Format errors as JSON when in JSON progress mode.

Signed-off-by: Felix Fontein <felix@fontein.de>

cmd/compose/compose.go

@@ -18,6 +18,7 @@ package compose
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"os"
@@ -98,6 +99,9 @@ func AdaptCmd(fn CobraCommand) func(cmd *cobra.Command, args []string) error {
 				Status:     err.Error(),
 			}
 		}
+		if ui.Mode == ui.ModeJSON {
+			err = makeJSONError(err)
+		}
 		return err
 	}
 }
@@ -152,6 +156,37 @@ func (o *ProjectOptions) WithServices(dockerCli command.Cli, fn ProjectServicesF
 	})
 }
 
+type jsonErrorData struct {
+	Error   bool   `json:"error,omitempty"`
+	Message string `json:"message,omitempty"`
+}
+
+func errorAsJSON(message string) string {
+	var errorMessage = &jsonErrorData{
+		Error:   true,
+		Message: message,
+	}
+	marshal, err := json.Marshal(errorMessage)
+	if err == nil {
+		return string(marshal)
+	} else {
+		return message
+	}
+}
+
+func makeJSONError(err error) error {
+	if err == nil {
+		return err
+	}
+	if statusErr, ok := err.(dockercli.StatusError); ok {
+		return dockercli.StatusError{
+			StatusCode: statusErr.StatusCode,
+			Status:     errorAsJSON(statusErr.Status),
+		}
+	}
+	return fmt.Errorf("%s", errorAsJSON(err.Error()))
+}
+
 func (o *ProjectOptions) addProjectFlags(f *pflag.FlagSet) {
 	f.StringArrayVar(&o.Profiles, "profile", []string{}, "Specify a profile to enable")
 	f.StringVarP(&o.ProjectName, "project-name", "p", "", "Project name")