Add `tcp_opts` connect option. Fixes #240

README.md

@@ -71,6 +71,7 @@ connect(Opts) -> {ok, Connection :: epgsql:connection()} | {error, Reason :: epg
       port =>     inet:port_number(),
       ssl =>      boolean() | required,
       ssl_opts => [ssl:ssl_option()],    % @see OTP ssl app, ssl_api.hrl
+      tcp_opts => [gen_tcp:option()],    % @see OTP gen_tcp module documentation
       timeout =>  timeout(),             % socket connect timeout, default: 5000 ms
       async =>    pid() | atom(),        % process to receive LISTEN/NOTIFY msgs
       codecs =>   [{epgsql_codec:codec_mod(), any()}]}
@@ -84,7 +85,10 @@ connect(Host, Username, Password, Opts) -> {ok, C} | {error, Reason}.
 example:
 
 ```erlang
-{ok, C} = epgsql:connect("localhost", "username", "psss", #{
+{ok, C} = epgsql:connect(#{
+    host => "localhost",
+    username => "username",
+    password => "psss",
     database => "test_db",
     timeout => 4000
 }),
@@ -103,6 +107,10 @@ Only `host` and `username` are mandatory, but most likely you would need `databa
   if encryption isn't supported by server. if set to `required` connection will fail if encryption
   is not available.
 - `ssl_opts` will be passed as is to `ssl:connect/3`
+- `tcp_opts` will be passed as is to `gen_tcp:connect/3`. Some options are forbidden, such as
+  `mode`, `packet`, `header`, `active`. When `tcp_opts` is not provided, epgsql does some tuning
+  (eg, sets TCP `keepalive` and auto-tunes `buffer`), but when `tcp_opts` is provided, no
+  additional tweaks are added by epgsql itself, other than necessary ones (`active`, `packet` and `mode`).
 - `async` see [Server notifications](#server-notifications)
 - `codecs` see [Pluggable datatype codecs](#pluggable-datatype-codecs)
 - `nulls` terms which will be used to represent SQL `NULL`. If any of those has been encountered in

src/commands/epgsql_cmd_connect.erl

@@ -48,7 +48,7 @@ init(#{host := _, username := _} = Opts) ->
     #connect{opts = Opts}.
 
 execute(PgSock, #connect{opts = #{username := Username} = Opts, stage = connect} = State) ->
-    SockOpts = [{active, false}, {packet, raw}, binary, {nodelay, true}, {keepalive, true}],
+    SockOpts = prepare_tcp_opts(maps:get(tcp_opts, Opts, [])),
     FilteredOpts = filter_sensitive_info(Opts),
     PgSock1 = epgsql_sock:set_attr(connect_opts, FilteredOpts, PgSock),
     case open_socket(SockOpts, Opts) of
@@ -100,14 +100,19 @@ open_socket(SockOpts, #{host := Host} = ConnectOpts) ->
     end.
 
 client_handshake(Sock, ConnectOpts, Deadline) ->
-    %% Increase the buffer size.  Following the recommendation in the inet man page:
-    %%
-    %%    It is recommended to have val(buffer) >=
-    %%    max(val(sndbuf),val(recbuf)).
-
-    {ok, [{recbuf, RecBufSize}, {sndbuf, SndBufSize}]} =
-        inet:getopts(Sock, [recbuf, sndbuf]),
-    inet:setopts(Sock, [{buffer, max(RecBufSize, SndBufSize)}]),
+    case maps:is_key(tcp_opts, ConnectOpts) of
+        false ->
+            %% Increase the buffer size.  Following the recommendation in the inet man page:
+            %%
+            %%    It is recommended to have val(buffer) >=
+            %%    max(val(sndbuf),val(recbuf)).
+            {ok, [{recbuf, RecBufSize}, {sndbuf, SndBufSize}]} =
+                inet:getopts(Sock, [recbuf, sndbuf]),
+            inet:setopts(Sock, [{buffer, max(RecBufSize, SndBufSize)}]);
+        true ->
+            %% All TCP options are provided by the user
+            noop
+    end,
     maybe_ssl(Sock, maps:get(ssl, ConnectOpts, false), ConnectOpts, Deadline).
 
 maybe_ssl(Sock, false, _ConnectOpts, _Deadline) ->
@@ -282,6 +287,24 @@ handle_message(?ERROR, #error{code = Code} = Err, Sock, #connect{stage = Stage}
 handle_message(_, _, _, _) ->
     unknown.
 
+prepare_tcp_opts([]) ->
+    [{active, false}, {packet, raw}, {mode, binary}, {nodelay, true}, {keepalive, true}];
+prepare_tcp_opts(Opts0) ->
+    case lists:filter(fun(binary) -> true;
+                         (list) -> true;
+                         ({mode, _}) -> true;
+                         ({packet, _}) -> true;
+                         ({packet_size, _}) -> true;
+                         ({header, _}) -> true;
+                         ({active, _}) -> true;
+                         (_) -> false
+                      end, Opts0) of
+        [] ->
+            [{active, false}, {packet, raw}, {mode, binary} | Opts0];
+        Forbidden ->
+            error({forbidden_tcp_opts, Forbidden})
+    end.
+
 
 get_password(Opts) ->
     PasswordFun = maps:get(password, Opts),
@@ -298,4 +321,4 @@ deadline(Timeout) ->
     erlang:monotonic_time(milli_seconds) + Timeout.
 
 timeout(Deadline) ->
-    erlang:max(0, Deadline - erlang:monotonic_time(milli_seconds)).
+    erlang:max(0, Deadline - erlang:monotonic_time(milli_seconds)).

src/epgsql.erl

@@ -58,6 +58,7 @@
     {port,     PortNum    :: inet:port_number()}   |
     {ssl,      IsEnabled  :: boolean() | required} |
     {ssl_opts, SslOptions :: [ssl:ssl_option()]}   | % see OTP ssl app, ssl_api.hrl
+    {tcp_opts, TcpOptions :: [gen_tcp:option()]}   | % see OTP ssl app, ssl_api.hrl
     {timeout,  TimeoutMs  :: timeout()}            | % default: 5000 ms
     {async,    Receiver   :: pid() | atom()}       | % process to receive LISTEN/NOTIFY msgs
     {codecs,   Codecs     :: [{epgsql_codec:codec_mod(), any()}]} |
@@ -74,6 +75,7 @@
           port => inet:port_number(),
           ssl => boolean() | required,
           ssl_opts => [ssl:ssl_option()],
+          tcp_opts => [gen_tcp:option()],
           timeout => timeout(),
           async => pid() | atom(),
           codecs => [{epgsql_codec:codec_mod(), any()}],