fix protocol negotiation error handling

In CASSGO-97 and #1920 the handling was changed to better support non-zero stream id
error responses. But because of hardcoding of version 5 in the test harness there was
a regression where older protocol responses were not supported anymore.

By adding an Unwrap method to ErrProtocol now the existing checking in
checkProtocolRelatedError will correctly catch the protocolError.

Patch by James Hartig; reviewed by Bohdan Siryk for CASSGO-131

Author: jameshartig

CHANGELOG.md

@@ -13,6 +13,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Improve host_source locking and ring refresh concurrency (CASSGO-121)
 - Add PreparedMetadata (Keyspace, Table) and IsPrepared fields to ObservedQuery, and parallel PreparedMetadata / IsPrepared slices to ObservedBatch, for statement-level observability without CQL parsing (CASSGO-119)
 
+### Fixed
+- Correct protocol negotiation with non-Cassandra servers (CASSGO-131)
+
 ## [2.1.2]
 
 ### Fixed

conn_test.go

@@ -1259,7 +1259,12 @@ func (srv *TestServer) process(conn net.Conn, reqFrame *framer, useProtoV5, star
 		srv.errorLocked("process frame with a nil header")
 		return
 	}
-	respFrame := newFramer(nil, byte(head.version), GlobalTypes)
+	// use the configured version unless it wasn't specified
+	version := srv.protocol
+	if version == 0 {
+		version = byte(head.version)
+	}
+	respFrame := newFramer(nil, version, GlobalTypes)
 
 	if srv.customRequestHandler != nil {
 		if err := srv.customRequestHandler(srv, reqFrame, respFrame); err != nil {

protocol_negotiation_test.go

@@ -231,9 +231,18 @@ func TestProtocolNegotiation(t *testing.T) {
 				forceZeroStreamID:         tc.forceZeroStreamID,
 			}
 
+			// use the maximum protocol supported
+			protocol := uint8(0)
+			for _, supportedVersion := range tc.supportedVersions {
+				supportedProto := uint8(supportedVersion)
+				if supportedProto > protocol {
+					protocol = supportedProto
+				}
+			}
+
 			srv := newTestServerOpts{
 				addr:                       "127.0.0.1:0",
-				protocol:                   5,
+				protocol:                   protocol,
 				customRequestHandler:       handler.handle,
 				dontFailOnProtocolMismatch: true,
 			}.newServer(t, context.Background())

session.go

@@ -2532,6 +2532,10 @@ var (
 // ErrProtocol represents a protocol-level error.
 type ErrProtocol struct{ error }
 
+func (e ErrProtocol) Unwrap() error {
+	return e.error
+}
+
 // NewErrProtocol creates a new protocol error with the specified format and arguments.
 func NewErrProtocol(format string, args ...interface{}) error {
 	return ErrProtocol{fmt.Errorf(format, args...)}