more logging for registry credential plugins

registry/external.go

@@ -60,7 +60,12 @@ func (p *external) List(ctx context.Context, in *Request) ([]*drone.Registry, er
 		return nil, nil
 	}
 
-	logger.Trace("registry: external: credential list returned")
+	for _, v := range res {
+		logger.
+			WithField("address", v.Address).
+			WithField("username", v.Username).
+			Trace("registry: external: received credentials")
+	}
 
 	return res, nil
 }

registry/file.go

@@ -8,6 +8,7 @@ import (
 	"context"
 
 	"github.com/drone/drone-go/drone"
+	"github.com/drone/runner-go/logger"
 	"github.com/drone/runner-go/registry/auths"
 )
 
@@ -22,9 +23,37 @@ type file struct {
 	path string
 }
 
-func (p *file) List(context.Context, *Request) ([]*drone.Registry, error) {
+func (p *file) List(ctx context.Context, _ *Request) ([]*drone.Registry, error) {
 	if p.path == "" {
 		return nil, nil
 	}
-	return auths.ParseFile(p.path)
+
+	logger := logger.FromContext(ctx)
+	logger.WithField("path", p.path).
+		Trace("registry: file: parsing credentials file")
+
+	// load the registry credentials from the file.
+	res, err := auths.ParseFile(p.path)
+	if err != nil {
+		logger.WithError(err).
+			Debug("registry: file: cannot parse credentials file")
+		return nil, err
+	}
+
+	// if no error is returned and the list is empty,
+	// this indicates the client returned No Content,
+	// and we should exit with no credentials, but no error.
+	if len(res) == 0 {
+		logger.Trace("registry: file: credential list is empty")
+		return nil, nil
+	}
+
+	for _, v := range res {
+		logger.
+			WithField("address", v.Address).
+			WithField("username", v.Username).
+			Trace("registry: file: received credentials")
+	}
+
+	return res, err
 }