Sub2API v1.0 - AI API 网关（二开初始版本，基于上游 Wei-Shaw/sub2api）

backend/internal/service/upstream_response_limit.go

@@ -0,0 +1,83 @@
+package service
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+
+	"github.com/Wei-Shaw/sub2api/internal/config"
+	"github.com/gin-gonic/gin"
+)
+
+var ErrUpstreamResponseBodyTooLarge = errors.New("upstream response body too large")
+
+// defaultUpstreamResponseReadMaxBytes 源自 config.DefaultUpstreamResponseReadMaxBytes，
+// 仅在 cfg 为 nil 时作为兜底（测试或极端场景）。
+const defaultUpstreamResponseReadMaxBytes = config.DefaultUpstreamResponseReadMaxBytes
+
+func resolveUpstreamResponseReadLimit(cfg *config.Config) int64 {
+	if cfg != nil && cfg.Gateway.UpstreamResponseReadMaxBytes > 0 {
+		return cfg.Gateway.UpstreamResponseReadMaxBytes
+	}
+	return defaultUpstreamResponseReadMaxBytes
+}
+
+func readUpstreamResponseBodyLimited(reader io.Reader, maxBytes int64) ([]byte, error) {
+	if reader == nil {
+		return nil, errors.New("response body is nil")
+	}
+	if maxBytes <= 0 {
+		maxBytes = defaultUpstreamResponseReadMaxBytes
+	}
+
+	body, err := io.ReadAll(io.LimitReader(reader, maxBytes+1))
+	if err != nil {
+		return nil, err
+	}
+	if int64(len(body)) > maxBytes {
+		return nil, fmt.Errorf("%w: limit=%d", ErrUpstreamResponseBodyTooLarge, maxBytes)
+	}
+	return body, nil
+}
+
+// TooLargeWriter 在响应超限时向客户端写格式化的错误响应。
+type TooLargeWriter func(c *gin.Context)
+
+// ReadUpstreamResponseBody 读取上游非流式响应体。
+// 超限时自动记录 ops error 并调用 onTooLarge 向客户端写错误。
+func ReadUpstreamResponseBody(reader io.Reader, cfg *config.Config, c *gin.Context, onTooLarge TooLargeWriter) ([]byte, error) {
+	maxBytes := resolveUpstreamResponseReadLimit(cfg)
+	body, err := readUpstreamResponseBodyLimited(reader, maxBytes)
+	if err != nil {
+		if errors.Is(err, ErrUpstreamResponseBodyTooLarge) {
+			setOpsUpstreamError(c, http.StatusBadGateway, "upstream response too large", "")
+			if onTooLarge != nil {
+				onTooLarge(c)
+			}
+		}
+		return nil, err
+	}
+	return body, nil
+}
+
+// anthropicTooLargeError 以 Anthropic Messages API 格式写入超限错误。
+func anthropicTooLargeError(c *gin.Context) {
+	c.JSON(http.StatusBadGateway, gin.H{
+		"type": "error",
+		"error": gin.H{
+			"type":    "upstream_error",
+			"message": "Upstream response too large",
+		},
+	})
+}
+
+// openAITooLargeError 以 OpenAI / Gemini 格式写入超限错误。
+func openAITooLargeError(c *gin.Context) {
+	c.JSON(http.StatusBadGateway, gin.H{
+		"error": gin.H{
+			"type":    "upstream_error",
+			"message": "Upstream response too large",
+		},
+	})
+}