chore: centralized error formatting

Author: olevski

cmd/gateway/main.go

@@ -66,6 +66,7 @@ func main() {
 	}
 	// Setup
 	e := echo.New()
+	e.HTTPErrorHandler = revproxy.ErrorHandler
 	e.Pre(middleware.RequestID(), middleware.RemoveTrailingSlash(), revproxy.UiServerPathRewrite())
 	e.Use(middleware.Recover())
 	// Sentry middleware

internal/revproxy/main.go

@@ -3,8 +3,11 @@
 package revproxy
 
 import (
+	"errors"
 	"fmt"
+	"net/http"
 	"path"
+	"strings"
 
 	"github.com/SwissDataScienceCenter/renku-gateway/internal/config"
 	"github.com/SwissDataScienceCenter/renku-gateway/internal/models"
@@ -151,3 +154,56 @@ func NewServer(options ...RevproxyOption) (*Revproxy, error) {
 	}
 	return &server, nil
 }
+
+// The same error content as the data services API
+const gwBaseErrorCode int = 6000
+
+type errorContent struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+	Detail  string `json:"detail,omitempty"`
+	TraceId string `json:"trace_id,omitempty"`
+}
+
+type errorResponse struct {
+	Error errorContent `json:"error"`
+}
+
+// Adapted from https://echo.labstack.com/docs/error-handling
+func ErrorHandler(err error, c echo.Context) {
+	if c.Response() != nil && c.Response().Committed {
+		return // response has been already sent to the client by handler or some middleware
+	}
+
+	accept := c.Request().Header.Get("Accept")
+	isHTML := strings.Contains(accept, echo.MIMETextHTML)
+
+	// If the accept header is html then we fall back to the default handler (for now).
+	// If the acceptt header is not html or is blank we return json
+	if isHTML {
+		c.Echo().DefaultHTTPErrorHandler(err, c)
+		return
+	}
+
+	code := http.StatusInternalServerError
+	message := err.Error()
+	var he *echo.HTTPError
+	if errors.As(err, &he) { // find error in an error chain that implements HTTPError
+		if tmp := he.Code; tmp != 0 {
+			code = tmp
+		}
+		if msg := fmt.Sprintf("%v", he.Message); len(msg) > 0 {
+			message = msg
+		}
+	}
+
+	var cErr error
+	if c.Request().Method == http.MethodHead {
+		cErr = c.NoContent(code)
+	} else {
+		cErr = c.JSON(code, errorResponse{Error: errorContent{Code: gwBaseErrorCode + code, Message: message}})
+	}
+	if cErr != nil {
+		c.Logger().Error("failed to send error page to client", "error", errors.Join(err, cErr))
+	}
+}