1 files changed, 96 insertions, 0 deletions
diff --git a/workhorse/internal/git/error.go b/workhorse/internal/git/error.go
index 2b7cad6bb64..86a2ba44767 100644
--- a/workhorse/internal/git/error.go
+++ b/workhorse/internal/git/error.go
@@ -1,4 +1,100 @@
 package git
 
+import (
+	"errors"
+	"fmt"
+	"io"
+
+	"gitlab.com/gitlab-org/gitaly/v14/proto/go/gitalypb"
+	"google.golang.org/grpc/status"
+
+	"gitlab.com/gitlab-org/gitlab/workhorse/internal/log"
+)
+
+// For unwrapping google.golang.org/grpc/internal/status.Error
+type grpcErr interface {
+	GRPCStatus() *status.Status
+	Error() string
+}
+
 // For cosmetic purposes in Sentry
 type copyError struct{ error }
+
+// handleLimitErr handles errors that come back from Gitaly that may be a
+// LimitError. A LimitError is returned by Gitaly when it is at its limit in
+// handling requests. Since this is a known error, we should print a sensible
+// error message to the end user.
+func handleLimitErr(err error, w io.Writer, f func(w io.Writer) error) {
+	var statusErr grpcErr
+	if !errors.As(err, &statusErr) {
+		return
+	}
+
+	if st, ok := status.FromError(statusErr); ok {
+		details := st.Details()
+		for _, detail := range details {
+			switch detail.(type) {
+			case *gitalypb.LimitError:
+				if err := f(w); err != nil {
+					log.WithError(fmt.Errorf("handling limit error: %w", err))
+				}
+			}
+		}
+	}
+}
+
+// writeReceivePackError writes a "server is busy" error message to the
+// git-recieve-pack-result.
+//
+// 0023\x01001aunpack server is busy
+// 00000044\x2GitLab is currently unable to handle this request due to load.
+// 0000
+//
+// We write a line reporting that unpack failed, and then provide some progress
+// information through the side-band 2 channel.
+// See https://gitlab.com/gitlab-org/gitaly/-/tree/jc-return-structured-error-limits
+// for more details.
+func writeReceivePackError(w io.Writer) error {
+	if _, err := fmt.Fprintf(w, "%04x", 35); err != nil {
+		return err
+	}
+
+	if _, err := w.Write([]byte{0x01}); err != nil {
+		return err
+	}
+
+	if _, err := fmt.Fprintf(w, "%04xunpack server is busy\n", 26); err != nil {
+		return err
+	}
+
+	if _, err := w.Write([]byte("0000")); err != nil {
+		return err
+	}
+
+	if _, err := fmt.Fprintf(w, "%04x", 68); err != nil {
+		return err
+	}
+
+	if _, err := w.Write([]byte{0x2}); err != nil {
+		return err
+	}
+
+	if _, err := fmt.Fprint(w, "GitLab is currently unable to handle this request due to load.\n"); err != nil {
+		return err
+	}
+
+	if _, err := w.Write([]byte("0000")); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// writeUploadPackError writes a "server is busy" error message that git
+// understands and prints to stdout. UploadPack expects to receive pack data in
+// PKT-LINE format. An error-line can be passed that begins with ERR.
+// See https://git-scm.com/docs/pack-protocol/2.29.0#_pkt_line_format.
+func writeUploadPackError(w io.Writer) error {
+	_, err := fmt.Fprintf(w, "%04xERR GitLab is currently unable to handle this request due to load.\n", 71)
+	return err
+}