server: read/write now goes through connection fn's

depending on whether the connection is over a socket
or pipe, the read is done differently.

pipes can return -1 when writing 0 bytes, make 0 byte
writes a successful no-op. 0 byte writes falls out
naturally of tcl server code.

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

src/server/server.h

@@ -83,6 +83,9 @@ int server_loop(struct command_context *command_context);
 
 int server_register_commands(struct command_context *context);
 
+int connection_write(struct connection *connection, const void *data, int len);
+int connection_read(struct connection *connection, void *data, int len);
+
 /**
  * Used by server_loop(), defined in server_stubs.c, httpd.c, or ecosboard.c
  */