1	# Hairpin: an HTTP client with a base URL, default headers, a pool, cookies, mTLS, redirects, and proven retries. Source: https://github.com/paymog/bend-kit/tree/main/hairpin
2	import Base
3	import bend-kit-http@0.36.0.0/http.bend as Http
4	import bend-kit-time@0.2.0.0/time.bend as Time
5	import bend-kit-url@0.4.1.0/url.bend as Url
6	import bend-kit-json@0.6.1.1/json.bend as Json
7	import bend-kit-bytes@0.3.2.0/bytes.bend as Bytes
8	import bend-kit-retry@0.1.0.0/retry.bend as Retry
9	
10	# base: "" for none. headers: lowercase names. ms: the step timeout. policy: attempts, backoff, and deadline of each request.
11	# ca: a PEM CA file to trust; "" trusts the default store.
12	type Opts is Data:
13	  Opts{base: String, headers: Map<&2, List<&2, String>>, ms: U32, mode: Http.Mode, policy: Retry.Policy, cert: Maybe<&2, Http.Cert>, ca: String}
14	
15	# breaker: the circuit breaker of every request on this client.
16	type Client is Type:
17	  Client{opts: Opts, pool: Http.Pool, jar: Maybe<&2, Http.Jar>, breaker: Retry.Breaker}
18	
19	# ErrHttp: the last attempt failed. ErrDenied: no attempt started, for why.
20	type Err is Data:
21	  ErrHttp{error: Http.Err}
22	  ErrDenied{why: Retry.Deny}
23	
24	# One attempt, the first included; backoff from 500 ms, doubled to at most 30 s; no deadline.
25	def policy() -> Retry.Policy:
26	  Retry.Policy{1n, 500n, 30000, None{}}
27	
28	# A pool of up to cap idle sockets per origin, no base, no default headers, 30 s steps, follow redirects,
29	# no retries, and no circuit breaker.
30	def new.with(+cap: U32) -> Client:
31	  Client{Opts{"", Http.empty(), 30000, Http.ModeFollow{}, policy(), None{}, ""}, Http.pool.new.with(cap), None{}, Retry.BreakerOff{}}
32	
33	def new() -> Client:
34	  new.with(8)
35	
36	def base(c: Client, url: String) -> Client:
37	  Client{Opts{b, h, ms, mode, p, cert, ca}, pool, j, br} = c
38	  Client{Opts{url, h, ms, mode, p, cert, ca}, pool, j, br}
39	
40	# A default header. It replaces an earlier default of the same name; a request header of that name replaces it.
41	def header(c: Client, k: String, v: String) -> Client:
42	  Client{Opts{b, h, ms, mode, p, cert, ca}, pool, j, br} = c
43	  Client{Opts{b, Http.set(h, String.to_lower(k), v), ms, mode, p, cert, ca}, pool, j, br}
44	
45	def timeout(c: Client, ms: U32) -> Client:
46	  Client{Opts{b, h, old, mode, p, cert, ca}, pool, j, br} = c
47	  Client{Opts{b, h, ms, mode, p, cert, ca}, pool, j, br}
48	
49	def redirect(c: Client, mode: Http.Mode) -> Client:
50	  Client{Opts{b, h, ms, old, p, cert, ca}, pool, j, br} = c
51	  Client{Opts{b, h, ms, mode, p, cert, ca}, pool, j, br}
52	
53	# Up to n retries after the first attempt: n + 1 attempts in all.
54	def retry(c: Client, n: U32) -> Client:
55	  Client{Opts{b, h, ms, mode, Retry.Policy{old, base, cap, d}, cert, ca}, pool, j, br} = c
56	  Client{Opts{b, h, ms, mode, Retry.Policy{1n+U32.to_nat(n), base, cap, d}, cert, ca}, pool, j, br}
57	
58	# No attempt of a request starts ms or more after the request starts.
59	def deadline(c: Client, ms: U32) -> Client:
60	  Client{Opts{b, h, t, mode, Retry.Policy{a, base, cap, old}, cert, ca}, pool, j, br} = c
61	  Client{Opts{b, h, t, mode, Retry.Policy{a, base, cap, Some{U32.to_nat(ms)}}, cert, ca}, pool, j, br}
62	
63	# A circuit breaker in front of every request, starting closed.
64	def circuit(c: Client, circ: Retry.Circuit) -> Client:
65	  Client{o, pool, j, old} = c
66	  Client{o, pool, j, Retry.Breaker.new(circ)}
67	
68	# The breaker, for inspection.
69	def breaker.of(c: Client) -> Client & Retry.Breaker:
70	  Client{o, pool, j, +br} = c
71	  (Client{o, pool, j, br}, br)
72	
73	# Paths to a PEM client chain and its private key, presented to every HTTPS origin.
74	def cert(c: Client, chain: String, key: String) -> Client:
75	  Client{Opts{b, h, ms, mode, p, old, ca}, pool, j, br} = c
76	  Client{Opts{b, h, ms, mode, p, Some{Http.Cert{chain, key}}, ca}, pool, j, br}
77	
78	# Path to a PEM CA file, trusted in place of the default store. Like the certificate, it follows same-origin redirects only.
79	def ca(c: Client, path: String) -> Client:
80	  Client{Opts{b, h, ms, mode, p, cert, old}, pool, j, br} = c
81	  Client{Opts{b, h, ms, mode, p, cert, path}, pool, j, br}
82	
83	# Every request stores and sends cookies through jar. Its clock moves to Time.now() before each try.
84	def jar(c: Client, jar: Http.Jar) -> Client:
85	  Client{o, pool, old, br} = c
86	  Client{o, pool, Some{jar}, br}
87	
88	# The jar, if the client has one.
89	def jar.of(c: Client) -> Client & Maybe<&2, Http.Jar>:
90	  Client{o, pool, +j, br} = c
91	  (Client{o, pool, j, br}, j)
92	
93	def close(c: Client) -> IO(Unit):
94	  Client{o, pool, j, br} = c
95	  Http.pool.close(pool)
96	
97	def target.pick(none: Bool, b: String, ref: String) -> Maybe<&2, String>:
98	  match none:
99	    case True{}:
100	      Some{ref}
101	    case False{}:
102	      Http.resolve(b, ref)
103	
104	# ref against the base (RFC 3986 §5.2); with no base, ref as given. None when the base is not absolute.
105	def target(+b: String, ref: String) -> Maybe<&2, String>:
106	  target.pick(String.is_empty(b), b, ref)
107	
108	def target.abs(m: Maybe<&2, String>) -> Maybe<&2, Url.Abs>:
109	  match m:
110	    case None{}:
111	      None{}
112	    case Some{s}:
113	      Url.absolute(s)
114	
115	# The defaults under the request headers, names lowercased; a request header replaces a default of its name.
116	# Host, Connection, Content-Length, and Transfer-Encoding are the client's own, so both sides drop them.
117	def merge(defaults: Map<&2, List<&2, String>>, headers: Map<&2, List<&2, String>>) -> Map<&2, List<&2, String>>:
118	  Http.req.put(Map.to_list(&2, List<&2, String>, headers), Http.req.put(Map.to_list(&2, List<&2, String>, defaults), Http.empty()))
119	
120	def jar.now(j: Maybe<&2, Http.Jar>) -> IO(Maybe<&2, Http.Jar>):
121	  match j:
122	    case None{}:
123	      IO.pure(Maybe<&2, Http.Jar>, None{})
124	    case Some{jar}:
125	      do IO<Maybe<&2, Http.Jar>>:
126	        now : Time.Instant <- Time.now()
127	        return Some{Http.jar.at(jar, now)}
128	
129	def once.final(+enc: String, x: Http.Pool & Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, Http.Jar>) ->
130	    IO(Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Res>):
131	  (p, r, j) = x
132	  do IO<Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Res>>:
133	    d : Result<&1, &1, Http.Err, Http.Res> <- Http.fetch.final(enc, r)
134	    return (p, j, d)
135	
136	# One try: the redirect loop on the pool, with the jar, the certificate, and the CA file, then the body decoded.
137	def once(+ms: U32, +mode: Http.Mode, +cert: Maybe<&2, Http.Cert>, +ca: String, +enc: String, p: Http.Pool, j: Maybe<&2, Http.Jar>,
138	    +method: String, +u: Maybe<&2, Url.Abs>, +headers: Map<&2, List<&2, String>>, body: Bytes.Bytes) ->
139	    IO(Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Res>):
140	  do IO<Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Res>>:
141	    now : Maybe<&2, Http.Jar> <- jar.now(j)
142	    x : Http.Pool & Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, Http.Jar> <-
143	      Http.pool.hops(mode, ms, Http.Hops{p, Http.fetch.start(method, headers, body, u, enc), cert, now, ca})
144	    once.final(enc, x)
145	
146	def hint.ms(m: Maybe<&2, U32>) -> Maybe<&2, Nat>:
147	  match m:
148	    case None{}:
149	      None{}
150	    case Some{ms}:
151	      Some{U32.to_nat(ms)}
152	
153	# m is Http.retry.judge's verdict for an idempotent request: Some{Retry-After} when another try may help.
154	# A non-idempotent request with that verdict is Unsafe: the breaker counts it, but it never repeats.
155	def outcome(+idem: Bool, m: Maybe<&2, String>, now: Time.Instant) -> Retry.Outcome:
156	  match m:
157	    case None{}:
158	      Retry.Settled{}
159	    case Some{+v}:
160	      Bool.pick(Retry.Outcome, idem, Retry.Transient{hint.ms(Http.retry.after(v, now))}, Retry.Unsafe{})
161	
162	def lift(-R: Type, r: Result<&1, &1, Http.Err, R>) -> Result<&1, &1, Err, R>:
163	  match r:
164	    case Fail{e}:
165	      Fail{ErrHttp{e}}
166	    case Done{res}:
167	      Done{res}
168	
169	# The live state of one request between attempts. R: a response or a stream. last: the result of the last
170	# attempt, None before the first.
171	type Step<-R: Type> is Type:
172	  Step{pool: Http.Pool, jar: Maybe<&2, Http.Jar>, breaker: Retry.Breaker, budget: Retry.Budget, body: Bytes.Bytes,
173	    last: Maybe<&1, Result<&1, &1, Err, R>>, plan: Retry.Plan}
174	
175	# The clock, read only when a decision depends on it; 0 otherwise, which no such decision reads.
176	def clock(need: Bool) -> IO(Nat):
177	  match need:
178	    case True{}:
179	      Time.mono.ms()
180	    case False{}:
181	      IO.pure(Nat, 0n)
182	
183	def breaker.on(br: Retry.Breaker) -> Bool:
184	  match br:
185	    case Retry.BreakerOff{}:
186	      False{}
187	    case Retry.BreakerOn{c, s}:
188	      True{}
189	
190	def transient(o: Retry.Outcome) -> Bool:
191	  match o:
192	    case Retry.Transient{after}:
193	      True{}
194	    case Retry.Settled{}:
195	      False{}
196	    case Retry.Unsafe{}:
197	      False{}
198	
199	def some(m: Maybe<&2, Nat>) -> Bool:
200	  match m:
201	    case None{}:
202	      False{}
203	    case Some{t}:
204	      True{}
205	
206	def deadline.some(b: Retry.Budget) -> Bool:
207	  Retry.Budget{l, d} = b
208	  some(d)
209	
210	# The wall clock dates a Retry-After, so it is read only for a transient failure.
211	def outcome.io(+idem: Bool, m: Maybe<&2, String>) -> IO(Retry.Outcome):
212	  match m:
213	    case None{}:
214	      IO.pure(Retry.Outcome, Retry.Settled{})
215	    case Some{v}:
216	      do IO<Retry.Outcome>:
217	        wall : Time.Instant <- Time.now()
218	        return outcome(idem, Some{v}, wall)
219	
220	# Jitter for the backoff, drawn only when a retry may follow.
221	def jitter.io(need: Bool) -> IO(Nat):
222	  match need:
223	    case True{}:
224	      do IO<Nat>:
225	        rnd : Result<&1, &1, U32 & String, U32> <- IO.random_u32()
226	        return U32.to_nat(Http.retry.jitter(rnd))
227	    case False{}:
228	      IO.pure(Nat, 0n)
229	
230	def settle.at(-R: Type, +now: Nat, +rnd: Nat, +p: Retry.Policy, +n: Nat, +o: Retry.Outcome, br: Retry.Breaker, +b: Retry.Budget,
231	    body: Bytes.Bytes, pool: Http.Pool, jar: Maybe<&2, Http.Jar>, r: Result<&1, &1, Http.Err, R>) -> Step<R>:
232	  Step{pool, jar, Retry.Breaker.done(br, now, Retry.failed(o)), b, body, Some{lift(R, r)}, Retry.plan(o, p, b, n, now, rnd)}
233	
234	# The attempt has ended: tell the breaker, and plan the next step.
235	def settle.outcome(-R: Type, +p: Retry.Policy, +n: Nat, +o: Retry.Outcome, +br: Retry.Breaker, b: Retry.Budget, body: Bytes.Bytes,
236	    pool: Http.Pool, jar: Maybe<&2, Http.Jar>, r: Result<&1, &1, Http.Err, R>) -> IO(Step<R>):
237	  do IO<Step<R>>:
238	    now : Nat <- clock(Bool.or(breaker.on(br), transient(o)))
239	    rnd : Nat <- jitter.io(transient(o))
240	    return settle.at(R, now, rnd, p, n, o, br, b, body, pool, jar, r)
241	
242	def settle.judged(-R: Type, +p: Retry.Policy, +idem: Bool, +n: Nat, br: Retry.Breaker, b: Retry.Budget, body: Bytes.Bytes,
243	    pool: Http.Pool, jar: Maybe<&2, Http.Jar>, j: Result<&1, &1, Http.Err, R> & Maybe<&2, String>) -> IO(Step<R>):
244	  (r, m) = j
245	  do IO<Step<R>>:
246	    o : Retry.Outcome <- outcome.io(idem, m)
247	    settle.outcome(R, p, n, o, br, b, body, pool, jar, r)
248	
249	# The default judge: Http.retry.judge, as if the request were idempotent; outcome then applies idem.
250	def judge(r: Result<&1, &1, Http.Err, Http.Res>) -> Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, String>:
251	  Http.retry.judge(True{}, r)
252	
253	def settle(~R: Type, ~judge: Result<&1, &1, Http.Err, R> -> Result<&1, &1, Http.Err, R> & Maybe<&2, String>,
254	    +p: Retry.Policy, +idem: Bool, +n: Nat, br: Retry.Breaker, b: Retry.Budget, body: Bytes.Bytes,
255	    x: Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, R>) -> IO(Step<R>):
256	  (pool, jar, r) = x
257	  settle.judged(R, p, idem, n, br, b, body, pool, jar, judge(r))
258	
259	# The inputs of one attempt. u: the target, None when it is not absolute. headers: the merged headers.
260	type Call is Data:
261	  Call{enc: String, method: String, u: Maybe<&2, Url.Abs>, headers: Map<&2, List<&2, String>>}
262	
263	# One attempt that reads a whole response: the redirect loop on the pool, with the jar and the certificate.
264	def try.res(o: Opts, call: Call, pool: Http.Pool, jar: Maybe<&2, Http.Jar>, body: Bytes.Bytes) ->
265	    IO(Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Res>):
266	  Opts{base, h, +ms, +mode, p, +cert, +ca} = o
267	  Call{+enc, +method, +u, +headers} = call
268	  once(ms, mode, cert, ca, enc, pool, jar, method, u, headers, body)
269	
270	def try.stream.got(pool: Http.Pool, x: Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Stream>) ->
271	    Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Stream>:
272	  (jar, s) = x
273	  (pool, jar, s)
274	
275	# One attempt that opens a stream on its own connection, outside the pool: the redirect loop with the mode,
276	# the jar, and the certificate, then the body decoded by enc.
277	def try.stream(o: Opts, call: Call, pool: Http.Pool, jar: Maybe<&2, Http.Jar>, body: Bytes.Bytes) ->
278	    IO(Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Stream>):
279	  Opts{base, h, +ms, mode, p, cert, ca} = o
280	  Call{+enc, method, u, headers} = call
281	  do IO<Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Stream>>:
282	    now : Maybe<&2, Http.Jar> <- jar.now(jar)
283	    r : Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Stream> <-
284	      Http.stream.hops(mode, ms, Http.StreamHops{Http.stream.start(method, Http.accept.enc(headers, enc), body, u), cert, now, ca})
285	    x : Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Stream> <- Http.stream.init.jar(enc, r)
286	    return try.stream.got(pool, x)
287	
288	def close.res(r: Http.Res) -> IO(Unit):
289	  IO.pure(Unit, Unit{})
290	
291	def close.last(~R: Type, ~close: R -> IO(Unit), last: Maybe<&1, Result<&1, &1, Err, R>>) -> IO(Unit):
292	  match last:
293	    case None{}:
294	      IO.pure(Unit, Unit{})
295	    case Some{r}:
296	      match r:
297	        case Fail{e}:
298	          IO.pure(Unit, Unit{})
299	        case Done{x}:
300	          close(x)
301	
302	def attempt.run(~R: Type, ~judge: Result<&1, &1, Http.Err, R> -> Result<&1, &1, Http.Err, R> & Maybe<&2, String>,
303	    ~try: Opts -> Call -> Http.Pool -> Maybe<&2, Http.Jar> -> Bytes.Bytes -> IO(Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, R>),
304	    +o: Opts, +call: Call, +idem: Bool, +n: Nat, pool: Http.Pool, jar: Maybe<&2, Http.Jar>, br: Retry.Breaker,
305	    b: Retry.Budget, r: Bytes.Bytes & Bytes.Bytes) -> IO(Step<R>):
306	  Opts{base, h, ms, mode, +p, cert, ca} = o
307	  (body, spare) = r
308	  do IO<Step<R>>:
309	    x : Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, R> <- try(o, call, pool, jar, spare)
310	    settle(~R, ~judge, p, idem, n, br, b, body, x)
311	
312	def denied(-R: Type, why: Retry.Deny, last: Maybe<&1, Result<&1, &1, Err, R>>) -> Maybe<&1, Result<&1, &1, Err, R>>:
313	  match last:
314	    case None{}:
315	      Some{Fail{ErrDenied{why}}}
316	    case Some{r}:
317	      Some{r}
318	
319	# A refused stream closes only when the next attempt is admitted, so a denied attempt still returns it.
320	def attempt.gate(~R: Type, ~judge: Result<&1, &1, Http.Err, R> -> Result<&1, &1, Http.Err, R> & Maybe<&2, String>,
321	    ~try: Opts -> Call -> Http.Pool -> Maybe<&2, Http.Jar> -> Bytes.Bytes -> IO(Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, R>),
322	    ~close: R -> IO(Unit),
323	    x: Retry.Breaker & Retry.Budget & Retry.Gate, +o: Opts, +call: Call, +idem: Bool, +n: Nat, pool: Http.Pool,
324	    jar: Maybe<&2, Http.Jar>, body: Bytes.Bytes, last: Maybe<&1, Result<&1, &1, Err, R>>) -> IO(Step<R>):
325	  (br, b, g) = x
326	  match g:
327	    case Retry.GateNo{why}:
328	      IO.pure(Step<R>, Step{pool, jar, br, b, body, denied(R, why, last), Retry.PlanStop{}})
329	    case Retry.GateGo{}:
330	      do IO<Step<R>>:
331	        close.last(~R, ~close, last)
332	        attempt.run(~R, ~judge, ~try, o, call, idem, n, pool, jar, br, b, Bytes.slice(body, 0, 4294967295))
333	
334	# Ask the gate; when it admits, make attempt n (0 first) of this layer. With no deadline and no breaker,
335	# admission does not read the clock.
336	def attempt(~R: Type, ~judge: Result<&1, &1, Http.Err, R> -> Result<&1, &1, Http.Err, R> & Maybe<&2, String>,
337	    ~try: Opts -> Call -> Http.Pool -> Maybe<&2, Http.Jar> -> Bytes.Bytes -> IO(Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, R>),
338	    ~close: R -> IO(Unit),
339	    +o: Opts, +call: Call, +idem: Bool, +n: Nat, s: Step<R>) -> IO(Step<R>):
340	  Step{pool, jar, +br, +b, body, last, plan} = s
341	  do IO<Step<R>>:
342	    now : Nat <- clock(Bool.or(breaker.on(br), deadline.some(b)))
343	    attempt.gate(~R, ~judge, ~try, ~close, Retry.admit(br, b, now), o, call, idem, n, pool, jar, body, last)
344	
345	def pause(ms: Nat) -> IO(Unit):
346	  match ms:
347	    case 0n:
348	      IO.pure(Unit, Unit{})
349	    case 1n+k:
350	      IO.sleep(U32.from_nat(1n+k))
351	
352	# left: attempts this layer may still make. n: attempts made so far. Each turn follows the plan of the last step.
353	def go(~R: Type, ~judge: Result<&1, &1, Http.Err, R> -> Result<&1, &1, Http.Err, R> & Maybe<&2, String>,
354	    ~try: Opts -> Call -> Http.Pool -> Maybe<&2, Http.Jar> -> Bytes.Bytes -> IO(Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, R>),
355	    ~close: R -> IO(Unit),
356	    left: Nat, +n: Nat, +o: Opts, +call: Call, +idem: Bool, s: Step<R>) -> IO(Step<R>):
357	  match left:
358	    case 0n:
359	      IO.pure(Step<R>, s)
360	    case 1n+rest:
361	      Step{pool, jar, br, b, body, last, plan} = s
362	      match plan:
363	        case Retry.PlanStop{}:
364	          IO.pure(Step<R>, Step{pool, jar, br, b, body, last, Retry.PlanStop{}})
365	        case Retry.PlanWait{ms}:
366	          do IO<Step<R>>:
367	            pause(ms)
368	            next : Step<R> <- attempt(~R, ~judge, ~try, ~close, o, call, idem, n, Step{pool, jar, br, b, body, last, Retry.PlanStop{}})
369	            go(~R, ~judge, ~try, ~close, rest, 1n+n, o, call, idem, next)
370	
371	def result.of(-R: Type, m: Maybe<&1, Result<&1, &1, Err, R>>) -> Result<&1, &1, Err, R>:
372	  match m:
373	    case None{}:
374	      Fail{ErrDenied{Retry.DenySpent{}}}
375	    case Some{r}:
376	      r
377	
378	def request.done(-R: Type, +o: Opts, s: Step<R>) -> Client & Retry.Budget & Result<&1, &1, Err, R>:
379	  Step{pool, jar, br, b, body, last, plan} = s
380	  (Client{o, pool, jar, br}, b, result.of(R, last))
381	
382	def attempts(p: Retry.Policy) -> Nat:
383	  Retry.Policy{a, base, cap, d} = p
384	  a
385	
386	# The budget of one plain request: the policy's attempts, and its deadline from now. The clock is read only for a deadline.
387	def budget(c: Client) -> IO(Client & Retry.Budget):
388	  Client{+o, pool, jar, br} = c
389	  Opts{base, h, ms, mode, Retry.Policy{+a, bs, cap, +d}, cert, ca} = o
390	  do IO<Client & Retry.Budget>:
391	    now : Nat <- clock(some(d))
392	    return (Client{o, pool, jar, br}, Retry.Budget.new(a, now, d))
393	
394	def run(~R: Type, ~judge: Result<&1, &1, Http.Err, R> -> Result<&1, &1, Http.Err, R> & Maybe<&2, String>,
395	    ~try: Opts -> Call -> Http.Pool -> Maybe<&2, Http.Jar> -> Bytes.Bytes -> IO(Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, R>),
396	    ~close: R -> IO(Unit),
397	    c: Client, b: Retry.Budget, +idem: Bool, enc: String, method: String, url: String,
398	    headers: Map<&2, List<&2, String>>, body: Bytes.Bytes) -> IO(Client & Retry.Budget & Result<&1, &1, Err, R>):
399	  Client{+o, pool, jar, br} = c
400	  Opts{+base, +h, ms, mode, +p, cert, ca} = o
401	  +call = {Call{enc, method, target.abs(target(base, url)), merge(h, headers)} : Call}
402	  do IO<Client & Retry.Budget & Result<&1, &1, Err, R>>:
403	    s : Step<R> <- go(~R, ~judge, ~try, ~close, attempts(p), 0n, o, call, idem, Step{pool, jar, br, b, body, None{}, Retry.PlanWait{0n}})
404	    return request.done(R, o, s)
405	
406	# One request inside a caller's retry layer, with every choice explicit. Every attempt takes from b, the
407	# caller's shared budget, and obeys its deadline; the client's own policy caps the attempts of this call.
408	# The budget left comes back beside the result: pass it to the next call, so nested layers never reset or
409	# multiply it. The client's own deadline does not apply here; b's does.
410	# judge: Some{Retry-After} when another attempt may help. idem: the request is safe to repeat, so a judged
411	# failure is retried; else the breaker counts it and it never repeats. enc: the Accept-Encoding codings.
412	def request.as(~judge: Result<&1, &1, Http.Err, Http.Res> -> Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, String>,
413	    c: Client, b: Retry.Budget, +idem: Bool, +enc: String, +method: String, url: String,
414	    headers: Map<&2, List<&2, String>>, body: Bytes.Bytes) -> IO(Client & Retry.Budget & Result<&1, &1, Err, Http.Res>):
415	  run(~Http.Res, ~judge, ~try.res, ~close.res, c, b, idem, enc, method, url, headers, body)
416	
417	# A streamed request under the same budget, deadline, backoff, and breaker as request.as. The stream opens its
418	# own connection outside the pool. It follows the client's redirect mode, presents its certificate, and sends
419	# and stores cookies through its jar, as request.as does. judge reads the status and headers through
420	# Http.stream.res. A refused stream closes before the next attempt; the last one comes back open, so the
421	# caller can read its body.
422	def open.as(~judge: Result<&1, &1, Http.Err, Http.Stream> -> Result<&1, &1, Http.Err, Http.Stream> & Maybe<&2, String>,
423	    c: Client, b: Retry.Budget, +idem: Bool, +enc: String, +method: String, url: String,
424	    headers: Map<&2, List<&2, String>>, body: Bytes.Bytes) -> IO(Client & Retry.Budget & Result<&1, &1, Err, Http.Stream>):
425	  run(~Http.Stream, ~judge, ~try.stream, ~Http.stream.close, c, b, idem, enc, method, url, headers, body)
426	
427	# request.as with judge, the idempotency of method, and every coding Http decodes.
428	def request.in(c: Client, b: Retry.Budget, +method: String, url: String, headers: Map<&2, List<&2, String>>,
429	    body: Bytes.Bytes) -> IO(Client & Retry.Budget & Result<&1, &1, Err, Http.Res>):
430	  do IO<Client & Retry.Budget & Result<&1, &1, Err, Http.Res>>:
431	    enc : String <- Http.codings()
432	    request.as(~judge, c, b, Http.pool.idempotent(method), enc, method, url, headers, body)
433	
434	def request.drop(x: Client & Retry.Budget & Result<&1, &1, Err, Http.Res>) -> Client & Result<&1, &1, Err, Http.Res>:
435	  (c, b, r) = x
436	  (c, r)
437	
438	def request.budget(+method: String, url: String, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes,
439	    x: Client & Retry.Budget) -> IO(Client & Retry.Budget & Result<&1, &1, Err, Http.Res>):
440	  (c, b) = x
441	  request.in(c, b, method, url, headers, body)
442	
443	# url resolves against the base; headers go over the defaults. Redirects follow the client's mode, at most 20.
444	# Each request gets a fresh budget from budget(c). Before each attempt the deadline, the
445	# budget, and the breaker must admit it. GET, HEAD, OPTIONS, TRACE, PUT, and DELETE try again after a connect
446	# error, a timeout, or 408, 429, 500, 502, 503, or 504, as Http.retry.judge says, on the same pool.
447	# When the attempts run out, the last result comes back; when none started, ErrDenied says why.
448	def request(c: Client, +method: String, url: String, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes) ->
449	    IO(Client & Result<&1, &1, Err, Http.Res>):
450	  do IO<Client & Result<&1, &1, Err, Http.Res>>:
451	    y : Client & Retry.Budget <- budget(c)
452	    x : Client & Retry.Budget & Result<&1, &1, Err, Http.Res> <- request.budget(method, url, headers, body, y)
453	    return request.drop(x)
454	
455	def get(c: Client, url: String) -> IO(Client & Result<&1, &1, Err, Http.Res>):
456	  request(c, "GET", url, Http.empty(), Bytes.new(0))
457	
458	# POST v as compact JSON, with content-type: application/json.
459	def post.json(c: Client, url: String, v: Json.Val) -> IO(Client & Result<&1, &1, Err, Http.Res>):
460	  request(c, "POST", url, Http.set(Http.empty(), "content-type", "application/json"), Json.encode.bytes(v))