Fix flaky registry test (#2374)

* print the actual error message so we can add it to the list

* helper to match common net errors

Author: michaeldwan

pkg/docker/docker_client_test.go

@@ -343,11 +343,7 @@ func runDockerClientTests(t *testing.T, dockerClient command.Command) {
 			err = dockerClient.Push(t.Context(), ref.String())
 			require.Error(t, err, "Push should fail with unreachable registry")
 
-			// error message varies between dev and CI host environments, cover them all...
-			assert.Condition(t, func() bool {
-				msg := err.Error()
-				return strings.Contains(msg, "connection refused") || strings.Contains(msg, "EOF")
-			}, "Error should indicate registry is unreachable")
+			assert.True(t, isNetworkError(err), "Error should be a network error, got: %q", err.Error())
 		})
 
 		t.Run("missing image", func(t *testing.T) {

pkg/docker/errors.go

@@ -1,6 +1,9 @@
 package docker
 
-import "strings"
+import (
+	"errors"
+	"strings"
+)
 
 // Error messages vary between different backends (dockerd, containerd, podman, orbstack, etc) or even versions of docker.
 // These helpers normalize the check so callers can handle situations without worrying about the underlying implementation.
@@ -47,3 +50,33 @@ func isMissingDeviceDriverError(err error) bool {
 	return strings.Contains(msg, "could not select device driver") ||
 		strings.Contains(msg, "nvidia-container-cli: initialization error")
 }
+
+func isNetworkError(err error) bool {
+	// for both CLI and API clients, network errors are wrapped and lose the net.Error interface
+	// CLI client: wrapped by exec.Command as exec.ExitError
+	// API client: wrapped by JSON message stream processing
+	// Sad as it may be, we rely on string matching for common network error messages
+
+	msg := err.Error()
+	networkErrorStrings := []string{
+		"connection refused",
+		"connection reset by peer",
+		"dial tcp",
+		"EOF",
+		"no route to host",
+		"network is unreachable",
+	}
+
+	for _, errStr := range networkErrorStrings {
+		if strings.Contains(msg, errStr) {
+			return true
+		}
+	}
+
+	// also check wrapped errors
+	if unwrapped := errors.Unwrap(err); unwrapped != nil {
+		return isNetworkError(unwrapped)
+	}
+
+	return false
+}