1	# Fixed prepared HTTP applications and bounded affine dependency bundles.
2	import Base
3	import bend-kit-http@0.25.0.2/http.bend as Http
4	import bend-kit-router@0.2.0.0/router.bend as Router
5	import bend-kit-router@0.2.0.0/target.bend as Target
6	import bend-kit-json@0.5.1.0/json.bend as Json
7	import ./response.bend as Response
8	
9	type ResponseError is Data:
10	  InvalidResponse{}
11	  InvalidRedirect{}
12	
13	def validate.checked(valid: Bool, response: Http.Res) -> Result<&2, &1, ResponseError, Http.Res>:
14	  match valid:
15	    case True{}:
16	      Done{response}
17	    case False{}:
18	      Fail{InvalidResponse{}}
19	
20	def validate(response: Http.Res) -> Result<&2, &1, ResponseError, Http.Res>:
21	  Http.Res{+status, +headers, body} = response
22	  validate.checked(Response.valid(status, headers), Http.Res{status, headers, body})
23	
24	# The encoder is an explicit public projection, never record reflection.
25	def json(~T: Type, ~encode: T -> Json.Val, status: U32, value: T) -> Http.Res:
26	  Http.Res{status, Http.set(Http.empty(), "content-type", "application/json"), Json.encode.bytes(encode(value))}
27	
28	def text(status: U32, value: String) -> Http.Res:
29	  Http.Res{status, Http.set(Http.empty(), "content-type", "text/plain; charset=utf-8"), Json.utf8(value)}
30	
31	def raw(status: U32, body: Http.Body) -> Http.Res:
32	  Http.Res{status, Http.empty(), body}
33	
34	def empty(status: U32) -> Http.Res:
35	  raw(status, Http.from_string(""))
36	
37	def redirect.checked(valid: Bool, status: U32, location: String) -> Result<&2, &1, ResponseError, Http.Res>:
38	  match valid:
39	    case False{}:
40	      Fail{InvalidRedirect{}}
41	    case True{}:
42	      Done{Http.Res{status, Http.set(Http.empty(), "location", location), Http.from_string("")}}
43	
44	def redirect(+status: U32, +location: String) -> Result<&2, &1, ResponseError, Http.Res>:
45	  redirect.checked((U32.is_eq(status, 301) || U32.is_eq(status, 302) || U32.is_eq(status, 303) || U32.is_eq(status, 307) || U32.is_eq(status, 308)) && Bool.not(String.eq(location, "")) && Response.value(location), status, location)
46	
47	type Counts is Data:
48	  Counts{capacity: Nat, in_use: Nat, completed: Nat, rejected: Nat}
49	
50	type Outcome<-E: Data, -O: Data> is Data:
51	  Success{value: O}
52	  Expected{error: E}
53	  Exhausted{}
54	  Stopped{}
55	
56	type CloseResult is Data:
57	  Closed{}
58	  Busy{counts: Counts}
59	
60	type Message<-R: Type, -P: Data, -I: Data, -E: Data, -O: Data> is Type:
61	  Submit{principal: P, input: I, reply: Chan(Outcome<E, O>)}
62	  Returned{resource: R}
63	  Inspect{reply: Chan(Counts)}
64	  Shutdown{reply: Chan(CloseResult)}
65	
66	# Copy only this context, never the resources. The inbox bounds queued commands;
67	# callers must count blocked submissions inside their transport admission limit.
68	type Context<-R: Type, -P: Data, -I: Data, -E: Data, -O: Data> is Data:
69	  Context{messages: Chan(Message<R, P, I, E, O>)}
70	
71	def outcome.value(-E: Data, -O: Data, result: Result<&2, &2, E, O>) -> Outcome<E, O>:
72	  match result:
73	    case Fail{error}:
74	      Expected{error}
75	    case Done{value}:
76	      Success{value}
77	
78	# The resources return through the private owner protocol BEFORE a disposable
79	# caller reply. A closed caller reply cannot erase a handle or strand capacity.
80	def work.return(-R: Type, -P: Data, -I: Data, -E: Data, -O: Data,
81	  messages: Chan(Message<R, P, I, E, O>), reply: Chan(Outcome<E, O>),
82	  result: R & Result<&2, &2, E, O>
83	) -> IO(Unit):
84	  (returned, outcome) = result
85	  do IO<Unit>:
86	    accepted : Bool <- Chan.send(Message<R, P, I, E, O>, messages, Returned{returned})
87	    sent : Bool <- Chan.send(Outcome<E, O>, reply, outcome.value(E, O, outcome))
88	    return Unit{}
89	
90	def work(~R: Type, ~P: Data, ~I: Data, ~E: Data, ~O: Data,
91	  ~handler: R -> P -> I -> IO(R & Result<&2, &2, E, O>),
92	  resource: R, principal: P, input: I,
93	  messages: Chan(Message<R, P, I, E, O>), reply: Chan(Outcome<E, O>)
94	) -> IO(Unit):
95	  do IO<Unit>:
96	    result : R & Result<&2, &2, E, O> <- handler(resource, principal, input)
97	    work.return(R, P, I, E, O, messages, reply, result)
98	
99	def dispose(~R: Type, ~destroy: R -> IO(Unit), resources: List<R>) -> IO(Unit):
100	  match resources:
101	    case Nil{}:
102	      IO.pure(Unit, Unit{})
103	    case Con{resource, rest}:
104	      do IO<Unit>:
105	        destroy(resource)
106	        dispose(~R, ~destroy, rest)
107	
108	# Closing Base channels retains buffered messages. Drain them and answer stopped
109	# callers, rather than stranding accepted commands behind the close command.
110	def drain.message(~R: Type, ~P: Data, ~I: Data, ~E: Data, ~O: Data,
111	  ~destroy: R -> IO(Unit), message: Message<R, P, I, E, O>
112	) -> IO(Unit):
113	  match message:
114	    case Submit{principal, input, reply}:
115	      do IO<Unit>:
116	        sent : Bool <- Chan.send(Outcome<E, O>, reply, Stopped{})
117	        return Unit{}
118	    case Inspect{reply}:
119	      Chan.close(Counts, reply)
120	    case Shutdown{reply}:
121	      do IO<Unit>:
122	        sent : Bool <- Chan.send(CloseResult, reply, Closed{})
123	        return Unit{}
124	    case Returned{resource}:
125	      destroy(resource)
126	
127	def drain.step(~R: Type, ~P: Data, ~I: Data, ~E: Data, ~O: Data,
128	  ~destroy: R -> IO(Unit), pending: Maybe<&1, Message<R, P, I, E, O>>,
129	  next: Unit -> IO(Unit)
130	) -> IO(Unit):
131	  match pending:
132	    case None{}:
133	      IO.pure(Unit, Unit{})
134	    case Some{message}:
135	      do IO<Unit>:
136	        drain.message(~R, ~P, ~I, ~E, ~O, ~destroy, message)
137	        next(Unit{})
138	
139	# The closed inbox contains at most room buffered messages.
140	def drain(~R: Type, ~P: Data, ~I: Data, ~E: Data, ~O: Data,
141	  ~destroy: R -> IO(Unit), fuel: Nat, +messages: Chan(Message<R, P, I, E, O>)
142	) -> IO(Unit):
143	  match fuel:
144	    case 0n:
145	      IO.pure(Unit, Unit{})
146	    case 1n+p:
147	      do IO<Unit>:
148	        pending : Maybe<&1, Message<R, P, I, E, O>> <- Chan.recv(Message<R, P, I, E, O>, messages)
149	        drain.step(~R, ~P, ~I, ~E, ~O, ~destroy, pending, u => drain(~R, ~P, ~I, ~E, ~O, ~destroy, p, messages))
150	
151	type OwnerStep<-R: Type, -P: Data, -I: Data, -E: Data, -O: Data> is Type:
152	  Waiting{resources: List<R>, counts: Counts}
153	  Received{message: Message<R, P, I, E, O>, counts: Counts, resources: List<R>}
154	
155	# IO.join closes a one-shot channel; the owner inbox must remain reusable.
156	def receive.value(-A: Type, value: Maybe<&1, A>) -> IO(A):
157	  match value:
158	    case None{}:
159	      IO.die(A, 1, "camber internal channel closed unexpectedly")
160	    case Some{message}:
161	      IO.pure(A, message)
162	
163	def receive(-A: Type, channel: Chan(A)) -> IO(A):
164	  do IO<A>:
165	    value : Maybe<&1, A> <- Chan.recv(A, channel)
166	    receive.value(A, value)
167	
168	# Only idle close ends this loop. Busy close never waits on a stalled handler.
169	# @unsafe is solely the lifecycle receive loop, not a termination/proof claim.
170	@unsafe def owner(~R: Type, ~P: Data, ~I: Data, ~E: Data, ~O: Data,
171	  ~handler: R -> P -> I -> IO(R & Result<&2, &2, E, O>), ~destroy: R -> IO(Unit),
172	  +messages: Chan(Message<R, P, I, E, O>), +room: U32, step: OwnerStep<R, P, I, E, O>
173	) -> IO(Unit):
174	  match step:
175	    case Waiting{resources, counts}:
176	      do IO<Unit>:
177	        message : Message<R, P, I, E, O> <- receive(Message<R, P, I, E, O>, messages)
178	        owner(~R, ~P, ~I, ~E, ~O, ~handler, ~destroy, messages, room, Received{message, counts, resources})
179	    case Received{message, counts, resources}:
180	      match message:
181	        case Returned{resource}:
182	          Counts{capacity, in_use, completed, rejected} = counts
183	          owner(~R, ~P, ~I, ~E, ~O, ~handler, ~destroy, messages, room, Waiting{resource <> resources, Counts{capacity, Nat.sub(in_use, 1n), 1n+completed, rejected}})
184	        case Inspect{reply}:
185	          Counts{+capacity, +in_use, +completed, +rejected} = counts
186	          do IO<Unit>:
187	            sent : Bool <- Chan.send(Counts, reply, Counts{capacity, in_use, completed, rejected})
188	            owner(~R, ~P, ~I, ~E, ~O, ~handler, ~destroy, messages, room, Waiting{resources, Counts{capacity, in_use, completed, rejected}})
189	        case Shutdown{reply}:
190	          Counts{+capacity, in_use, +completed, +rejected} = counts
191	          match in_use:
192	            case 0n:
193	              do IO<Unit>:
194	                dispose(~R, ~destroy, resources)
195	                Chan.close(Message<R, P, I, E, O>, messages)
196	                sent : Bool <- Chan.send(CloseResult, reply, Closed{})
197	                drain(~R, ~P, ~I, ~E, ~O, ~destroy, U32.to_nat(room), messages)
198	            case 1n+ +p:
199	              do IO<Unit>:
200	                sent : Bool <- Chan.send(CloseResult, reply, Busy{Counts{capacity, 1n+p, completed, rejected}})
201	                owner(~R, ~P, ~I, ~E, ~O, ~handler, ~destroy, messages, room, Waiting{resources, Counts{capacity, 1n+p, completed, rejected}})
202	        case Submit{principal, input, reply}:
203	          Counts{capacity, in_use, completed, rejected} = counts
204	          match resources:
205	            case Nil{}:
206	              do IO<Unit>:
207	                sent : Bool <- Chan.send(Outcome<E, O>, reply, Exhausted{})
208	                owner(~R, ~P, ~I, ~E, ~O, ~handler, ~destroy, messages, room, Waiting{Nil{}, Counts{capacity, in_use, completed, 1n+rejected}})
209	            case Con{resource, rest}:
210	              do IO<Unit>:
211	                IO.spawn(Unit, work(~R, ~P, ~I, ~E, ~O, ~handler, resource, principal, input, messages, reply))
212	                owner(~R, ~P, ~I, ~E, ~O, ~handler, ~destroy, messages, room, Waiting{rest, Counts{capacity, 1n+in_use, completed, rejected}})
213	
214	def build.step(~R: Type, ~E: Data, ~destroy: R -> IO(Unit),
215	  result: Result<&2, &1, E, R>, resources: List<R>,
216	  next: List<R> -> IO(Result<&2, &1, E, List<R>>)
217	) -> IO(Result<&2, &1, E, List<R>>):
218	  match result:
219	    case Fail{error}:
220	      do IO<Result<&2, &1, E, List<R>>>:
221	        dispose(~R, ~destroy, resources)
222	        return Fail{error}
223	    case Done{resource}:
224	      next(resource <> resources)
225	
226	def build(~K: Data, ~R: Type, ~E: Data, ~create: K -> Nat -> IO(Result<&2, &1, E, R>), ~destroy: R -> IO(Unit),
227	  remaining: Nat, +config: K, resources: List<R>
228	) -> IO(Result<&2, &1, E, List<R>>):
229	  match remaining:
230	    case 0n:
231	      IO.pure(Result<&2, &1, E, List<R>>, Done{resources})
232	    case 1n+ +p:
233	      do IO<Result<&2, &1, E, List<R>>>:
234	        result : Result<&2, &1, E, R> <- create(config, p)
235	        build.step(~R, ~E, ~destroy, result, resources, next => build(~K, ~R, ~E, ~create, ~destroy, p, config, next))
236	
237	def start.ready(~R: Type, ~P: Data, ~I: Data, ~E: Data, ~O: Data,
238	  ~handler: R -> P -> I -> IO(R & Result<&2, &2, E, O>), ~destroy: R -> IO(Unit),
239	  capacity: Nat, +room: U32, result: Result<&2, &1, E, List<R>>
240	) -> IO(Result<&2, &2, E, Context<R, P, I, E, O>>):
241	  match result:
242	    case Fail{error}:
243	      IO.pure(Result<&2, &2, E, Context<R, P, I, E, O>>, Fail{error})
244	    case Done{resources}:
245	      do IO<Result<&2, &2, E, Context<R, P, I, E, O>>>:
246	        channel : Chan(Message<R, P, I, E, O>) <- Chan.new(Message<R, P, I, E, O>, room)
247	        +messages : Chan(Message<R, P, I, E, O>) = channel
248	        IO.spawn(Unit, owner(~R, ~P, ~I, ~E, ~O, ~handler, ~destroy, messages, room, Waiting{resources, Counts{capacity, 0n, 0n, 0n}}))
249	        return Done{Context{messages}}
250	
251	# The initializer closes partial handles within a failed bundle; start closes
252	# all prior whole bundles. No workers exist until the complete set opens.
253	def start(~K: Data, ~R: Type, ~P: Data, ~I: Data, ~E: Data, ~O: Data,
254	  ~create: K -> Nat -> IO(Result<&2, &1, E, R>),
255	  ~handler: R -> P -> I -> IO(R & Result<&2, &2, E, O>), ~destroy: R -> IO(Unit),
256	  config: K, +capacity: Nat, room: U32
257	) -> IO(Result<&2, &2, E, Context<R, P, I, E, O>>):
258	  do IO<Result<&2, &2, E, Context<R, P, I, E, O>>>:
259	    result : Result<&2, &1, E, List<R>> <- build(~K, ~R, ~E, ~create, ~destroy, capacity, config, Nil{})
260	    start.ready(~R, ~P, ~I, ~E, ~O, ~handler, ~destroy, capacity, room, result)
261	
262	def submit(-R: Type, -P: Data, -I: Data, -E: Data, -O: Data,
263	  context: Context<R, P, I, E, O>, principal: P, input: I, reply: Chan(Outcome<E, O>)
264	) -> IO(Bool):
265	  Context{messages} = context
266	  Chan.send(Message<R, P, I, E, O>, messages, Submit{principal, input, reply})
267	
268	def call.accepted(-E: Data, -O: Data, accepted: Bool, +reply: Chan(Outcome<E, O>)) -> IO(Outcome<E, O>):
269	  match accepted:
270	    case False{}:
271	      do IO<Outcome<E, O>>:
272	        Chan.close(Outcome<E, O>, reply)
273	        return Stopped{}
274	    case True{}:
275	      do IO<Outcome<E, O>>:
276	        result : Outcome<E, O> <- IO.join(Outcome<E, O>, reply)
277	        Chan.close(Outcome<E, O>, reply)
278	        return result
279	
280	def call(-R: Type, -P: Data, -I: Data, -E: Data, -O: Data,
281	  context: Context<R, P, I, E, O>, principal: P, input: I
282	) -> IO(Outcome<E, O>):
283	  do IO<Outcome<E, O>>:
284	    channel : Chan(Outcome<E, O>) <- Chan.new(Outcome<E, O>, 1)
285	    +reply : Chan(Outcome<E, O>) = channel
286	    accepted : Bool <- submit(R, P, I, E, O, context, principal, input, reply)
287	    call.accepted(E, O, accepted, reply)
288	
289	def inspect.value(value: Maybe<&1, Counts>) -> Maybe<&2, Counts>:
290	  match value:
291	    case None{}:
292	      None{}
293	    case Some{counts}:
294	      Some{counts}
295	
296	def inspect.sent(sent: Bool, +reply: Chan(Counts)) -> IO(Maybe<&2, Counts>):
297	  match sent:
298	    case False{}:
299	      do IO<Maybe<&2, Counts>>:
300	        Chan.close(Counts, reply)
301	        return None{}
302	    case True{}:
303	      do IO<Maybe<&2, Counts>>:
304	        value : Maybe<&1, Counts> <- Chan.recv(Counts, reply)
305	        Chan.close(Counts, reply)
306	        return inspect.value(value)
307	
308	def inspect(-R: Type, -P: Data, -I: Data, -E: Data, -O: Data, context: Context<R, P, I, E, O>) -> IO(Maybe<&2, Counts>):
309	  Context{messages} = context
310	  do IO<Maybe<&2, Counts>>:
311	    channel : Chan(Counts) <- Chan.new(Counts, 1)
312	    +reply : Chan(Counts) = channel
313	    sent : Bool <- Chan.send(Message<R, P, I, E, O>, messages, Inspect{reply})
314	    inspect.sent(sent, reply)
315	
316	def close.sent(sent: Bool, +reply: Chan(CloseResult)) -> IO(CloseResult):
317	  match sent:
318	    case False{}:
319	      do IO<CloseResult>:
320	        Chan.close(CloseResult, reply)
321	        return Closed{}
322	    case True{}:
323	      do IO<CloseResult>:
324	        value : CloseResult <- IO.join(CloseResult, reply)
325	        Chan.close(CloseResult, reply)
326	        return value
327	
328	# Stop external admissions before close. Busy preserves live context/capacity;
329	# retry after admitted operations finish. Stalled operations remain observable.
330	def close(-R: Type, -P: Data, -I: Data, -E: Data, -O: Data, context: Context<R, P, I, E, O>) -> IO(CloseResult):
331	  Context{messages} = context
332	  do IO<CloseResult>:
333	    channel : Chan(CloseResult) <- Chan.new(CloseResult, 1)
334	    +reply : Chan(CloseResult) = channel
335	    sent : Bool <- Chan.send(Message<R, P, I, E, O>, messages, Shutdown{reply})
336	    close.sent(sent, reply)
337	
338	# Policies are prepared Data, not callbacks. Later lifecycle stages can consume
339	# these root-to-route declarations without splitting patterns or finding groups.
340	type Group<-P: Data> is Data:
341	  Group{id: U32, ancestors: List<&2, U32>, policy: P}
342	
343	type Route<-A: Data, -P: Data> is Data:
344	  Route{method: String, pattern: String, action: A, groups: List<&2, U32>, policy: P}
345	
346	type Endpoint<-A: Data, -P: Data> is Data:
347	  Endpoint{action: A, policies: List<&2, P>}
348	
349	type Application<-A: Data, -C: Data, -P: Data> is Data:
350	  Application{table: Router.Table<Endpoint<A, P>>, context: C, root: P}
351	
352	type RegistrationError is Data:
353	  RouteError{error: Router.Error}
354	  InvalidGroups{groups: List<&2, U32>}
355	
356	type Match<-P: Data> is Data:
357	  Match{target: Target.Target, params: Map<&2, String>, groups: List<&2, U32>, method: String, pattern: String, policies: List<&2, P>}
358	
359	def groups.equal(xs: List<&2, U32>, ys: List<&2, U32>) -> Bool:
360	  match xs ys:
361	    case Nil{} Nil{}:
362	      True{}
363	    case x <> xt y <> yt:
364	      U32.is_eq(x, y) && groups.equal(xt, yt)
365	    case _ _:
366	      False{}
367	
368	def group.pick(~P: Data, same: Bool, group: Group<P>, later: Unit -> Maybe<&2, Group<P>>) -> Maybe<&2, Group<P>>:
369	  match same:
370	    case True{}:
371	      Some{group}
372	    case False{}:
373	      later(Unit{})
374	
375	def group.find(~P: Data, groups: List<&2, Group<P>>, +id: U32) -> Maybe<&2, Group<P>>:
376	  match groups:
377	    case Nil{}:
378	      None{}
379	    case Group{+here, ancestors, policy} <> rest:
380	      group.pick(~P, U32.is_eq(here, id), Group{here, ancestors, policy}, u => group.find(~P, rest, id))
381	
382	def group.checked(~P: Data, same: Bool, policy: P) -> Maybe<&2, P>:
383	  match same:
384	    case False{}:
385	      None{}
386	    case True{}:
387	      Some{policy}
388	
389	def group.policy(~P: Data, found: Maybe<&2, Group<P>>, ancestors: List<&2, U32>) -> Maybe<&2, P>:
390	  match found:
391	    case None{}:
392	      None{}
393	    case Some{Group{id, expected, policy}}:
394	      group.checked(~P, groups.equal(expected, ancestors), policy)
395	
396	def groups.policies(~P: Data, ids: List<&2, U32>, +declared: List<&2, Group<P>>, +ancestors: List<&2, U32>) -> Maybe<&2, List<&2, P>>:
397	  match ids:
398	    case Nil{}:
399	      Some{Nil{}}
400	    case +id <> rest:
401	      do Maybe<&2, List<&2, P>>:
402	        policy : P <- group.policy(~P, group.find(~P, declared, id), ancestors)
403	        policies : List<&2, P> <- groups.policies(~P, rest, declared, List.append(&2, U32, ancestors, [id]))
404	        return policy <> policies
405	
406	def groups.unique(~P: Data, found: Maybe<&2, Group<P>>) -> Bool:
407	  match found:
408	    case None{}:
409	      True{}
410	    case Some{group}:
411	      False{}
412	
413	def groups.valid(~P: Data, groups: List<&2, Group<P>>, +all: List<&2, Group<P>>) -> Bool:
414	  match groups:
415	    case Nil{}:
416	      True{}
417	    case Group{+id, +ancestors, policy} <> +rest:
418	      chain = groups.policies(~P, List.append(&2, U32, ancestors, [id]), all, Nil{})
419	      groups.unique(~P, group.find(~P, rest, id)) && Maybe.is_some(&2, List<&2, P>, chain) && groups.valid(~P, rest, all)
420	
421	def routes.policies(~P: Data, result: Maybe<&2, List<&2, P>>, ids: List<&2, U32>) -> Result<&2, &2, RegistrationError, List<&2, P>>:
422	  match result:
423	    case None{}:
424	      Fail{InvalidGroups{ids}}
425	    case Some{policies}:
426	      Done{policies}
427	
428	def routes.prepare(~A: Data, ~P: Data, routes: List<&2, Route<A, P>>, +groups: List<&2, Group<P>>, +root: P) -> Result<&2, &2, RegistrationError, List<&2, Router.Entry<Endpoint<A, P>>>>:
429	  match routes:
430	    case Nil{}:
431	      Done{Nil{}}
432	    case Route{method, pattern, action, +ids, policy} <> rest:
433	      do Result<&2, &2, RegistrationError, List<&2, Router.Entry<Endpoint<A, P>>>>:
434	        policies : List<&2, P> <- routes.policies(~P, groups.policies(~P, ids, groups, Nil{}), ids)
435	        entries : List<&2, Router.Entry<Endpoint<A, P>>> <- routes.prepare(~A, ~P, rest, groups, root)
436	        return Router.Entry{method, pattern, Endpoint{action, root <> List.append(&2, P, policies, [policy])}, ids} <> entries
437	
438	def application.table(~A: Data, ~C: Data, ~P: Data, result: Result<&2, &2, Router.Error, Router.Table<Endpoint<A, P>>>, context: C, root: P) -> Result<&2, &2, RegistrationError, Application<A, C, P>>:
439	  match result:
440	    case Fail{error}:
441	      Fail{RouteError{error}}
442	    case Done{table}:
443	      Done{Application{table, context, root}}
444	
445	def application.valid(~A: Data, ~C: Data, ~P: Data, valid: Bool, routes: List<&2, Route<A, P>>, groups: List<&2, Group<P>>, context: C, +root: P) -> Result<&2, &2, RegistrationError, Application<A, C, P>>:
446	  match valid:
447	    case False{}:
448	      Fail{InvalidGroups{Nil{}}}
449	    case True{}:
450	      do Result<&2, &2, RegistrationError, Application<A, C, P>>:
451	        entries : List<&2, Router.Entry<Endpoint<A, P>>> <- routes.prepare(~A, ~P, routes, groups, root)
452	        application.table(~A, ~C, ~P, Router.prepare(~Endpoint<A, P>, entries), context, root)
453	
454	# Construction is pure and fallible; no listener or owner is started here.
455	def application(~A: Data, ~C: Data, ~P: Data, routes: List<&2, Route<A, P>>, +groups: List<&2, Group<P>>, context: C, root: P) -> Result<&2, &2, RegistrationError, Application<A, C, P>>:
456	  application.valid(~A, ~C, ~P, groups.valid(~P, groups, groups), routes, groups, context, root)
457	
458	def describe(~A: Data, ~C: Data, ~P: Data, app: Application<A, C, P>) -> List<&2, Router.Description>:
459	  Application{table, context, root} = app
460	  Router.describe(~Endpoint<A, P>, table)
461	
462	def request.authority(authority: Maybe<&2, String>, req: Http.Req) -> Http.Req:
463	  match authority:
464	    case None{}:
465	      req
466	    case Some{host}:
467	      Http.Req{method, path, headers, body} = req
468	      Http.Req{method, path, Http.set(headers, "host", host), body}
469	
470	# A closed template can run repeatedly; an affine callback registry cannot.
471	def plain(~handler: Http.Req -> IO(Http.Res), req: Http.Req) -> IO(Result<&2, &1, ResponseError, Http.Res>):
472	  do IO<Result<&2, &1, ResponseError, Http.Res>>:
473	    response : Http.Res <- handler(req)
474	    return validate(response)
475	
476	def dispatch.choice(~A: Data, ~C: Data, ~P: Data,
477	  ~run: A -> C -> Match<P> -> Http.Req -> IO(Http.Res),
478	  choice: Router.Choice<Endpoint<A, P>>, context: C, target: Target.Target, req: Http.Req
479	) -> IO(Http.Res):
480	  match choice:
481	    case Router.NotFound{}:
482	      IO.pure(Http.Res, Http.Res{404, Http.empty(), Http.from_string("")})
483	    case Router.MethodMissing{groups, allow}:
484	      IO.pure(Http.Res, Http.Res{405, Http.set(Http.empty(), "allow", allow), Http.from_string("")})
485	    case Router.Options{groups, allow}:
486	      IO.pure(Http.Res, Http.Res{204, Http.set(Http.empty(), "allow", allow), Http.from_string("")})
487	    case Router.Found{Endpoint{action, policies}, params, groups, method, pattern}:
488	      run(action, context, Match{target, params, groups, method, pattern, policies}, req)
489	
490	def dispatch.resolved(~A: Data, ~C: Data, ~P: Data,
491	  ~run: A -> C -> Match<P> -> Http.Req -> IO(Http.Res),
492	  result: Result<&2, &2, Router.Error, Router.Resolved<Endpoint<A, P>>>, context: C, req: Http.Req
493	) -> IO(Http.Res):
494	  match result:
495	    case Fail{error}:
496	      IO.pure(Http.Res, Http.Res{400, Http.empty(), Http.from_string("")})
497	    case Done{Router.Resolved{+target, choice}}:
498	      Target.Target{segments, query, authority, star} = target
499	      dispatch.choice(~A, ~C, ~P, ~run, choice, context, target, request.authority(authority, req))
500	
501	# Dispatch moves the original packed body once and returns application bytes.
502	# In particular it never performs transport's HEAD/204/304 body suppression.
503	def dispatch(~A: Data, ~C: Data, ~P: Data,
504	  ~run: A -> C -> Match<P> -> Http.Req -> IO(Http.Res),
505	  app: Application<A, C, P>, req: Http.Req
506	) -> IO(Result<&2, &1, ResponseError, Http.Res>):
507	  Application{table, context, root} = app
508	  Http.Req{+method, +path, headers, body} = req
509	  do IO<Result<&2, &1, ResponseError, Http.Res>>:
510	    response : Http.Res <- dispatch.resolved(~A, ~C, ~P, ~run, Router.resolve(~Endpoint<A, P>, table, method, path), context, Http.Req{method, path, headers, body})
511	    return validate(response)