Add WithHeaders option for Zipkin exporter (#5530)

- Added `WithHeaders` option func, which allows user to set custom http
request headers while exporting spans.
- Closes: #3474

---------

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -17,6 +17,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Store and provide the emitted `context.Context` in `ScopeRecords` of `go.opentelemetry.io/otel/sdk/log/logtest`. (#5468)
 - `SimpleProcessor.OnEmit` in `go.opentelemetry.io/otel/sdk/log` no longer allocates a slice which makes it possible to have a zero-allocation log processing using `SimpleProcessor`. (#5493)
 - The `AssertRecordEqual` method to `go.opentelemetry.io/otel/log/logtest` to allow comparison of two log records in tests. (#5499)
+- The `WithHeaders` option to `go.opentelemetry.io/otel/exporters/zipkin` to allow configuring custom http headers while exporting spans. (#5530)
 - `service.instance.id` is populated for a `Resource` created with `"go.opentelemetry.io/otel/sdk/resource".Default` with a default value when `OTEL_GO_X_RESOURCE` is set. (#5520)
 
 ### Changed

exporters/zipkin/zipkin.go

@@ -12,6 +12,7 @@ import (
 	"log"
 	"net/http"
 	"net/url"
+	"strings"
 	"sync"
 
 	"github.com/go-logr/logr"
@@ -26,9 +27,10 @@ const (
 
 // Exporter exports spans to the zipkin collector.
 type Exporter struct {
-	url    string
-	client *http.Client
-	logger logr.Logger
+	url     string
+	client  *http.Client
+	logger  logr.Logger
+	headers map[string]string
 
 	stoppedMu sync.RWMutex
 	stopped   bool
@@ -40,8 +42,9 @@ var emptyLogger = logr.Logger{}
 
 // Options contains configuration for the exporter.
 type config struct {
-	client *http.Client
-	logger logr.Logger
+	client  *http.Client
+	logger  logr.Logger
+	headers map[string]string
 }
 
 // Option defines a function that configures the exporter.
@@ -70,6 +73,14 @@ func WithLogr(logger logr.Logger) Option {
 	})
 }
 
+// WithHeaders configures the exporter to use the passed HTTP request headers.
+func WithHeaders(headers map[string]string) Option {
+	return optionFunc(func(cfg config) config {
+		cfg.headers = headers
+		return cfg
+	})
+}
+
 // WithClient configures the exporter to use the passed HTTP client.
 func WithClient(client *http.Client) Option {
 	return optionFunc(func(cfg config) config {
@@ -101,9 +112,10 @@ func New(collectorURL string, opts ...Option) (*Exporter, error) {
 		cfg.client = http.DefaultClient
 	}
 	return &Exporter{
-		url:    collectorURL,
-		client: cfg.client,
-		logger: cfg.logger,
+		url:     collectorURL,
+		client:  cfg.client,
+		logger:  cfg.logger,
+		headers: cfg.headers,
 	}, nil
 }
 
@@ -132,6 +144,15 @@ func (e *Exporter) ExportSpans(ctx context.Context, spans []sdktrace.ReadOnlySpa
 		return e.errf("failed to create request to %s: %v", e.url, err)
 	}
 	req.Header.Set("Content-Type", "application/json")
+
+	for k, v := range e.headers {
+		if strings.ToLower(k) == "host" {
+			req.Host = v
+		} else {
+			req.Header.Set(k, v)
+		}
+	}
+
 	resp, err := e.client.Do(req)
 	if err != nil {
 		return e.errf("request to %s failed: %v", e.url, err)

exporters/zipkin/zipkin_test.go

@@ -12,6 +12,7 @@ import (
 	"log"
 	"net"
 	"net/http"
+	"net/http/httptest"
 	"sync"
 	"testing"
 	"time"
@@ -375,3 +376,48 @@ func TestLogrFormatting(t *testing.T) {
 	got := buf.String()
 	assert.Equal(t, want, got)
 }
+
+func TestWithHeaders(t *testing.T) {
+	headers := map[string]string{
+		"name1": "value1",
+		"name2": "value2",
+		"host":  "example",
+	}
+
+	exp, err := New("", WithHeaders(headers))
+	require.NoError(t, err)
+
+	want := headers
+	got := exp.headers
+	assert.Equal(t, want, got)
+
+	spans := tracetest.SpanStubs{
+		{
+			SpanContext: trace.NewSpanContext(trace.SpanContextConfig{
+				TraceID: trace.TraceID{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F},
+				SpanID:  trace.SpanID{0xFF, 0xFE, 0xFD, 0xFC, 0xFB, 0xFA, 0xF9, 0xF8},
+			}),
+		},
+	}.Snapshots()
+
+	var req *http.Request
+	handler := func(w http.ResponseWriter, r *http.Request) {
+		req = r
+		w.WriteHeader(http.StatusOK)
+	}
+
+	srv := httptest.NewServer(http.HandlerFunc(handler))
+	defer srv.Close()
+
+	e := &Exporter{
+		url:     srv.URL,
+		client:  srv.Client(),
+		headers: headers,
+	}
+
+	_ = e.ExportSpans(context.Background(), spans)
+
+	assert.Equal(t, headers["host"], req.Host)
+	assert.Equal(t, headers["name1"], req.Header.Get("name1"))
+	assert.Equal(t, headers["name2"], req.Header.Get("name2"))
+}