perf(service): 优化重试场景 thinking 过滤性能

- 避免全量 Unmarshal 请求体，改为仅解析 messages 子树

- 顶层 thinking 使用 sjson 直接删除，减少整体重写

- content 仅在需要修改时延迟分配 new slice

- 增加 FilterThinkingBlocksForRetry 基准测试

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/service/gateway_request.go

@@ -10,6 +10,23 @@ import (
 	"github.com/Wei-Shaw/sub2api/internal/domain"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/antigravity"
 	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
+)
+
+var (
+	// 这些字节模式用于 fast-path 判断，避免每次 []byte("...") 产生临时分配。
+	patternTypeThinking         = []byte(`"type":"thinking"`)
+	patternTypeThinkingSpaced   = []byte(`"type": "thinking"`)
+	patternTypeRedactedThinking = []byte(`"type":"redacted_thinking"`)
+	patternTypeRedactedSpaced   = []byte(`"type": "redacted_thinking"`)
+
+	patternThinkingField       = []byte(`"thinking":`)
+	patternThinkingFieldSpaced = []byte(`"thinking" :`)
+
+	patternEmptyContent       = []byte(`"content":[]`)
+	patternEmptyContentSpaced = []byte(`"content": []`)
+	patternEmptyContentSp1    = []byte(`"content" : []`)
+	patternEmptyContentSp2    = []byte(`"content" :[]`)
 )
 
 // SessionContext 粘性会话上下文，用于区分不同来源的请求。
@@ -238,49 +255,63 @@ func FilterThinkingBlocks(body []byte) []byte {
 //   - Remove `redacted_thinking` blocks (cannot be converted to text).
 //   - Ensure no message ends up with empty content.
 func FilterThinkingBlocksForRetry(body []byte) []byte {
-	hasThinkingContent := bytes.Contains(body, []byte(`"type":"thinking"`)) ||
-		bytes.Contains(body, []byte(`"type": "thinking"`)) ||
-		bytes.Contains(body, []byte(`"type":"redacted_thinking"`)) ||
-		bytes.Contains(body, []byte(`"type": "redacted_thinking"`)) ||
-		bytes.Contains(body, []byte(`"thinking":`)) ||
-		bytes.Contains(body, []byte(`"thinking" :`))
+	hasThinkingContent := bytes.Contains(body, patternTypeThinking) ||
+		bytes.Contains(body, patternTypeThinkingSpaced) ||
+		bytes.Contains(body, patternTypeRedactedThinking) ||
+		bytes.Contains(body, patternTypeRedactedSpaced) ||
+		bytes.Contains(body, patternThinkingField) ||
+		bytes.Contains(body, patternThinkingFieldSpaced)
 
 	// Also check for empty content arrays that need fixing.
 	// Note: This is a heuristic check; the actual empty content handling is done below.
-	hasEmptyContent := bytes.Contains(body, []byte(`"content":[]`)) ||
-		bytes.Contains(body, []byte(`"content": []`)) ||
-		bytes.Contains(body, []byte(`"content" : []`)) ||
-		bytes.Contains(body, []byte(`"content" :[]`))
+	hasEmptyContent := bytes.Contains(body, patternEmptyContent) ||
+		bytes.Contains(body, patternEmptyContentSpaced) ||
+		bytes.Contains(body, patternEmptyContentSp1) ||
+		bytes.Contains(body, patternEmptyContentSp2)
 
 	// Fast path: nothing to process
 	if !hasThinkingContent && !hasEmptyContent {
 		return body
 	}
 
-	var req map[string]any
-	if err := json.Unmarshal(body, &req); err != nil {
+	// 尽量避免把整个 body Unmarshal 成 map（会产生大量 map/接口分配）。
+	// 这里先用 gjson 把 messages 子树摘出来，后续只对 messages 做 Unmarshal/Marshal。
+	jsonStr := *(*string)(unsafe.Pointer(&body))
+	msgsRes := gjson.Get(jsonStr, "messages")
+	if !msgsRes.Exists() || !msgsRes.IsArray() {
+		return body
+	}
+
+	// Fast path：只需要删除顶层 thinking，不需要改 messages。
+	// 注意：patternThinkingField 可能来自嵌套字段（如 tool_use.input.thinking），因此必须用 gjson 判断顶层字段是否存在。
+	containsThinkingBlocks := bytes.Contains(body, patternTypeThinking) ||
+		bytes.Contains(body, patternTypeThinkingSpaced) ||
+		bytes.Contains(body, patternTypeRedactedThinking) ||
+		bytes.Contains(body, patternTypeRedactedSpaced) ||
+		bytes.Contains(body, patternThinkingFieldSpaced)
+	if !hasEmptyContent && !containsThinkingBlocks {
+		if topThinking := gjson.Get(jsonStr, "thinking"); topThinking.Exists() {
+			if out, err := sjson.DeleteBytes(body, "thinking"); err == nil {
+				return out
+			}
+			return body
+		}
+		return body
+	}
+
+	var messages []any
+	if err := json.Unmarshal(sliceRawFromBody(body, msgsRes), &messages); err != nil {
 		return body
 	}
 
 	modified := false
 
-	messages, ok := req["messages"].([]any)
-	if !ok {
-		return body
-	}
-
 	// Disable top-level thinking mode for retry to avoid structural/signature constraints upstream.
-	if _, exists := req["thinking"]; exists {
-		delete(req, "thinking")
-		modified = true
-	}
+	deleteTopLevelThinking := gjson.Get(jsonStr, "thinking").Exists()
 
-	newMessages := make([]any, 0, len(messages))
-
-	for _, msg := range messages {
-		msgMap, ok := msg.(map[string]any)
+	for i := 0; i < len(messages); i++ {
+		msgMap, ok := messages[i].(map[string]any)
 		if !ok {
-			newMessages = append(newMessages, msg)
 			continue
 		}
 
@@ -288,17 +319,30 @@ func FilterThinkingBlocksForRetry(body []byte) []byte {
 		content, ok := msgMap["content"].([]any)
 		if !ok {
 			// String content or other format - keep as is
-			newMessages = append(newMessages, msg)
 			continue
 		}
 
-		newContent := make([]any, 0, len(content))
+		// 延迟分配：只有检测到需要修改的块，才构建新 slice。
+		var newContent []any
 		modifiedThisMsg := false
 
-		for _, block := range content {
+		ensureNewContent := func(prefixLen int) {
+			if newContent != nil {
+				return
+			}
+			newContent = make([]any, 0, len(content))
+			if prefixLen > 0 {
+				newContent = append(newContent, content[:prefixLen]...)
+			}
+		}
+
+		for bi := 0; bi < len(content); bi++ {
+			block := content[bi]
 			blockMap, ok := block.(map[string]any)
 			if !ok {
-				newContent = append(newContent, block)
+				if newContent != nil {
+					newContent = append(newContent, block)
+				}
 				continue
 			}
 
@@ -308,17 +352,15 @@ func FilterThinkingBlocksForRetry(body []byte) []byte {
 			switch blockType {
 			case "thinking":
 				modifiedThisMsg = true
+				ensureNewContent(bi)
 				thinkingText, _ := blockMap["thinking"].(string)
-				if thinkingText == "" {
-					continue
+				if thinkingText != "" {
+					newContent = append(newContent, map[string]any{"type": "text", "text": thinkingText})
 				}
-				newContent = append(newContent, map[string]any{
-					"type": "text",
-					"text": thinkingText,
-				})
 				continue
 			case "redacted_thinking":
 				modifiedThisMsg = true
+				ensureNewContent(bi)
 				continue
 			}
 
@@ -326,6 +368,7 @@ func FilterThinkingBlocksForRetry(body []byte) []byte {
 			if blockType == "" {
 				if rawThinking, hasThinking := blockMap["thinking"]; hasThinking {
 					modifiedThisMsg = true
+					ensureNewContent(bi)
 					switch v := rawThinking.(type) {
 					case string:
 						if v != "" {
@@ -340,40 +383,64 @@ func FilterThinkingBlocksForRetry(body []byte) []byte {
 				}
 			}
 
-			newContent = append(newContent, block)
+			if newContent != nil {
+				newContent = append(newContent, block)
+			}
 		}
 
 		// Handle empty content: either from filtering or originally empty
+		if newContent == nil {
+			if len(content) == 0 {
+				modified = true
+				placeholder := "(content removed)"
+				if role == "assistant" {
+					placeholder = "(assistant content removed)"
+				}
+				msgMap["content"] = []any{map[string]any{"type": "text", "text": placeholder}}
+			}
+			continue
+		}
+
 		if len(newContent) == 0 {
 			modified = true
 			placeholder := "(content removed)"
 			if role == "assistant" {
 				placeholder = "(assistant content removed)"
 			}
-			newContent = append(newContent, map[string]any{
-				"type": "text",
-				"text": placeholder,
-			})
-			msgMap["content"] = newContent
-		} else if modifiedThisMsg {
+			msgMap["content"] = []any{map[string]any{"type": "text", "text": placeholder}}
+			continue
+		}
+
+		if modifiedThisMsg {
 			modified = true
 			msgMap["content"] = newContent
 		}
-		newMessages = append(newMessages, msgMap)
 	}
 
-	if modified {
-		req["messages"] = newMessages
-	} else {
+	if !modified && !deleteTopLevelThinking {
 		// Avoid rewriting JSON when no changes are needed.
 		return body
 	}
 
-	newBody, err := json.Marshal(req)
-	if err != nil {
-		return body
+	out := body
+	if deleteTopLevelThinking {
+		if b, err := sjson.DeleteBytes(out, "thinking"); err == nil {
+			out = b
+		} else {
+			return body
+		}
 	}
-	return newBody
+	if modified {
+		msgsBytes, err := json.Marshal(messages)
+		if err != nil {
+			return body
+		}
+		out, err = sjson.SetRawBytes(out, "messages", msgsBytes)
+		if err != nil {
+			return body
+		}
+	}
+	return out
 }
 
 // FilterSignatureSensitiveBlocksForRetry is a stronger retry filter for cases where upstream errors indicate