1	# ezhttp/src/step: what the server decides for one connection, kept pure so
2	# a law can state it. server.bend runs the effects and asks this module what
3	# each outcome means; it decides nothing itself.
4	import Base
5	import ./http.bend as Http
6	import ./qs.bend as Qs
7	
8	# what a request asks of the server: answer it now, or call the handler
9	type Step is Data:
10	  Answer{reply: Http.Reply}
11	  Call{req: Http.Request}
12	
13	# an effect's outcome on one connection: the value, or the line to log for
14	# a connection that is lost
15	type Got<-A: Type> is Type:
16	  Kept{value: A}
17	  Lost{line: String}
18	
19	# a request received as octets, as text: its method, target, header names
20	# and values and body each decoded as UTF-8 (SPEC.md HTTP-SRV-2); a bad one
21	# keeps its reason
22	def step.text(req: Http.Request) -> Http.Request:
23	  match req:
24	    case Http.Bad{why}:
25	      Http.Bad{why}
26	    case Http.Request{method, target, headers, body}:
27	      Http.Request{Qs.octets.text(method), Qs.octets.text(target),
28	        Qs.octets.headers(headers), Qs.octets.text(body)}
29	
30	# a bad request is answered 400 with its reason and never reaches the
31	# handler; a good one goes to the handler as it was parsed
32	def step.of(req: Http.Request) -> Step:
33	  match req:
34	    case Http.Bad{why}:
35	      Answer{Http.Reply{400, [], why}}
36	    case Http.Request{method, target, headers, body}:
37	      Call{Http.Request{method, target, headers, body}}
38	
39	# the line logged for a failed effect: `ezhttp: <phase>: <why>`
40	def step.line(phase: String, why: String) -> String:
41	  "ezhttp: " ++ phase ++ ": " ++ why
42	
43	# a failed accept or recv loses the connection instead of ending the server
44	def step.got(
45	  -A: Type,
46	  phase: String,
47	  res: Result<&1, &1, U32 & String, A>
48	) -> Got<A>:
49	  match res:
50	    case Fail{(code, why)}:
51	      Lost{step.line(phase, why)}
52	    case Done{value}:
53	      Kept{value}
54	
55	# a failed send loses the connection too; the bytes it did not send are dropped
56	def step.sent(res: Result<&1, &1, (U32 & String) & List<&2, U32>, Unit>)
57	  -> Got<Unit>:
58	  match res:
59	    case Fail{((code, why), left)}:
60	      Lost{step.line("write", why)}
61	    case Done{value}:
62	      Kept{value}
63	
64	# --- the replies and the handler's request (SPEC.md HTTP-SRV-8, 9) ---
65	
66	# whether a reply is written with its head only: a reply to HEAD, or a 204
67	# or 304 (RFC 9110 §9.3.2, §15.3.5, §15.4.5)
68	def step.bare(+method: String, +status: U32) -> Bool:
69	  Bool.or(String.eq(method, "HEAD"), Http.status.nocontent(status))
70	
71	# the body octets of a request, as they arrived; none for a bad one
72	def step.octets(req: Http.Request) -> String:
73	  match req:
74	    case Http.Bad{why}:
75	      ""
76	    case Http.Request{method, target, headers, body}:
77	      body
78	
79	# what an accept with a deadline brought: a connection, nothing before the
80	# deadline, or a lost accept with its line (SPEC.md HTTP-SRV-4)
81	type Accept<-A: Type> is Type:
82	  Took{value: A}
83	  Idle{}
84	  Missed{line: String}
85	
86	# a failed accept once it is known whether its deadline passed
87	def step.missed(-A: Type, +why: String, late: Bool) -> Accept<A>:
88	  match late:
89	    case True{}:
90	      Idle{}
91	    case False{}:
92	      Missed{step.line("accept", why)}
93	
94	# an accept's outcome: ETIMEDOUT (110) is a deadline that passed
95	def step.accepted(-A: Type, res: Result<&1, &1, U32 & String, A>)
96	  -> Accept<A>:
97	  match res:
98	    case Fail{(+code, why)}:
99	      step.missed(A, why, U32.is_eq(code, 110))
100	    case Done{value}:
101	      Took{value}
102	
103	# --- when a request has all arrived (SPEC.md HTTP-TRUST-2) ---
104	
105	# a Content-Length that reads, or none
106	def step.clen(m: Maybe<&2, Nat>) -> Nat:
107	  match m:
108	    case None{}:
109	      0n
110	    case Some{n}:
111	      n
112	
113	# octets a request needs in all once its head has ended: the head, its blank
114	# line and the octets its Content-Length names (0 when it names none)
115	def step.need.of(c: Http.Cut) -> Maybe<&2, Nat>:
116	  match c:
117	    case Http.NoCut{}:
118	      None{}
119	    case Http.Cut{+before, after}:
120	      Some{Nat.add(Nat.add(String.length(before), 4n),
121	        step.clen(Http.digits.read(Http.first(
122	          Http.head.values(String.lines(before), "content-length")))))}
123	
124	# octets a request needs in all, none while its head has not ended
125	def step.need(+text: String) -> Maybe<&2, Nat>:
126	  step.need.of(Http.divide(text, "\r\n\r\n"))