start websocket stuff
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Peter Harpending
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673bc3ae52
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159
src/fd_ws.erl
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159
src/fd_ws.erl
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% @doc websockets
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%
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% ref: https://datatracker.ietf.org/doc/html/rfc6455
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-module(fd_ws).
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-export_type([
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]).
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-export([
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handshake/1,
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response_token/1
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]).
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-include("http.hrl").
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-type request() :: #request{}.
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-type response() :: #response{}.
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-spec handshake(Req) -> Result
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when Req :: request(),
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Result :: {ok, ClientProtocols, ClientExtensions, DraftResponse}
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| {error, Reason},
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ClientProtocols :: [binary()],
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ClientExtensions :: [binary()],
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DraftResponse :: response(),
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Reason :: any().
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% @doc
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% This mostly just validates that all the 't's have been dotted and 'i's have
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% been crossed.
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%
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% given an HTTP request:
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%
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% - if it is NOT a valid websocket handshake request, error
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% - if it IS a valid websocket handshake request, form an initial candidate
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% response record with the following fields:
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%
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% code = 101
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% slogan = "Switching Protocols"
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% headers = [{"Sec-WebSocket-Accept", ChallengeResponse},
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% {"Connection", "Upgrade"},
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% {"Upgrade", "websocket"}].
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%
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% YOU are responsible for dealing with any cookie logic, adding the retarded
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% web date, rendering the response, etc.
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handshake(R = #request{method = get, headers = Hs}) ->
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%% downcase the headers because have to match on them
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handshake2(R#request{headers = casefold_headers(Hs)});
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handshake(_) ->
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{error, bad_request}.
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casefold_headers([{K, V} | Rest]) ->
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[{unicode:characters_to_binary(string:casefold(K)), V} | casefold_headers(Rest)];
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casefold_headers([]) ->
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[].
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handshake2(Req = #request{headers = DowncaseHeaders}) ->
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% headers MUST contain fields:
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% sec-websocket-key: _ % arbitrary
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% sec-websocket-version: 13 % must be EXACTLY 13
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% connection: Upgrade % must include the token "Upgrade"
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% upgrade: websocket % must include the token "websocket"
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MapHeaders = maps:from_list(DowncaseHeaders)
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ClientProtocols = client_protocols(MapHeaders),
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ClientExtensions = client_extensions(MapHeaders),
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case validate_headers(MapHeaders) of
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{ok, ResponseToken} ->
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{ok, ClientProtocols,
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ClientExtensions,
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#response{code = 101,
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slogan = "Switching Protocols",
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headers = [{"Sec-WebSocket-Accept", ResponseToken},
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{"Connection", "Upgrade"},
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{"Upgrade", "websocket"}]}};
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Error ->
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Error
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end.
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client_protocols(#{<<"sec-websocket-protocol">> := CommaSeparatedProtocols}) ->
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Protocols = string:split(CommaSeparatedProtocols, ",", all),
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Clean =
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fun(String) ->
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unicode:characters_to_binary(string:trim(String))
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end,
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lists:map(Clean, Protocols).
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client_extensions(#{<<"sec-websocket-extensions">> := CommaSeparatedExtensions}) ->
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Extensions = string:split(CommaSeparatedExtensions, ",", all),
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Clean =
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fun(String) ->
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unicode:characters_to_binary(string:trim(String))
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end,
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lists:map(Clean, Extensions).
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validate_headers(#{<<"sec-websocket-key">> := ChallengeToken,
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<<"sec-websocket-version">> := WS_Vsn,
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<<"connection">> := Connection,
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<<"upgrade">> := Upgrade}) ->
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if
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bad_upgrade(Upgrade) -> {error, {bad_upgrade, Upgrade}};
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bad_connection(Connection) -> {error, {bad_connection, Connection}};
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bad_version(WS_Vsn) -> {error, {bad_version, WS_Vsn}};
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true -> {ok, response_token(ChallengeToken)}
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end.
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% string must include "websocket" as a token
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bad_upgrade(Str) ->
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case string:find(Str, "websocket") of
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nomatch -> true;
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_ -> false
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end.
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% string must include "Upgrade" as a token
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bad_connection(Str) ->
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case string:find(Str, "Upgrade") of
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nomatch -> true;
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_ -> false
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end.
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% version must be EXACTLY <<"13">>
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bad_version(<<"13">> -> false;
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bad_version(_) -> true.
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-spec response_token(binary()) -> binary().
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% @doc
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% Quoth the RFC:
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%
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% > Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
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% >
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% > For this header field, the server has to take the value (as present
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% > in the header field, e.g., the base64-encoded [RFC4648] version minus
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% > any leading and trailing whitespace) and concatenate this with the
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% > Globally Unique Identifier (GUID, [RFC4122]) "258EAFA5-E914-47DA-
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% > 95CA-C5AB0DC85B11" in string form, which is unlikely to be used by
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% > network endpoints that do not understand the WebSocket Protocol. A
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% > SHA-1 hash (160 bits) [FIPS.180-3], base64-encoded (see Section 4 of
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% > [RFC4648]), of this concatenation is then returned in the server's
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% > handshake.
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% >
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% > Concretely, if as in the example above, the |Sec-WebSocket-Key|
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% > header field had the value "dGhlIHNhbXBsZSBub25jZQ==", the server
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% > would concatenate the string "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
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% > to form the string "dGhlIHNhbXBsZSBub25jZQ==258EAFA5-E914-47DA-95CA-
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% > C5AB0DC85B11". The server would then take the SHA-1 hash of this,
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% > giving the value 0xb3 0x7a 0x4f 0x2c 0xc0 0x62 0x4f 0x16 0x90 0xf6
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% > 0x46 0x06 0xcf 0x38 0x59 0x45 0xb2 0xbe 0xc4 0xea. This value is
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% > then base64-encoded (see Section 4 of [RFC4648]), to give the value
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% > "s3pPLMBiTxaQ9kYGzzhZRbK+xOo=". This value would then be echoed in
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% > the |Sec-WebSocket-Accept| header field.
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response_token(ChallengeToken) when is_binary(ChallengeToken) ->
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MagicString = <<"258EAFA5-E914-47DA-95CA-C5AB0DC85B11">>,
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ConcatString = <<ChallengeToken/binary, MagicString/binary>>,
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Sha1 = crypto:hash(sha, ConcatString),
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base64:encode(Sha1).
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