1	# Header / trailer metadata helpers. Pure.
2	# Metadata maps are Map<&2, List<&2, String>> with lowercase keys.
3	import Base
4	
5	def trailer_prefix() -> String:
6	  "trailer-"
7	
8	def trailers_to_headers.go(xs: List<&2, Sigma<&2, &2, String, _ => List<&2, String>>>, acc: Map<&2, List<&2, String>>) -> Map<&2, List<&2, String>>:
9	  match xs:
10	    case Nil{}:
11	      acc
12	    case Con{Tuple{k, v}, rest}:
13	      trailers_to_headers.go(rest, Map.set(&2, List<&2, String>, acc, String.append(trailer_prefix(), k), v))
14	
15	# Every key gets the "trailer-" prefix (unary responses carry trailers as headers).
16	def trailers_to_headers(m: Map<&2, List<&2, String>>) -> Map<&2, List<&2, String>>:
17	  trailers_to_headers.go(Map.to_list(&2, List<&2, String>, m), Map.new(&2, List<&2, String>))
18	
19	# Adds k (with prefix stripped when want) when its prefix status equals want.
20	def bool_eq(a: Bool, +b: Bool) -> Bool:
21	  Bool.pick(Bool, a, b, Bool.not(b))
22	
23	def split.add(take: Bool, +want: Bool, +k: String, v: List<&2, String>, acc: Map<&2, List<&2, String>>) -> Map<&2, List<&2, String>>:
24	  match take:
25	    case False{}:
26	      acc
27	    case True{}:
28	      Map.set(&2, List<&2, String>, acc, Bool.pick(String, want, String.drop(k, 8n), k), v)
29	
30	def split.go(xs: List<&2, Sigma<&2, &2, String, _ => List<&2, String>>>, +want: Bool, acc: Map<&2, List<&2, String>>) -> Map<&2, List<&2, String>>:
31	  match xs:
32	    case Nil{}:
33	      acc
34	    case Con{Tuple{+k, v}, rest}:
35	      split.go(rest, want, split.add(bool_eq(String.starts_with(k, trailer_prefix()), want), want, k, v, acc))
36	
37	# (non-trailer headers, trailers with the "trailer-" prefix stripped)
38	def split_trailers(h: Map<&2, List<&2, String>>) -> Map<&2, List<&2, String>> & Map<&2, List<&2, String>>:
39	  +l = Map.to_list(&2, List<&2, String>, h)
40	  (split.go(l, False{}, Map.new(&2, List<&2, String>)), split.go(l, True{}, Map.new(&2, List<&2, String>)))
41	
42	# Keys starting with "connect-" belong to the protocol.
43	def is_reserved(+key: String) -> Bool:
44	  String.starts_with(key, "connect-")
45	
46	# Keys ending in "-bin" carry base64 values.
47	def is_binary(+key: String) -> Bool:
48	  String.ends_with(key, "-bin")
49	
50	def key_char(+c: U32) -> Bool:
51	  Bool.or(Bool.and(U32.is_ge(c, 48), U32.is_le(c, 57)),
52	  Bool.or(Bool.and(U32.is_ge(c, 97), U32.is_le(c, 122)),
53	  Bool.or(U32.is_eq(c, 95), Bool.or(U32.is_eq(c, 46), U32.is_eq(c, 45)))))
54	
55	def key_chars(s: String) -> Bool:
56	  match s:
57	    case SNil{}:
58	      True{}
59	    case SCon{Chr{+c}, t}:
60	      Bool.and(key_char(c), key_chars(t))
61	
62	# 1*[0-9a-z_.-]
63	def valid_key(+key: String) -> Bool:
64	  Bool.and(Bool.not(String.is_empty(key)), key_chars(key))