implemented JSON distributed trace converter

v3/go.mod

@@ -3,6 +3,6 @@ module github.com/newrelic/go-agent/v3
 go 1.7
 
 require (
-	github.com/golang/protobuf v1.3.3
-	google.golang.org/grpc v1.27.0
+	github.com/golang/protobuf v1.4.3
+	google.golang.org/grpc v1.39.0
 )

v3/newrelic/trace_context_test.go

@@ -9,6 +9,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"reflect"
 	"strings"
 	"testing"
 
@@ -46,6 +47,47 @@ type TraceContextTestCase struct {
 	} `json:"intrinsics"`
 }
 
+func TestJsonDTHeaders(t *testing.T) {
+	type testcase struct {
+		in  string
+		out http.Header
+		err bool
+	}
+
+	for i, test := range []testcase{
+		{"", http.Header{}, false},
+		{"{}", http.Header{}, false},
+		{" invalid ", http.Header{}, true},
+		{`"foo"`, http.Header{}, true},
+		{`{"foo": "bar"}`, map[string][]string{
+			"Foo": {"bar"},
+		}, false},
+		{`{
+			"foo": "bar",
+			"baz": "quux",
+			"multiple": [
+				"alpha",
+				"beta",
+				"gamma"
+			]
+		}`, map[string][]string{
+			"Foo":      {"bar"},
+			"Baz":      {"quux"},
+			"Multiple": {"alpha", "beta", "gamma"},
+		}, false},
+	} {
+		h, err := DistributedTraceHeadersFromJson(test.in)
+
+		if err != nil {
+			if !test.err {
+				t.Errorf("case %d: %v: error expected but not generated", i, test.in)
+			}
+		} else if !reflect.DeepEqual(test.out, h) {
+			t.Errorf("case %d, %v -> %v but expected %v", i, test.in, h, test.out)
+		}
+	}
+}
+
 func TestCrossAgentW3CTraceContext(t *testing.T) {
 	var tcs []TraceContextTestCase
 

v3/newrelic/transaction.go

@@ -4,6 +4,8 @@
 package newrelic
 
 import (
+	"encoding/json"
+	"fmt"
 	"net/http"
 	"net/url"
 	"strings"
@@ -269,6 +271,76 @@ func (txn *Transaction) AcceptDistributedTraceHeaders(t TransportType, hdrs http
 	txn.thread.logAPIError(txn.thread.AcceptDistributedTraceHeaders(t, hdrs), "accept trace payload", nil)
 }
 
+//
+// AcceptDistributedTraceHeadersFromJson() works just like AcceptDistributedTraceHeaders(), except
+// that it takes the header data as a JSON string à la DistributedTraceHeadersFromJson(). Additionally
+// (unlike AcceptDistributedTraceHeaders()) it returns an error if it was unable to successfully
+// convert the JSON string to http headers. There is no guarantee that the header data found in JSON
+// is correct beyond conforming to the expected types and syntax.
+//
+func (txn *Transaction) AcceptDistributedTraceHeadersFromJson(t TransportType, jsondata string) error {
+	hdrs, err := DistributedTraceHeadersFromJson(jsondata)
+	if err != nil {
+		return err
+	}
+	txn.AcceptDistributedTraceHeaders(t, hdrs)
+	return nil
+}
+
+//
+// DistributedTraceHeadersFromJson() takes a set of distributed trace headers as a JSON-encoded string
+// and emits a http.Header value suitable for passing on to the
+// txn.AcceptDistributedTraceHeaders() function.
+//
+// For example, given the input string
+//   `{"traceparent": "frob", "tracestate": "blorfl", "newrelic": "xyzzy"}`
+// This will emit an http.Header value with headers "traceparent", "tracestate", and "newrelic".
+//
+// This is a convenience function provided for cases where you receive the trace header data
+// already as a JSON string and want to avoid manually converting that to an http.Header.
+//
+// The JSON string must be a single object whose values may be strings or arrays of strings.
+// These are translated directly to http headers with singleton or multiple values.
+//
+func DistributedTraceHeadersFromJson(jsondata string) (hdrs http.Header, err error) {
+	var raw interface{}
+	hdrs = http.Header{}
+	if jsondata == "" {
+		return
+	}
+	err = json.Unmarshal([]byte(jsondata), &raw)
+	if err != nil {
+		return
+	}
+
+	switch d := raw.(type) {
+	case map[string]interface{}:
+		for k, v := range d {
+			switch hval := v.(type) {
+			case string:
+				hdrs.Set(k, hval)
+			case []interface{}:
+				for _, subval := range hval {
+					switch sval := subval.(type) {
+					case string:
+						hdrs.Add(k, sval)
+					default:
+						err = fmt.Errorf("JSON object must have only strings or arrays of strings.")
+						return
+					}
+				}
+			default:
+				err = fmt.Errorf("JSON object must have only strings or arrays of strings.")
+				return
+			}
+		}
+	default:
+		err = fmt.Errorf("JSON string must be a single object.")
+		return
+	}
+	return
+}
+
 // Application returns the Application which started the transaction.
 func (txn *Transaction) Application() *Application {
 	if nil == txn {