Add cowboy:get_protocol_options/1 and cowboy_set_protocol_options/2

This allows any application to upgrade the protocol options without
having to restart the listener. This is most useful to update the
dispatch list of HTTP servers, for example.

The upgrade is done at the acceptor level, meaning only new connections
receive the new protocol options.

1 files changed, 66 insertions, 28 deletions

diff --git a/src/cowboy_listener.erl b/src/cowboy_listener.erl
index 8998e13..8a4f056 100644
--- a/src/cowboy_listener.erl
+++ b/src/cowboy_listener.erl
@@ -16,16 +16,21 @@
 -module(cowboy_listener).
 -behaviour(gen_server).
 
--export([start_link/1, stop/1,
-	add_connection/3, move_connection/3, remove_connection/2]). %% API.
+-export([start_link/2, stop/1,
+	add_connection/4, move_connection/3, remove_connection/2,
+	get_protocol_options/1, set_protocol_options/2]). %% API.
 -export([init/1, handle_call/3, handle_cast/2,
 	handle_info/2, terminate/2, code_change/3]). %% gen_server.
 
+-type pools() :: [{atom(), non_neg_integer()}].
+
 -record(state, {
-	req_pools = [] :: [{atom(), non_neg_integer()}],
+	req_pools = [] :: pools(),
 	reqs_table :: ets:tid(),
 	queue = [] :: [{pid(), reference()}],
-	max_conns = undefined :: non_neg_integer()
+	max_conns = undefined :: non_neg_integer(),
+	proto_opts :: any(),
+	proto_opts_vsn = 1 :: non_neg_integer()
 }).
 
 %% API.
@@ -37,9 +42,9 @@
 %% Setting the process priority to high ensures the connection-related code
 %% will always be executed when a connection needs it, allowing Cowboy to
 %% scale far beyond what it would with a normal priority.
--spec start_link(non_neg_integer()) -> {ok, pid()}.
-start_link(MaxConns) ->
-	gen_server:start_link(?MODULE, [MaxConns],
+-spec start_link(non_neg_integer(), any()) -> {ok, pid()}.
+start_link(MaxConns, ProtoOpts) ->
+	gen_server:start_link(?MODULE, [MaxConns, ProtoOpts],
 		[{spawn_opt, [{priority, high}]}]).
 
 %% @private
@@ -59,9 +64,15 @@ stop(ServerPid) ->
 %% pool. If the socket has been sent to another process, it is up to the
 %% protocol code to inform the listener of the new <em>ConnPid</em> by removing
 %% the previous and adding the new one.
--spec add_connection(pid(), atom(), pid()) -> ok.
-add_connection(ServerPid, Pool, ConnPid) ->
-	gen_server:call(ServerPid, {add_connection, Pool, ConnPid}, infinity).
+%%
+%% This function also returns whether the protocol options have been modified.
+%% If so, then an {upgrade, ProtoOpts, OptsVsn} will be returned instead of
+%% the atom 'ok'. The acceptor can then continue with the new protocol options.
+-spec add_connection(pid(), atom(), pid(), non_neg_integer())
+	-> ok | {upgrade, any(), non_neg_integer()}.
+add_connection(ServerPid, Pool, ConnPid, OptsVsn) ->
+	gen_server:call(ServerPid, {add_connection, Pool, ConnPid, OptsVsn},
+		infinity).
 
 %% @doc Move a connection from one pool to another.
 -spec move_connection(pid(), atom(), pid()) -> ok.
@@ -73,35 +84,46 @@ move_connection(ServerPid, DestPool, ConnPid) ->
 remove_connection(ServerPid, ConnPid) ->
 	gen_server:cast(ServerPid, {remove_connection, ConnPid}).
 
+%% @doc Return the current protocol options.
+-spec get_protocol_options(pid()) -> {ok, any()}.
+get_protocol_options(ServerPid) ->
+	gen_server:call(ServerPid, get_protocol_options).
+
+%% @doc Upgrade the protocol options.
+-spec set_protocol_options(pid(), any()) -> ok.
+set_protocol_options(ServerPid, ProtoOpts) ->
+	gen_server:call(ServerPid, {set_protocol_options, ProtoOpts}).
+
 %% gen_server.
 
 %% @private
 -spec init(list()) -> {ok, #state{}}.
-init([MaxConns]) ->
-	ReqsTablePid = ets:new(requests_table, [set, private]),
-	{ok, #state{reqs_table=ReqsTablePid, max_conns=MaxConns}}.
+init([MaxConns, ProtoOpts]) ->
+	ReqsTable = ets:new(requests_table, [set, private]),
+	{ok, #state{reqs_table=ReqsTable, max_conns=MaxConns,
+		proto_opts=ProtoOpts}}.
 
 %% @private
 -spec handle_call(_, _, State)
 	-> {reply, ignored, State} | {stop, normal, stopped, State}.
-handle_call({add_connection, Pool, ConnPid}, From, State=#state{
+handle_call({add_connection, Pool, ConnPid, AccOptsVsn}, From, State=#state{
 		req_pools=Pools, reqs_table=ReqsTable,
-		queue=Queue, max_conns=MaxConns}) ->
-	MonitorRef = erlang:monitor(process, ConnPid),
-	ConnPid ! {shoot, self()},
-	{NbConnsRet, Pools2} = case lists:keyfind(Pool, 1, Pools) of
-		false ->
-			{1, [{Pool, 1}|Pools]};
-		{Pool, NbConns} ->
-			NbConns2 = NbConns + 1,
-			{NbConns2, [{Pool, NbConns2}|lists:keydelete(Pool, 1, Pools)]}
-	end,
-	ets:insert(ReqsTable, {ConnPid, {MonitorRef, Pool}}),
-	if	NbConnsRet > MaxConns ->
-			{noreply, State#state{req_pools=Pools2, queue=[From|Queue]}};
+		queue=Queue, max_conns=MaxConns,
+		proto_opts=ProtoOpts, proto_opts_vsn=LisOptsVsn}) ->
+	{NbConns, Pools2} = add_pid(ConnPid, Pool, Pools, ReqsTable),
+	State2 = State#state{req_pools=Pools2},
+	if	AccOptsVsn =/= LisOptsVsn ->
+			{reply, {ugprade, ProtoOpts, LisOptsVsn}, State2};
+		NbConns > MaxConns ->
+			{noreply, State2#state{queue=[From|Queue]}};
 		true ->
-			{reply, ok, State#state{req_pools=Pools2}}
+			{reply, ok, State2}
 	end;
+handle_call(get_protocol_options, _From, State=#state{proto_opts=ProtoOpts}) ->
+	{reply, {ok, ProtoOpts}, State};
+handle_call({set_protocol_options, ProtoOpts}, _From,
+		State=#state{proto_opts_vsn=OptsVsn}) ->
+	{reply, ok, State#state{proto_opts=ProtoOpts, proto_opts_vsn=OptsVsn + 1}};
 handle_call(stop, _From, State) ->
 	{stop, normal, stopped, State};
 handle_call(_Request, _From, State) ->
@@ -148,6 +170,22 @@ code_change(_OldVsn, State, _Extra) ->
 %% Internal.
 
 %% @private
+-spec add_pid(pid(), atom(), pools(), ets:tid())
+	-> {non_neg_integer(), pools()}.
+add_pid(ConnPid, Pool, Pools, ReqsTable) ->
+	MonitorRef = erlang:monitor(process, ConnPid),
+	ConnPid ! {shoot, self()},
+	{NbConnsRet, Pools2} = case lists:keyfind(Pool, 1, Pools) of
+		false ->
+			{1, [{Pool, 1}|Pools]};
+		{Pool, NbConns} ->
+			NbConns2 = NbConns + 1,
+			{NbConns2, [{Pool, NbConns2}|lists:keydelete(Pool, 1, Pools)]}
+	end,
+	ets:insert(ReqsTable, {ConnPid, {MonitorRef, Pool}}),
+	{NbConnsRet, Pools2}.
+
+%% @private
 -spec remove_pid(pid(), State) -> State.
 remove_pid(Pid, State=#state{
 		req_pools=Pools, reqs_table=ReqsTable, queue=Queue}) ->