hairpin.bend
bend-kit-hairpin@0.3.0.0 · 399 lines · 0 definitions
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
2import Base
3import bend-kit-http@0.32.0.0/http.bend as Http
4import bend-kit-time@0.1.2.1/time.bend as Time
5# By hash, as http imports them: bend-kit-url@0.4.1.0, -json@0.5.0.1, -bytes@0.3.0.0.
6import bend-kit-url@0.4.1.0/url.bend as Url
7import bend-kit-json@0.5.0.1/json.bend as Json
8import bend-kit-bytes@0.3.0.0/bytes.bend as Bytes
9import bend-kit-hairpin@0.3.0.0/retry.bend as Retry
10
11# base: "" for none. headers: lowercase names. ms: the step timeout. policy: attempts, backoff, and deadline of each request.
12type 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>}
14
15# breaker: the circuit breaker of every request on this client.
16type 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.
20type 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.
25def 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.
30def new.with(+cap: U32) -> Client:
31 Client{Opts{"", Http.empty(), 30000, Http.ModeFollow{}, policy(), None{}}, Http.pool.new.with(cap), None{}, Retry.BreakerOff{}}
32
33def new() -> Client:
34 new.with(8)
35
36def base(c: Client, url: String) -> Client:
37 Client{Opts{b, h, ms, mode, p, cert}, pool, j, br} = c
38 Client{Opts{url, h, ms, mode, p, cert}, 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.
41def header(c: Client, k: String, v: String) -> Client:
42 Client{Opts{b, h, ms, mode, p, cert}, pool, j, br} = c
43 Client{Opts{b, Http.set(h, String.to_lower(k), v), ms, mode, p, cert}, pool, j, br}
44
45def timeout(c: Client, ms: U32) -> Client:
46 Client{Opts{b, h, old, mode, p, cert}, pool, j, br} = c
47 Client{Opts{b, h, ms, mode, p, cert}, pool, j, br}
48
49def redirect(c: Client, mode: Http.Mode) -> Client:
50 Client{Opts{b, h, ms, old, p, cert}, pool, j, br} = c
51 Client{Opts{b, h, ms, mode, p, cert}, pool, j, br}
52
53# Up to n retries after the first attempt: n + 1 attempts in all.
54def retry(c: Client, n: U32) -> Client:
55 Client{Opts{b, h, ms, mode, Retry.Policy{old, base, cap, d}, cert}, pool, j, br} = c
56 Client{Opts{b, h, ms, mode, Retry.Policy{1n+U32.to_nat(n), base, cap, d}, cert}, pool, j, br}
57
58# No attempt of a request starts ms or more after the request starts.
59def deadline(c: Client, ms: U32) -> Client:
60 Client{Opts{b, h, t, mode, Retry.Policy{a, base, cap, old}, cert}, pool, j, br} = c
61 Client{Opts{b, h, t, mode, Retry.Policy{a, base, cap, Some{U32.to_nat(ms)}}, cert}, pool, j, br}
62
63# A circuit breaker in front of every request, starting closed.
64def 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.
69def 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.
74def cert(c: Client, chain: String, key: String) -> Client:
75 Client{Opts{b, h, ms, mode, p, old}, pool, j, br} = c
76 Client{Opts{b, h, ms, mode, p, Some{Http.Cert{chain, key}}}, pool, j, br}
77
78# Every request stores and sends cookies through jar. Its clock moves to Time.now() before each try.
79def jar(c: Client, jar: Http.Jar) -> Client:
80 Client{o, pool, old, br} = c
81 Client{o, pool, Some{jar}, br}
82
83# The jar, if the client has one.
84def jar.of(c: Client) -> Client & Maybe<&2, Http.Jar>:
85 Client{o, pool, +j, br} = c
86 (Client{o, pool, j, br}, j)
87
88def close(c: Client) -> IO(Unit):
89 Client{o, pool, j, br} = c
90 Http.pool.close(pool)
91
92def ms.of(r: U32 & U32 & U32) -> Nat:
93 (hi, lo, ns) = r
94 Nat.add(Nat.mul(Nat.add(Nat.mul(U32.to_nat(hi), 1n+4294967295n), U32.to_nat(lo)), 1000n), U32.to_nat((ns / 1000000 : U32)))
95
96# Milliseconds on the monotonic clock that Retry budgets and breakers use.
97def now.ms() -> IO(Nat):
98 do IO<Nat>:
99 r : U32 & U32 & U32 <- Time.mono.raw()
100 return ms.of(r)
101
102def target.pick(none: Bool, b: String, ref: String) -> Maybe<&2, String>:
103 match none:
104 case True{}:
105 Some{ref}
106 case False{}:
107 Http.resolve(b, ref)
108
109# ref against the base (RFC 3986 §5.2); with no base, ref as given. None when the base is not absolute.
110def target(+b: String, ref: String) -> Maybe<&2, String>:
111 target.pick(String.is_empty(b), b, ref)
112
113def target.abs(m: Maybe<&2, String>) -> Maybe<&2, Url.Abs>:
114 match m:
115 case None{}:
116 None{}
117 case Some{s}:
118 Url.absolute(s)
119
120# The defaults under the request headers, names lowercased; a request header replaces a default of its name.
121# Host, Connection, Content-Length, and Transfer-Encoding are the client's own, so both sides drop them.
122def merge(defaults: Map<&2, List<&2, String>>, headers: Map<&2, List<&2, String>>) -> Map<&2, List<&2, String>>:
123 Http.req.put(Map.to_list(&2, List<&2, String>, headers), Http.req.put(Map.to_list(&2, List<&2, String>, defaults), Http.empty()))
124
125def jar.now(j: Maybe<&2, Http.Jar>) -> IO(Maybe<&2, Http.Jar>):
126 match j:
127 case None{}:
128 IO.pure(Maybe<&2, Http.Jar>, None{})
129 case Some{jar}:
130 do IO<Maybe<&2, Http.Jar>>:
131 now : Time.Instant <- Time.now()
132 return Some{Http.jar.at(jar, now)}
133
134def once.final(+enc: String, x: Http.Pool & Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, Http.Jar>) ->
135 IO(Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Res>):
136 (p, r, j) = x
137 do IO<Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Res>>:
138 d : Result<&1, &1, Http.Err, Http.Res> <- Http.fetch.final(enc, r)
139 return (p, j, d)
140
141# One try: the redirect loop on the pool, with the jar and the certificate, then the body decoded.
142def once(+ms: U32, +mode: Http.Mode, +cert: Maybe<&2, Http.Cert>, +enc: String, p: Http.Pool, j: Maybe<&2, Http.Jar>,
143 +method: String, +u: Maybe<&2, Url.Abs>, +headers: Map<&2, List<&2, String>>, body: Bytes.Bytes) ->
144 IO(Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Res>):
145 do IO<Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Res>>:
146 now : Maybe<&2, Http.Jar> <- jar.now(j)
147 x : Http.Pool & Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, Http.Jar> <-
148 Http.pool.hops(mode, ms, Http.Hops{p, Http.fetch.start(method, headers, body, u, enc), cert, now, ""})
149 once.final(enc, x)
150
151def hint.ms(m: Maybe<&2, U32>) -> Maybe<&2, Nat>:
152 match m:
153 case None{}:
154 None{}
155 case Some{ms}:
156 Some{U32.to_nat(ms)}
157
158# m is Http.retry.judge's verdict for an idempotent request: Some{Retry-After} when another try may help.
159# A non-idempotent request with that verdict is Unsafe: the breaker counts it, but it never repeats.
160def outcome(+idem: Bool, m: Maybe<&2, String>, now: Time.Instant) -> Retry.Outcome:
161 match m:
162 case None{}:
163 Retry.Settled{}
164 case Some{+v}:
165 Bool.pick(Retry.Outcome, idem, Retry.Transient{hint.ms(Http.retry.after(v, now))}, Retry.Unsafe{})
166
167def lift(r: Result<&1, &1, Http.Err, Http.Res>) -> Result<&1, &1, Err, Http.Res>:
168 match r:
169 case Fail{e}:
170 Fail{ErrHttp{e}}
171 case Done{res}:
172 Done{res}
173
174# The live state of one request between attempts. last: the result of the last attempt, None before the first.
175type Step is Type:
176 Step{pool: Http.Pool, jar: Maybe<&2, Http.Jar>, breaker: Retry.Breaker, budget: Retry.Budget, body: Bytes.Bytes,
177 last: Maybe<&1, Result<&1, &1, Err, Http.Res>>, plan: Retry.Plan}
178
179# The clock, read only when a decision depends on it; 0 otherwise, which no such decision reads.
180def clock(need: Bool) -> IO(Nat):
181 match need:
182 case True{}:
183 now.ms()
184 case False{}:
185 IO.pure(Nat, 0n)
186
187def breaker.on(br: Retry.Breaker) -> Bool:
188 match br:
189 case Retry.BreakerOff{}:
190 False{}
191 case Retry.BreakerOn{c, s}:
192 True{}
193
194def transient(o: Retry.Outcome) -> Bool:
195 match o:
196 case Retry.Transient{after}:
197 True{}
198 case Retry.Settled{}:
199 False{}
200 case Retry.Unsafe{}:
201 False{}
202
203def some(m: Maybe<&2, Nat>) -> Bool:
204 match m:
205 case None{}:
206 False{}
207 case Some{t}:
208 True{}
209
210def deadline.some(b: Retry.Budget) -> Bool:
211 Retry.Budget{l, d} = b
212 some(d)
213
214# The wall clock dates a Retry-After, so it is read only for a transient failure.
215def outcome.io(+idem: Bool, m: Maybe<&2, String>) -> IO(Retry.Outcome):
216 match m:
217 case None{}:
218 IO.pure(Retry.Outcome, Retry.Settled{})
219 case Some{v}:
220 do IO<Retry.Outcome>:
221 wall : Time.Instant <- Time.now()
222 return outcome(idem, Some{v}, wall)
223
224# Jitter for the backoff, drawn only when a retry may follow.
225def jitter.io(need: Bool) -> IO(Nat):
226 match need:
227 case True{}:
228 do IO<Nat>:
229 rnd : Result<&1, &1, U32 & String, U32> <- IO.random_u32()
230 return U32.to_nat(Http.retry.jitter(rnd))
231 case False{}:
232 IO.pure(Nat, 0n)
233
234def settle.at(+now: Nat, +rnd: Nat, +p: Retry.Policy, +n: Nat, +o: Retry.Outcome, br: Retry.Breaker, +b: Retry.Budget,
235 body: Bytes.Bytes, pool: Http.Pool, jar: Maybe<&2, Http.Jar>, r: Result<&1, &1, Http.Err, Http.Res>) -> Step:
236 Step{pool, jar, Retry.Breaker.done(br, now, Retry.failed(o)), b, body, Some{lift(r)}, Retry.plan(o, p, b, n, now, rnd)}
237
238# The attempt has ended: tell the breaker, and plan the next step.
239def settle.outcome(+p: Retry.Policy, +n: Nat, +o: Retry.Outcome, +br: Retry.Breaker, b: Retry.Budget, body: Bytes.Bytes,
240 pool: Http.Pool, jar: Maybe<&2, Http.Jar>, r: Result<&1, &1, Http.Err, Http.Res>) -> IO(Step):
241 do IO<Step>:
242 now : Nat <- clock(Bool.or(breaker.on(br), transient(o)))
243 rnd : Nat <- jitter.io(transient(o))
244 return settle.at(now, rnd, p, n, o, br, b, body, pool, jar, r)
245
246def settle.judged(+p: Retry.Policy, +idem: Bool, +n: Nat, br: Retry.Breaker, b: Retry.Budget, body: Bytes.Bytes,
247 pool: Http.Pool, jar: Maybe<&2, Http.Jar>, j: Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, String>) -> IO(Step):
248 (r, m) = j
249 do IO<Step>:
250 o : Retry.Outcome <- outcome.io(idem, m)
251 settle.outcome(p, n, o, br, b, body, pool, jar, r)
252
253# The default judge: Http.retry.judge, as if the request were idempotent; outcome then applies idem.
254def judge(r: Result<&1, &1, Http.Err, Http.Res>) -> Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, String>:
255 Http.retry.judge(True{}, r)
256
257def settle(~judge: Result<&1, &1, Http.Err, Http.Res> -> Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, String>,
258 +p: Retry.Policy, +idem: Bool, +n: Nat, br: Retry.Breaker, b: Retry.Budget, body: Bytes.Bytes,
259 x: Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Res>) -> IO(Step):
260 (pool, jar, r) = x
261 settle.judged(p, idem, n, br, b, body, pool, jar, judge(r))
262
263def attempt.run(~judge: Result<&1, &1, Http.Err, Http.Res> -> Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, String>,
264 +o: Opts, +enc: String, +idem: Bool, +method: String, +u: Maybe<&2, Url.Abs>,
265 +headers: Map<&2, List<&2, String>>, +n: Nat, pool: Http.Pool, jar: Maybe<&2, Http.Jar>, br: Retry.Breaker,
266 b: Retry.Budget, r: Bytes.Bytes & Bytes.Bytes) -> IO(Step):
267 Opts{base, h, +ms, +mode, +p, +cert} = o
268 (body, spare) = r
269 do IO<Step>:
270 x : Http.Pool & Maybe<&2, Http.Jar> & Result<&1, &1, Http.Err, Http.Res> <- once(ms, mode, cert, enc, pool, jar, method, u, headers, spare)
271 settle(~judge, p, idem, n, br, b, body, x)
272
273def denied(why: Retry.Deny, last: Maybe<&1, Result<&1, &1, Err, Http.Res>>) -> Maybe<&1, Result<&1, &1, Err, Http.Res>>:
274 match last:
275 case None{}:
276 Some{Fail{ErrDenied{why}}}
277 case Some{r}:
278 Some{r}
279
280def attempt.gate(~judge: Result<&1, &1, Http.Err, Http.Res> -> Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, String>,
281 x: Retry.Breaker & Retry.Budget & Retry.Gate, +o: Opts, +enc: String, +idem: Bool, +method: String,
282 +u: Maybe<&2, Url.Abs>, +headers: Map<&2, List<&2, String>>, +n: Nat, pool: Http.Pool, jar: Maybe<&2, Http.Jar>,
283 body: Bytes.Bytes, last: Maybe<&1, Result<&1, &1, Err, Http.Res>>) -> IO(Step):
284 (br, b, g) = x
285 match g:
286 case Retry.GateNo{why}:
287 IO.pure(Step, Step{pool, jar, br, b, body, denied(why, last), Retry.PlanStop{}})
288 case Retry.GateGo{}:
289 attempt.run(~judge, o, enc, idem, method, u, headers, n, pool, jar, br, b, Bytes.slice(body, 0, 4294967295))
290
291# Ask the gate; when it admits, make attempt n (0 first) of this layer. With no deadline and no breaker,
292# admission does not read the clock.
293def attempt(~judge: Result<&1, &1, Http.Err, Http.Res> -> Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, String>,
294 +o: Opts, +enc: String, +idem: Bool, +method: String, +u: Maybe<&2, Url.Abs>,
295 +headers: Map<&2, List<&2, String>>, +n: Nat, s: Step) -> IO(Step):
296 Step{pool, jar, +br, +b, body, last, plan} = s
297 do IO<Step>:
298 now : Nat <- clock(Bool.or(breaker.on(br), deadline.some(b)))
299 attempt.gate(~judge, Retry.admit(br, b, now), o, enc, idem, method, u, headers, n, pool, jar, body, last)
300
301def pause(ms: Nat) -> IO(Unit):
302 match ms:
303 case 0n:
304 IO.pure(Unit, Unit{})
305 case 1n+k:
306 IO.sleep(U32.from_nat(1n+k))
307
308# left: attempts this layer may still make. n: attempts made so far. Each turn follows the plan of the last step.
309def go(~judge: Result<&1, &1, Http.Err, Http.Res> -> Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, String>,
310 left: Nat, +n: Nat, +o: Opts, +enc: String, +idem: Bool, +method: String, +u: Maybe<&2, Url.Abs>,
311 +headers: Map<&2, List<&2, String>>, s: Step) -> IO(Step):
312 match left:
313 case 0n:
314 IO.pure(Step, s)
315 case 1n+rest:
316 Step{pool, jar, br, b, body, last, plan} = s
317 match plan:
318 case Retry.PlanStop{}:
319 IO.pure(Step, Step{pool, jar, br, b, body, last, Retry.PlanStop{}})
320 case Retry.PlanWait{ms}:
321 do IO<Step>:
322 pause(ms)
323 next : Step <- attempt(~judge, o, enc, idem, method, u, headers, n, Step{pool, jar, br, b, body, last, Retry.PlanStop{}})
324 go(~judge, rest, 1n+n, o, enc, idem, method, u, headers, next)
325
326def result.of(m: Maybe<&1, Result<&1, &1, Err, Http.Res>>) -> Result<&1, &1, Err, Http.Res>:
327 match m:
328 case None{}:
329 Fail{ErrDenied{Retry.DenySpent{}}}
330 case Some{r}:
331 r
332
333def request.done(+o: Opts, s: Step) -> Client & Retry.Budget & Result<&1, &1, Err, Http.Res>:
334 Step{pool, jar, br, b, body, last, plan} = s
335 (Client{o, pool, jar, br}, b, result.of(last))
336
337def attempts(p: Retry.Policy) -> Nat:
338 Retry.Policy{a, base, cap, d} = p
339 a
340
341# The budget of one plain request: the policy's attempts, and its deadline from now. The clock is read only for a deadline.
342def budget(c: Client) -> IO(Client & Retry.Budget):
343 Client{+o, pool, jar, br} = c
344 Opts{base, h, ms, mode, Retry.Policy{+a, bs, cap, +d}, cert} = o
345 do IO<Client & Retry.Budget>:
346 now : Nat <- clock(some(d))
347 return (Client{o, pool, jar, br}, Retry.Budget.new(a, now, d))
348
349# One request inside a caller's retry layer, with every choice explicit. Every attempt takes from b, the
350# caller's shared budget, and obeys its deadline; the client's own policy caps the attempts of this call.
351# The budget left comes back beside the result: pass it to the next call, so nested layers never reset or
352# multiply it. The client's own deadline does not apply here; b's does.
353# judge: Some{Retry-After} when another attempt may help. idem: the request is safe to repeat, so a judged
354# failure is retried; else the breaker counts it and it never repeats. enc: the Accept-Encoding codings.
355def request.as(~judge: Result<&1, &1, Http.Err, Http.Res> -> Result<&1, &1, Http.Err, Http.Res> & Maybe<&2, String>,
356 c: Client, b: Retry.Budget, +idem: Bool, +enc: String, +method: String, url: String,
357 headers: Map<&2, List<&2, String>>, body: Bytes.Bytes) -> IO(Client & Retry.Budget & Result<&1, &1, Err, Http.Res>):
358 Client{+o, pool, jar, br} = c
359 Opts{+base, +h, ms, mode, +p, cert} = o
360 +u = target.abs(target(base, url))
361 +hs = merge(h, headers)
362 do IO<Client & Retry.Budget & Result<&1, &1, Err, Http.Res>>:
363 s : Step <- go(~judge, attempts(p), 0n, o, enc, idem, method, u, hs, Step{pool, jar, br, b, body, None{}, Retry.PlanWait{0n}})
364 return request.done(o, s)
365
366# request.as with judge, the idempotency of method, and every coding Http decodes.
367def request.in(c: Client, b: Retry.Budget, +method: String, url: String, headers: Map<&2, List<&2, String>>,
368 body: Bytes.Bytes) -> IO(Client & Retry.Budget & Result<&1, &1, Err, Http.Res>):
369 do IO<Client & Retry.Budget & Result<&1, &1, Err, Http.Res>>:
370 enc : String <- Http.codings()
371 request.as(~judge, c, b, Http.pool.idempotent(method), enc, method, url, headers, body)
372
373def request.drop(x: Client & Retry.Budget & Result<&1, &1, Err, Http.Res>) -> Client & Result<&1, &1, Err, Http.Res>:
374 (c, b, r) = x
375 (c, r)
376
377def request.budget(+method: String, url: String, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes,
378 x: Client & Retry.Budget) -> IO(Client & Retry.Budget & Result<&1, &1, Err, Http.Res>):
379 (c, b) = x
380 request.in(c, b, method, url, headers, body)
381
382# url resolves against the base; headers go over the defaults. Redirects follow the client's mode, at most 20.
383# Each request gets a fresh budget from budget(c). Before each attempt the deadline, the
384# budget, and the breaker must admit it. GET, HEAD, OPTIONS, TRACE, PUT, and DELETE try again after a connect
385# error, a timeout, or 408, 429, 500, 502, 503, or 504, as Http.retry.judge says, on the same pool.
386# When the attempts run out, the last result comes back; when none started, ErrDenied says why.
387def request(c: Client, +method: String, url: String, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes) ->
388 IO(Client & Result<&1, &1, Err, Http.Res>):
389 do IO<Client & Result<&1, &1, Err, Http.Res>>:
390 y : Client & Retry.Budget <- budget(c)
391 x : Client & Retry.Budget & Result<&1, &1, Err, Http.Res> <- request.budget(method, url, headers, body, y)
392 return request.drop(x)
393
394def get(c: Client, url: String) -> IO(Client & Result<&1, &1, Err, Http.Res>):
395 request(c, "GET", url, Http.empty(), Bytes.new(0))
396
397# POST v as compact JSON, with content-type: application/json.
398def post.json(c: Client, url: String, v: Json.Val) -> IO(Client & Result<&1, &1, Err, Http.Res>):
399 request(c, "POST", url, Http.set(Http.empty(), "content-type", "application/json"), Json.encode.bytes(v))