otlpmetrichttp: Add WithHTTPClient option (#6752)

Follows https://github.com/open-telemetry/opentelemetry-go/pull/6688

Towards (for OTLP metric exporter):
- https://github.com/open-telemetry/opentelemetry-go/issues/4536
- https://github.com/open-telemetry/opentelemetry-go/issues/5129
- https://github.com/open-telemetry/opentelemetry-go/issues/2632

CHANGELOG.md

@@ -16,6 +16,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
   See the [migration documentation](./semconv/v1.31.0/MIGRATION.md) for information on how to upgrade from `go.opentelemetry.io/otel/semconv/v1.30.0`(#6479)
 - Add `Recording`, `Scope`, and `Record` types in `go.opentelemetry.io/otel/log/logtest`. (#6507)
 - Add `WithHTTPClient` option to configure the `http.Client` used by `go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#6688)
+- Add `WithHTTPClient` option to configure the `http.Client` used by `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`. (#6752)
 
 ### Removed
 

exporters/otlp/otlpmetric/otlpmetricgrpc/internal/oconf/options.go

@@ -57,13 +57,15 @@ type (
 		Timeout     time.Duration
 		URLPath     string
 
-		// gRPC configurations
-		GRPCCredentials credentials.TransportCredentials
-
 		TemporalitySelector metric.TemporalitySelector
 		AggregationSelector metric.AggregationSelector
 
-		Proxy HTTPTransportProxyFunc
+		// gRPC configurations
+		GRPCCredentials credentials.TransportCredentials
+
+		// HTTP configurations
+		Proxy      HTTPTransportProxyFunc
+		HTTPClient *http.Client
 	}
 
 	Config struct {
@@ -373,3 +375,10 @@ func WithProxy(pf HTTPTransportProxyFunc) GenericOption {
 		return cfg
 	})
 }
+
+func WithHTTPClient(c *http.Client) GenericOption {
+	return newGenericOption(func(cfg Config) Config {
+		cfg.Metrics.HTTPClient = c
+		return cfg
+	})
+}

exporters/otlp/otlpmetric/otlpmetricgrpc/internal/oconf/options_test.go

@@ -533,6 +533,24 @@ func TestConfigs(t *testing.T) {
 				assert.Nil(t, c.Metrics.Proxy)
 			},
 		},
+
+		// HTTP Client Tests
+		{
+			name: "Test With HTTP Client",
+			opts: []GenericOption{
+				WithHTTPClient(http.DefaultClient),
+			},
+			asserts: func(t *testing.T, c *Config, grpcOption bool) {
+				assert.Equal(t, http.DefaultClient, c.Metrics.HTTPClient)
+			},
+		},
+		{
+			name: "Test Without HTTP Client",
+			opts: []GenericOption{},
+			asserts: func(t *testing.T, c *Config, grpcOption bool) {
+				assert.Nil(t, c.Metrics.HTTPClient)
+			},
+		},
 	}
 
 	for _, tt := range tests {

exporters/otlp/otlpmetric/otlpmetrichttp/client.go

@@ -55,20 +55,23 @@ var ourTransport = &http.Transport{
 
 // newClient creates a new HTTP metric client.
 func newClient(cfg oconf.Config) (*client, error) {
-	httpClient := &http.Client{
+	httpClient := cfg.Metrics.HTTPClient
-		Transport: ourTransport,
+	if httpClient == nil {
-		Timeout:   cfg.Metrics.Timeout,
+		httpClient = &http.Client{
-	}
+			Transport: ourTransport,
-
+			Timeout:   cfg.Metrics.Timeout,
-	if cfg.Metrics.TLSCfg != nil || cfg.Metrics.Proxy != nil {
-		clonedTransport := ourTransport.Clone()
-		httpClient.Transport = clonedTransport
-
-		if cfg.Metrics.TLSCfg != nil {
-			clonedTransport.TLSClientConfig = cfg.Metrics.TLSCfg
 		}
-		if cfg.Metrics.Proxy != nil {
+
-			clonedTransport.Proxy = cfg.Metrics.Proxy
+		if cfg.Metrics.TLSCfg != nil || cfg.Metrics.Proxy != nil {
+			clonedTransport := ourTransport.Clone()
+			httpClient.Transport = clonedTransport
+
+			if cfg.Metrics.TLSCfg != nil {
+				clonedTransport.TLSClientConfig = cfg.Metrics.TLSCfg
+			}
+			if cfg.Metrics.Proxy != nil {
+				clonedTransport.Proxy = cfg.Metrics.Proxy
+			}
 		}
 	}
 

exporters/otlp/otlpmetric/otlpmetrichttp/client_test.go

@@ -254,6 +254,28 @@ func TestConfig(t *testing.T) {
 	})
 
 	t.Run("WithProxy", func(t *testing.T) {
+		headerKeySetInProxy := http.CanonicalHeaderKey("X-Using-Proxy")
+		headerValueSetInProxy := "true"
+		exp, coll := factoryFunc("", nil, WithHTTPClient(&http.Client{
+			Transport: &http.Transport{
+				Proxy: func(r *http.Request) (*url.URL, error) {
+					r.Header.Set(headerKeySetInProxy, headerValueSetInProxy)
+					return r.URL, nil
+				},
+			},
+		}))
+		ctx := context.Background()
+		t.Cleanup(func() { require.NoError(t, coll.Shutdown(ctx)) })
+		require.NoError(t, exp.Export(ctx, &metricdata.ResourceMetrics{}))
+		// Ensure everything is flushed.
+		require.NoError(t, exp.Shutdown(ctx))
+
+		got := coll.Headers()
+		require.Contains(t, got, headerKeySetInProxy)
+		assert.Equal(t, []string{headerValueSetInProxy}, got[headerKeySetInProxy])
+	})
+
+	t.Run("WithHTTPClient", func(t *testing.T) {
 		headerKeySetInProxy := http.CanonicalHeaderKey("X-Using-Proxy")
 		headerValueSetInProxy := "true"
 		exp, coll := factoryFunc("", nil, WithProxy(func(r *http.Request) (*url.URL, error) {

exporters/otlp/otlpmetric/otlpmetrichttp/config.go

@@ -222,3 +222,19 @@ func WithAggregationSelector(selector metric.AggregationSelector) Option {
 func WithProxy(pf HTTPTransportProxyFunc) Option {
 	return wrappedOption{oconf.WithProxy(oconf.HTTPTransportProxyFunc(pf))}
 }
+
+// WithHTTPClient sets the HTTP client to used by the exporter.
+//
+// This option will take precedence over [WithProxy], [WithTimeout],
+// [WithTLSClientConfig] options as well as OTEL_EXPORTER_OTLP_CERTIFICATE,
+// OTEL_EXPORTER_OTLP_METRICS_CERTIFICATE, OTEL_EXPORTER_OTLP_TIMEOUT,
+// OTEL_EXPORTER_OTLP_METRICS_TIMEOUT environment variables.
+//
+// Timeout and all other fields of the passed [http.Client] are left intact.
+//
+// Be aware that passing an HTTP client with transport like
+// [go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp.NewTransport] can
+// cause the client to be instrumented twice and cause infinite recursion.
+func WithHTTPClient(c *http.Client) Option {
+	return wrappedOption{oconf.WithHTTPClient(c)}
+}

exporters/otlp/otlpmetric/otlpmetrichttp/internal/oconf/options.go

@@ -57,13 +57,15 @@ type (
 		Timeout     time.Duration
 		URLPath     string
 
-		// gRPC configurations
-		GRPCCredentials credentials.TransportCredentials
-
 		TemporalitySelector metric.TemporalitySelector
 		AggregationSelector metric.AggregationSelector
 
-		Proxy HTTPTransportProxyFunc
+		// gRPC configurations
+		GRPCCredentials credentials.TransportCredentials
+
+		// HTTP configurations
+		Proxy      HTTPTransportProxyFunc
+		HTTPClient *http.Client
 	}
 
 	Config struct {
@@ -373,3 +375,10 @@ func WithProxy(pf HTTPTransportProxyFunc) GenericOption {
 		return cfg
 	})
 }
+
+func WithHTTPClient(c *http.Client) GenericOption {
+	return newGenericOption(func(cfg Config) Config {
+		cfg.Metrics.HTTPClient = c
+		return cfg
+	})
+}

exporters/otlp/otlpmetric/otlpmetrichttp/internal/oconf/options_test.go

@@ -533,6 +533,24 @@ func TestConfigs(t *testing.T) {
 				assert.Nil(t, c.Metrics.Proxy)
 			},
 		},
+
+		// HTTP Client Tests
+		{
+			name: "Test With HTTP Client",
+			opts: []GenericOption{
+				WithHTTPClient(http.DefaultClient),
+			},
+			asserts: func(t *testing.T, c *Config, grpcOption bool) {
+				assert.Equal(t, http.DefaultClient, c.Metrics.HTTPClient)
+			},
+		},
+		{
+			name: "Test Without HTTP Client",
+			opts: []GenericOption{},
+			asserts: func(t *testing.T, c *Config, grpcOption bool) {
+				assert.Nil(t, c.Metrics.HTTPClient)
+			},
+		},
 	}
 
 	for _, tt := range tests {

internal/shared/otlp/otlpmetric/oconf/options.go.tmpl

@@ -57,13 +57,15 @@ type (
 		Timeout     time.Duration
 		URLPath     string
 
-		// gRPC configurations
-		GRPCCredentials credentials.TransportCredentials
-
 		TemporalitySelector metric.TemporalitySelector
 		AggregationSelector metric.AggregationSelector
 
-		Proxy HTTPTransportProxyFunc
+		// gRPC configurations
+		GRPCCredentials credentials.TransportCredentials
+
+		// HTTP configurations
+		Proxy      HTTPTransportProxyFunc
+		HTTPClient *http.Client
 	}
 
 	Config struct {
@@ -373,3 +375,10 @@ func WithProxy(pf HTTPTransportProxyFunc) GenericOption {
 		return cfg
 	})
 }
+
+func WithHTTPClient(c *http.Client) GenericOption {
+	return newGenericOption(func(cfg Config) Config {
+		cfg.Metrics.HTTPClient = c
+		return cfg
+	})
+}

internal/shared/otlp/otlpmetric/oconf/options_test.go.tmpl

@@ -533,6 +533,24 @@ func TestConfigs(t *testing.T) {
 				assert.Nil(t, c.Metrics.Proxy)
 			},
 		},
+
+		// HTTP Client Tests
+		{
+			name: "Test With HTTP Client",
+			opts: []GenericOption{
+				WithHTTPClient(http.DefaultClient),
+			},
+			asserts: func(t *testing.T, c *Config, grpcOption bool) {
+				assert.Equal(t, http.DefaultClient, c.Metrics.HTTPClient)
+			},
+		},
+		{
+			name: "Test Without HTTP Client",
+			opts: []GenericOption{},
+			asserts: func(t *testing.T, c *Config, grpcOption bool) {
+				assert.Nil(t, c.Metrics.HTTPClient)
+			},
+		},
 	}
 
 	for _, tt := range tests {