Error chaining and handler selection (#595)

* wrap error with errors.Sequence if it is not already an errors.Sequence

* get _all_ kinds of inner error _first_

* now the backend timeout error is wrapped with a sequence error, resulting in a different HTTP status code

* added test cases for error handler selection: because an error occurs in a request sequence, the default error handling has endpoint error for client, whereas the specific error is logged

* changelog entry

* Simplify code

Co-authored-by: Alex Schneider <alex.schneider@avenga.com>

CHANGELOG.md

@@ -7,6 +7,7 @@ Unreleased changes are available as `avenga/couper:edge` container.
 * **Fixed**
   * Aligned the evaluation of [`beta_oauth2`](https://docs.couper.io/configuration/block/oauth2_ac)/[`oidc`](https://docs.couper.io/configuration/block/oidc) `redirect_uri` to `saml` `sp_acs_url` ([#589](https://github.com/avenga/couper/pull/589))
   * Proper handling of empty [`beta_oauth2`](https://docs.couper.io/configuration/block/oauth2_ac)/[`oidc`](https://docs.couper.io/configuration/block/oidc) `scope` ([#593](https://github.com/avenga/couper/pull/593))
+  * Throwing [sequence errors](https://docs.couper.io/configuration/error-handling#endpoint-error-types) and selecting appropriate [error handlers](https://docs.couper.io/configuration/error-handling) ([#595](https://github.com/avenga/couper/pull/595))
 
 ---
 

errors/error.go

@@ -58,26 +58,20 @@ func (e *Error) Kind(name string) *Error {
 	err := e.clone()
 	e.isParent = true
 	err.isParent = false
-	err.kinds = append(err.kinds, name)
+	err.kinds = append([]string{name}, err.kinds...)
 	return err
 }
 
-// Kinds returns all configured kinds in reversed order so the
+// Kinds returns all configured kinds, the
 // most specific one gets evaluated first.
 func (e *Error) Kinds() []string {
-	var reversed []string
-	for i := len(e.kinds); i > 0; i-- {
-		reversed = append(reversed, e.kinds[i-1])
-	}
+	var kinds []string
 
 	if eer, ok := e.inner.(*Error); ok {
-		k := eer.Kinds()
-		if len(k) > 0 {
-			reversed = append(reversed, k[0])
-		}
+		kinds = eer.Kinds()[:]
 	}
 
-	return reversed
+	return append(kinds, e.kinds...)
 }
 
 // Context appends the given context block type to the existing ones.

handler/producer/sequence.go

@@ -84,7 +84,9 @@ func (s Sequence) Produce(req *http.Request, results chan<- *Result) {
 		}
 
 		if lastResult.Err != nil {
-			if _, ok := lastResult.Err.(*errors.Error); !ok {
+			// only wrap if lastResult.Err is not already an errors.Sequence
+			cErr, ok := lastResult.Err.(*errors.Error)
+			if !ok || !hasSequenceKind(cErr) {
 				lastResult.Err = errors.Sequence.With(lastResult.Err)
 			}
 			results <- lastResult
@@ -99,6 +101,15 @@ func (s Sequence) Produce(req *http.Request, results chan<- *Result) {
 	results <- lastResult
 }
 
+func hasSequenceKind(cerr *errors.Error) bool {
+	for _, kind := range cerr.Kinds() {
+		if kind == "sequence" {
+			return true
+		}
+	}
+	return false
+}
+
 func (s Sequence) Len() int {
 	var sum int
 	for _, t := range s {

server/http_endpoints_test.go

@@ -760,8 +760,8 @@ func TestEndpointSequenceBackendTimeout(t *testing.T) {
 		helper.Must(err)
 	}
 
-	if res.StatusCode != http.StatusGatewayTimeout {
-		t.Fatalf("Expected status 504, got: %d", res.StatusCode)
+	if res.StatusCode != http.StatusBadGateway {
+		t.Fatalf("Expected status 502, got: %d", res.StatusCode)
 	}
 
 	time.Sleep(time.Second / 4)
@@ -849,6 +849,24 @@ func TestEndpointErrorHandler(t *testing.T) {
 		{"error_handler triggered with beresp body", "/not-ok", test.Header{"x": "200", "y": "item1"}, http.StatusTeapot, "unexpected_status"},
 		{"error_handler triggered with beresp body handled by endpoint", "/not-ok-endpoint", test.Header{"x": "200", "y": "item1"}, http.StatusTeapot, "unexpected_status"},
 		{"error_handler triggered with beresp body - sequence", "/not-ok-sequence", test.Header{"x": "application/json"}, http.StatusTeapot, "unexpected_status"},
+
+		{"unexpected status; handlers for unexpected_status, sequence, endpoint", "/1.1", test.Header{"handled-by": "unexpected_status"}, http.StatusOK, "unexpected_status"},
+		{"unexpected status; handlers for sequence, endpoint", "/1.2", test.Header{"handled-by": "endpoint"}, http.StatusOK, "unexpected_status"},
+		{"unexpected status; handler for sequence", "/1.3", test.Header{"handled-by": "sequence"}, http.StatusOK, "unexpected_status"},
+		{"unexpected status; handler for endpoint", "/1.4", test.Header{"handled-by": "endpoint"}, http.StatusOK, "unexpected_status"},
+		{"unexpected status; no handlers", "/1.5", test.Header{"couper-error": "endpoint error"}, http.StatusBadGateway, "unexpected_status"},
+
+		{"backend timeout; handlers for backend_timeout, backend, sequence, endpoint", "/2.1", test.Header{"handled-by": "backend_timeout"}, http.StatusOK, "backend_timeout"},
+		{"backend timeout; handlers for backend, sequence, endpoint", "/2.2", test.Header{"handled-by": "backend"}, http.StatusOK, "backend_timeout"},
+		{"backend timeout; handlers for sequence, endpoint", "/2.3", test.Header{"handled-by": "sequence"}, http.StatusOK, "backend_timeout"},
+		{"backend timeout; handler for endpoint", "/2.4", test.Header{"handled-by": "endpoint"}, http.StatusOK, "backend_timeout"},
+		{"backend timeout; no handler", "/2.5", test.Header{"couper-error": "endpoint error"}, http.StatusBadGateway, "backend_timeout"},
+
+		{"backend openapi validation; handlers for backend_openapi_validation, backend, sequence, endpoint", "/3.1", test.Header{"handled-by": "backend_openapi_validation"}, http.StatusOK, "backend_openapi_validation"},
+		{"backend openapi validation; handlers for backend, sequence, endpoint", "/3.2", test.Header{"handled-by": "backend"}, http.StatusOK, "backend_openapi_validation"},
+		{"backend openapi validation; handlers for sequence, endpoint", "/3.3", test.Header{"handled-by": "sequence"}, http.StatusOK, "backend_openapi_validation"},
+		{"backend openapi validation; handler for endpoint", "/3.4", test.Header{"handled-by": "endpoint"}, http.StatusOK, "backend_openapi_validation"},
+		{"backend openapi validation; no handler", "/3.5", test.Header{"couper-error": "endpoint error"}, http.StatusBadGateway, "backend_openapi_validation"},
 	} {
 		t.Run(tc.name, func(st *testing.T) {
 			hook.Reset()