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fix: handle unexpected 'content_block_start' event order (fixes #4) #11

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fix: handle unexpected 'content_block_start' event order (fixes #4) #11

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53 changes: 34 additions & 19 deletions internal/translator/openai/claude/openai_claude_response.go
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Original file line number Diff line number Diff line change
Expand Up @@ -128,29 +128,40 @@ func convertOpenAIStreamingChunkToAnthropic(rawJSON []byte, param *ConvertOpenAI
param.CreatedAt = root.Get("created").Int()
}

// Helper to ensure message_start is sent before any content_block_start
// This is required by the Anthropic SSE protocol - message_start must come first.
// Some OpenAI-compatible providers (like GitHub Copilot) may not send role: "assistant"
// in the first chunk, so we need to emit message_start when we first see content.
ensureMessageStarted := func() {
if param.MessageStarted {
return
}
messageStart := map[string]interface{}{
"type": "message_start",
"message": map[string]interface{}{
"id": param.MessageID,
"type": "message",
"role": "assistant",
"model": param.Model,
"content": []interface{}{},
"stop_reason": nil,
"stop_sequence": nil,
"usage": map[string]interface{}{
"input_tokens": 0,
"output_tokens": 0,
},
},
}
messageStartJSON, _ := json.Marshal(messageStart)
results = append(results, "event: message_start\ndata: "+string(messageStartJSON)+"\n\n")
Comment on lines +155 to +156
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@gemini-code-assist gemini-code-assist bot Dec 7, 2025

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medium

The error from json.Marshal is ignored. While it's unlikely to fail for this static data structure, it's a good practice to handle errors to prevent silent failures or sending malformed events. Consider checking the error and returning if it's not nil. This would prevent a malformed event from being sent. Ideally, the error should also be logged.

		messageStartJSON, err := json.Marshal(messageStart)
		if err != nil {
			return
		}
		results = append(results, "event: message_start\ndata: "+string(messageStartJSON)+"\n\n")

param.MessageStarted = true
}
Comment on lines +135 to +158
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@gemini-code-assist gemini-code-assist bot Dec 7, 2025

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medium

This new helper is defined as a closure. For consistency with other helper functions in this file like stopThinkingContentBlock and stopTextContentBlock, consider making it a standalone package-level function. This would look like func ensureMessageStarted(param *ConvertOpenAIResponseToAnthropicParams, results *[]string) and would improve code consistency and maintainability.


// Check if this is the first chunk (has role)
if delta := root.Get("choices.0.delta"); delta.Exists() {
if role := delta.Get("role"); role.Exists() && role.String() == "assistant" && !param.MessageStarted {
// Send message_start event
messageStart := map[string]interface{}{
"type": "message_start",
"message": map[string]interface{}{
"id": param.MessageID,
"type": "message",
"role": "assistant",
"model": param.Model,
"content": []interface{}{},
"stop_reason": nil,
"stop_sequence": nil,
"usage": map[string]interface{}{
"input_tokens": 0,
"output_tokens": 0,
},
},
}
messageStartJSON, _ := json.Marshal(messageStart)
results = append(results, "event: message_start\ndata: "+string(messageStartJSON)+"\n\n")
param.MessageStarted = true
ensureMessageStarted()

// Don't send content_block_start for text here - wait for actual content
}
Expand All @@ -163,6 +174,7 @@ func convertOpenAIStreamingChunkToAnthropic(rawJSON []byte, param *ConvertOpenAI
}
stopTextContentBlock(param, &results)
if !param.ThinkingContentBlockStarted {
ensureMessageStarted() // Must send message_start before content_block_start
if param.ThinkingContentBlockIndex == -1 {
param.ThinkingContentBlockIndex = param.NextContentBlockIndex
param.NextContentBlockIndex++
Expand Down Expand Up @@ -197,6 +209,7 @@ func convertOpenAIStreamingChunkToAnthropic(rawJSON []byte, param *ConvertOpenAI
if content := delta.Get("content"); content.Exists() && content.String() != "" {
// Send content_block_start for text if not already sent
if !param.TextContentBlockStarted {
ensureMessageStarted() // Must send message_start before content_block_start
stopThinkingContentBlock(param, &results)
if param.TextContentBlockIndex == -1 {
param.TextContentBlockIndex = param.NextContentBlockIndex
Expand Down Expand Up @@ -257,6 +270,8 @@ func convertOpenAIStreamingChunkToAnthropic(rawJSON []byte, param *ConvertOpenAI
if name := function.Get("name"); name.Exists() {
accumulator.Name = name.String()

ensureMessageStarted() // Must send message_start before content_block_start

stopThinkingContentBlock(param, &results)

stopTextContentBlock(param, &results)
Expand Down