Server: use uv_getaddrinfo() for $NVIM_LISTEN_ADDRESS

This change implicitly adds IPv6 support.

If the address contains ":", we try to use a TCP socket instead of a Unix domain
socket. Everything in front of the last occurrence of ":" is the hostname and
everything after it the port.

If the hostname lookup fails, we fall back to using a Unix domain socket.

If the port is empty ("localhost:"), a random port will be assigned.

Examples:

  NVIM_LISTEN_ADDRESS=localhost:12345 -> TCP (IPv4 or IPv6), port: 12345
  NVIM_LISTEN_ADDRESS=localhost:      -> TCP (IPv4 or IPv6), port: random (> 1024)
  NVIM_LISTEN_ADDRESS=localhost:0     -> TCP (IPv4 or IPv6), port: random (> 1024)
  NVIM_LISTEN_ADDRESS=localhost       -> Unix domain socket "localhost" in current dir

1 files changed, 16 insertions, 11 deletions

diff --git a/src/nvim/msgpack_rpc/server.c b/src/nvim/msgpack_rpc/server.c
index b6958088ca..ee96fa1a74 100644
--- a/src/nvim/msgpack_rpc/server.c
+++ b/src/nvim/msgpack_rpc/server.c
@@ -97,31 +97,36 @@ char *server_address_new(void)
 #endif
 }
 
-/// Starts listening for API calls on the TCP address or pipe path `endpoint`.
+/// Starts listening for API calls.
+///
 /// The socket type is determined by parsing `endpoint`: If it's a valid IPv4
-/// address in 'ip[:port]' format, then it will be TCP socket. The port is
-/// optional and if omitted defaults to NVIM_DEFAULT_TCP_PORT. Otherwise it
-/// will be a unix socket or named pipe.
+/// or IPv6 address in 'ip:[port]' format, then it will be a TCP socket.
+/// Otherwise it will be a Unix socket or named pipe (Windows).
+///
+/// If no port is given, a random one will be assigned.
 ///
-/// @param endpoint Address of the server. Either a 'ip[:port]' string or an
-///        arbitrary identifier (trimmed to 256 bytes) for the unix socket or
-///        named pipe.
+/// @param endpoint Address of the server. Either a 'ip:[port]' string or an
+///                 arbitrary identifier (trimmed to 256 bytes) for the Unix
+///                 socket or named pipe.
 /// @returns 0 on success, 1 on a regular error, and negative errno
-///          on failure to bind or connect.
+///          on failure to bind or listen.
 int server_start(const char *endpoint)
 {
-  if (endpoint == NULL) {
-    ELOG("Attempting to start server on NULL endpoint");
+  if (endpoint == NULL || endpoint[0] == '\0') {
+    ELOG("Empty or NULL endpoint");
     return 1;
   }
 
   SocketWatcher *watcher = xmalloc(sizeof(SocketWatcher));
-  socket_watcher_init(&main_loop, watcher, endpoint, NULL);
+  socket_watcher_init(&main_loop, watcher, endpoint);
 
   // Check if a watcher for the endpoint already exists
   for (int i = 0; i < watchers.ga_len; i++) {
     if (!strcmp(watcher->addr, ((SocketWatcher **)watchers.ga_data)[i]->addr)) {
       ELOG("Already listening on %s", watcher->addr);
+      if (watcher->stream->type == UV_TCP) {
+        uv_freeaddrinfo(watcher->uv.tcp.addrinfo);
+      }
       socket_watcher_close(watcher, free_server);
       return 1;
     }