gdb.debug: avoid 2s timeout if possible

CHANGELOG.md

@@ -88,6 +88,7 @@ The table below shows which release corresponds to each branch, and what date th
 - [#2405][2405] Add "none" ssh authentication method
 - [#2427][2427] Document behaviour of remote()'s sni argument as string.
 - [#2382][2382] added optional port, gdb_args and gdbserver_args parameters to gdb.debug()
+- [#2435][2435] Speed up gdbserver handshake in gdb.debug()
 
 [2360]: https://github.com/Gallopsled/pwntools/pull/2360
 [2356]: https://github.com/Gallopsled/pwntools/pull/2356

pwnlib/gdb.py

@@ -717,12 +717,13 @@ def debug(args, gdbscript=None, gdb_args=None, exe=None, ssh=None, env=None, por
 
     # gdbserver outputs a message when a client connects
     garbage = gdbserver.recvline(timeout=1)
-
     # Some versions of gdbserver output an additional message
-    try:
-        garbage2 = gdbserver.recvline_startswith(b"Remote debugging from host ", timeout=2)
-    except EOFError:
-        pass
+    message = b"Remote debugging from host "
+    if not garbage.startswith(message):
+        try:
+            garbage2 = gdbserver.recvline_startswith(message, timeout=2)
+        except EOFError:
+            pass
 
     return gdbserver