Add application_name as an optional parameter while establishing a connection

README.md

@@ -112,6 +112,9 @@ Only `host` and `username` are mandatory, but most likely you would need `databa
    Default is `[null, undefined]`, i.e. encode `null` or `undefined` in parameters as `NULL`
    and decode `NULL`s as atom `null`.
 - `replication` see [Streaming replication protocol](#streaming-replication-protocol)
+- `application_name` is an optional string parameter. It is usually set by an application upon
+   connection to the server. The name will be displayed in the `pg_stat_activity`
+   view and included in CSV log entries.
 
 Options may be passed as proplist or as map with the same key names.
 

src/commands/epgsql_cmd_connect.erl

@@ -89,7 +89,13 @@ client_handshake(Sock, PgSock, #connect{opts = #{username := Username} = Opts} =
                          epgsql_sock:init_replication_state(PgSock1)};
                     _ -> {Opts3, PgSock1}
                 end,
-            ok = epgsql_sock:send(PgSock2, [<<196608:?int32>>, Opts4, 0]),
+            Opts5 = case Opts of
+                        #{application_name := ApplicationName}  ->
+                            [Opts3 | ["application_name", 0, ApplicationName, 0]];
+                        _ ->
+                            Opts4
+                    end,
+            ok = epgsql_sock:send(PgSock2, [<<196608:?int32>>, Opts5, 0]),
             PgSock3 = case Opts of
                           #{async := Async} ->
                               epgsql_sock:set_attr(async, Async, PgSock2);

src/epgsql.erl

@@ -62,7 +62,8 @@
     {async,    Receiver   :: pid() | atom()}       | % process to receive LISTEN/NOTIFY msgs
     {codecs,   Codecs     :: [{epgsql_codec:codec_mod(), any()}]} |
     {nulls,    Nulls      :: [any(), ...]} |    % terms to be used as NULL
-    {replication, Replication :: string()}. % Pass "database" to connect in replication mode
+    {replication, Replication :: string()} | % Pass "database" to connect in replication mode
+    {application_name, ApplicationName :: string()}.
 
 -type connect_opts() ::
         [connect_option()]
@@ -77,7 +78,9 @@
           async => pid() | atom(),
           codecs => [{epgsql_codec:codec_mod(), any()}],
           nulls => [any(), ...],
-          replication => string()}.
+          replication => string(),
+          application_name => string()
+          }.
 
 -type connect_error() :: epgsql_cmd_connect:connect_error().
 -type query_error() :: #error{}.              % Error report generated by server