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Simple HTTP client with HTTP/1.1, HTTP/2, and HTTP/3 support

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hackney src hackney_keepalive.erl
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src/hackney_keepalive.erl 

%%% -*- erlang -*-

%%%

%%% This file is part of hackney released under the Apache 2 license.

%%% See the NOTICE for more information.

%%%

%%% Copyright (c) 2012-2024, Benoît Chesneau <benoitc@e-engura.org>



%% @doc HTTP/1.x keepalive semantics.

%%

%% Single source of truth for deciding whether an HTTP/1.x connection must be

%% closed (not reused) after a response, per RFC 7230. The `Connection' header

%% is a list-valued, hop-by-hop field (RFC 7230 3.2.2, 6.1): a recipient may get

%% it as several header lines or as one comma-joined value, and both are

%% equivalent. It is forbidden in HTTP/2 and HTTP/3, so these rules apply only to

%% HTTP/1.x; multiplexed conns are never pooled in `available'.

%%

%% Every function tolerates undefined or malformed header objects so a bad header

%% can never crash the keepalive decision.

-module(hackney_keepalive).



-export([should_close/3,

         request_closes/1,

         connection_tokens/1]).



%% @doc Whether a parsed HTTP/1.x response means the connection must close.

%%

%% The caller (hackney_conn:should_close_connection/1) guards the "no response

%% observed yet" case; here `Version'/`RespHeaders' describe a response that was

%% actually parsed. Order matters: an explicit `close' wins over version default.

-spec should_close(Version, RespHeaders, RequestClose) -> boolean() when

      Version :: {integer(), integer()} | undefined,

      RespHeaders :: term(),

      RequestClose :: boolean().

should_close(_Version, _RespHeaders, true) ->

    %% We asked the server to close (request carried Connection: close).

    true;

should_close(Version, RespHeaders, false) ->

    Tokens = connection_tokens(RespHeaders),

    case lists:member(<<"close">>, Tokens) of

        true ->

            true;

        false ->

            case Version of

                {1, 1} ->

                    %% HTTP/1.1 default is keep-alive; an absent Connection header

                    %% stays persistent and poolable.

                    false;

                {1, 0} ->

                    %% HTTP/1.0 default is close unless it opts into keep-alive.

                    not lists:member(<<"keep-alive">>, Tokens);

                _ ->

                    %% Unknown version on a parsed response: close on the safe side.

                    true

            end

    end.



%% @doc Whether request headers carry `Connection: close'.

-spec request_closes(term()) -> boolean().

request_closes(ReqHeaders) ->

    lists:member(<<"close">>, connection_tokens(ReqHeaders)).



%% @doc Lower-cased, trimmed tokens from every `Connection' header.

%%

%% Defensive at each layer: an undefined or malformed header object yields `[]',

%% and a value that does not convert to a binary is skipped rather than crashing.

-spec connection_tokens(term()) -> [binary()].

connection_tokens(undefined) ->

    [];

connection_tokens(Headers) ->

    Values = try hackney_headers:lookup(<<"connection">>, Headers)

             catch _:_ -> []

             end,

    lists:flatmap(fun({_Key, Value}) -> value_tokens(Value) end, Values).



%% @private

value_tokens(Value) ->

    case (try hackney_bstr:to_binary(Value) catch _:_ -> error end) of

        error ->

            [];

        Bin ->

            Lower = hackney_bstr:to_lower(Bin),

            Parts = binary:split(Lower, <<",">>, [global]),

            Trimmed = [hackney_bstr:trim(P) || P <- Parts],

            [T || T <- Trimmed, T =/= <<>>]

    end.