Qiao-yq opened a new issue, #142:
URL: https://github.com/apache/dubbo-go-pixiu-samples/issues/142
**问题描述**：
使用 dubbo-go-pixiu 作为 MCP（Model Context Protocol）Server 网关时，`streamable-http`
传输模式下，只有 `tools/call` 请求（需要代理到后端 HTTP 服务的工具调用）会触发 `http: wrote more than the
declared Content-Length` 错误（位于 `pkg/common/http/manager.go:139`）。该错误导致 HTTP
连接被强制关闭，客户端收到 `unexpected EOF`。
MCP 协议本身的操作（`initialize`、`tools/list`）工作正常。
**预期行为**：
`tools/call` 应成功代理到后端 mock server，并返回合法的 MCP JSON-RPC 响应，不应出现 HTTP 协议层错误。
**复现步骤**：
1. 克隆 `dubbo-go-pixiu-samples`，进入 `mcp/simple/` 目录
2. 启动后端 mock server：
```markdown
cd server/app && go run server.go # 监听 :8081
```
3. 启动 pixiu 网关：
```
cd dubbo-go-pixiu
go run cmd/pixiu/*.go gateway start -c
~/dubbo-go-pixiu-samples/mcp/simple/pixiu/conf.yaml
```
4. 运行测试：
```
cd dubbo-go-pixiu-samples/mcp/simple/test
go test -v
```
5. 或用 MCP Inspector 连接：
```
npx @modelcontextprotocol/inspector
# 连接 http://localhost:8888/mcp，选择 streamable-http 传输方式
```
**环境信息**：
- dubbo-go-pixiu 版本：v1.0.1-rc1
- dubbo-go-pixiu-samples 版本：main 分支最新代码
- 操作系统：Ubuntu 22.04
- Go 版本：1.25.0
**关键日志**：
**Pixiu 网关日志**（区分正常与异常）：
```
# ✅ MCP 协议操作正常
11:03:10.295 INFO mcp server received POST request: initialize (id:
int64:0)
11:03:10.295 INFO mcp server initialize: client=inspector-client
11:03:10.295 INFO mcp server created new session:
1fdb6cc0ef950789e49e00582b511511
11:03:10.317 INFO mcp server received POST request:
notifications/initialized
11:03:29.589 INFO mcp server received POST request: tools/list (id:
int64:1)
11:03:29.590 INFO mcp server response sent: tools/list (id: int64:1)
# ❌ tools/call 全部失败
11:03:29.592 INFO mcp server forwarding tool call: get_user -> GET
/api/users/1
11:03:29.593 ERROR Write response failed: http: wrote more than the
declared Content-Length
11:03:29.595 INFO mcp server forwarding tool call: search_users -> GET
/api/users/search
11:03:29.596 ERROR Write response failed: http: wrote more than the
declared Content-Length
11:03:29.600 INFO mcp server forwarding tool call: create_user -> POST
/api/users
11:03:29.601 ERROR Write response failed: http: wrote more than the
declared Content-Length
11:03:29.602 ERROR Write response failed: http: wrote more than the
declared Content-Length ← 出现两次
11:03:29.604 INFO mcp server forwarding tool call: health_check -> GET
/api/health
11:03:29.604 ERROR Write response failed: http: wrote more than the
declared Content-Length
```
**Mock 后端日志**（证明后端**正常接收并处理**了请求）：
```plain
2026/05/08 11:03:29 GET /api/users/1 77.025µs
2026/05/08 11:03:29 GET /api/users/search 43.923µs
2026/05/08 11:03:29 POST /api/users 45.726µs
2026/05/08 11:03:29 GET /api/health 5.931µs
```
**Go 测试输出**：
```plain
=== RUN TestServiceAvailability --- PASS (0.01s)
=== RUN TestMCPInitialize --- PASS (0.00s) ← MCP 初始化正常
=== RUN TestToolsList --- PASS (0.00s) ← 工具列表正常
=== RUN TestGetUser --- FAIL (0.00s) ← tools/call 失败
mcp_test.go:90: Failed to read response: unexpected EOF
=== RUN TestSearchUsers --- FAIL (0.00s)
mcp_test.go:90: Failed to read response: unexpected EOF
=== RUN TestCreateUser --- FAIL (0.01s)
mcp_test.go:90: Failed to read response: unexpected EOF
=== RUN TestHealthCheck --- FAIL (0.00s)
mcp_test.go:90: Failed to read response: unexpected EOF
FAIL
```
**MCP Inspector 日志**：
```plain
Error from MCP server: FetchError: request to http://localhost:8888/mcp
failed, reason: socket hang up
{
type: 'system',
errno: 'ECONNRESET',
code: 'ECONNRESET'
}
```
**初步分析**：
问题定位在 `pkg/common/http/manager.go` 第 139 行的 `writeResponse` 方法。
错误 `http: wrote more than the declared Content-Length` 表明：HTTP
响应体的实际写入字节数超过了 `Content-Length` 头部声明的长度。
请求处理流程：
1. MCP Server filter 收到 `tools/call` JSON-RPC 请求
2. 通过 HTTP proxy 转发到后端 mock server
3. 后端正常返回响应（后端日志确认）
4. Pixiu 尝试将响应包装为 MCP JSON-RPC 格式并写回客户端
5. **Bug**：`Content-Length` 与实际写入的字节数不匹配
可能原因：
- `Content-Length` 按上游原始响应长度计算，但最终返回给客户端的是包装后的 MCP JSON-RPC 响应，长度发生了变化却未更新头部
- 响应体被重复写入
- 缓冲区未正确重置
**关键区别**：`tools/list` 和 `initialize` 不需要代理到后端 HTTP 服务，直接由 MCP filter
处理并返回，因此不会触发 `HttpConnectionManager.handleHTTPRequest` → `writeResponse` 路径。
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