Add HTTPTransport setting to gremlin-go driver

CHANGELOG.asciidoc

@@ -25,6 +25,7 @@ image::https://raw.githubusercontent.com/apache/tinkerpop/master/docs/static/ima
 [[release-4-0-0]]
 === TinkerPop 4.0.0 (NOT OFFICIALLY RELEASED YET)
 
+* Added `HTTPTransport` setting to `gremlin-go` to allow users to provide a custom `http.RoundTripper` for transport-level instrumentation.
 * Added grammar-based `Translator` for `gremlin-javascript` supporting translation to JavaScript, Python, Go, .NET, Java, Groovy, canonical, and anonymized output.
 * Added `translate_gremlin_query` tool to `gremlin-mcp` that translates Gremlin queries to a target language variant, with optional LLM-assisted normalization via MCP sampling for non-canonical input.
 * Modified `gremlin-mcp` to support offline mode where utility tools (translate, format) remain available without a configured `GREMLIN_MCP_ENDPOINT`.

gremlin-go/driver/client.go

@@ -21,6 +21,7 @@ package gremlingo
 
 import (
 	"crypto/tls"
+	"net/http"
 	"reflect"
 	"time"
 
@@ -61,6 +62,18 @@ type ClientSettings struct {
 
 	EnableUserAgentOnConnect bool
 
+	// HTTPTransport is the http.RoundTripper used for Gremlin HTTP requests.
+	//
+	// When set, the driver uses this transport directly. The following settings
+	// are ignored as they configure the driver's default transport:
+	// MaximumConcurrentConnections, MaxIdleConnections, IdleConnectionTimeout,
+	// KeepAliveInterval, TlsConfig, and EnableCompression. Configure these on
+	// your transport directly.
+	//
+	// When nil (the default), the driver creates an http.Transport configured
+	// with the above settings.
+	HTTPTransport http.RoundTripper
+
 	// RequestInterceptors are functions that modify HTTP requests before sending.
 	RequestInterceptors []RequestInterceptor
 }
@@ -105,6 +118,7 @@ func NewClient(url string, configurations ...func(settings *ClientSettings)) (*C
 		keepAliveInterval:        settings.KeepAliveInterval,
 		enableCompression:        settings.EnableCompression,
 		enableUserAgentOnConnect: settings.EnableUserAgentOnConnect,
+		httpTransport:            settings.HTTPTransport,
 	}
 
 	logHandler := newLogHandler(settings.Logger, settings.LogVerbosity, settings.Language)

gremlin-go/driver/connection.go

@@ -95,6 +95,7 @@ type connectionSettings struct {
 	keepAliveInterval        time.Duration
 	enableCompression        bool
 	enableUserAgentOnConnect bool
+	httpTransport            http.RoundTripper
 }
 
 // connection handles HTTP request/response for Gremlin queries.
@@ -118,7 +119,24 @@ const (
 )
 
 func newConnection(handler *logHandler, url string, connSettings *connectionSettings) *connection {
-	// Apply defaults for zero values
+	var rt http.RoundTripper
+	if connSettings.httpTransport != nil {
+		// user supplied their own transport, so use it
+		rt = connSettings.httpTransport
+	} else {
+		rt = newDefaultTransport(connSettings)
+	}
+
+	return &connection{
+		url:          url,
+		httpClient:   &http.Client{Transport: rt}, // No Timeout - allows streaming
+		connSettings: connSettings,
+		logHandler:   handler,
+		serializer:   newGraphBinarySerializer(handler),
+	}
+}
+
+func newDefaultTransport(connSettings *connectionSettings) *http.Transport {
 	connectionTimeout := connSettings.connectionTimeout
 	if connectionTimeout == 0 {
 		connectionTimeout = defaultConnectionTimeout
@@ -144,7 +162,7 @@ func newConnection(handler *logHandler, url string, connSettings *connectionSett
 		keepAliveInterval = defaultKeepAliveInterval
 	}
 
-	transport := &http.Transport{
+	return &http.Transport{
 		DialContext: (&net.Dialer{
 			Timeout:   connectionTimeout,
 			KeepAlive: keepAliveInterval,
@@ -155,14 +173,6 @@ func newConnection(handler *logHandler, url string, connSettings *connectionSett
 		IdleConnTimeout:     idleConnTimeout,
 		DisableCompression:  !connSettings.enableCompression,
 	}
-
-	return &connection{
-		url:          url,
-		httpClient:   &http.Client{Transport: transport}, // No Timeout - allows streaming
-		connSettings: connSettings,
-		logHandler:   handler,
-		serializer:   newGraphBinarySerializer(handler),
-	}
 }
 
 // AddInterceptor adds a request interceptor to the chain.

gremlin-go/driver/connection_test.go

@@ -1134,3 +1134,77 @@ func TestDriverRemoteConnectionSettingsWiring(t *testing.T) {
 		assert.Equal(t, 180*time.Second, transport.IdleConnTimeout)
 	})
 }
+
+// countingRoundTripper is a test RoundTripper that counts requests.
+type countingRoundTripper struct {
+	base  http.RoundTripper
+	count int
+}
+
+func (c *countingRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	c.count++
+	return c.base.RoundTrip(req)
+}
+
+func TestHTTPTransport(t *testing.T) {
+	t.Run("custom transport is used for requests", func(t *testing.T) {
+		server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.WriteHeader(http.StatusOK)
+		}))
+		defer server.Close()
+
+		counting := &countingRoundTripper{base: http.DefaultTransport}
+		conn := newConnection(newTestLogHandler(), server.URL, &connectionSettings{
+			httpTransport: counting,
+		})
+
+		rs, err := conn.submit(&request{gremlin: "g.V()", fields: map[string]interface{}{}})
+		require.NoError(t, err)
+		_, _ = rs.All() // drain
+
+		assert.Equal(t, 1, counting.count, "custom transport should have been called")
+	})
+
+	t.Run("nil transport uses default http.Transport", func(t *testing.T) {
+		conn := newConnection(newTestLogHandler(), "http://localhost:8182/gremlin", &connectionSettings{})
+
+		// When no custom transport is set, the driver creates an *http.Transport
+		_, ok := conn.httpClient.Transport.(*http.Transport)
+		assert.True(t, ok, "default transport should be *http.Transport")
+	})
+
+	t.Run("custom transport ignores pool settings", func(t *testing.T) {
+		counting := &countingRoundTripper{base: http.DefaultTransport}
+		conn := newConnection(newTestLogHandler(), "http://localhost:8182/gremlin", &connectionSettings{
+			httpTransport:   counting,
+			maxConnsPerHost: 256, // should be ignored
+		})
+
+		// The transport should be our custom one, not an http.Transport with pool settings
+		assert.Equal(t, counting, conn.httpClient.Transport, "custom transport should be used directly")
+	})
+
+	t.Run("ClientSettings wires HTTPTransport", func(t *testing.T) {
+		counting := &countingRoundTripper{base: http.DefaultTransport}
+		client, err := NewClient("http://localhost:8182/gremlin",
+			func(settings *ClientSettings) {
+				settings.HTTPTransport = counting
+			})
+		require.NoError(t, err)
+		defer client.Close()
+
+		assert.Equal(t, counting, client.conn.httpClient.Transport, "custom transport should be wired through")
+	})
+
+	t.Run("DriverRemoteConnectionSettings wires HTTPTransport", func(t *testing.T) {
+		counting := &countingRoundTripper{base: http.DefaultTransport}
+		drc, err := NewDriverRemoteConnection("http://localhost:8182/gremlin",
+			func(settings *DriverRemoteConnectionSettings) {
+				settings.HTTPTransport = counting
+			})
+		require.NoError(t, err)
+		defer drc.Close()
+
+		assert.Equal(t, counting, drc.client.conn.httpClient.Transport, "custom transport should be wired through")
+	})
+}

gremlin-go/driver/driverRemoteConnection.go

@@ -21,6 +21,7 @@ package gremlingo
 
 import (
 	"crypto/tls"
+	"net/http"
 	"time"
 
 	"golang.org/x/text/language"
@@ -37,6 +38,18 @@ type DriverRemoteConnectionSettings struct {
 	EnableCompression        bool
 	EnableUserAgentOnConnect bool
 
+	// HTTPTransport is the http.RoundTripper used for Gremlin HTTP requests.
+	//
+	// When set, the driver uses this transport directly. The following settings
+	// are ignored as they configure the driver's default transport:
+	// MaximumConcurrentConnections, MaxIdleConnections, IdleConnectionTimeout,
+	// KeepAliveInterval, TlsConfig, and EnableCompression. Configure these on
+	// your transport directly.
+	//
+	// When nil (the default), the driver creates an http.Transport configured
+	// with the above settings.
+	HTTPTransport http.RoundTripper
+
 	// MaximumConcurrentConnections is the maximum number of concurrent TCP connections
 	// to the Gremlin server. This limits how many requests can be in-flight simultaneously.
 	// Default: 128. Set to 0 to use the default.
@@ -103,6 +116,7 @@ func NewDriverRemoteConnection(
 		keepAliveInterval:        settings.KeepAliveInterval,
 		enableCompression:        settings.EnableCompression,
 		enableUserAgentOnConnect: settings.EnableUserAgentOnConnect,
+		httpTransport:            settings.HTTPTransport,
 	}
 
 	logHandler := newLogHandler(settings.Logger, settings.LogVerbosity, settings.Language)