matcher: simplify concurrency

internal/matcher/match.go

@@ -28,28 +28,30 @@ func Match(ctx context.Context, ir *claircore.IndexReport, matchers []driver.Mat
 	// a channel where concurrent controllers will deliver vulnerabilities affecting a package.
 	// maps a package id to a list of vulnerabilities.
 	ctrlC := make(chan map[string][]*claircore.Vulnerability, 1024)
-	// a channel where controller errors will be reported
-	errorC := make(chan error, 1024)
 	// fan out all controllers, write their output to ctrlC, close ctrlC once all writers finish
+	g, ctx := errgroup.WithContext(ctx)
+	for _, m := range matchers {
+		mm := m
+		g.Go(func() error {
+			mc := NewController(mm, store)
+			vulns, err := mc.Match(ctx, records)
+			if err != nil {
+				return err
+			}
+			// in event of slow reader go routines will block
+			// if one function fails the context is cancelled and the rest will exit
+			// without needing to add to channel and be processed
+			select {
+			case ctrlC <- vulns:
+			case <-ctx.Done():
+				return ctx.Err()
+			}
+			return nil
+		})
+	}
 	go func() {
-		defer close(ctrlC)
-		var g errgroup.Group
-		for _, m := range matchers {
-			mm := m
-			g.Go(func() error {
-				mc := NewController(mm, store)
-				vulns, err := mc.Match(ctx, records)
-				if err != nil {
-					return err
-				}
-				// in event of slow reader go routines will block
-				ctrlC <- vulns
-				return nil
-			})
-		}
-		if err := g.Wait(); err != nil {
-			errorC <- err
-		}
+		g.Wait()
+		close(ctrlC)
 	}()
 	// loop ranges until ctrlC is closed and fully drained, ctrlC is guaranteed to close
 	for vulnsByPackage := range ctrlC {
@@ -60,10 +62,8 @@ func Match(ctx context.Context, ir *claircore.IndexReport, matchers []driver.Mat
 			}
 		}
 	}
-	select {
-	case err := <-errorC:
+	if err := g.Wait(); err != nil {
 		return nil, err
-	default:
 	}
 	return vr, nil
 }