llm.bend

bend-kit-llm@0.13.0.1 · 620 lines · 91 definitions

1# LLM client for the Anthropic Messages and OpenAI Chat Completions APIs, with SSE streaming. Source: https://github.com/paymog/bend-kit/tree/main/llm
2import Base
3import bend-kit-llm@0.13.0.1/sse.bend as Sse
4import bend-kit-hairpin@0.13.0.1/hairpin.bend as Hairpin
5import bend-kit-retry@0.2.0.0/retry.bend as Retry
6import bend-kit-http@0.38.1.1/http.bend as Http
7import bend-kit-json@0.7.0.0/json.bend as Json
8import bend-kit-bytes@0.3.3.0/bytes.bend as Bytes
9import bend-kit-encoding@0.5.0.0/encoding.bend as Enc
10
11# Anthropic: POST {base}/v1/messages. OpenAI: POST {base}/chat/completions, which many other providers serve too.
12type Api is Data:
13  Anthropic{}
14  OpenAI{}
15
16type Role is Data:
17  User{}
18  Assistant{}
19
20type Msg is Data:
21  Msg{role: Role, text: String}
22
23# system: "" for none. max: the most tokens to write.
24type Req is Data:
25  Req{model: String, system: String, msgs: List<&2, Msg>, max: U32}
26
27# stop: the API's reason, as "end_turn" or "stop". input and output count tokens.
28type Reply is Data:
29  Reply{id: String, model: String, text: String, stop: String, input: U32, output: U32}
30
31# ErrNet: the request did not complete, or Hairpin's breaker admitted no attempt. ErrApi: the API refused, with
32# its status and error text; an error event in a stream has status 200. ErrReply: a reply that is not the API's JSON, with its text.
33type Err is Data:
34  ErrNet{e: Hairpin.Err}
35  ErrApi{status: U32, body: String}
36  ErrReply{body: String}
37
38# headers go on every request. ms: the step timeout. retries: extra tries after a retryable failure.
39type Client is Type:
40  Client{api: Api, base: String, headers: Map<&2, List<&2, String>>, ms: U32, retries: U32, http: Hairpin.Client}
41
42# ---- JSON
43
44def str(s: String) -> Json.Val:
45  Json.Str{Json.utf8(s)}
46
47def kv(k: String, v: Json.Val) -> Bytes.Bytes & Json.Val:
48  (Json.utf8(k), v)
49
50def num(+n: U32) -> Json.Val:
51  Json.Num{Bytes.from_string(U32.show(n))}
52
53def obj(kvs: List<&1, Bytes.Bytes & Json.Val>) -> Json.Val:
54  Json.Obj{kvs}
55
56def when(on: Bool, x: Bytes.Bytes & Json.Val, xs: List<&1, Bytes.Bytes & Json.Val>) -> List<&1, Bytes.Bytes & Json.Val>:
57  match on:
58    case True{}:
59      Con{x, xs}
60    case False{}:
61      xs
62
63def role(r: Role) -> String:
64  match r:
65    case User{}:
66      "user"
67    case Assistant{}:
68      "assistant"
69
70def msg(+r: String, t: String) -> Json.Val:
71  obj([kv("role", str(r)), kv("content", str(t))])
72
73def msgs(xs: List<&2, Msg>) -> List<&1, Json.Val>:
74  match xs:
75    case Nil{}:
76      Nil{}
77    case Con{Msg{r, t}, rest}:
78      Con{msg(role(r), t), msgs(rest)}
79
80def sys(on: Bool, s: String, xs: List<&1, Json.Val>) -> List<&1, Json.Val>:
81  match on:
82    case True{}:
83      Con{msg("system", s), xs}
84    case False{}:
85      xs
86
87# The request body for api. stream asks for SSE.
88def body(api: Api, req: Req, stream: Bool) -> Json.Val:
89  match api:
90    case Anthropic{}:
91      Req{model, +system, ms, max} = req
92      obj(Con{kv("model", str(model)), Con{kv("max_tokens", num(max)),
93        when(Bool.not(String.is_empty(system)), kv("system", str(system)),
94          Con{kv("messages", Json.Arr{msgs(ms)}), when(stream, kv("stream", Json.Flag{True{}}), Nil{})})}})
95    case OpenAI{}:
96      Req{model, +system, ms, max} = req
97      obj(Con{kv("model", str(model)), Con{kv("max_completion_tokens", num(max)),
98        Con{kv("messages", Json.Arr{sys(Bool.not(String.is_empty(system)), system, msgs(ms))}),
99          when(stream, kv("stream", Json.Flag{True{}}), Nil{})}}})
100
101# A JSON leaf: its path, as "content.0.text", and its text.
102type Leaf is Data:
103  Leaf{p: String, v: String}
104
105def path(+p: String, +k: String) -> String:
106  Bool.pick(String, String.is_empty(p), k, p ++ "." ++ k)
107
108def push.arr(xs: List<&1, Json.Val>, +p: String, +i: U32, t: List<&1, String & Json.Val>) -> List<&1, String & Json.Val>:
109  match xs:
110    case Nil{}:
111      t
112    case Con{x, rest}:
113      Con{(path(p, U32.show(i)), x), push.arr(rest, p, (i + 1 : U32), t)}
114
115def push.obj(kvs: List<&1, Bytes.Bytes & Json.Val>, +p: String, t: List<&1, String & Json.Val>) -> List<&1, String & Json.Val>:
116  match kvs:
117    case Nil{}:
118      t
119    case Con{(k, x), rest}:
120      Con{(path(p, Enc.utf8.decode(k)), x), push.obj(rest, p, t)}
121
122# The leaves under the stack's values, last first. f: at least the values left.
123def flat(f: Nat, stack: List<&1, String & Json.Val>, acc: List<&2, Leaf>) -> List<&2, Leaf>:
124  match f:
125    case 0n:
126      acc
127    case 1n+g:
128      match stack:
129        case Nil{}:
130          acc
131        case Con{(p, v), t}:
132          match v:
133            case Json.Null{}:
134              flat(g, t, acc)
135            case Json.Flag{on}:
136              flat(g, t, Con{Leaf{p, Bool.pick(String, on, "true", "false")}, acc})
137            case Json.Num{s}:
138              flat(g, t, Con{Leaf{p, Bytes.to_string(s)}, acc})
139            case Json.Str{s}:
140              flat(g, t, Con{Leaf{p, Enc.utf8.decode(s)}, acc})
141            case Json.Arr{xs}:
142              flat(g, push.arr(xs, p, 0, t), acc)
143            case Json.Obj{kvs}:
144              flat(g, push.obj(kvs, p, t), acc)
145
146def doc.of(+n: U32, m: Maybe<&1, Json.Val>) -> Maybe<&2, List<&2, Leaf>>:
147  match m:
148    case None{}:
149      None{}
150    case Some{v}:
151      Some{List.reverse(&2, Leaf, flat(Nat.add(U32.to_nat(n), 1n), [("", v)], Nil{}))}
152
153# Every non-null leaf of a JSON text in document order, keyed by its path, as ("content.0.text", "Hi").
154# Strings are decoded; numbers keep their text. None when b is not JSON. Each value takes a byte, so n + 1 steps suffice.
155def doc(b: Bytes.Bytes) -> Maybe<&2, List<&2, Leaf>>:
156  Bytes.Bytes{+n, buf} = b
157  doc.of(n, Json.parse.bytes(Bytes.Bytes{n, buf}))
158
159# The first value at path k, or "".
160def look(d: List<&2, Leaf>, +k: String) -> String:
161  match d:
162    case Nil{}:
163      ""
164    case Con{Leaf{p, v}, t}:
165      Bool.pick(String, String.eq(p, k), v, look(t, k))
166
167def count(s: String) -> U32:
168  Maybe.default(&2, U32, Json.u32.num(s), 0)
169
170def dots(s: String, +n: U32) -> U32:
171  match s:
172    case SNil{}:
173      n
174    case SCon{Chr{+c}, t}:
175      dots(t, Bool.pick(U32, U32.is_eq(c, 46), (n + 1 : U32), n))
176
177# Is p the text of a content block, "content.<i>.text"?
178def block(+p: String) -> Bool:
179  Bool.and(Bool.and(String.starts_with(p, "content."), String.ends_with(p, ".text")), U32.is_eq(dots(p, 0), 2))
180
181# The text blocks of an Anthropic message, joined.
182def blocks(d: List<&2, Leaf>) -> String:
183  match d:
184    case Nil{}:
185      ""
186    case Con{Leaf{+p, v}, t}:
187      Bool.pick(String, block(p), v, "") ++ blocks(t)
188
189def reply.of(api: Api, +d: List<&2, Leaf>) -> Reply:
190  match api:
191    case Anthropic{}:
192      Reply{look(d, "id"), look(d, "model"), blocks(d), look(d, "stop_reason"),
193        count(look(d, "usage.input_tokens")), count(look(d, "usage.output_tokens"))}
194    case OpenAI{}:
195      Reply{look(d, "id"), look(d, "model"), look(d, "choices.0.message.content"), look(d, "choices.0.finish_reason"),
196        count(look(d, "usage.prompt_tokens")), count(look(d, "usage.completion_tokens"))}
197
198def reply.got(api: Api, b: Bytes.Bytes, m: Maybe<&2, List<&2, Leaf>>) -> Result<&1, &1, Err, Reply>:
199  match m:
200    case None{}:
201      Fail{ErrReply{Enc.utf8.decode(b)}}
202    case Some{d}:
203      Done{reply.of(api, d)}
204
205def reply.copy(api: Api, r: Bytes.Bytes & Bytes.Bytes) -> Result<&1, &1, Err, Reply>:
206  (b, c) = r
207  reply.got(api, b, doc(c))
208
209# A 2xx response body as a Reply.
210def reply(api: Api, b: Bytes.Bytes) -> Result<&1, &1, Err, Reply>:
211  reply.copy(api, Bytes.slice(b, 0, 4294967295))
212
213# ---- stream events
214
215# A text piece, the end, an error, or an event with no text.
216type Ev is Data:
217  EText{s: String}
218  EEnd{}
219  EFail{e: Err}
220  ESkip{}
221
222def ev.text(+s: String) -> Ev:
223  Bool.pick(Ev, String.is_empty(s), ESkip{}, EText{s})
224
225def ev.doc(m: Maybe<&2, List<&2, Leaf>>) -> List<&2, Leaf>:
226  Maybe.default(&2, List<&2, Leaf>, m, Nil{})
227
228def ev.anthropic(+name: String, data: Bytes.Bytes) -> Ev:
229  +d = ev.doc(doc(data))
230  Bool.pick(Ev, String.eq(name, "content_block_delta"), ev.text(look(d, "delta.text")),
231    Bool.pick(Ev, String.eq(name, "message_stop"), EEnd{},
232      Bool.pick(Ev, String.eq(name, "error"), EFail{ErrApi{200, look(d, "error.message")}}, ESkip{})))
233
234def ev.openai(+s: String) -> Ev:
235  +d = ev.doc(doc(Bytes.from_string(s)))
236  +why = look(d, "error.message")
237  Bool.pick(Ev, String.eq(s, "[DONE]"), EEnd{},
238    Bool.pick(Ev, String.is_empty(why), ev.text(look(d, "choices.0.delta.content")), EFail{ErrApi{200, why}}))
239
240# What one SSE event of api means.
241def ev(api: Api, e: Sse.Message) -> Ev:
242  match api:
243    case Anthropic{}:
244      Sse.Message{name, data, id} = e
245      ev.anthropic(name, data)
246    case OpenAI{}:
247      Sse.Message{name, data, id} = e
248      ev.openai(Bytes.to_string(data))
249
250# ---- requests
251
252def ok(+s: U32) -> Bool:
253  Bool.and(U32.is_le(200, s), U32.is_lt(s, 300))
254
255# Statuses a later try may clear: 408, 409, 429, and 5xx, which holds Anthropic's 529.
256def again.status(+s: U32) -> Bool:
257  Bool.or(Bool.or(U32.is_eq(s, 408), U32.is_eq(s, 409)), Bool.or(U32.is_eq(s, 429), U32.is_le(500, s)))
258
259# A refused connect or a timeout may clear.
260def again.err(+e: Http.Err) -> Maybe<&2, String>:
261  match e:
262    case Http.ErrConnect{code, why}:
263      Some{""}
264    case Http.ErrTimeout{}:
265      Some{""}
266    case other:
267      None{}
268
269def again.of(+status: U32, +h: Map<&2, List<&2, String>>) -> Maybe<&2, String>:
270  Bool.pick(Maybe<&2, String>, again.status(status), Some{Http.header(h, "retry-after")}, None{})
271
272# Again when another try may help; otherwise settled, as Hairpin.judge would settle it.
273def verdict(m: Maybe<&2, String>, settled: Hairpin.Verdict) -> Hairpin.Verdict:
274  match m:
275    case Some{after}:
276      Hairpin.VerdictAgain{after}
277    case None{}:
278      settled
279
280# Hairpin's judge for every call.
281def again(r: Result<&1, &1, Http.Err, Http.Res>) -> Result<&1, &1, Http.Err, Http.Res> & Hairpin.Verdict:
282  match r:
283    case Fail{+e}:
284      (Fail{e}, verdict(again.err(e), Hairpin.VerdictTarget{}))
285    case Done{res}:
286      Http.Res{+status, +h, b} = res
287      (Done{Http.Res{status, h, b}}, verdict(again.of(status, h), Hairpin.judge.status(status)))
288
289def body.ok(good: Bool, +status: U32, b: Bytes.Bytes) -> Result<&1, &1, Err, Bytes.Bytes>:
290  match good:
291    case True{}:
292      Done{b}
293    case False{}:
294      Fail{ErrApi{status, Enc.utf8.decode(b)}}
295
296# The 2xx body, or why there is none.
297def body.of(r: Result<&1, &1, Hairpin.Err, Http.Res>) -> Result<&1, &1, Err, Bytes.Bytes>:
298  match r:
299    case Fail{e}:
300      Fail{ErrNet{e}}
301    case Done{res}:
302      Http.Res{+status, h, b} = res
303      body.ok(ok(status), status, b)
304
305def url(api: Api, +base: String) -> String:
306  match api:
307    case Anthropic{}:
308      base ++ "/v1/messages"
309    case OpenAI{}:
310      base ++ "/chat/completions"
311
312# ---- the client
313
314def new(+api: Api, base: String, headers: Map<&2, List<&2, String>>) -> Client:
315  Client{api, base, headers, 600000, 2, Hairpin.timeout(Hairpin.new(), 600000)}
316
317def json(h: Map<&2, List<&2, String>>) -> Map<&2, List<&2, String>>:
318  Http.set(h, "content-type", "application/json")
319
320# base https://api.anthropic.com, 10 min steps, 2 retries.
321def anthropic(key: String) -> Client:
322  new(Anthropic{}, "https://api.anthropic.com", json(Http.set(Http.set(Http.empty(), "x-api-key", key), "anthropic-version", "2023-06-01")))
323
324# base https://api.openai.com/v1, 10 min steps, 2 retries.
325def openai(key: String) -> Client:
326  new(OpenAI{}, "https://api.openai.com/v1", json(Http.set(Http.empty(), "authorization", "Bearer " ++ key)))
327
328# Another base URL, as for a provider that serves the same API.
329def base(c: Client, url: String) -> Client:
330  Client{api, old, h, ms, n, http} = c
331  Client{api, url, h, ms, n, http}
332
333# A header on every request, as anthropic-beta. It replaces one of the same name.
334def header(c: Client, k: String, v: String) -> Client:
335  Client{api, b, h, ms, n, http} = c
336  Client{api, b, Http.set(h, String.to_lower(k), v), ms, n, http}
337
338def timeout(c: Client, +ms: U32) -> Client:
339  Client{api, b, h, old, n, http} = c
340  Client{api, b, h, ms, n, Hairpin.timeout(http, ms)}
341
342def retry(c: Client, n: U32) -> Client:
343  Client{api, b, h, ms, old, http} = c
344  Client{api, b, h, ms, n, http}
345
346def close(c: Client) -> IO(Unit):
347  Client{api, b, h, ms, n, http} = c
348  Hairpin.close(http)
349
350def call.done(+api: Api, base: String, headers: Map<&2, List<&2, String>>, +ms: U32, +n: U32,
351    x: Hairpin.Client & Retry.Budget & Result<&1, &1, Hairpin.Err, Http.Res>) -> Client & Result<&1, &1, Err, Bytes.Bytes>:
352  (h, b, r) = x
353  (Client{api, base, headers, ms, n, h}, body.of(r))
354
355def call.budget(+api: Api, +base: String, +headers: Map<&2, List<&2, String>>, body: Bytes.Bytes, y: Hairpin.Client & Retry.Budget) ->
356    IO(Hairpin.Client & Retry.Budget & Result<&1, &1, Hairpin.Err, Http.Res>):
357  (h, b) = y
358  do IO<Hairpin.Client & Retry.Budget & Result<&1, &1, Hairpin.Err, Http.Res>>:
359    enc : String <- Http.codings()
360    Hairpin.request.as(~again, h, b, True{}, enc, "POST", url(api, base), headers, body)
361
362# POST body to the API with n retries on a budget of n + 1; the 2xx body comes back.
363# These POSTs are safe to repeat, so Hairpin retries them as again judges.
364def call(c: Client, body: Bytes.Bytes) -> IO(Client & Result<&1, &1, Err, Bytes.Bytes>):
365  Client{+api, +base, +headers, +ms, +n, h} = c
366  do IO<Client & Result<&1, &1, Err, Bytes.Bytes>>:
367    y : Hairpin.Client & Retry.Budget <- Hairpin.budget(Hairpin.retry(h, n))
368    x : Hairpin.Client & Retry.Budget & Result<&1, &1, Hairpin.Err, Http.Res> <- call.budget(api, base, headers, body, y)
369    return call.done(api, base, headers, ms, n, x)
370
371def raw.got(b: Bytes.Bytes, m: Maybe<&1, Json.Val>) -> Result<&1, &1, Err, Json.Val>:
372  match m:
373    case None{}:
374      Fail{ErrReply{Enc.utf8.decode(b)}}
375    case Some{v}:
376      Done{v}
377
378def raw.copy(r: Bytes.Bytes & Bytes.Bytes) -> Result<&1, &1, Err, Json.Val>:
379  (b, c) = r
380  raw.got(b, Json.parse.bytes(c))
381
382def raw.of(r: Result<&1, &1, Err, Bytes.Bytes>) -> Result<&1, &1, Err, Json.Val>:
383  match r:
384    case Fail{e}:
385      Fail{e}
386    case Done{b}:
387      raw.copy(Bytes.slice(b, 0, 4294967295))
388
389def raw.done(x: Client & Result<&1, &1, Err, Bytes.Bytes>) -> Client & Result<&1, &1, Err, Json.Val>:
390  (c, r) = x
391  (c, raw.of(r))
392
393# Any request body, as for tools or images, and the reply as JSON.
394def send.raw(c: Client, v: Json.Val) -> IO(Client & Result<&1, &1, Err, Json.Val>):
395  do IO<Client & Result<&1, &1, Err, Json.Val>>:
396    x : Client & Result<&1, &1, Err, Bytes.Bytes> <- call(c, Json.encode.bytes(v))
397    return raw.done(x)
398
399def send.of(r: Result<&1, &1, Err, Bytes.Bytes>, +api: Api) -> Result<&1, &1, Err, Reply>:
400  match r:
401    case Fail{e}:
402      Fail{e}
403    case Done{b}:
404      reply(api, b)
405
406def send.done(+api: Api, x: Client & Result<&1, &1, Err, Bytes.Bytes>) -> Client & Result<&1, &1, Err, Reply>:
407  (c, r) = x
408  (c, send.of(r, api))
409
410# One whole reply.
411def send(c: Client, req: Req) -> IO(Client & Result<&1, &1, Err, Reply>):
412  Client{+api, b, h, ms, n, http} = c
413  do IO<Client & Result<&1, &1, Err, Reply>>:
414    x : Client & Result<&1, &1, Err, Bytes.Bytes> <- call(Client{api, b, h, ms, n, http}, Json.encode.bytes(body(api, req, False{})))
415    return send.done(api, x)
416
417# ---- streams
418
419type Stream is Type:
420  Stream{api: Api, h: Http.Stream, rd: Sse.Reader}
421
422def open.res(x: Http.Stream & Http.Res) -> Result<&1, &1, Http.Err, Http.Stream> & Hairpin.Verdict:
423  (st, res) = x
424  Http.Res{+status, +h, b} = res
425  (Done{st}, verdict(again.of(status, h), Hairpin.judge.status(status)))
426
427def open.judge(r: Result<&1, &1, Http.Err, Http.Stream>) -> Result<&1, &1, Http.Err, Http.Stream> & Hairpin.Verdict:
428  match r:
429    case Fail{+e}:
430      (Fail{e}, verdict(again.err(e), Hairpin.VerdictTarget{}))
431    case Done{st}:
432      open.res(Http.stream.res(st))
433
434# A refused stream's error body, at most f more pieces, then the stream closed.
435def drain(f: Nat, x: Http.Stream & Result<&1, &1, Http.Err, Maybe<&1, Bytes.Bytes>>, acc: Bytes.Bytes) -> IO(Bytes.Bytes):
436  match f:
437    case 0n:
438      (h, r) = x
439      do IO<Bytes.Bytes>:
440        Http.stream.close(h)
441        return acc
442    case 1n+g:
443      (h, r) = x
444      match r:
445        case Fail{e}:
446          do IO<Bytes.Bytes>:
447            Http.stream.close(h)
448            return acc
449        case Done{m}:
450          match m:
451            case None{}:
452              do IO<Bytes.Bytes>:
453                Http.stream.close(h)
454                return acc
455            case Some{b}:
456              do IO<Bytes.Bytes>:
457                y : Http.Stream & Result<&1, &1, Http.Err, Maybe<&1, Bytes.Bytes>> <- Http.stream.read(h)
458                drain(g, y, Bytes.append(acc, b))
459
460def start.refused(+status: U32, h: Http.Stream) -> IO(Result<&1, &1, Err, Http.Stream>):
461  do IO<Result<&1, &1, Err, Http.Stream>>:
462    y : Http.Stream & Result<&1, &1, Http.Err, Maybe<&1, Bytes.Bytes>> <- Http.stream.read(h)
463    b : Bytes.Bytes <- drain(64n, y, Bytes.new(0))
464    return Fail{ErrApi{status, Enc.utf8.decode(b)}}
465
466def start.ok(good: Bool, +status: U32, h: Http.Stream) -> IO(Result<&1, &1, Err, Http.Stream>):
467  match good:
468    case True{}:
469      IO.pure(Result<&1, &1, Err, Http.Stream>, Done{h})
470    case False{}:
471      start.refused(status, h)
472
473def start.res(x: Http.Stream & Http.Res) -> IO(Result<&1, &1, Err, Http.Stream>):
474  (h, res) = x
475  Http.Res{+status, hd, b} = res
476  start.ok(ok(status), status, h)
477
478def start(r: Result<&1, &1, Hairpin.Err, Http.Stream>) -> IO(Result<&1, &1, Err, Http.Stream>):
479  match r:
480    case Fail{e}:
481      IO.pure(Result<&1, &1, Err, Http.Stream>, Fail{ErrNet{e}})
482    case Done{h}:
483      start.res(Http.stream.res(h))
484
485def stream.of(r: Result<&1, &1, Err, Http.Stream>, +api: Api) -> Result<&1, &1, Err, Stream>:
486  match r:
487    case Fail{e}:
488      Fail{e}
489    case Done{h}:
490      Done{Stream{api, h, Sse.reader()}}
491
492def stream.done(+api: Api, base: String, headers: Map<&2, List<&2, String>>, +ms: U32, +n: U32,
493    x: Hairpin.Client & Retry.Budget & Result<&1, &1, Hairpin.Err, Http.Stream>) -> IO(Client & Result<&1, &1, Err, Stream>):
494  (h, b, r) = x
495  do IO<Client & Result<&1, &1, Err, Stream>>:
496    s : Result<&1, &1, Err, Http.Stream> <- start(r)
497    return (Client{api, base, headers, ms, n, h}, stream.of(s, api))
498
499def open.budget(+api: Api, +base: String, +headers: Map<&2, List<&2, String>>, body: Bytes.Bytes, y: Hairpin.Client & Retry.Budget) ->
500    IO(Hairpin.Client & Retry.Budget & Result<&1, &1, Hairpin.Err, Http.Stream>):
501  (h, b) = y
502  do IO<Hairpin.Client & Retry.Budget & Result<&1, &1, Hairpin.Err, Http.Stream>>:
503    enc : String <- Http.codings()
504    Hairpin.open.as(~open.judge, h, b, True{}, enc, "POST", url(api, base), headers, body)
505
506# Any request body that asks for SSE, as for tools. The open retries as call does, on a budget of n + 1.
507# A stream opens on the client's pool. Close it with stream.close to give its connection back.
508def stream.raw(c: Client, v: Json.Val) -> IO(Client & Result<&1, &1, Err, Stream>):
509  Client{+api, +base, +headers, +ms, +n, h} = c
510  do IO<Client & Result<&1, &1, Err, Stream>>:
511    y : Hairpin.Client & Retry.Budget <- Hairpin.budget(Hairpin.retry(h, n))
512    x : Hairpin.Client & Retry.Budget & Result<&1, &1, Hairpin.Err, Http.Stream> <- open.budget(api, base, headers, Json.encode.bytes(v), y)
513    stream.done(api, base, headers, ms, n, x)
514
515# The reply as it is written: read it with next.
516def stream(c: Client, req: Req) -> IO(Client & Result<&1, &1, Err, Stream>):
517  Client{+api, b, h, ms, n, http} = c
518  stream.raw(Client{api, b, h, ms, n, http}, body(api, req, True{}))
519
520# Close a stream. A stream read to its end gives its connection to the client's pool.
521def stream.close(c: Client, s: Stream) -> IO(Client):
522  Client{api, base, headers, ms, n, h} = c
523  Stream{sa, st, rd} = s
524  do IO<Client>:
525    p : Hairpin.Client <- Hairpin.stream.close(h, st)
526    return Client{api, base, headers, ms, n, p}
527
528# The reader after the next event, or the stream's result.
529type Rn is Type:
530  RnNext{h: Http.Stream, r: Sse.Reader & Sse.Next}
531  RnOut{h: Http.Stream, rd: Sse.Reader, r: Result<&1, &1, Err, Maybe<&1, Sse.Message>>}
532
533def event.read(rd: Sse.Reader, x: Http.Stream & Result<&1, &1, Http.Err, Maybe<&1, Bytes.Bytes>>) -> Rn:
534  (h, r) = x
535  match r:
536    case Fail{e}:
537      RnOut{h, rd, Fail{ErrNet{Hairpin.ErrHttp{e}}}}
538    case Done{m}:
539      match m:
540        case None{}:
541          RnOut{h, rd, Done{None{}}}
542        case Some{b}:
543          RnNext{h, Sse.next(Sse.feed(rd, b))}
544
545# f: pieces left to read before the stream counts as stalled.
546def event.loop(f: Nat, st: Rn) -> IO(Http.Stream & Sse.Reader & Result<&1, &1, Err, Maybe<&1, Sse.Message>>):
547  match f:
548    case 0n:
549      match st:
550        case RnNext{h, r}:
551          (rd, n) = r
552          IO.pure(Http.Stream & Sse.Reader & Result<&1, &1, Err, Maybe<&1, Sse.Message>>, (h, rd, Fail{ErrReply{"too many pieces without an event"}}))
553        case RnOut{h, rd, r}:
554          IO.pure(Http.Stream & Sse.Reader & Result<&1, &1, Err, Maybe<&1, Sse.Message>>, (h, rd, r))
555    case 1n+g:
556      match st:
557        case RnNext{h, r}:
558          (rd, n) = r
559          match n:
560            case Sse.Got{e}:
561              IO.pure(Http.Stream & Sse.Reader & Result<&1, &1, Err, Maybe<&1, Sse.Message>>, (h, rd, Done{Some{e}}))
562            case Sse.Want{}:
563              do IO<Http.Stream & Sse.Reader & Result<&1, &1, Err, Maybe<&1, Sse.Message>>>:
564                x : Http.Stream & Result<&1, &1, Http.Err, Maybe<&1, Bytes.Bytes>> <- Http.stream.read(h)
565                event.loop(g, event.read(rd, x))
566        case RnOut{h, rd, r}:
567          IO.pure(Http.Stream & Sse.Reader & Result<&1, &1, Err, Maybe<&1, Sse.Message>>, (h, rd, r))
568
569def event.done(+api: Api, x: Http.Stream & Sse.Reader & Result<&1, &1, Err, Maybe<&1, Sse.Message>>) -> Stream & Result<&1, &1, Err, Maybe<&1, Sse.Message>>:
570  (h, rd, r) = x
571  (Stream{api, h, rd}, r)
572
573# The next SSE event, or None when the stream ends. An event the end cuts off is dropped.
574def event(s: Stream) -> IO(Stream & Result<&1, &1, Err, Maybe<&1, Sse.Message>>):
575  Stream{+api, h, rd} = s
576  do IO<Stream & Result<&1, &1, Err, Maybe<&1, Sse.Message>>>:
577    x : Http.Stream & Sse.Reader & Result<&1, &1, Err, Maybe<&1, Sse.Message>> <- event.loop(Nat.mul(65536n, 256n), RnNext{h, Sse.next(rd)})
578    return event.done(api, x)
579
580def next.ev(r: Result<&1, &1, Err, Maybe<&1, Sse.Message>>, +api: Api) -> Ev:
581  match r:
582    case Fail{e}:
583      EFail{e}
584    case Done{m}:
585      match m:
586        case None{}:
587          EEnd{}
588        case Some{e}:
589          ev(api, e)
590
591def next.of(x: Stream & Result<&1, &1, Err, Maybe<&1, Sse.Message>>) -> Stream & Ev:
592  (s, r) = x
593  Stream{+api, h, rd} = s
594  (Stream{api, h, rd}, next.ev(r, api))
595
596# f: events left to skip.
597def next.loop(f: Nat, x: Stream & Ev) -> IO(Stream & Result<&1, &1, Err, Maybe<&2, String>>):
598  match f:
599    case 0n:
600      (s, e) = x
601      IO.pure(Stream & Result<&1, &1, Err, Maybe<&2, String>>, (s, Fail{ErrReply{"too many events without text"}}))
602    case 1n+g:
603      (s, e) = x
604      match e:
605        case EText{t}:
606          IO.pure(Stream & Result<&1, &1, Err, Maybe<&2, String>>, (s, Done{Some{t}}))
607        case EEnd{}:
608          IO.pure(Stream & Result<&1, &1, Err, Maybe<&2, String>>, (s, Done{None{}}))
609        case EFail{err}:
610          IO.pure(Stream & Result<&1, &1, Err, Maybe<&2, String>>, (s, Fail{err}))
611        case ESkip{}:
612          do IO<Stream & Result<&1, &1, Err, Maybe<&2, String>>>:
613            y : Stream & Result<&1, &1, Err, Maybe<&1, Sse.Message>> <- event(s)
614            next.loop(g, next.of(y))
615
616# The next piece of reply text, or None at the end.
617def next(s: Stream) -> IO(Stream & Result<&1, &1, Err, Maybe<&2, String>>):
618  do IO<Stream & Result<&1, &1, Err, Maybe<&2, String>>>:
619    y : Stream & Result<&1, &1, Err, Maybe<&1, Sse.Message>> <- event(s)
620    next.loop(Nat.mul(65536n, 256n), next.of(y))