Add content handlers and built-in SSE support

Content handlers are a chain of modules implementing callbacks
that receive the body of responses and may modify it (for example
for decompressing the content) or act upon it (like sending a
message to the owner process.

The gun_sse content handler module can be used to translate
text/event-stream events on the fly and deliver them to the
owner process as a {gun_sse...} message.

This feature is currently not documented and is only tested
against a public server. It requires an up to date Cowlib.

1 files changed, 69 insertions, 0 deletions

diff --git a/src/gun_content_handler.erl b/src/gun_content_handler.erl
new file mode 100644
index 0000000..b268f56
--- /dev/null
+++ b/src/gun_content_handler.erl
@@ -0,0 +1,69 @@
+%% Copyright (c) 2017, Loïc Hoguin <[email protected]>
+%%
+%% Permission to use, copy, modify, and/or distribute this software for any
+%% purpose with or without fee is hereby granted, provided that the above
+%% copyright notice and this permission notice appear in all copies.
+%%
+%% THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+%% WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+%% MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+%% ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+%% WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+%% ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+%% OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+-module(gun_content_handler).
+
+-export([init/5]).
+-export([handle/3]).
+-export([check_option/1]).
+
+-type opt() :: [module() | {module(), map()}].
+-export_type([opt/0]).
+
+-type state() :: opt() | [{module(), any()}].
+-export_type([state/0]).
+
+-callback init(pid(), reference(), cow_http:status(),
+	cow_http:headers(), map()) -> {ok, any()} | disable.
+%% @todo Make fin | nofin its own type.
+-callback handle(fin | nofin, any(), State)
+	-> {ok, any(), State} | {done, State} when State::any().
+
+-spec init(pid(), reference(), cow_http:status(),
+	cow_http:headers(), State) -> State when State::state().
+init(_, _, _, _, []) ->
+	[];
+init(ReplyTo, Owner, Status, Headers, [Handler|Tail]) ->
+	{Mod, Opts} = case Handler of
+		Tuple = {_, _} -> Tuple;
+		Atom -> {Atom, #{}}
+	end,
+	case Mod:init(ReplyTo, Owner, Status, Headers, Opts) of
+		{ok, State} -> [{Mod, State}|init(ReplyTo, Owner, Status, Headers, Tail)];
+		disable -> init(ReplyTo, Owner, Status, Headers, Tail)
+	end.
+
+-spec handle(fin | nofin, any(), State) -> State when State::state().
+handle(_, _, []) ->
+	[];
+handle(IsFin, Data0, [{Mod, State0}|Tail]) ->
+	case Mod:handle(IsFin, Data0, State0) of
+		{ok, Data, State} -> [{Mod, State}|handle(IsFin, Data, Tail)];
+		{done, State} -> [{Mod, State}|Tail]
+	end.
+
+-spec check_option(list()) -> ok | error.
+check_option([]) ->
+	error;
+check_option(Opt) ->
+	check_option1(Opt).
+
+check_option1([]) ->
+	ok;
+check_option1([Atom|Tail]) when is_atom(Atom) ->
+	check_option1(Tail);
+check_option1([{Atom, #{}}|Tail]) when is_atom(Atom) ->
+	check_option1(Tail);
+check_option1(_) ->
+	error.