Add http3 module: HTTP/3 in the Java HTTP Client (JEP 517), opt-in, discovery modes, fallback timings, proxy downgrade and a packet-loss comparison

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01KqJyCidz3ZgRyHABv2GVJh

http3/server/serve.py

@@ -0,0 +1,29 @@
+"""serve.py MODE [PORT]
+  h3  HTTP/1.1 + HTTP/2 on TCP (Hypercorn) and HTTP/3 on UDP (aioquic), same port number, Alt-Svc advertised
+  h2  TCP only, ALPN h2 + http/1.1
+  h1  TCP only, ALPN http/1.1
+"""
+import asyncio, os, sys
+mode = sys.argv[1]; port = sys.argv[2] if len(sys.argv) > 2 else "4433"
+if mode == "h3": os.environ["ALT_SVC_PORT"] = port
+from hypercorn.asyncio import serve
+from hypercorn.config import Config
+from app import app
+
+root = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+c = Config()
+c.certfile, c.keyfile = f"{root}/certs/cert.pem", f"{root}/certs/key.pem"
+c.bind = [f"127.0.0.1:{port}"]
+c.loglevel = "WARNING"
+if mode == "h1":
+    c.alpn_protocols = ["http/1.1"]
+elif mode not in ("h2", "h3"):
+    sys.exit("mode must be h3, h2 or h1")
+
+async def main():
+    tasks = [serve(app, c)]
+    if mode == "h3":
+        import h3server
+        tasks.append(h3server.start(int(port), c.certfile, c.keyfile))
+    await asyncio.gather(*tasks)
+asyncio.run(main())