net: chat client - async receive + OSK send over the link port

The application layer of the link-port demo, and it ties the whole system
together: the LCD terminal displays, the on-screen keyboard types, and the
link port carries a live chat.

Kernel: sys_srecv_nb (non-blocking link receive; A=byte, CF=none) and
sys_pollin (poll the OSK for a typed char without blocking) - syscalls
31/32. Both are what a poll loop needs to receive and type at once.

Userland: c/chat.c runs a poll loop - it feeds non-blocking bytes through a
SLIP receive state machine and prints whole incoming frames as messages,
while pollin() drives the on-screen keyboard; SELECT shows the keys, type a
line, START sends it as a frame. libc srecv_nb()/pollin().

Host: tools/gateway.py --mode chat is a simple bot peer (echoes each GB
message and injects a few async ones); --keys can drive the OSK for tests.

Verified: the gateway pushes 'welcome', '<alice> hey gameboy!', '<bob> nice
link cable' unprompted and the GB displays all three (async receive); typing
'hi' on the OSK echoes it and emits the SLIP frame \xC0hi\xC0 (send). A Game
Boy in the chat, keyboard on screen, over the link cable.

1 files changed, 14 insertions, 2 deletions

diff --git a/tools/gateway.py b/tools/gateway.py
index 3129773..3b18024 100644
--- a/tools/gateway.py
+++ b/tools/gateway.py
@@ -46,6 +46,10 @@ def http_fetch(payload):
 def handle(payload, mode):
     if mode == "http":
         return http_fetch(payload)
+    if mode == "chat":
+        msg = bytes(payload).decode("latin1", "replace")
+        sys.stderr.write("\n[gw] GB says: %s\n" % msg)
+        return [("<bot> " + msg).encode()]     # a simple echo-bot peer
     return [bytes(payload)]        # echo
 
 def reader(out, inp, mode):
@@ -75,15 +79,23 @@ def reader(out, inp, mode):
 
 def main():
     ap = argparse.ArgumentParser()
-    ap.add_argument("--mode", default="echo", choices=["echo", "http"])
+    ap.add_argument("--mode", default="echo", choices=["echo", "http", "chat"])
     ap.add_argument("--cmd", default="necho")
     ap.add_argument("--rom", default=os.path.join(os.path.dirname(__file__), "..", "gbos.gb"))
+    ap.add_argument("--keys", default=None)
     a = ap.parse_args()
-    p = subprocess.Popen([EMU, "--headless", "--uncapped", a.rom],
+    cmd = [EMU, "--headless", "--uncapped"]
+    if a.keys: cmd += ["--keys", a.keys]
+    cmd.append(a.rom)
+    p = subprocess.Popen(cmd,
                          stdin=subprocess.PIPE, stdout=subprocess.PIPE, bufsize=0)
     threading.Thread(target=reader, args=(p.stdout, p.stdin, a.mode), daemon=True).start()
     time.sleep(1.0)
     p.stdin.write((a.cmd + "\n").encode()); p.stdin.flush()
+    if a.mode == "chat":
+        time.sleep(1.0)
+        for m in [b"welcome to sl0pchat", b"<alice> hey gameboy!", b"<bob> nice link cable"]:
+            p.stdin.write(slip_encode(m)); p.stdin.flush(); time.sleep(0.6)
     time.sleep(4.0)
     p.stdin.write(b"exit\n"); p.stdin.flush()
     try: p.wait(timeout=3)