917	def parse.res.body(+h: Map<&2, List<&2, String>>, rest: String) -> Hold:
918	  parse.res.te(h, rest, has_header(h, "transfer-encoding"))
919	
920	# Bad: never a message. More: a valid prefix; read on. Done: a whole response.
921	type Frame is Type:
922	  FrameBad{}
923	  FrameMore{}
924	  FrameDone{res: Res}
925	
926	# RFC 9112 §8: a message cut short by close is incomplete, not valid.
927	def frame.cut(closed: Bool) -> Frame:
928	  match closed:
929	    case True{}:
930	      FrameBad{}
931	    case False{}:
932	      FrameMore{}
933	
934	def frame.wait(res: Res, wait: Bool) -> Frame:
935	  match wait:
936	    case True{}:
937	      FrameMore{}
938	    case False{}:
939	      FrameDone{res}
940	
941	def frame.done(status: U32, h: Map<&2, List<&2, String>>, body: Hold, +closed: Bool, open: Bool) -> Frame:
942	  match body:
943	    case HoldBad{}:
944	      FrameBad{}
945	    case HoldMore{}:
946	      frame.cut(closed)
947	    case HoldUntil{b}:
948	      frame.wait(Res{status, h, Bytes.from_string(b)}, Bool.not(closed))
949	    case HoldBody{b}:
950	      frame.wait(Res{status, h, Bytes.from_string(b)}, Bool.and(open, Bool.not(closed)))
951	
952	# RFC 9112 §6.3 (8): no TE and no CL ⇒ the body runs until the server closes.
953	def frame.open(+h: Map<&2, List<&2, String>>) -> Bool:
954	  Bool.not(Bool.or(has_header(h, "transfer-encoding"), has_header(h, "content-length")))
955	
956	# RFC 9112 §6.3 (1): HEAD, 1xx, 204 and 304 responses end at the blank line.
957	def frame.nobody(+status: U32, head: Bool) -> Bool:
958	  Bool.or(head, Bool.or(U32.is_lt(status, 200), Bool.or(U32.is_eq(status, 204), U32.is_eq(status, 304))))
959	
960	# 101 is the final response. Other 1xx are interim; a final response follows.
961	def frame.interim(+status: U32) -> Bool:
962	  Bool.and(U32.is_lt(status, 200), Bool.not(U32.is_eq(status, 101)))
963	
964	def frame.status(status: U32, +h: Map<&2, List<&2, String>>, rest: String, closed: Bool, nobody: Bool) -> Frame:
965	  match nobody:
966	    case True{}:
967	      FrameDone{Res{status, h, Bytes.new(0)}}
968	    case False{}:
969	      frame.done(status, h, parse.res.body(h, rest), closed, frame.open(h))
970	
971	def parse.res.fields(+status: U32, rest: String, fs: Maybe<&2, Map<&2, List<&2, String>>>, closed: Bool, head: Bool) -> Frame:
972	  match fs:
973	    case None{}:
974	      FrameBad{}
975	    case Some{h}:
976	      frame.status(status, h, rest, closed, frame.nobody(status, head))
977	
978	def parse.res.num(code: Maybe<&2, U32>, headers: String, rest: String, closed: Bool, head: Bool) -> Frame:
979	  match code:
980	    case None{}:
981	      FrameBad{}
982	    case Some{n}:
983	      parse.res.fields(n, rest, parse.headers.raw(headers), closed, head)
984	
985	def parse.res.ver(code: String, headers: String, rest: String, closed: Bool, head: Bool, ok: Bool) -> Frame:
986	  match ok:
987	    case False{}:
988	      FrameBad{}
989	    case True{}:
990	      parse.res.num(parse_u32(code), headers, rest, closed, head)
991	
992	def parse.res.start3(mpv: String & String & String, headers: String, rest: String, closed: Bool, head: Bool) -> Frame:
993	  (+ver, code, reason) = mpv
994	  parse.res.ver(code, headers, rest, closed, head, Bool.or(String.eq(ver, "HTTP/1.1"), String.eq(ver, "HTTP/1.0")))
995	
996	def parse.res.lines(lr: String & String, rest: String, closed: Bool, head: Bool) -> Frame:
997	  (line, headers) = lr
998	  parse.res.start3(start_line(line), headers, rest, closed, head)
999	
1000	def parse.res.blank(hd: String, rest: String, +closed: Bool, head: Bool, ok: Bool) -> Frame:
1001	  match ok:
1002	    case False{}:
1003	      frame.cut(closed)
1004	    case True{}:
1005	      parse.res.lines(parse.first(hd, SNil{}), rest, closed, head)
1006	
1007	def parse.res.of(hb: String & String, closed: Bool, head: Bool) -> Frame:
1008	  (+hd, rest) = hb
1009	  parse.res.blank(hd, rest, closed, head, blank_end(hd))
1010	
1011	type Lead is Data:
1012	  LeadCut{}
1013	  LeadFinal{}
1014	  LeadSkip{+rest: String}
1015	
1016	def frame.lead.if(rest: String, interim: Bool) -> Lead:
1017	  match interim:
1018	    case True{}:
1019	      LeadSkip{rest}
1020	    case False{}:
1021	      LeadFinal{}
1022	
1023	def frame.lead.num(n: Maybe<&2, U32>, rest: String) -> Lead:
1024	  match n:
1025	    case None{}:
1026	      LeadFinal{}
1027	    case Some{s}:
1028	      frame.lead.if(rest, frame.interim(s))
1029	
1030	def frame.lead.code(mpv: String & String & String, rest: String) -> Lead:
1031	  (ver, code, reason) = mpv
1032	  frame.lead.num(parse_u32(code), rest)
1033	
1034	def frame.lead.lines(xs: List<&2, String>, rest: String) -> Lead:
1035	  match xs:
1036	    case Nil{}:
1037	      LeadFinal{}
1038	    case Con{line, headers}:
1039	      frame.lead.code(start_line(line), rest)
1040	
1041	def frame.lead.blank(+hd: String, rest: String, ok: Bool) -> Lead:
1042	  match ok:
1043	    case False{}:
1044	      LeadCut{}
1045	    case True{}:
1046	      frame.lead.lines(String.lines(hd), rest)
1047	
1048	def frame.lead(hb: String & String) -> Lead:
1049	  (+hd, rest) = hb
1050	  frame.lead.blank(hd, rest, blank_end(hd))
1051	
1052	def frame.at.cont(+raw: String, lead: Lead) -> String:
1053	  match lead:
1054	    case LeadCut{}:
1055	      raw
1056	    case LeadFinal{}:
1057	      raw
1058	    case LeadSkip{rest}:
1059	      rest
1060	
1061	def frame.at.zero.go(+raw: String, closed: Bool, head: Bool, lead: Lead) -> Frame:
1062	  match lead:
1063	    case LeadCut{}:
1064	      frame.cut(closed)
1065	    case LeadFinal{}:
1066	      parse.res.of(split_at_blank(raw), closed, head)
1067	    case LeadSkip{rest}:
1068	      FrameBad{}
1069	
1070	def frame.at.zero.of(+raw: String, closed: Bool, head: Bool) -> Frame:
1071	  frame.at.zero.go(raw, closed, head, frame.lead(split_at_blank(raw)))
1072	
1073	def frame.at.pos.do(f: Nat, +raw: String, closed: Bool, head: Bool, hb: String & String, lead: Lead) -> Frame:
1074	  match f:
1075	    case 0n:
1076	      match lead:
1077	        case LeadCut{}:
1078	          frame.cut(closed)
1079	        case LeadFinal{}:
1080	          parse.res.of(hb, closed, head)
1081	        case LeadSkip{+rest}:
1082	          frame.at.zero.of(rest, closed, head)
1083	    case 1n+g:
1084	      match lead:
1085	        case LeadCut{}:
1086	          frame.cut(closed)
1087	        case LeadFinal{}:
1088	          parse.res.of(hb, closed, head)
1089	        case LeadSkip{+rest}:
1090	          frame.at.pos.do(g, rest, closed, head, split_at_blank(rest), frame.lead(split_at_blank(rest)))
1091	
1092	def frame.at.zero(+raw: String, closed: Bool, head: Bool) -> Frame:
1093	  frame.at.zero.of(raw, closed, head)
1094	
1095	# ponytail: 8 interim responses; raise the fuel if a server sends more
1096	def frame.at(fuel: Nat, +raw: String, closed: Bool, head: Bool) -> Frame:
1097	  match fuel:
1098	    case 0n:
1099	      frame.at.zero(raw, closed, head)
1100	    case 1n+f:
1101	      frame.at.pos.do(f, raw, closed, head, split_at_blank(raw), frame.lead(split_at_blank(raw)))
1102	
1103	# frame(bytes so far, server closed?, request was HEAD?)
1104	def frame(raw: String, closed: Bool, head: Bool) -> Frame:
1105	  frame.at(8n, raw, closed, head)
1106	
1107	def frame.res(f: Frame) -> Maybe<&1, Res>:
1108	  match f:
1109	    case FrameDone{res}:
1110	      Some{res}
1111	    case FrameBad{}:
1112	      None{}
1113	    case FrameMore{}:
1114	      None{}
1115	
1116	def parse_res(raw: String) -> Maybe<&1, Res>:
1117	  frame.res(frame(raw, True{}, False{}))
1118	
1119	def res_fields.res(res: Res, k: String) -> List<&2, String>:
1120	  Res{status, headers, body} = res
1121	  fields(headers, k)
1122	
1123	def res_fields(m: Maybe<&1, Res>, k: String) -> List<&2, String>:
1124	  match m:
1125	    case None{}:
1126	      Nil{}
1127	    case Some{res}:
1128	      res_fields.res(res, k)
1129	
1130	# The response body as it arrives. Len: bytes left. Chunk: the decoder. Close: until the
1131	# server closes. Done: the body is whole. Bad: it cannot become a body.
1132	type Rb is Data:
1133	  RbLen{left: U32}
1134	  RbChunk{st: Dc}
1135	  RbClose{}
1136	  RbDone{}
1137	  RbBad{}
1138	
1139	def rb.cl(n: Maybe<&2, U32>) -> Maybe<&2, Rb>:
1140	  match n:
1141	    case None{}:
1142	      None{}
1143	    case Some{+k}:
1144	      Some{Bool.pick(Rb, U32.is_zero(k), RbDone{}, RbLen{k})}
1145	
1146	def rb.te(+h: Map<&2, List<&2, String>>, cl: Bool) -> Maybe<&2, Rb>:
1147	  match cl:
1148	    case True{}:
1149	      None{}
1150	    case False{}:
1151	      Some{Bool.pick(Rb, String.eq(String.to_lower(header.last(h, "transfer-encoding")), "chunked"), RbChunk{dc.start()}, RbClose{})}
1152	
1153	def rb.len(+h: Map<&2, List<&2, String>>, te: Bool) -> Maybe<&2, Rb>:
1154	  match te:
1155	    case True{}:
1156	      rb.te(h, has_header(h, "content-length"))
1157	    case False{}:
1158	      Bool.pick(Maybe<&2, Rb>, has_header(h, "content-length"), rb.cl(parse_u32(header(h, "content-length"))), Some{RbClose{}})
1159	
1160	# RFC 9112 §6.3: how the body of this response ends. None: it cannot be framed.
1161	def rb.of(+h: Map<&2, List<&2, String>>, nobody: Bool) -> Maybe<&2, Rb>:
1162	  match nobody:
1163	    case True{}:
1164	      Some{RbDone{}}
1165	    case False{}:
1166	      rb.len(h, has_header(h, "transfer-encoding"))
1167	
1168	# rb: how the body goes on. parts: body bytes so far, newest first. rest: bytes past a Done body.
1169	type Bf is Type:
1170	  Bf{rb: Rb, parts: List<&1, Bytes.Bytes>, rest: Bytes.Bytes}
1171	
1172	def rb.len.cut(parts: List<&1, Bytes.Bytes>, +len: U32, +left: U32, r: Bytes.Bytes & Bytes.Bytes) -> Bf:
1173	  (piece, data) = r
1174	  Bf{RbDone{}, Con{data, parts}, bytes.snd(Bytes.slice(piece, left, (len - left : U32)))}
1175	
1176	def rb.len.have(short: Bool, +left: U32, parts: List<&1, Bytes.Bytes>, +len: U32, piece: Bytes.Bytes) -> Bf:
1177	  match short:
1178	    case True{}:
1179	      Bf{RbLen{(left - len : U32)}, Con{piece, parts}, Bytes.new(0)}
1180	    case False{}:
1181	      rb.len.cut(parts, len, left, Bytes.slice(piece, 0, left))
1182	
1183	def rb.chunk(c: Ck) -> Bf:
1184	  Ck{st, parts, rest} = c
1185	  match st:
1186	    case DcDone{}:
1187	      Bf{RbDone{}, parts, rest}
1188	    case DcBad{}:
1189	      Bf{RbBad{}, parts, rest}
1190	    case DcSize{a, b}:
1191	      Bf{RbChunk{DcSize{a, b}}, parts, rest}
1192	    case DcExt{x}:
1193	      Bf{RbChunk{DcExt{x}}, parts, rest}
1194	    case DcSizeLf{x}:
1195	      Bf{RbChunk{DcSizeLf{x}}, parts, rest}
1196	    case DcData{k}:
1197	      Bf{RbChunk{DcData{k}}, parts, rest}
1198	    case DcDataCr{}:
1199	      Bf{RbChunk{DcDataCr{}}, parts, rest}
1200	    case DcDataLf{}:
1201	      Bf{RbChunk{DcDataLf{}}, parts, rest}
1202	    case DcTr{j}:
1203	      Bf{RbChunk{DcTr{j}}, parts, rest}
1204	
1205	# The body bytes in piece, added to parts.
1206	def rb.feed(rb: Rb, parts: List<&1, Bytes.Bytes>, piece: Bytes.Bytes) -> Bf:
1207	  match rb:
1208	    case RbLen{+left}:
1209	      Bytes.Bytes{+len, buf} = piece
1210	      rb.len.have(U32.is_lt(len, left), left, parts, len, Bytes.Bytes{len, buf})
1211	    case RbChunk{st}:
1212	      rb.chunk(ck(piece, st, parts))
1213	    case RbClose{}:
1214	      Bf{RbClose{}, Con{piece, parts}, Bytes.new(0)}
1215	    case RbDone{}:
1216	      Bf{RbDone{}, parts, piece}
1217	    case RbBad{}:
1218	      Bf{RbBad{}, parts, piece}
1219	
1220	# RFC 9112 §8: only a close-delimited body may end at close.
1221	def rb.eof(rb: Rb) -> Bool:
1222	  match rb:
1223	    case RbClose{}:
1224	      True{}
1225	    case RbDone{}:
1226	      True{}
1227	    case RbLen{n}:
1228	      False{}
1229	    case RbChunk{st}:
1230	      False{}
1231	    case RbBad{}:
1232	      False{}
1233	
1234	def rb.body(parts: List<&1, Bytes.Bytes>) -> Bytes.Bytes:
1235	  Bytes.concat(List.reverse(&1, Bytes.Bytes, parts))
1236	
1237	# The head scan. Seek: look for the blank line from byte from; k interim heads are behind.
1238	# Wait: no blank line yet. Res: the final head, how its body ends, and the bytes after it.
1239	type Hs is Type:
1240	  HsSeek{buf: Bytes.Bytes, from: U32, k: U32}
1241	  HsWait{buf: Bytes.Bytes, k: U32}
1242	  HsBad{}
1243	  HsRes{res: Res, rb: Rb, rest: Bytes.Bytes}
1244	
1245	def hs.final(+status: U32, +h: Map<&2, List<&2, String>>, rest: Bytes.Bytes, m: Maybe<&2, Rb>) -> Hs:
1246	  match m:
1247	    case None{}:
1248	      HsBad{}
1249	    case Some{rb}:
1250	      HsRes{Res{status, h, Bytes.new(0)}, rb, rest}
1251	
1252	def hs.skip(more: Bool, +k: U32, rest: Bytes.Bytes) -> Hs:
1253	  match more:
1254	    case True{}:
1255	      HsSeek{rest, 0, (k + 1 : U32)}
1256	    case False{}:
1257	      HsBad{}
1258	
1259	def hs.pick(interim: Bool, +head: Bool, +k: U32, +status: U32, +h: Map<&2, List<&2, String>>, rest: Bytes.Bytes) -> Hs:
1260	  match interim:
1261	    case True{}:
1262	      hs.skip(U32.is_lt(k, 8), k, rest)
1263	    case False{}:
1264	      hs.final(status, h, rest, rb.of(h, frame.nobody(status, head)))
1265	
1266	def hs.res(+head: Bool, +k: U32, rest: Bytes.Bytes, res: Res) -> Hs:
1267	  Res{+status, +h, body} = res
1268	  hs.pick(frame.interim(status), head, k, status, h, rest)
1269	
1270	# The head alone, framed as a HEAD response so it stops at the blank line.
1271	def hs.parsed(+head: Bool, +k: U32, rest: Bytes.Bytes, f: Frame) -> Hs:
1272	  match f:
1273	    case FrameDone{res}:
1274	      hs.res(head, k, rest, res)
1275	    case FrameBad{}:
1276	      HsBad{}
1277	    case FrameMore{}:
1278	      HsBad{}
1279	
1280	def hs.split(+head: Bool, +k: U32, +hlen: U32, +len: U32, r: Bytes.Bytes & Bytes.Bytes) -> Hs:
1281	  (buf, hb) = r
1282	  hs.parsed(head, k, bytes.snd(Bytes.slice(buf, hlen, (len - hlen : U32))), parse.res.of(split_at_blank(Bytes.to_string(hb)), False{}, True{}))
1283	
1284	def hs.hit(+head: Bool, +k: U32, +len: U32, buf: Bytes.Bytes, at: Maybe<&2, U32>) -> Hs:
1285	  match at:
1286	    case None{}:
1287	      HsWait{buf, k}
1288	    case Some{+i}:
1289	      +hlen = (i + 4 : U32)
1290	      hs.split(head, k, hlen, len, Bytes.slice(buf, 0, hlen))
1291	
1292	def hs.seek.of(+head: Bool, +k: U32, +len: U32, +from: U32, buf: Bytes.Bytes, r: Bytes.Bytes & Maybe<&2, U32>) -> Hs:
1293	  (tail, m) = r
1294	  hs.hit(head, k, len, buf, found.at(from, m))
1295	
1296	def hs.seek(+head: Bool, +k: U32, +len: U32, +from: U32, r: Bytes.Bytes & Bytes.Bytes) -> Hs:
1297	  (buf, tail) = r
1298	  hs.seek.of(head, k, len, from, buf, Bytes.find(tail, "\r\n\r\n"))
1299	
1300	def hs.step(+head: Bool, st: Hs) -> Hs:
1301	  match st:
1302	    case HsSeek{buf, +from, +k}:
1303	      Bytes.Bytes{+len, b} = buf
1304	      hs.seek(head, k, len, from, Bytes.slice(Bytes.Bytes{len, b}, from, (len - from : U32)))
1305	    case HsWait{buf, k}:
1306	      HsWait{buf, k}
1307	    case HsBad{}:
1308	      HsBad{}
1309	    case HsRes{res, rb, rest}:
1310	      HsRes{res, rb, rest}
1311	
1312	# Each step ends the scan or passes one interim head, and at most 8 interim heads pass.
1313	def hs.scan(fuel: Nat, +head: Bool, st: Hs) -> Hs:
1314	  match fuel:
1315	    case 0n:
1316	      match st:
1317	        case HsSeek{buf, from, k}:
1318	          HsBad{}
1319	        case HsWait{buf, k}:
1320	          HsWait{buf, k}
1321	        case HsBad{}:
1322	          HsBad{}
1323	        case HsRes{res, rb, rest}:
1324	          HsRes{res, rb, rest}
1325	    case 1n+f:
1326	      hs.scan(f, head, hs.step(head, st))
1327	
1328	# piece joins buf; only the new bytes, and the 3 before them, can finish the blank line.
1329	def hs.more(+head: Bool, +k: U32, buf: Bytes.Bytes, piece: Bytes.Bytes) -> Hs:
1330	  Bytes.Bytes{+ol, ob} = buf
1331	  hs.scan(10n, head, HsSeek{Bytes.append(Bytes.Bytes{ol, ob}, piece), Bool.pick(U32, U32.is_lt(ol, 3), 0, (ol - 3 : U32)), k})
1332	
1333	# Untrusted servers must not grow the buffer without bound.
1334	def fetch.max() -> Nat:
1335	  U32.to_nat(16777216)
1336	
1337	# A response read in pieces. Head: the head is not whole yet. Body: it is, and parts is the body so far.
1338	# Len: a Content-Length body in one buffer of that size, with left bytes still to come.
1339	type Rv is Type:
1340	  RvHead{buf: Bytes.Bytes, k: U32}
1341	  RvBody{res: Res, rb: Rb, parts: List<&1, Bytes.Bytes>}
1342	  RvLen{res: Res, left: U32, body: Bytes.Bytes}
1343	
1344	# More: read on. Done: the response, and the bytes after it when the body is self-delimited.
1345	type Rt is Type:
1346	  RtMore{rv: Rv}
1347	  RtBad{}
1348	  RtDone{res: Res, rest: Maybe<&1, Bytes.Bytes>}
1349	
1350	def rv.start() -> Rv:
1351	  RvHead{Bytes.new(0), 0}
1352	
1353	def rv.whole(res: Res, b: Bytes.Bytes, rest: Maybe<&1, Bytes.Bytes>) -> Rt:
1354	  Res{status, headers, body} = res
1355	  RtDone{Res{status, headers, b}, rest}
1356	
1357	def rv.done(res: Res, parts: List<&1, Bytes.Bytes>, rest: Maybe<&1, Bytes.Bytes>) -> Rt:
1358	  rv.whole(res, rb.body(parts), rest)
1359	
1360	def rl.put.of(+total: U32, +len: U32, r: Array<U32> & Array<U32>) -> Bytes.Bytes & Bytes.Bytes:
1361	  (src, dst) = r
1362	  (Bytes.Bytes{total, dst}, Bytes.Bytes{len, src})
1363	
1364	# The first m bytes of piece, written into body after the total - left bytes already there.
1365	def rl.put(+m: U32, +left: U32, body: Bytes.Bytes, piece: Bytes.Bytes) -> Bytes.Bytes & Bytes.Bytes:
1366	  Bytes.Bytes{+total, dst} = body
1367	  Bytes.Bytes{+len, src} = piece
1368	  rl.put.of(total, len, Bytes.copy(m, src, dst, 0, (total - left : U32)))
1369	
1370	def rl.fed(short: Bool, res: Res, +left: U32, +len: U32, r: Bytes.Bytes & Bytes.Bytes) -> Rt:
1371	  match short:
1372	    case True{}:
1373	      (body, piece) = r
1374	      RtMore{RvLen{res, (left - len : U32), body}}
1375	    case False{}:
1376	      (body, piece) = r
1377	      rv.whole(res, body, Some{bytes.snd(Bytes.slice(piece, left, (len - left : U32)))})
1378	
1379	def rl.feed(res: Res, +left: U32, body: Bytes.Bytes, piece: Bytes.Bytes) -> Rt:
1380	  Bytes.Bytes{+len, buf} = piece
1381	  rl.fed(U32.is_lt(len, left), res, left, len, rl.put(U32.min(len, left), left, body, Bytes.Bytes{len, buf}))
1382	
1383	def rv.fed(res: Res, bf: Bf) -> Rt:
1384	  Bf{rb, parts, rest} = bf
1385	  match rb:
1386	    case RbDone{}:
1387	      rv.done(res, parts, Some{rest})
1388	    case RbBad{}:
1389	      RtBad{}
1390	    case RbLen{n}:
1391	      RtMore{RvBody{res, RbLen{n}, parts}}
1392	    case RbChunk{st}:
1393	      RtMore{RvBody{res, RbChunk{st}, parts}}
1394	    case RbClose{}:
1395	      RtMore{RvBody{res, RbClose{}, parts}}
1396	
1397	# Some{left}: a Content-Length body small enough to allocate up front. Larger ones fail at the fetch cap.
1398	def rb.buf(rb: Rb) -> Maybe<&2, U32>:
1399	  match rb:
1400	    case RbLen{+left}:
1401	      Bool.pick(Maybe<&2, U32>, Nat.is_lt(fetch.max(), U32.to_nat(left)), None{}, Some{left})
1402	    case RbChunk{st}:
1403	      None{}
1404	    case RbClose{}:
1405	      None{}
1406	    case RbDone{}:
1407	      None{}
1408	    case RbBad{}:
1409	      None{}
1410	
1411	def rv.body(m: Maybe<&2, U32>, res: Res, rb: Rb, rest: Bytes.Bytes) -> Rt:
1412	  match m:
1413	    case None{}:
1414	      rv.fed(res, rb.feed(rb, Nil{}, rest))
1415	    case Some{+left}:
1416	      rl.feed(res, left, Bytes.new(left), rest)
1417	
1418	def rv.head(hs: Hs) -> Rt:
1419	  match hs:
1420	    case HsWait{buf, k}:
1421	      RtMore{RvHead{buf, k}}
1422	    case HsBad{}:
1423	      RtBad{}
1424	    case HsSeek{buf, from, k}:
1425	      RtBad{}
1426	    case HsRes{res, +rb, rest}:
1427	      rv.body(rb.buf(rb), res, rb, rest)
1428	
1429	def rv.eof(res: Res, parts: List<&1, Bytes.Bytes>, ok: Bool) -> Rt:
1430	  match ok:
1431	    case True{}:
1432	      rv.done(res, parts, None{})
1433	    case False{}:
1434	      RtBad{}
1435	
1436	# One read: piece, or the server closed (RFC 9112 §8: a message cut short is not a message).
1437	def rv.step(closed: Bool, +head: Bool, rv: Rv, piece: Bytes.Bytes) -> Rt:
1438	  match closed:
1439	    case True{}:
1440	      match rv:
1441	        case RvHead{buf, k}:
1442	          RtBad{}
1443	        case RvBody{res, rb, parts}:
1444	          rv.eof(res, parts, rb.eof(rb))
1445	        case RvLen{res, left, body}:
1446	          RtBad{}
1447	    case False{}:
1448	      match rv:
1449	        case RvHead{buf, +k}:
1450	          rv.head(hs.more(head, k, buf, piece))
1451	        case RvBody{res, rb, parts}:
1452	          rv.fed(res, rb.feed(rb, parts, piece))
1453	        case RvLen{res, +left, body}:
1454	          rl.feed(res, left, body, piece)
1455	
1456	def rv.end(closed: Bool, +head: Bool, t: Rt) -> Rt:
1457	  match closed:
1458	    case False{}:
1459	      t
1460	    case True{}:
1461	      match t:
1462	        case RtMore{rv}:
1463	          rv.step(True{}, head, rv, Bytes.new(0))
1464	        case RtBad{}:
1465	          RtBad{}
1466	        case RtDone{res, rest}:
1467	          RtDone{res, rest}
1468	
1469	def rv.go(xs: List<&2, String>, closed: Bool, +head: Bool, t: Rt) -> Rt:
1470	  match xs:
1471	    case Nil{}:
1472	      rv.end(closed, head, t)
1473	    case Con{+x, rest}:
1474	      match t:
1475	        case RtMore{rv}:
1476	          rv.go(rest, closed, head, rv.step(False{}, head, rv, Bytes.from_string(x)))
1477	        case RtBad{}:
1478	          RtBad{}
1479	        case RtDone{res, r}:
1480	          RtDone{res, r}
1481	
1482	def rt.frame(t: Rt) -> Frame:
1483	  match t:
1484	    case RtMore{rv}:
1485	      FrameMore{}
1486	    case RtBad{}:
1487	      FrameBad{}
1488	    case RtDone{res, rest}:
1489	      FrameDone{res}
1490	
1491	# What the read loop makes of these pieces, then a close when closed is set.
1492	def res.frame(xs: List<&2, String>, closed: Bool, +head: Bool) -> Frame:
1493	  rt.frame(rv.go(xs, closed, head, RtMore{rv.start()}))
1494	
1495	def rt.rest(t: Rt) -> Maybe<&1, Bytes.Bytes>:
1496	  match t:
1497	    case RtMore{rv}:
1498	      None{}
1499	    case RtBad{}:
1500	      None{}
1501	    case RtDone{res, rest}:
1502	      rest
1503	
1504	def after.of(m: Maybe<&1, Bytes.Bytes>) -> Maybe<&2, String>:
1505	  match m:
1506	    case None{}:
1507	      None{}
1508	    case Some{b}:
1509	      Some{Bytes.to_string(b)}
1510	
1511	# Bytes after a complete self-delimited message. None if it is not one yet.
1512	def after(+raw: String, +head: Bool) -> Maybe<&2, String>:
1513	  after.of(rt.rest(rv.go([raw], False{}, head, RtMore{rv.start()})))
1514	
1515	def req.v11.ver(mpv: String & String & String) -> Bool:
1516	  (+method, path, v) = mpv
1517	  String.eq(v, "HTTP/1.1")
1518	
1519	def req.v11.line(+line: String) -> Bool:
1520	  req.v11.ver(start_line(line))
1521	
1522	def req.v11.lines(xs: List<&2, String>) -> Bool:
1523	  match xs:
1524	    case Nil{}:
1525	      False{}
1526	    case Con{line, headers}:
1527	      req.v11.line(line)
1528	
1529	def req.v11.pick(+head: String, ok: Bool) -> Bool:
1530	  match ok:
1531	    case False{}:
1532	      False{}
1533	    case True{}:
1534	      req.v11.lines(String.lines(head))
1535	
1536	def req.v11.of(hb: String & String) -> Bool:
1537	  (+head, rest) = hb
1538	  req.v11.pick(head, blank_end(head))
1539	
1540	def req.v11(+raw: String) -> Bool:
1541	  req.v11.of(split_at_blank(raw))
1542	
1543	def req.conn_close(+headers: Map<&2, List<&2, String>>) -> Bool:
1544	  String.eq(String.to_lower(header(headers, "connection")), "close")
1545	
1546	def res.conn_close(+headers: Map<&2, List<&2, String>>) -> Bool:
1547	  String.eq(String.to_lower(header(headers, "connection")), "close")
1548	
1549	def serve.fail_close(+status: U32) -> Bool:
1550	  Bool.or(U32.is_eq(status, 400), Bool.or(U32.is_eq(status, 413), U32.is_eq(status, 431)))
1551	
1552	def serve.keep.ok(fail: Bool, res_close: Bool) -> Bool:
1553	  match fail:
1554	    case True{}:
1555	      False{}
1556	    case False{}:
1557	      Bool.not(res_close)
1558	
1559	def serve.keep.v11(v11: Bool, +req_close: Bool, +status: U32, res_close: Bool) -> Bool:
1560	  match v11:
1561	    case False{}:
1562	      False{}
1563	    case True{}:
1564	      match req_close:
1565	        case True{}:
1566	          False{}
1567	        case False{}:
1568	          serve.keep.ok(serve.fail_close(status), res_close)
1569	
1570	def serve.keep(+headers: Map<&2, List<&2, String>>, v11: Bool, +status: U32, +res: Map<&2, List<&2, String>>) -> Bool:
1571	  serve.keep.v11(v11, req.conn_close(headers), status, res.conn_close(res))
1572	
1573	
1574	def again.keep(close: Bool, x: Bytes.Bytes) -> Maybe<&1, Bytes.Bytes>:
1575	  match close:
1576	    case True{}:
1577	      None{}
1578	    case False{}:
1579	      Some{x}
1580	
1581	def again.rest(close: Bool, rest: Maybe<&1, Bytes.Bytes>) -> Maybe<&1, Bytes.Bytes>:
1582	  match rest:
1583	    case None{}:
1584	      None{}
1585	    case Some{x}:
1586	      again.keep(close, x)
1587	
1588	# The bytes past the response when the socket can take another request: the request did not
1589	# ask to close, the response is self-delimited, and the peer did not say close.
1590	def again(close: Bool, +h: Map<&2, List<&2, String>>, rest: Maybe<&1, Bytes.Bytes>) -> Maybe<&1, Bytes.Bytes>:
1591	  match close:
1592	    case True{}:
1593	      None{}
1594	    case False{}:
1595	      again.rest(String.eq(String.to_lower(header(h, "connection")), "close"), rest)
1596	
1597	def res_body.res(res: Res) -> Bytes.Bytes:
1598	  Res{status, headers, body} = res
1599	  body
1600	
1601	def res_body(m: Maybe<&1, Res>) -> Bytes.Bytes:
1602	  match m:
1603	    case None{}:
1604	      Bytes.new(0)
1605	    case Some{res}:
1606	      res_body.res(res)
1607	
1608	def text(res: Res) -> String:
1609	  Enc.utf8.decode(res_body.res(res))
1610	
1611	# UTF-8 is checked, not repaired: bad UTF-8 in a string gives None (RFC 8259 §8.1).
1612	def json(res: Res) -> Maybe<&1, Json.Val>:
1613	  Json.parse.bytes(res_body.res(res))
1614	
1615	def got_body.req(req: Req) -> Bytes.Bytes:
1616	  Req{method, path, headers, body} = req
1617	  body
1618	
1619	def got_body(m: Maybe<&1, Req>) -> Bytes.Bytes:
1620	  match m:
1621	    case None{}:
1622	      Bytes.new(0)
1623	    case Some{req}:
1624	      got_body.req(req)
1625	
1626	def body.of(hb: String & String) -> String:
1627	  (h, b) = hb
1628	  b
1629	
1630	def body(s: String) -> String:
1631	  body.of(split_at_blank.go(s, False{}, 0, SNil{}))
1632	
1633	def headers_lines(+k: String, vs: List<&2, String>, acc: String) -> String:
1634	  match vs:
1635	    case Nil{}:
1636	      acc
1637	    case Con{v, t}:
1638	      headers_lines(k, t, acc ++ ("\r\n" ++ sanitize(k) ++ ": " ++ sanitize(v)))
1639	
1640	def headers_block.go(xs: List<&2, Sigma<&2, &2, String, _ => List<&2, String>>>, acc: String) -> String:
1641	  match xs:
1642	    case Nil{}:
1643	      acc
1644	    case (k, vs) <> t:
1645	      headers_block.go(t, headers_lines(k, vs, acc))
1646	
1647	def headers_block(h: Map<&2, List<&2, String>>) -> String:
1648	  headers_block.go(Map.to_list(&2, List<&2, String>, h), "")
1649	
1650	# RFC 9110 §15. An unknown code gets an empty reason, which RFC 9112 §4 allows.
1651	type Reason is Data:
1652	  Reason{code: U32, text: String}
1653	
1654	def reasons() -> List<&2, Reason>:
1655	  [Reason{100, "Continue"}, Reason{101, "Switching Protocols"}, Reason{103, "Early Hints"},
1656	   Reason{200, "OK"}, Reason{201, "Created"}, Reason{202, "Accepted"}, Reason{203, "Non-Authoritative Information"}, Reason{204, "No Content"}, Reason{205, "Reset Content"}, Reason{206, "Partial Content"},
1657	   Reason{300, "Multiple Choices"}, Reason{301, "Moved Permanently"}, Reason{302, "Found"}, Reason{303, "See Other"}, Reason{304, "Not Modified"}, Reason{307, "Temporary Redirect"}, Reason{308, "Permanent Redirect"},
1658	   Reason{400, "Bad Request"}, Reason{401, "Unauthorized"}, Reason{402, "Payment Required"}, Reason{403, "Forbidden"}, Reason{404, "Not Found"}, Reason{405, "Method Not Allowed"}, Reason{406, "Not Acceptable"}, Reason{407, "Proxy Authentication Required"}, Reason{408, "Request Timeout"}, Reason{409, "Conflict"}, Reason{410, "Gone"}, Reason{411, "Length Required"}, Reason{412, "Precondition Failed"}, Reason{413, "Content Too Large"}, Reason{414, "URI Too Long"}, Reason{415, "Unsupported Media Type"}, Reason{416, "Range Not Satisfiable"}, Reason{417, "Expectation Failed"}, Reason{421, "Misdirected Request"}, Reason{422, "Unprocessable Content"}, Reason{426, "Upgrade Required"}, Reason{428, "Precondition Required"}, Reason{429, "Too Many Requests"}, Reason{431, "Request Header Fields Too Large"},
1659	   Reason{500, "Internal Server Error"}, Reason{501, "Not Implemented"}, Reason{502, "Bad Gateway"}, Reason{503, "Service Unavailable"}, Reason{504, "Gateway Timeout"}, Reason{505, "HTTP Version Not Supported"}]
1660	
1661	def reason.go(xs: List<&2, Reason>, +status: U32) -> String:
1662	  match xs:
1663	    case Nil{}:
1664	      ""
1665	    case Con{Reason{k, v}, t}:
1666	      Bool.pick(String, U32.is_eq(k, status), v, reason.go(t, status))
1667	
1668	def reason(+status: U32) -> String:
1669	  reason.go(reasons(), status)
1670	
1671	def response(+status: U32, headers: Map<&2, List<&2, String>>, body: String) -> String:
1672	  ("HTTP/1.1 " ++ U32.show(status) ++ " " ++ reason(status) ++ headers_block(headers)) ++ ("\r\n\r\n" ++ body)
1673	
1674	def encode.body(head: Bool, top: Bytes.Bytes, body: Bytes.Bytes) -> Bytes.Bytes:
1675	  match head:
1676	    case True{}:
1677	      top
1678	    case False{}:
1679	      Bytes.append(top, body)
1680	
1681	def encode.len(+status: U32, headers: Map<&2, List<&2, String>>, head: Bool, body: Bytes.Bytes) -> Bytes.Bytes:
1682	  Bytes.Bytes{+len, buf} = body
1683	  encode.body(head, Bytes.from_string(response(status, set(headers, "content-length", U32.show(len)), "")), Bytes.Bytes{len, buf})
1684	
1685	# RFC 9110 §6.4.1, §8.6: 1xx, 204 and 304 have no body; HEAD gets the length but no body.
1686	def encode.pick(+status: U32, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes, head: Bool, nobody: Bool) -> Bytes.Bytes:
1687	  match nobody:
1688	    case True{}:
1689	      Bytes.from_string(response(status, headers, ""))
1690	    case False{}:
1691	      encode.len(status, headers, head, body)
1692	
1693	def encode.on(r: Res, head: Bool) -> Bytes.Bytes:
1694	  Res{+status, headers, body} = r
1695	  encode.pick(status, headers, body, head, frame.nobody(status, False{}))
1696	
1697	def encode(r: Res) -> Bytes.Bytes:
1698	  encode.on(r, False{})
1699	
1700	def request(method: String, path: String, headers: Map<&2, List<&2, String>>, body: String) -> String:
1701	  (method ++ " " ++ path ++ " HTTP/1.1" ++ headers_block(headers)) ++ ("\r\n\r\n" ++ body)
1702	
1703	def req.reserved(+k: String) -> Bool:
1704	  Bool.or(Bool.or(String.eq(k, "host"), String.eq(k, "connection")), Bool.or(String.eq(k, "content-length"), String.eq(k, "transfer-encoding")))
1705	
1706	def req.put.one(m: Map<&2, List<&2, String>>, +k: String, vs: List<&2, String>, skip: Bool) -> Map<&2, List<&2, String>>:
1707	  match skip:
1708	    case True{}:
1709	      m
1710	    case False{}:
1711	      Map.set(&2, List<&2, String>, m, k, vs)
1712	
1713	def req.put(xs: List<&2, Sigma<&2, &2, String, _ => List<&2, String>>>, m: Map<&2, List<&2, String>>) -> Map<&2, List<&2, String>>:
1714	  match xs:
1715	    case Nil{}:
1716	      m
1717	    case (k, vs) <> t:
1718	      +lk = String.to_lower(k)
1719	      req.put(t, req.put.one(m, lk, vs, req.reserved(lk)))
1720	
1721	# RFC 9110 §8.6: no Content-Length on a bodiless request whose method gives a body no meaning.
1722	def req.cl(+m: Map<&2, List<&2, String>>, +method: String, +len: U32) -> Map<&2, List<&2, String>>:
1723	  +bodied = Bool.or(Bool.not(U32.is_zero(len)), Bool.or(String.eq(method, "POST"), Bool.or(String.eq(method, "PUT"), String.eq(method, "PATCH"))))
1724	  Bool.pick(Map<&2, List<&2, String>>, bodied, set(m, "content-length", U32.show(len)), m)
1725	
1726	# Caller headers are lowercased so they cannot duplicate ours; host, connection,
1727	# content-length and transfer-encoding are always ours (no smuggling through them).
1728	def encode_req.word(close: Bool) -> String:
1729	  match close:
1730	    case True{}:
1731	      "close"
1732	    case False{}:
1733	      "keep-alive"
1734	
1735	def encode_req.on(+method: String, target: String, host: String, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes, close: Bool) -> Bytes.Bytes:
1736	  Bytes.Bytes{+len, buf} = body
1737	  +h = set(set(req.put(Map.to_list(&2, List<&2, String>, headers), empty()), "host", host), "connection", encode_req.word(close))
1738	  Bytes.append(Bytes.from_string(request(method, target, req.cl(h, method, len), "")), Bytes.Bytes{len, buf})
1739	
1740	def encode_req(+method: String, target: String, host: String, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes) -> Bytes.Bytes:
1741	  encode_req.on(method, target, host, headers, body, True{})
1742	
1743	# Redirects (RFC 9110 §15.4, as WHATWG fetch applies them)
1744	# --------------------------------------------------------
1745	
1746	# One request to make: headers are already lowercased (see req.put).
1747	type Hop is Type:
1748	  Hop{method: String, url: Url.Abs, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes}
1749	
1750	def redirect.code(+s: U32) -> Bool:
1751	  Bool.or(Bool.or(U32.is_eq(s, 301), U32.is_eq(s, 302)), Bool.or(U32.is_eq(s, 303), Bool.or(U32.is_eq(s, 307), U32.is_eq(s, 308))))
1752	
1753	def redirect.origin(a: Url.Abs) -> String:
1754	  Url.Abs{scheme, host, port, target} = a
1755	  scheme ++ "://" ++ host ++ ":" ++ U32.show(port)
1756	
1757	def redirect.del(ks: List<&2, String>, m: Map<&2, List<&2, String>>) -> Map<&2, List<&2, String>>:
1758	  match ks:
1759	    case Nil{}:
1760	      m
1761	    case Con{k, t}:
1762	      redirect.del(t, Map.del(&2, List<&2, String>, m, k))
1763	
1764	def redirect.hdrs(+h: Map<&2, List<&2, String>>, drop: Bool, cross: Bool) -> Map<&2, List<&2, String>>:
1765	  +h2 = Bool.pick(Map<&2, List<&2, String>>, drop, redirect.del(["content-type", "content-encoding", "content-language", "content-location"], h), h)
1766	  Bool.pick(Map<&2, List<&2, String>>, cross, redirect.del(["authorization", "cookie", "proxy-authorization"], h2), h2)
1767	
1768	# 303 turns any method but HEAD into GET; 301 and 302 turn POST into GET;
1769	# 307 and 308 keep method and body. A GET carries no body or body headers.
1770	# Credentials do not follow a hop to another origin.
1771	def redirect.body(drop: Bool, body: Bytes.Bytes) -> Bytes.Bytes:
1772	  match drop:
1773	    case True{}:
1774	      Bytes.new(0)
1775	    case False{}:
1776	      body
1777	
1778	def redirect.to(+status: U32, +method: String, +from: Url.Abs, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes, next: Maybe<&2, Url.Abs>) -> Maybe<&1, Hop>:
1779	  match next:
1780	    case None{}:
1781	      None{}
1782	    case Some{+to}:
1783	      +drop = Bool.or(Bool.and(U32.is_eq(status, 303), Bool.not(String.eq(method, "HEAD"))), Bool.and(Bool.or(U32.is_eq(status, 301), U32.is_eq(status, 302)), String.eq(method, "POST")))
1784	      Some{Hop{Bool.pick(String, drop, "GET", method), to, redirect.hdrs(headers, drop, Bool.not(String.eq(redirect.origin(from), redirect.origin(to)))), redirect.body(drop, body)}}
1785	
1786	def redirect.hop(status: U32, h: Hop, loc: String) -> Maybe<&1, Hop>:
1787	  Hop{method, +url, headers, body} = h
1788	  redirect.to(status, method, url, headers, body, Url.resolve(url, loc))
1789	
1790	def redirect.if(status: U32, h: Hop, loc: String, ok: Bool) -> Maybe<&1, Hop>:
1791	  match ok:
1792	    case False{}:
1793	      None{}
1794	    case True{}:
1795	      redirect.hop(status, h, loc)
1796	
1797	# The next request after a response, or None when it is not a redirect we follow.
1798	def redirect(+status: U32, +headers: Map<&2, List<&2, String>>, h: Hop) -> Maybe<&1, Hop>:
1799	  redirect.if(status, h, header(headers, "location"), Bool.and(redirect.code(status), has_header(headers, "location")))
1800	
1801	# Cookies (RFC 6265bis §5)
1802	# ------------------------
1803	
1804	# A stored cookie. domain is lowercase, with no leading dot; host_only sends it to that host alone.
1805	# expiry None is a session cookie. http_only and same_site ("strict", "lax", "none" or "default")
1806	# are kept, not enforced: fetch has no browsing client, so its requests are same-site (§5.2).
1807	type Cookie is Data:
1808	  Cookie{name: String, value: String, domain: String, host_only: Bool, path: String, secure: Bool, http_only: Bool, same_site: String, expiry: Maybe<&2, Time.Instant>}
1809	
1810	# The cookies, oldest first, and the caller's clock. No cookie in it has expired by now.
1811	type Jar is Data:
1812	  Jar{now: Time.Instant, cookies: List<&2, Cookie>}
1813	
1814	def jar.new(now: Time.Instant) -> Jar:
1815	  Jar{now, Nil{}}
1816	
1817	def jar.cookies(j: Jar) -> List<&2, Cookie>:
1818	  Jar{now, cs} = j
1819	  cs
1820	
1821	def cookie.live.at(+now: Time.Instant, e: Maybe<&2, Time.Instant>) -> Bool:
1822	  match e:
1823	    case None{}:
1824	      True{}
1825	    case Some{t}:
1826	      Cmp.is_lt(Time.Instant.cmp(now, t))
1827	
1828	# Alive at now: no expiry, or an expiry after now.
1829	def cookie.live(+now: Time.Instant, c: Cookie) -> Bool:
1830	  Cookie{name, value, domain, host_only, path, secure, http_only, same_site, expiry} = c
1831	  cookie.live.at(now, expiry)
1832	
1833	def jar.live(cs: List<&2, Cookie>, +now: Time.Instant) -> List<&2, Cookie>:
1834	  match cs:
1835	    case Nil{}:
1836	      Nil{}
1837	    case Con{+c, t}:
1838	      List.filter.put(Cookie, c, jar.live(t, now), cookie.live(now, c))
1839	
1840	# The jar at a later time: cookies expired by now are evicted (§5.7).
1841	def jar.at(j: Jar, +now: Time.Instant) -> Jar:
1842	  Jar{old, cs} = j
1843	  Jar{now, jar.live(cs, now)}
1844	
1845	def cookie.cut.found(r: String & String) -> String & String & Bool:
1846	  (a, b) = r
1847	  (a, b, True{})
1848	
1849	# hit: the last char pushed onto acc was c.
1850	def cookie.cut.go(s: String, +c: U32, acc: String, hit: Bool) -> String & String & Bool:
1851	  match s:
1852	    case SNil{}:
1853	      match hit:
1854	        case True{}:
1855	          cookie.cut.found(take.cut(acc, SNil{}))
1856	        case False{}:
1857	          (String.reverse(acc), SNil{}, False{})
1858	    case SCon{Chr{+x}, t}:
1859	      match hit:
1860	        case True{}:
1861	          cookie.cut.found(take.cut(acc, SCon{Chr{x}, t}))
1862	        case False{}:
1863	          cookie.cut.go(t, c, SCon{Chr{x}, acc}, U32.is_eq(x, c))
1864	
1865	# s split at its first c: before, after, and whether c was there.
1866	def cookie.cut(s: String, +c: U32) -> String & String & Bool:
1867	  cookie.cut.go(s, c, SNil{}, False{})
1868	
1869	def cookie.fst(r: String & String & Bool) -> String:
1870	  (a, b, found) = r
1871	  a
1872	
1873	# The path of an origin-form target: the part before "?".
1874	def cookie.target_path(t: String) -> String:
1875	  cookie.fst(cookie.cut(t, 63))
1876	
1877	# Longer than n octets.
1878	def cookie.over(s: String, +n: U32) -> Bool:
1879	  match s:
1880	    case SNil{}:
1881	      False{}
1882	    case SCon{c, t}:
1883	      Bool.or(U32.is_eq(n, 0), cookie.over(t, (n - 1 : U32)))
1884	
1885	# %x00-08 / %x0A-1F / %x7F: control characters other than HTAB.
1886	def cookie.ctl(s: String) -> Bool:
1887	  match s:
1888	    case SNil{}:
1889	      False{}
1890	    case SCon{Chr{+c}, t}:
1891	      Bool.or(Bool.or(U32.is_lt(c, 9), Bool.and(U32.is_gt(c, 9), U32.is_lt(c, 32))), Bool.or(U32.is_eq(c, 127), cookie.ctl(t)))
1892	
1893	def cookie.ascii(s: String) -> Bool:
1894	  match s:
1895	    case SNil{}:
1896	      True{}
1897	    case SCon{Chr{+c}, t}:
1898	      Bool.and(U32.is_lt(c, 128), cookie.ascii(t))
1899	
1900	def cookie.ip4(s: String) -> Bool:
1901	  match s:
1902	    case SNil{}:
1903	      True{}
1904	    case SCon{Chr{+c}, t}:
1905	      Bool.and(Bool.or(parse_u32.digit(c), U32.is_eq(c, 46)), cookie.ip4(t))
1906	
1907	# An IP literal rather than a host name: IPv6 has a colon, IPv4 is digits and dots.
1908	def cookie.ip(+h: String) -> Bool:
1909	  Bool.or(String.contains(h, ":"), cookie.ip4(h))
1910	
1911	# §5.1.3: s is d, or a host name under d on a label boundary.
1912	def cookie.domain_match(+s: String, +d: String) -> Bool:
1913	  Bool.or(String.eq(s, d), Bool.and(String.ends_with(s, "." ++ d), Bool.not(cookie.ip(s))))
1914	
1915	# A reversed path with its last segment and slash dropped.
1916	def cookie.up(rs: String) -> String:
1917	  match rs:
1918	    case SNil{}:
1919	      SNil{}
1920	    case SCon{Chr{47}, t}:
1921	      t
1922	    case SCon{Chr{c}, t}:
1923	      cookie.up(t)
1924	
1925	# §5.1.4: the request path up to its last "/", or "/".
1926	def cookie.default_path(+p: String) -> String:
1927	  +up = String.reverse(cookie.up(String.reverse(p)))
1928	  Bool.pick(String, Bool.or(Bool.not(String.starts_with(p, "/")), String.is_empty(up)), "/", up)
1929	
1930	# §5.1.4: request path p path-matches cookie path c.
1931	def cookie.path_match(+p: String, +c: String) -> Bool:
1932	  Bool.or(String.eq(p, c), Bool.and(String.starts_with(p, c), Bool.or(String.ends_with(c, "/"), String.starts_with(String.drop(p, String.length(c)), "/"))))
1933	
1934	type Hms is Data:
1935	  Hms{h: U32, m: U32, s: U32}
1936	
1937	# §5.1.1 cookie-date: the first time, day, month and year tokens found.
1938	type Cdate is Data:
1939	  Cdate{time: Maybe<&2, Hms>, day: Maybe<&2, U32>, month: Maybe<&2, U32>, year: Maybe<&2, U32>}
1940	
1941	def cookie.date.delim(+c: U32) -> Bool:
1942	  Bool.or(U32.is_eq(c, 9), Bool.or(Bool.and(U32.is_ge(c, 32), U32.is_le(c, 47)), Bool.or(Bool.and(U32.is_ge(c, 59), U32.is_le(c, 64)), Bool.or(Bool.and(U32.is_ge(c, 91), U32.is_le(c, 96)), Bool.and(U32.is_ge(c, 123), U32.is_le(c, 126))))))
1943	
1944	def cookie.date.push(acc: String, ts: List<&2, String>) -> List<&2, String>:
1945	  match acc:
1946	    case SNil{}:
1947	      ts
1948	    case SCon{h, t}:
1949	      Con{String.reverse(SCon{h, t}), ts}
1950	
1951	def cookie.date.step(d: Bool, +c: U32, acc: String, ts: List<&2, String>) -> String & List<&2, String>:
1952	  match d:
1953	    case True{}:
1954	      (SNil{}, cookie.date.push(acc, ts))
1955	    case False{}:
1956	      (SCon{Chr{c}, acc}, ts)
1957	
1958	# The date-tokens, last first. st: the token so far (reversed) and the tokens before it.
1959	def cookie.date.tokens(s: String, st: String & List<&2, String>) -> List<&2, String>:
1960	  match s:
1961	    case SNil{}:
1962	      (acc, ts) = st
1963	      cookie.date.push(acc, ts)
1964	    case SCon{Chr{+c}, t}:
1965	      (acc, ts) = st
1966	      cookie.date.tokens(t, cookie.date.step(cookie.date.delim(c), c, acc, ts))
1967	
1968	def cookie.date.head(+s: String) -> Bool:
1969	  match s:
1970	    case SNil{}:
1971	      False{}
1972	    case SCon{Chr{+c}, t}:
1973	      parse_u32.digit(c)
1974	
1975	# The digits at the start of s: (count, value, rest). d: s starts with a digit.
1976	def cookie.date.run(s: String, d: Bool, +n: U32, +acc: U32) -> U32 & U32 & String:
1977	  match s:
1978	    case SNil{}:
1979	      (n, acc, SNil{})
1980	    case SCon{Chr{+c}, +t}:
1981	      match d:
1982	        case True{}:
1983	          cookie.date.run(t, cookie.date.head(t), (n + 1 : U32), (acc * 10 + (c - 48 : U32) : U32))
1984	        case False{}:
1985	          (n, acc, SCon{Chr{c}, t})
1986	
1987	def cookie.date.within(r: U32 & U32 & String, +lo: U32, +hi: U32) -> Maybe<&1, U32 & String>:
1988	  (+n, v, rest) = r
1989	  Bool.pick(Maybe<&1, U32 & String>, Bool.and(U32.is_ge(n, lo), U32.is_le(n, hi)), Some{(v, rest)}, None{})
1990	
1991	# lo to hi digits and what follows them, which does not start with a digit.
1992	def cookie.date.num(+s: String, +lo: U32, +hi: U32) -> Maybe<&1, U32 & String>:
1993	  cookie.date.within(cookie.date.run(s, cookie.date.head(s), 0, 0), lo, hi)
1994	
1995	def cookie.date.val(m: Maybe<&1, U32 & String>) -> Maybe<&2, U32>:
1996	  match m:
1997	    case None{}:
1998	      None{}
1999	    case Some{(v, t)}:
2000	      Some{v}
Lines 1-2000 of 5782. More: https://jend.leeeet.dev/read.txt?path=bend-kit-http@0.25.0.2/http.bend&start_line=2001