feat(pubsub): enable project autodetection and detect empty project

pubsub/integration_test.go

@@ -2060,3 +2060,25 @@ func TestIntegration_TopicUpdateSchema(t *testing.T) {
 		t.Fatalf("schema settings for update -want, +got: %v", diff)
 	}
 }
+
+func TestIntegration_DetectProjectID(t *testing.T) {
+	ctx := context.Background()
+	testCreds := testutil.Credentials(ctx)
+	if testCreds == nil {
+		t.Skip("test credentials not present, skipping")
+	}
+
+	goodClient, err := NewClient(ctx, DetectProjectID, option.WithCredentials(testCreds))
+	if err != nil {
+		t.Errorf("test pubsub.NewClient: %v", err)
+	}
+	if goodClient.Project() != testutil.ProjID() {
+		t.Errorf("client.Project() got %q, want %q", goodClient.Project(), testutil.ProjID())
+	}
+
+	badTS := testutil.ErroringTokenSource{}
+
+	if badClient, err := NewClient(ctx, DetectProjectID, option.WithTokenSource(badTS)); err == nil {
+		t.Errorf("expected error from bad token source, NewClient succeeded with project: %s", badClient.projectID)
+	}
+}

pubsub/pubsub.go

@@ -16,13 +16,15 @@ package pubsub // import "cloud.google.com/go/pubsub"
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"reflect"
 	"runtime"
 	"strings"
 	"time"
 
+	"cloud.google.com/go/internal/detect"
 	vkit "cloud.google.com/go/pubsub/apiv1"
 	"cloud.google.com/go/pubsub/internal"
 	gax "github.com/googleapis/gax-go/v2"
@@ -113,13 +115,30 @@ func mergeSubscriberCallOptions(a *vkit.SubscriberCallOptions, b *vkit.Subscribe
 	return res
 }
 
+// DetectProjectID is a sentinel value that instructs NewClient to detect the
+// project ID. It is given in place of the projectID argument. NewClient will
+// use the project ID from the given credentials or the default credentials
+// (https://developers.google.com/accounts/docs/application-default-credentials)
+// if no credentials were provided. When providing credentials, not all
+// options will allow NewClient to extract the project ID. Specifically a JWT
+// does not have the project ID encoded.
+const DetectProjectID = "*detect-project-id*"
+
+// ErrEmptyProjectID denotes that the project string passed into NewClient was empty.
+// Please provide a valid project ID or use the DetectProjectID sentinel value to detect
+// project ID from well defined sources.
+var ErrEmptyProjectID = errors.New("pubsub: projectID string is empty")
+
 // NewClient creates a new PubSub client. It uses a default configuration.
 func NewClient(ctx context.Context, projectID string, opts ...option.ClientOption) (c *Client, err error) {
 	return NewClientWithConfig(ctx, projectID, nil, opts...)
 }
 
 // NewClientWithConfig creates a new PubSub client.
 func NewClientWithConfig(ctx context.Context, projectID string, config *ClientConfig, opts ...option.ClientOption) (c *Client, err error) {
+	if projectID == "" {
+		return nil, ErrEmptyProjectID
+	}
 	var o []option.ClientOption
 	// Environment variables for gcloud emulator:
 	// https://cloud.google.com/sdk/gcloud/reference/beta/emulators/pubsub/
@@ -157,13 +176,26 @@ func NewClientWithConfig(ctx context.Context, projectID string, config *ClientCo
 		subc.CallOptions = mergeSubscriberCallOptions(subc.CallOptions, config.SubscriberCallOptions)
 	}
 	pubc.SetGoogleClientInfo("gccl", internal.Version)
+
+	// Handle project autodetection.
+	projectID, err = detect.ProjectID(ctx, projectID, "", opts...)
+	if err != nil {
+		return nil, err
+	}
+
 	return &Client{
 		projectID: projectID,
 		pubc:      pubc,
 		subc:      subc,
 	}, nil
 }
 
+// Project returns the project ID or number for this instance of the client, which may have
+// either been explicitly specified or autodetected.
+func (c *Client) Project() string {
+	return c.projectID
+}
+
 // Close releases any resources held by the client,
 // such as memory and goroutines.
 //

pubsub/pubsub_test.go

@@ -117,3 +117,11 @@ func TestClient_ApplyClientConfig(t *testing.T) {
 		}
 	}
 }
+
+func TestClient_EmptyProjectID(t *testing.T) {
+	ctx := context.Background()
+	_, err := NewClient(ctx, "")
+	if err != ErrEmptyProjectID {
+		t.Fatalf("passing empty project ID got %v, want%v", err, ErrEmptyProjectID)
+	}
+}