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backend/internal/signature/claude.go

@@ -0,0 +1,113 @@
+package signature
+
+import (
+	"bytes"
+	"strings"
+
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
+)
+
+// StripInvalidClaudeThinkingBlocks removes Claude thinking blocks whose
+// signatures are empty or not valid Claude thinking signatures after stripping
+// an optional cache prefix, unless the validation options allow an empty
+// thinking placeholder.
+func StripInvalidClaudeThinkingBlocks(payload []byte, opts ...ClaudeSignatureValidationOptions) []byte {
+	messages := gjson.GetBytes(payload, "messages")
+	if !messages.IsArray() {
+		return payload
+	}
+	opt := claudeSignatureValidationOptions(opts)
+	messageResults := messages.Array()
+	keptMessages := make([]string, 0, len(messageResults))
+	modified := false
+	for _, msg := range messageResults {
+		content := msg.Get("content")
+		if !content.IsArray() {
+			keptMessages = append(keptMessages, msg.Raw)
+			continue
+		}
+		contentResults := content.Array()
+		keptParts := make([]string, 0, len(contentResults))
+		stripped := false
+		for _, part := range contentResults {
+			if part.Get("type").String() == "thinking" && shouldStripClaudeThinkingBlock(part, opt) {
+				stripped = true
+				continue
+			}
+			keptParts = append(keptParts, part.Raw)
+		}
+		if stripped {
+			modified = true
+			updated, _ := sjson.SetRaw(msg.Raw, "content", "["+strings.Join(keptParts, ",")+"]")
+			keptMessages = append(keptMessages, updated)
+			continue
+		}
+		keptMessages = append(keptMessages, msg.Raw)
+	}
+	if !modified {
+		return payload
+	}
+	output, _ := sjson.SetRawBytes(payload, "messages", []byte("["+strings.Join(keptMessages, ",")+"]"))
+	return output
+}
+
+// StripInvalidClaudeThinkingBlocksAndEmptyMessages also removes messages whose
+// content becomes empty after invalid thinking blocks are removed.
+func StripInvalidClaudeThinkingBlocksAndEmptyMessages(payload []byte, opts ...ClaudeSignatureValidationOptions) []byte {
+	stripped := StripInvalidClaudeThinkingBlocks(payload, opts...)
+	if bytes.Equal(stripped, payload) {
+		return payload
+	}
+	messages := gjson.GetBytes(stripped, "messages")
+	if !messages.IsArray() {
+		return stripped
+	}
+	kept := make([]string, 0, len(messages.Array()))
+	for _, message := range messages.Array() {
+		content := message.Get("content")
+		if content.IsArray() && len(content.Array()) == 0 {
+			continue
+		}
+		kept = append(kept, message.Raw)
+	}
+	stripped, _ = sjson.SetRawBytes(stripped, "messages", []byte("["+strings.Join(kept, ",")+"]"))
+	return stripped
+}
+
+func shouldStripClaudeThinkingBlock(part gjson.Result, opt ClaudeSignatureValidationOptions) bool {
+	if opt.AllowEmptySignatureWithEmptyText && isEmptyClaudeThinkingPlaceholder(part) {
+		return false
+	}
+	return !IsValidClaudeThinkingSignature(part.Get("signature").String(), opt)
+}
+
+func isEmptyClaudeThinkingPlaceholder(part gjson.Result) bool {
+	if strings.TrimSpace(part.Get("signature").String()) != "" {
+		return false
+	}
+	return strings.TrimSpace(claudeThinkingBlockText(part)) == ""
+}
+
+func claudeThinkingBlockText(part gjson.Result) string {
+	if text := part.Get("text"); text.Exists() && text.Type == gjson.String {
+		return text.String()
+	}
+
+	thinkingField := part.Get("thinking")
+	if !thinkingField.Exists() {
+		return ""
+	}
+	if thinkingField.Type == gjson.String {
+		return thinkingField.String()
+	}
+	if thinkingField.IsObject() {
+		if inner := thinkingField.Get("text"); inner.Exists() && inner.Type == gjson.String {
+			return inner.String()
+		}
+		if inner := thinkingField.Get("thinking"); inner.Exists() && inner.Type == gjson.String {
+			return inner.String()
+		}
+	}
+	return ""
+}