1	import Base
2	
3	# Distinguishes supported socket errors from missing host capabilities.
4	type Classification is Data:
5	  UnsupportedPlatform{}
6	  Transient{code: U32}
7	  Host{code: U32}
8	
9	# Carries the state for PollStatus.
10	type PollStatus is Data:
11	  Readable{}
12	  ReadableFailed{}
13	  Idle{}
14	  Failed{}
15	
16	# Carries the state for PollFailureAction.
17	type PollFailureAction is Data:
18	  Retry{}
19	  Stop{}
20	
21	def event.applies(connection_id: U32, event_id: U32) -> Bool:
22	  U32.is_eq(connection_id, event_id)
23	
24	# Classifies platform-specific errno values without performing host IO.
25	def classify_code(code: U32) -> Classification:
26	  match code:
27	    case 45: UnsupportedPlatform{}
28	    case 78: UnsupportedPlatform{}
29	    case 95: UnsupportedPlatform{}
30	    case 38: UnsupportedPlatform{}
31	    case 4: Transient{4}
32	    case 11: Transient{11}
33	    case 35: Transient{35}
34	    case _: Host{code}
35	
36	def poll.failure.action(classification: Classification) -> PollFailureAction:
37	  match classification:
38	    case Transient{_}: Retry{}
39	    case _: Stop{}
40	
41	def poll.failure(code: U32) -> PollFailureAction:
42	  poll.failure.action(classify_code(code))
43	
44	def poll.failed(flags: U32) -> Bool:
45	  Bool.not(U32.is_eq(U32.and(flags, 56), 0))
46	
47	def poll.readable(flags: U32) -> Bool:
48	  Bool.not(U32.is_eq(U32.and(flags, 1), 0))
49	
50	def poll.status.readable(readable: Bool, failed: Bool) -> PollStatus:
51	  match readable:
52	    case True{}:
53	      match failed:
54	        case True{}: ReadableFailed{}
55	        case False{}: Readable{}
56	    case False{}:
57	      match failed:
58	        case True{}: Failed{}
59	        case False{}: Idle{}
60	
61	# Handles poll status.
62	def poll_status(+flags: U32) -> PollStatus:
63	  poll.status.readable(poll.readable(flags), poll.failed(flags))