otlptracehttp, otlpmetrichttp: Add WithProxy option (#4906)

exporters/otlp/otlpmetric/otlpmetrichttp/client.go

@@ -58,10 +58,17 @@ func newClient(cfg oconf.Config) (*client, error) {
 		Transport: ourTransport,
 		Timeout:   cfg.Metrics.Timeout,
 	}
-	if cfg.Metrics.TLSCfg != nil {
-		transport := ourTransport.Clone()
-		transport.TLSClientConfig = cfg.Metrics.TLSCfg
-		httpClient.Transport = transport
+
+	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
+		}
 	}
 
 	u := &url.URL{

exporters/otlp/otlpmetric/otlpmetrichttp/client_test.go

@@ -9,6 +9,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"net/url"
 	"strings"
 	"testing"
 	"time"
@@ -227,4 +228,22 @@ func TestConfig(t *testing.T) {
 		require.Contains(t, got, key)
 		assert.Equal(t, got[key], []string{headers[key]})
 	})
+
+	t.Run("WithProxy", func(t *testing.T) {
+		headerKeySetInProxy := http.CanonicalHeaderKey("X-Using-Proxy")
+		headerValueSetInProxy := "true"
+		exp, coll := factoryFunc("", nil, WithProxy(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, got[headerKeySetInProxy], []string{headerValueSetInProxy})
+	})
 }

exporters/otlp/otlpmetric/otlpmetrichttp/config.go

@@ -5,6 +5,8 @@ package otlpmetrichttp // import "go.opentelemetry.io/otel/exporters/otlp/otlpme
 
 import (
 	"crypto/tls"
+	"net/http"
+	"net/url"
 	"time"
 
 	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp/internal/oconf"
@@ -16,6 +18,11 @@ import (
 // collector.
 type Compression oconf.Compression
 
+// HTTPTransportProxyFunc is a function that resolves which URL to use as proxy for a given request.
+// This type is compatible with http.Transport.Proxy and can be used to set a custom proxy function
+// to the OTLP HTTP client.
+type HTTPTransportProxyFunc func(*http.Request) (*url.URL, error)
+
 const (
 	// NoCompression tells the driver to send payloads without
 	// compression.
@@ -206,3 +213,10 @@ func WithTemporalitySelector(selector metric.TemporalitySelector) Option {
 func WithAggregationSelector(selector metric.AggregationSelector) Option {
 	return wrappedOption{oconf.WithAggregationSelector(selector)}
 }
+
+// WithProxy sets the Proxy function the client will use to determine the
+// proxy to use for an HTTP request. If this option is not used, the client
+// will use [http.ProxyFromEnvironment].
+func WithProxy(pf HTTPTransportProxyFunc) Option {
+	return wrappedOption{oconf.WithProxy(oconf.HTTPTransportProxyFunc(pf))}
+}

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

@@ -9,6 +9,7 @@ package oconf // import "go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlp
 import (
 	"crypto/tls"
 	"fmt"
+	"net/http"
 	"net/url"
 	"path"
 	"strings"
@@ -42,6 +43,10 @@ const (
 )
 
 type (
+	// HTTPTransportProxyFunc is a function that resolves which URL to use as proxy for a given request.
+	// This type is compatible with `http.Transport.Proxy` and can be used to set a custom proxy function to the OTLP HTTP client.
+	HTTPTransportProxyFunc func(*http.Request) (*url.URL, error)
+
 	SignalConfig struct {
 		Endpoint    string
 		Insecure    bool
@@ -56,6 +61,8 @@ type (
 
 		TemporalitySelector metric.TemporalitySelector
 		AggregationSelector metric.AggregationSelector
+
+		Proxy HTTPTransportProxyFunc
 	}
 
 	Config struct {
@@ -360,3 +367,10 @@ func WithAggregationSelector(selector metric.AggregationSelector) GenericOption
 		return cfg
 	})
 }
+
+func WithProxy(pf HTTPTransportProxyFunc) GenericOption {
+	return newGenericOption(func(cfg Config) Config {
+		cfg.Metrics.Proxy = pf
+		return cfg
+	})
+}

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

@@ -8,6 +8,8 @@ package oconf
 
 import (
 	"errors"
+	"net/http"
+	"net/url"
 	"testing"
 	"time"
 
@@ -444,6 +446,29 @@ func TestConfigs(t *testing.T) {
 				assert.Equal(t, metric.AggregationDrop{}, got(undefinedKind))
 			},
 		},
+
+		// Proxy Tests
+		{
+			name: "Test With Proxy",
+			opts: []GenericOption{
+				WithProxy(func(r *http.Request) (*url.URL, error) {
+					return url.Parse("http://proxy.com")
+				}),
+			},
+			asserts: func(t *testing.T, c *Config, grpcOption bool) {
+				assert.NotNil(t, c.Metrics.Proxy)
+				proxyURL, err := c.Metrics.Proxy(&http.Request{})
+				assert.NoError(t, err)
+				assert.Equal(t, "http://proxy.com", proxyURL.String())
+			},
+		},
+		{
+			name: "Test Without Proxy",
+			opts: []GenericOption{},
+			asserts: func(t *testing.T, c *Config, grpcOption bool) {
+				assert.Nil(t, c.Metrics.Proxy)
+			},
+		},
 	}
 
 	for _, tt := range tests {