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/app.py

@@ -0,0 +1,34 @@
+"""The test application. respond() is shared by the Hypercorn ASGI wrapper (HTTP/1.1, HTTP/2) and the aioquic
+HTTP/3 server. It reports which HTTP version the request arrived on, returns N bytes for /bytes/N, and can redirect."""
+import os
+
+ALT_SVC = os.environ.get("ALT_SVC_PORT")      # set by serve.py in h3 mode: advertise h3 on that UDP port
+
+def respond(path, version, host, port):
+    hdrs = []
+    if ALT_SVC:
+        hdrs.append((b"alt-svc", ('h3=":%s"; ma=3600' % ALT_SVC).encode()))
+    if path.startswith("/bytes/"):
+        body = b"x" * int(path.rsplit("/", 1)[1]); ctype = b"application/octet-stream"; status = 200
+    elif path == "/redirect":
+        hdrs.append((b"location", b"/hello")); return 302, hdrs, b""
+    else:
+        body = ("hello from %s:%s via HTTP/%s\n" % (host, port, version)).encode(); ctype = b"text/plain"; status = 200
+    hdrs += [(b"content-type", ctype), (b"content-length", str(len(body)).encode())]
+    return status, hdrs, body
+
+async def app(scope, receive, send):
+    if scope["type"] == "lifespan":
+        while True:
+            m = await receive()
+            if m["type"] == "lifespan.startup":
+                await send({"type": "lifespan.startup.complete"})
+            elif m["type"] == "lifespan.shutdown":
+                await send({"type": "lifespan.shutdown.complete"}); return
+    if scope["type"] != "http":
+        return
+    while (await receive()).get("more_body"):   # drain the request body
+        pass
+    status, headers, body = respond(scope["path"], scope["http_version"], scope["server"][0], scope["server"][1])
+    await send({"type": "http.response.start", "status": status, "headers": headers})
+    await send({"type": "http.response.body", "body": body})