From 3c6c7b736e9f419fcbd02e0ea03f5da3213526be Mon Sep 17 00:00:00 2001
From: Dmitry Rubtsov <me@mazy.wtf>
Date: Wed, 15 Jul 2026 18:21:00 +0600
Subject: [PATCH] perf(translator): build claude system and messages arrays in
 a single pass

- Replaced per-item `sjson.SetRawBytes(out, "system.-1"/"messages.-1", ...)` appends, which reparsed and rewrote the growing output document on every conversation item, causing O(n^2) work on long histories.
- Collected system and message blocks into slices and wrote each array once via `common.JoinRawArray`, moving the cache_control post-processing and system-only fallback turn onto the collected slices.
---
 .../chat-completions/claude_openai_request.go | 42 +++++++++----------
 1 file changed, 20 insertions(+), 22 deletions(-)

diff --git a/internal/translator/claude/openai/chat-completions/claude_openai_request.go b/internal/translator/claude/openai/chat-completions/claude_openai_request.go
index fb7fb2b8..611df009 100644
--- a/internal/translator/claude/openai/chat-completions/claude_openai_request.go
+++ b/internal/translator/claude/openai/chat-completions/claude_openai_request.go
@@ -163,39 +163,36 @@ func ConvertOpenAIRequestToClaude(modelName string, inputRawJSON []byte, stream
 
 	// Process messages and transform them to Claude Code format
 	if messages := root.Get("messages"); messages.Exists() && messages.IsArray() {
-		messageIndex := 0
+		systemBlocks := make([][]byte, 0)
+		messageBlocks := make([][]byte, 0)
 		messages.ForEach(func(_, message gjson.Result) bool {
 			role := message.Get("role").String()
 			contentResult := message.Get("content")
 
 			switch role {
 			case "system":
-				systemStart := len(gjson.GetBytes(out, "system").Array())
+				systemStart := len(systemBlocks)
 				if contentResult.Exists() && contentResult.Type == gjson.String && contentResult.String() != "" {
 					textPart := []byte(`{"type":"text","text":""}`)
 					textPart, _ = sjson.SetBytes(textPart, "text", contentResult.String())
 					textPart = common.AttachCacheControl(textPart, message)
-					out, _ = sjson.SetRawBytes(out, "system.-1", textPart)
+					systemBlocks = append(systemBlocks, textPart)
 				} else if contentResult.Exists() && contentResult.IsArray() {
 					contentResult.ForEach(func(_, part gjson.Result) bool {
 						if part.Get("type").String() == "text" {
 							textPart := []byte(`{"type":"text","text":""}`)
 							textPart, _ = sjson.SetBytes(textPart, "text", part.Get("text").String())
 							textPart = common.AttachCacheControl(textPart, part)
-							out, _ = sjson.SetRawBytes(out, "system.-1", textPart)
+							systemBlocks = append(systemBlocks, textPart)
 						}
 						return true
 					})
 					// Message-level cache_control applies to the last system block from this message.
 					if message.Get("cache_control").Exists() {
-						systemArr := gjson.GetBytes(out, "system").Array()
-						if len(systemArr) > systemStart {
-							lastIdx := len(systemArr) - 1
-							if !systemArr[lastIdx].Get("cache_control").Exists() {
-								path := fmt.Sprintf("system.%d", lastIdx)
-								block := []byte(systemArr[lastIdx].Raw)
-								block = common.AttachCacheControl(block, message)
-								out, _ = sjson.SetRawBytes(out, path, block)
+						if len(systemBlocks) > systemStart {
+							lastIdx := len(systemBlocks) - 1
+							if !gjson.GetBytes(systemBlocks[lastIdx], "cache_control").Exists() {
+								systemBlocks[lastIdx] = common.AttachCacheControl(systemBlocks[lastIdx], message)
 							}
 						}
 					}
@@ -258,8 +255,7 @@ func ConvertOpenAIRequestToClaude(modelName string, inputRawJSON []byte, stream
 				}
 
 				msg = common.AttachMessageCacheControl(msg, message)
-				out, _ = sjson.SetRawBytes(out, "messages.-1", msg)
-				messageIndex++
+				messageBlocks = append(messageBlocks, msg)
 
 			case "tool":
 				// Handle tool result messages conversion
@@ -276,20 +272,22 @@ func ConvertOpenAIRequestToClaude(modelName string, inputRawJSON []byte, stream
 					msg, _ = sjson.SetBytes(msg, "content.0.content", toolResultContent)
 				}
 				msg = common.AttachMessageCacheControl(msg, message)
-				out, _ = sjson.SetRawBytes(out, "messages.-1", msg)
-				messageIndex++
+				messageBlocks = append(messageBlocks, msg)
 			}
 			return true
 		})
 
 		// Preserve a minimal conversational turn for system-only inputs.
 		// Claude payloads with top-level system instructions but no messages are risky for downstream validation.
-		if messageIndex == 0 {
-			system := gjson.GetBytes(out, "system")
-			if system.Exists() && system.IsArray() && len(system.Array()) > 0 {
-				fallbackMsg := []byte(`{"role":"user","content":[{"type":"text","text":""}]}`)
-				out, _ = sjson.SetRawBytes(out, "messages.-1", fallbackMsg)
-			}
+		if len(messageBlocks) == 0 && len(systemBlocks) > 0 {
+			messageBlocks = append(messageBlocks, []byte(`{"role":"user","content":[{"type":"text","text":""}]}`))
+		}
+
+		if len(systemBlocks) > 0 {
+			out, _ = sjson.SetRawBytes(out, "system", common.JoinRawArray(systemBlocks))
+		}
+		if len(messageBlocks) > 0 {
+			out, _ = sjson.SetRawBytes(out, "messages", common.JoinRawArray(messageBlocks))
 		}
 	}