fix: improve json error detection and remove invalid rerank path header (#1591)

**Description**
Makes the JSON detection in ResponseError translator more robust: if the
upstream content-type contains application/json (e.g., application/json;
charset=utf-8), it now passes the upstream error body through unchanged
instead of wrapping it again.
Removes invalid `:path` pseudo-header from error response translation
for rerank to prevent Envoy stream aborts, yielding a 500 with an empty
body.

---------

Signed-off-by: ayush <[email protected]>
Co-authored-by: Takeshi Yoneda <[email protected]>

Author: AyushSawant18588

internal/translator/cohere_rerank_v2.go

@@ -11,6 +11,7 @@ import (
 	"io"
 	"path"
 	"strconv"
+	"strings"
 
 	"github.com/tidwall/sjson"
 
@@ -111,7 +112,7 @@ func (t *cohereToCohereTranslatorV2Rerank) ResponseBody(_ map[string]string, bod
 func (t *cohereToCohereTranslatorV2Rerank) ResponseError(respHeaders map[string]string, body io.Reader) (
 	newHeaders []internalapi.Header, newBody []byte, err error,
 ) {
-	if v, ok := respHeaders[contentTypeHeaderName]; ok && v != jsonContentType {
+	if v, ok := respHeaders[contentTypeHeaderName]; ok && !strings.Contains(v, jsonContentType) {
 		buf, err := io.ReadAll(body)
 		if err != nil {
 			return nil, nil, fmt.Errorf("failed to read error body: %w", err)
@@ -125,10 +126,10 @@ func (t *cohereToCohereTranslatorV2Rerank) ResponseError(respHeaders map[string]
 		if err != nil {
 			return nil, nil, fmt.Errorf("failed to marshal error body: %w", err)
 		}
-		newHeaders = []internalapi.Header{
-			{pathHeaderName, t.path},
-			{contentTypeHeaderName, jsonContentType},
-		}
+		newHeaders = append(newHeaders,
+			internalapi.Header{contentTypeHeaderName, jsonContentType},
+			internalapi.Header{contentLengthHeaderName, strconv.Itoa(len(newBody))},
+		)
 	}
 	return
 }

internal/translator/openai_awsbedrock.go

@@ -562,7 +562,7 @@ func (o *openAIToAWSBedrockTranslatorV1ChatCompletion) ResponseError(respHeaders
 ) {
 	statusCode := respHeaders[statusHeaderName]
 	var openaiError openai.Error
-	if v, ok := respHeaders[contentTypeHeaderName]; ok && v == jsonContentType {
+	if v, ok := respHeaders[contentTypeHeaderName]; ok && strings.Contains(v, jsonContentType) {
 		var bedrockError awsbedrock.BedrockException
 		if err = json.NewDecoder(body).Decode(&bedrockError); err != nil {
 			return nil, nil, fmt.Errorf("failed to unmarshal error body: %w", err)

internal/translator/openai_embeddings.go

@@ -11,6 +11,7 @@ import (
 	"io"
 	"path"
 	"strconv"
+	"strings"
 
 	"github.com/tidwall/sjson"
 
@@ -94,7 +95,7 @@ func (o *openAIToOpenAITranslatorV1Embedding) ResponseError(respHeaders map[stri
 	newHeaders []internalapi.Header, newBody []byte, err error,
 ) {
 	statusCode := respHeaders[statusHeaderName]
-	if v, ok := respHeaders[contentTypeHeaderName]; ok && v != jsonContentType {
+	if v, ok := respHeaders[contentTypeHeaderName]; ok && !strings.Contains(v, jsonContentType) {
 		var openaiError openai.Error
 		buf, err := io.ReadAll(body)
 		if err != nil {

internal/translator/openai_openai.go

@@ -13,6 +13,7 @@ import (
 	"io"
 	"path"
 	"strconv"
+	"strings"
 
 	"github.com/tidwall/sjson"
 
@@ -82,7 +83,7 @@ func (o *openAIToOpenAITranslatorV1ChatCompletion) ResponseError(respHeaders map
 	newHeaders []internalapi.Header, newBody []byte, err error,
 ) {
 	statusCode := respHeaders[statusHeaderName]
-	if v, ok := respHeaders[contentTypeHeaderName]; ok && v != jsonContentType {
+	if v, ok := respHeaders[contentTypeHeaderName]; ok && !strings.Contains(v, jsonContentType) {
 		var openaiError openai.Error
 		buf, err := io.ReadAll(body)
 		if err != nil {

tests/extproc/vcr/chat_completions_test.go

@@ -67,7 +67,7 @@ func TestOpenAIChatCompletions(t *testing.T) {
 		},
 		{
 			name:               testopenai.CassetteChatUnknownModel,
-			expectResponseBody: `{"type":"error","error":{"type":"OpenAIBackendError","code":"404","message":"{\n    \"error\": {\n        \"message\": \"The model ` + "`gpt-4.1-nano-wrong`" + ` does not exist or you do not have access to it.\",\n        \"type\": \"invalid_request_error\",\n        \"param\": null,\n        \"code\": \"model_not_found\"\n    }\n}\n"}}`,
+			expectResponseBody: "{\n    \"error\": {\n        \"message\": \"The model `gpt-4.1-nano-wrong` does not exist or you do not have access to it.\",\n        \"type\": \"invalid_request_error\",\n        \"param\": null,\n        \"code\": \"model_not_found\"\n    }\n}\n",
 			expectStatusCode:   http.StatusNotFound,
 		},
 		{

tests/extproc/vcr/embeddings_test.go

@@ -47,7 +47,7 @@ func TestOpenAIEmbeddings(t *testing.T) {
 		},
 		{
 			name:               testopenai.CassetteEmbeddingsUnknownModel,
-			expectResponseBody: `{"type":"error","error":{"type":"OpenAIBackendError","code":"404","message":"{\n    \"error\": {\n        \"message\": \"The model ` + "`text-embedding-4-ultra`" + ` does not exist or you do not have access to it.\",\n        \"type\": \"invalid_request_error\",\n        \"param\": null,\n        \"code\": \"model_not_found\"\n    }\n}\n"}}`,
+			expectResponseBody: "{\n    \"error\": {\n        \"message\": \"The model `text-embedding-4-ultra` does not exist or you do not have access to it.\",\n        \"type\": \"invalid_request_error\",\n        \"param\": null,\n        \"code\": \"model_not_found\"\n    }\n}\n",
 			expectStatusCode:   http.StatusNotFound,
 		},
 		{