redis/redis-py · error · ConnectionError

Invalid RESP version

Error message

Invalid RESP version

What it means

Raised in on_connect (connection.py:1187-1191) on the RESP3 path when HELLO succeeds (no auth case) but the returned handshake 'proto' field does not equal the requested protocol. The server claimed to negotiate HELLO 3 but reported a different proto number in its reply, indicating the server did not actually switch to the requested RESP version. Treated as a connection failure.

Solutions

1. Bypass the proxy and connect directly to a Redis node to confirm RESP3 works there.
2. Fall back to protocol=2 if the intermediary cannot carry RESP3 correctly.
3. Upgrade the proxy/middleware to one that transparently forwards HELLO.
4. Upgrade Redis to a version with correct HELLO/proto reporting.

Example fix

# before
r = redis.Redis(host='proxy', port=6379, protocol=3)
# after
r = redis.Redis(host='redis-node-0', port=6379, protocol=3)

# Detect a non-conforming intermediary before relying on RESP3
def negotiate_protocol(host, port):
    r = redis.Redis(host=host, port=port, protocol=3)
    try:
        r.ping()
        return 3
    except redis.exceptions.ConnectionError as e:
        if 'Invalid RESP version' in str(e):
            return 2  # proxy can't carry RESP3
        raise

r = redis.Redis(host=h, port=p, protocol=negotiate_protocol(h, p))

null

from redis.exceptions import ConnectionError
try:
    r = redis.Redis(host=h, port=p, protocol=3)
    r.ping()
except ConnectionError as e:
    if 'Invalid RESP version' in str(e):
        r = redis.Redis(host=h, port=p, protocol=2)  # fallback
    else:
        raise

When it happens

Trigger: Connecting with protocol=3 to a server that accepts HELLO but echoes back a different proto (misbehaving proxy, RESP3-incompatible middleware, or a server that silently downgrades); a man-in-the-middle/transparent proxy rewriting HELLO responses.

Common situations: HAProxy/Envoy/Nginx in front of Redis that doesn't forward HELLO correctly; Redis versions with RESP3 bugs; connecting through a sharding proxy that strips HELLO metadata.

Related errors

• Bad response from PING health check
• Invalid RESP version
• A non health check response was cleaned by execute_command
• Cannot retrieve information about server version
• Client caching is only supported with RESP version 3

AI-assisted analysis of redis/redis-py@6a6b581b48 (2026-08-10). Data as JSON: /api/errors/94cf415663e7716f. Report an issue: GitHub.

Appendix: source

Thrown at redis/connection.py:1191

                auth_response = self.read_response()

            if str_if_bytes(auth_response) != "OK":
                raise AuthenticationError("Invalid Username or Password")

        # if resp version is specified, switch to it
        elif check_protocol_version(self.protocol, 3):
            if isinstance(self._parser, _RESP2Parser):
                self.set_parser(_RESP3Parser)
                # update cluster exception classes
                self._parser.EXCEPTION_CLASSES = parser.EXCEPTION_CLASSES
                self._parser.on_connect(self)
            self.send_command("HELLO", self.protocol, check_health=check_health)
            self.handshake_metadata = self.read_response()
            if (
                self.handshake_metadata.get(b"proto") != self.protocol
                and self.handshake_metadata.get("proto") != self.protocol
            ):
                raise ConnectionError("Invalid RESP version")

        # Activate maintenance notifications for this connection
        # if enabled in the configuration
        # This is a no-op if maintenance notifications are not enabled
        self.activate_maint_notifications_handling_if_enabled(check_health=check_health)

        # if a client_name is given, set it
        if self.client_name:
            self.send_command(
                "CLIENT",
                "SETNAME",
                self.client_name,
                check_health=check_health,
            )
            if str_if_bytes(self.read_response()) != "OK":
                raise ConnectionError("Error setting client name")

        # Set the library name and version from driver_info

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