fix(apicompat): skip empty base64 image URLs

backend/internal/pkg/apicompat/chatcompletions_responses_test.go

@@ -181,6 +181,50 @@ func TestChatCompletionsToResponses_ImageURL(t *testing.T) {
 	assert.Equal(t, "data:image/png;base64,abc123", parts[1].ImageURL)
 }
 
+func TestChatCompletionsToResponses_EmptyBase64ImageURLSkipped(t *testing.T) {
+	content := `[{"type":"text","text":"Describe this"},{"type":"image_url","image_url":{"url":"data:image/png;base64,"}}]`
+	req := &ChatCompletionsRequest{
+		Model: "gpt-4o",
+		Messages: []ChatMessage{
+			{Role: "user", Content: json.RawMessage(content)},
+		},
+	}
+	resp, err := ChatCompletionsToResponses(req)
+	require.NoError(t, err)
+
+	var items []ResponsesInputItem
+	require.NoError(t, json.Unmarshal(resp.Input, &items))
+	require.Len(t, items, 1)
+
+	var parts []ResponsesContentPart
+	require.NoError(t, json.Unmarshal(items[0].Content, &parts))
+	require.Len(t, parts, 1)
+	assert.Equal(t, "input_text", parts[0].Type)
+	assert.Equal(t, "Describe this", parts[0].Text)
+}
+
+func TestChatCompletionsToResponses_WhitespaceOnlyBase64ImageURLSkipped(t *testing.T) {
+	content := `[{"type":"text","text":"Describe this"},{"type":"image_url","image_url":{"url":"data:image/png;base64,   "}}]`
+	req := &ChatCompletionsRequest{
+		Model: "gpt-4o",
+		Messages: []ChatMessage{
+			{Role: "user", Content: json.RawMessage(content)},
+		},
+	}
+	resp, err := ChatCompletionsToResponses(req)
+	require.NoError(t, err)
+
+	var items []ResponsesInputItem
+	require.NoError(t, json.Unmarshal(resp.Input, &items))
+	require.Len(t, items, 1)
+
+	var parts []ResponsesContentPart
+	require.NoError(t, json.Unmarshal(items[0].Content, &parts))
+	require.Len(t, parts, 1)
+	assert.Equal(t, "input_text", parts[0].Type)
+	assert.Equal(t, "Describe this", parts[0].Text)
+}
+
 func TestChatCompletionsToResponses_SystemArrayContent(t *testing.T) {
 	req := &ChatCompletionsRequest{
 		Model: "gpt-4o",

backend/internal/pkg/apicompat/chatcompletions_to_responses.go

@@ -339,7 +339,7 @@ func convertChatContentPartsToResponses(parts []ChatContentPart) []ResponsesCont
 				})
 			}
 		case "image_url":
-			if p.ImageURL != nil && p.ImageURL.URL != "" {
+			if p.ImageURL != nil && p.ImageURL.URL != "" && !isEmptyBase64DataURI(p.ImageURL.URL) {
 				responseParts = append(responseParts, ResponsesContentPart{
 					Type:     "input_image",
 					ImageURL: p.ImageURL.URL,
@@ -350,6 +350,22 @@ func convertChatContentPartsToResponses(parts []ChatContentPart) []ResponsesCont
 	return responseParts
 }
 
+func isEmptyBase64DataURI(raw string) bool {
+	if !strings.HasPrefix(raw, "data:") {
+		return false
+	}
+	rest := strings.TrimPrefix(raw, "data:")
+	semicolonIdx := strings.Index(rest, ";")
+	if semicolonIdx < 0 {
+		return false
+	}
+	rest = rest[semicolonIdx+1:]
+	if !strings.HasPrefix(rest, "base64,") {
+		return false
+	}
+	return strings.TrimSpace(strings.TrimPrefix(rest, "base64,")) == ""
+}
+
 func flattenChatContentParts(parts []ChatContentPart) string {
 	var textParts []string
 	for _, p := range parts {