Support http/json in otlptracehttp

CHANGELOG.md

@@ -38,6 +38,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Add `WithDefaultAttributes` to `go.opentelemetry.io/otel/metric/x` to support setting default attributes on instruments. (#8135)
 - Add `Settable` to `go.opentelemetry.io/otel/metric/x` to allow reusing attribute options. (#8178)
 - Add experimental self-observability metrics in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`. (#8194)
+- Support `http/json` in `otlptracehttp` (#8273)
 
 ### Changed
 

exporters/otlp/otlptrace/otlptracehttp/client.go

@@ -27,10 +27,14 @@ import (
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp/internal/counter"
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp/internal/observ"
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp/internal/otlpconfig"
+	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp/internal/otlpjson"
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp/internal/retry"
 )
 
-const contentTypeProto = "application/x-protobuf"
+const (
+	contentTypeProto = "application/x-protobuf"
+	contentTypeJSON  = "application/json"
+)
 
 // maxResponseBodySize is the maximum number of bytes to read from a response
 // body. It is set to 4 MiB per the OTLP specification recommendation to
@@ -160,19 +164,11 @@ func (d *client) UploadTraces(ctx context.Context, protoSpans []*tracepb.Resourc
 	pbRequest := &coltracepb.ExportTraceServiceRequest{
 		ResourceSpans: protoSpans,
 	}
-	rawRequest, err := proto.Marshal(pbRequest)
-	if err != nil {
-		return err
-	}
 
 	ctx, cancel := d.contextWithStop(ctx)
 	defer cancel()
 
-	if maxSize := d.cfg.MaxRequestSize; maxSize > 0 && len(rawRequest) > maxSize {
-		return fmt.Errorf("request body too large: exceeded %d bytes", maxSize)
-	}
-
-	request, err := d.newRequest(rawRequest)
+	request, err := d.newRequest(pbRequest)
 	if err != nil {
 		return err
 	}
@@ -232,19 +228,26 @@ func (d *client) UploadTraces(ctx context.Context, protoSpans []*tracepb.Resourc
 				return nil
 			}
 
-			if resp.Header.Get("Content-Type") == "application/x-protobuf" {
-				var respProto coltracepb.ExportTraceServiceResponse
+			var respProto coltracepb.ExportTraceServiceResponse
+			switch resp.Header.Get("Content-Type") {
+			case contentTypeProto:
 				if err := proto.Unmarshal(respData.Bytes(), &respProto); err != nil {
 					return err
 				}
+			case contentTypeJSON:
+				if err := otlpjson.UnmarshalExportTraceServiceResponse(respData.Bytes(), &respProto); err != nil {
+					return err
+				}
+			default:
+				return nil
+			}
 
-				if respProto.PartialSuccess != nil {
-					msg := respProto.PartialSuccess.GetErrorMessage()
-					n := respProto.PartialSuccess.GetRejectedSpans()
-					if n != 0 || msg != "" {
-						err := internal.TracePartialSuccessError(n, msg)
-						uploadErr = errors.Join(uploadErr, err)
-					}
+			if respProto.PartialSuccess != nil {
+				msg := respProto.PartialSuccess.GetErrorMessage()
+				n := respProto.PartialSuccess.GetRejectedSpans()
+				if n != 0 || msg != "" {
+					err := internal.TracePartialSuccessError(n, msg)
+					uploadErr = errors.Join(uploadErr, err)
 				}
 			}
 			return nil
@@ -283,7 +286,24 @@ func (d *client) UploadTraces(ctx context.Context, protoSpans []*tracepb.Resourc
 	}))
 }
 
-func (d *client) newRequest(body []byte) (request, error) {
+func (d *client) marshalRequest(pbRequst *coltracepb.ExportTraceServiceRequest) ([]byte, error) {
+	if d.cfg.Protocol == otlpconfig.ProtocolHTTPJSON {
+		rawRequest, err := otlpjson.MarshalExportTraceServiceRequest(pbRequst)
+		if err != nil {
+			return nil, fmt.Errorf("failed to marshal request body in json: %w", err)
+		}
+		return rawRequest, nil
+	}
+
+	rawRequest, err := proto.Marshal(pbRequst)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal request body in protobuf: %w", err)
+	}
+
+	return rawRequest, nil
+}
+
+func (d *client) newRequest(pbRequst *coltracepb.ExportTraceServiceRequest) (request, error) {
 	u := url.URL{Scheme: d.getScheme(), Host: d.cfg.Endpoint, Path: d.cfg.URLPath}
 	r, err := http.NewRequestWithContext(context.Background(), http.MethodPost, u.String(), http.NoBody)
 	if err != nil {
@@ -297,6 +317,18 @@ func (d *client) newRequest(body []byte) (request, error) {
 		r.Header.Set(k, v)
 	}
 	r.Header.Set("Content-Type", contentTypeProto)
+	if d.cfg.Protocol == otlpconfig.ProtocolHTTPJSON {
+		r.Header.Set("Content-Type", contentTypeJSON)
+	}
+
+	body, err := d.marshalRequest(pbRequst)
+	if err != nil {
+		return request{Request: r}, err
+	}
+
+	if maxSize := d.cfg.MaxRequestSize; maxSize > 0 && len(body) > maxSize {
+		return request{Request: r}, fmt.Errorf("request body too large: exceeded %d bytes", maxSize)
+	}
 
 	req := request{Request: r}
 	switch Compression(d.cfg.Compression) {

exporters/otlp/otlptrace/otlptracehttp/client_test.go

@@ -185,6 +185,40 @@ func TestEndToEnd(t *testing.T) {
 				ExpectedHeaders: customProxyHeader,
 			},
 		},
+		{
+			name: "with protobuf request encoding",
+			opts: []otlptracehttp.Option{
+				otlptracehttp.WithEncoding(otlptracehttp.EncodingProtobuf),
+			},
+		},
+		{
+			name: "with JSON request encoding",
+			opts: []otlptracehttp.Option{
+				otlptracehttp.WithEncoding(otlptracehttp.EncodingJSON),
+			},
+		},
+		{
+			name: "with JSON collector response encoding",
+			opts: []otlptracehttp.Option{
+				otlptracehttp.WithEncoding(otlptracehttp.EncodingJSON),
+			},
+			mcCfg: mockCollectorConfig{
+				InjectContentType: "application/json",
+			},
+		},
+		{
+			name: "with JSON collector response encoding and partial success",
+			opts: []otlptracehttp.Option{
+				otlptracehttp.WithEncoding(otlptracehttp.EncodingJSON),
+			},
+			mcCfg: mockCollectorConfig{
+				InjectContentType: "application/json",
+				Partial: &coltracepb.ExportTracePartialSuccess{
+					RejectedSpans: 1,
+					ErrorMessage:  "missing required attribute aaa",
+				},
+			},
+		},
 	}
 
 	for _, tc := range tests {

exporters/otlp/otlptrace/otlptracehttp/doc.go

@@ -63,6 +63,12 @@ the filepath to the client's private key to use in mTLS communication in PEM for
 OTEL_EXPORTER_OTLP_TRACES_CLIENT_KEY takes precedence over OTEL_EXPORTER_OTLP_CLIENT_KEY.
 The configuration can be overridden by [WithTLSClientConfig] option.
 
+OTEL_EXPORTER_OTLP_PROTOCOL, OTEL_EXPORTER_OTLP_TRACES_PROTOCOL (default: "http/protobuf") -
+the transport protocol the exporter uses. For OTLP/HTTP exporters, it indicates the encoding format of the payloads sent to the collector.
+Supported value: "http/protobuf", "http/json".
+OTEL_EXPORTER_OTLP_TRACES_PROTOCOL takes precedence over OTEL_EXPORTER_OTLP_PROTOCOL.
+The configuration can be overridden by [WithEncoding] option.
+
 [W3C Baggage HTTP Header Content Format]: https://www.w3.org/TR/baggage/#header-content
 */
 package otlptracehttp // import "go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"