fix: pass through Anthropic stream errors

internal/translator/anthropic_helper.go

@@ -9,6 +9,7 @@ import (
 	"bytes"
 	"cmp"
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"io"
 	"strings"
@@ -767,6 +768,13 @@ func newAnthropicStreamParser(requestModel string) *anthropicStreamParser {
 func (p *anthropicStreamParser) writeChunk(eventBlock []byte, buf *[]byte) error {
 	chunk, err := p.parseAndHandleEvent(eventBlock)
 	if err != nil {
+		var streamErr anthropicStreamErrorEvent
+		if errors.As(err, &streamErr) {
+			*buf = append(*buf, sseDataPrefix...)
+			*buf = append(*buf, streamErr.payload...)
+			*buf = append(*buf, '\n', '\n')
+			return nil
+		}
 		return err
 	}
 	if chunk != nil {
@@ -876,6 +884,14 @@ func (p *anthropicStreamParser) Process(body io.Reader, endOfStream bool, span t
 	return
 }
 
+type anthropicStreamErrorEvent struct {
+	payload []byte
+}
+
+func (e anthropicStreamErrorEvent) Error() string {
+	return "anthropic stream error event"
+}
+
 func (p *anthropicStreamParser) parseAndHandleEvent(eventBlock []byte) (*openai.ChatCompletionResponseChunk, error) {
 	var eventType []byte
 	var eventData []byte
@@ -1085,7 +1101,7 @@ func (p *anthropicStreamParser) handleAnthropicStreamEvent(eventType []byte, dat
 		if err := json.Unmarshal(data, &errEvent); err != nil {
 			return nil, fmt.Errorf("unparsable error event: %s", string(data))
 		}
-		return nil, fmt.Errorf("anthropic stream error: %s - %s", errEvent.Error.Type, errEvent.Error.Message)
+		return nil, anthropicStreamErrorEvent{payload: data}
 
 	case "ping":
 		// Per documentation, ping events can be ignored.

internal/translator/openai_awsanthropic_test.go

@@ -675,6 +675,19 @@ func TestAWSAnthropicStreamParser_ErrorHandling(t *testing.T) {
 		return err
 	}
 
+	runStreamBodyTest := func(t *testing.T, sseStream string, endOfStream bool) ([]byte, error) {
+		eventStreamData, err := wrapAnthropicSSEInEventStream(sseStream)
+		require.NoError(t, err)
+
+		openAIReq := &openai.ChatCompletionRequest{Stream: true, Model: "test-model", MaxTokens: new(int64)}
+		translator := NewChatCompletionOpenAIToAWSAnthropicTranslator("", "").(*openAIToAWSAnthropicTranslatorV1ChatCompletion)
+		_, _, err = translator.RequestBody(nil, openAIReq, false)
+		require.NoError(t, err)
+
+		_, body, _, _, err := translator.ResponseBody(map[string]string{}, bytes.NewReader(eventStreamData), endOfStream, nil)
+		return body, err
+	}
+
 	tests := []struct {
 		name          string
 		sseStream     string
@@ -706,6 +719,29 @@ func TestAWSAnthropicStreamParser_ErrorHandling(t *testing.T) {
 		})
 	}
 
+	t.Run("forwards anthropic error event and continues stream", func(t *testing.T) {
+		sseStream := `event: content_block_delta
+data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"before error"}}
+
+event: error
+data: {"type":"error","error":{"type":"overloaded_error","message":"Overloaded"}}
+
+event: content_block_delta
+data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"after error"}}
+
+event: message_stop
+data: {"type":"message_stop"}
+`
+		body, err := runStreamBodyTest(t, sseStream, true)
+		require.NoError(t, err)
+
+		bodyStr := string(body)
+		require.Contains(t, bodyStr, `"content":"before error"`)
+		require.Contains(t, bodyStr, `"error":{"type":"overloaded_error","message":"Overloaded"}`)
+		require.Contains(t, bodyStr, `"content":"after error"`)
+		require.Contains(t, bodyStr, string(sseDoneMessage))
+	})
+
 	t.Run("body read error", func(t *testing.T) {
 		parser := newAnthropicStreamParser("test-model")
 		_, _, _, _, err := parser.Process(&mockErrorReader{}, false, nil)