feat(v2): update Invoke to add retry count to context

v2/invoke.go

@@ -31,15 +31,26 @@ package gax
 
 import (
 	"context"
+	"strconv"
 	"strings"
 	"time"
 
 	"github.com/googleapis/gax-go/v2/apierror"
+	"google.golang.org/grpc/metadata"
 )
 
 // APICall is a user defined call stub.
 type APICall func(context.Context, CallSettings) error
 
+// withRetryCount returns a new context with the retry count appended to
+// gRPC metadata. The retry count is the number of retries that have been
+// attempted. Immediately after the initial request, retry count is 0.
+// Immediately after a second request (the first retry), retry count is 1.
+func withRetryCount(ctx context.Context, retryCount int) context.Context {
+	// Add to gRPC metadata so it's visible to StatsHandlers
+	return metadata.AppendToOutgoingContext(ctx, "gcp.grpc.resend_count", strconv.Itoa(retryCount))
+}
+
 // Invoke calls the given APICall, performing retries as specified by opts, if
 // any.
 func Invoke(ctx context.Context, call APICall, opts ...CallOption) error {
@@ -78,8 +89,15 @@ func invoke(ctx context.Context, call APICall, settings CallSettings, sp sleeper
 		ctx = c
 	}
 
+	retryCount := 0
+	// Feature gate: GOOGLE_SDK_GO_EXPERIMENTAL_TRACING=true
+	tracingEnabled := IsFeatureEnabled("TRACING")
 	for {
-		err := call(ctx, settings)
+		ctxToUse := ctx
+		if tracingEnabled {
+			ctxToUse = withRetryCount(ctx, retryCount)
+		}
+		err := call(ctxToUse, settings)
 		if err == nil {
 			return nil
 		}
@@ -110,5 +128,6 @@ func invoke(ctx context.Context, call APICall, settings CallSettings, sp sleeper
 		} else if err = sp(ctx, d); err != nil {
 			return err
 		}
+		retryCount++
 	}
 }

v2/invoke_test.go

@@ -32,6 +32,8 @@ package gax
 import (
 	"context"
 	"errors"
+	"fmt"
+	"strconv"
 	"testing"
 	"time"
 
@@ -40,6 +42,7 @@ import (
 	"github.com/googleapis/gax-go/v2/apierror"
 	"google.golang.org/genproto/googleapis/rpc/errdetails"
 	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/metadata"
 	"google.golang.org/grpc/status"
 )
 
@@ -264,3 +267,47 @@ func TestInvokeWithTimeout(t *testing.T) {
 		})
 	}
 }
+
+func TestInvokeRetryCount(t *testing.T) {
+	for _, tracingEnabled := range []bool{true, false} {
+		t.Run(fmt.Sprintf("tracingEnabled=%v", tracingEnabled), func(t *testing.T) {
+			TestOnlyResetIsFeatureEnabled()
+			defer TestOnlyResetIsFeatureEnabled()
+
+			if tracingEnabled {
+				t.Setenv("GOOGLE_SDK_GO_EXPERIMENTAL_TRACING", "true")
+			} else {
+				t.Setenv("GOOGLE_SDK_GO_EXPERIMENTAL_TRACING", "false")
+			}
+
+			const target = 3
+			var retryCounts []int
+			calls := 0
+			apiCall := func(ctx context.Context, _ CallSettings) error {
+				calls++
+				md, _ := metadata.FromOutgoingContext(ctx)
+				if vals := md["gcp.grpc.resend_count"]; len(vals) > 0 {
+					if count, err := strconv.Atoi(vals[0]); err == nil {
+						retryCounts = append(retryCounts, count)
+					}
+				}
+				if calls < target {
+					return errors.New("retry")
+				}
+				return nil
+			}
+			var settings CallSettings
+			WithRetry(func() Retryer { return boolRetryer(true) }).Resolve(&settings)
+			var sp recordSleeper
+			invoke(context.Background(), apiCall, settings, sp.sleep)
+
+			var want []int
+			if tracingEnabled {
+				want = []int{0, 1, 2}
+			}
+			if diff := cmp.Diff(want, retryCounts); diff != "" {
+				t.Errorf("retry count mismatch (-want +got):\n%s", diff)
+			}
+		})
+	}
+}