raft/example/web_admin/main.go

package main

import (
	"bufio"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"strings"
	"sync"
)

// Configuration
const (
	TargetTCPAddr = "127.0.0.1:9011"
	WebPort       = ":8088"
)

type APIRequest struct {
	Command string   `json:"command"`
	Args    []string `json:"args"`
}

type APIResponse struct {
	Status string `json:"status"`
	Data   any    `json:"data,omitempty"`
	Error  string `json:"error,omitempty"`
}

// TCPPool implements a simple connection pool
type TCPPool struct {
	mu    sync.Mutex
	conns []net.Conn
	addr  string
}

func NewTCPPool(addr string) *TCPPool {
	return &TCPPool{
		addr:  addr,
		conns: make([]net.Conn, 0),
	}
}

func (p *TCPPool) Get() (net.Conn, error) {
	p.mu.Lock()
	if len(p.conns) > 0 {
		conn := p.conns[len(p.conns)-1]
		p.conns = p.conns[:len(p.conns)-1]
		p.mu.Unlock()
		return conn, nil
	}
	p.mu.Unlock()
	return net.Dial("tcp", p.addr)
}

func (p *TCPPool) Put(conn net.Conn) {
	p.mu.Lock()
	p.conns = append(p.conns, conn)
	p.mu.Unlock()
}

func (p *TCPPool) Discard(conn net.Conn) {
	if conn != nil {
		conn.Close()
	}
}

var pool *TCPPool

func main() {
	// Initialize Connection Pool
	pool = NewTCPPool(TargetTCPAddr)

	// Serve static files (HTML)
	http.HandleFunc("/", handleIndex)

	// API Endpoint
	http.HandleFunc("/api/proxy", handleAPI)

	fmt.Printf("Web Admin started at http://localhost%s\n", WebPort)
	log.Fatal(http.ListenAndServe(WebPort, nil))
}

func handleIndex(w http.ResponseWriter, r *http.Request) {
	if r.URL.Path != "/" {
		http.NotFound(w, r)
		return
	}
	// Serve the embedded HTML directly
	http.ServeFile(w, r, "example/web_admin/index.html")
}

func handleAPI(w http.ResponseWriter, r *http.Request) {
	if r.Method != "POST" {
		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
		return
	}

	// 1. Parse Request
	body, _ := io.ReadAll(r.Body)
	var req APIRequest
	if err := json.Unmarshal(body, &req); err != nil {
		jsonResponse(w, APIResponse{Status: "error", Error: "Invalid JSON"})
		return
	}

	// 2. Get Token from Header
	token := r.Header.Get("X-Session-Token")

	// 3. Connect to TCP (via Pool)
	conn, err := pool.Get()
	if err != nil {
		jsonResponse(w, APIResponse{Status: "error", Error: "Connection failed: 无法连接到后端节点 (127.0.0.1:9011)。请确保 Raft 服务已启动。 (" + err.Error() + ")"})
		return
	}

	// Helper to execute request with retry logic
	execute := func(c net.Conn) error {
		// Set deadline to avoid hanging
		// c.SetDeadline(time.Now().Add(5 * time.Second))

		reader := bufio.NewReader(c)

		// 4. Authenticate if token present (Except for LOGIN command itself)
		if req.Command != "LOGIN" && token != "" {
			fmt.Fprintf(c, "AUTH %s\n", token)
			authResp, err := reader.ReadString('\n')
			if err != nil {
				return err
			}
			if !strings.HasPrefix(authResp, "OK") {
				// Special handling: if auth fails, we return a specific error that is NOT a network error
				// but we still want to return it to the client.
				// However, if we are reusing a connection, maybe the previous session is interfering?
				// AUTH command should override previous session.
				// If it fails here, it means the token is invalid.
				return fmt.Errorf("Session Expired")
			}
		}

		// 5. Construct TCP Command
		cmdStr := req.Command
		if len(req.Args) > 0 {
			cmdStr += " " + strings.Join(req.Args, " ")
		}
		fmt.Fprintf(c, "%s\n", cmdStr)

		// 6. Read TCP Response
		respStr, err := reader.ReadString('\n')
		if err != nil {
			return err
		}
		respStr = strings.TrimSpace(respStr)

		// 7. Parse Response
		if strings.HasPrefix(respStr, "OK") {
			payload := strings.TrimPrefix(respStr, "OK ")
			// If payload looks like JSON, try to parse it
			var jsonData any
			if strings.HasPrefix(payload, "[") || strings.HasPrefix(payload, "{") {
				if err := json.Unmarshal([]byte(payload), &jsonData); err == nil {
					jsonResponse(w, APIResponse{Status: "ok", Data: jsonData})
					return nil
				}
			}
			jsonResponse(w, APIResponse{Status: "ok", Data: payload})
		} else if strings.HasPrefix(respStr, "ERR") {
			errMsg := strings.TrimPrefix(respStr, "ERR ")
			jsonResponse(w, APIResponse{Status: "error", Error: errMsg})
		} else {
			jsonResponse(w, APIResponse{Status: "error", Error: "Unknown response: " + respStr})
		}
		return nil
	}

	// Try with pooled connection
	err = execute(conn)
	if err != nil {
		// If error is "Session Expired", it's a logic error, not network. Don't retry.
		if err.Error() == "Session Expired" {
			pool.Put(conn) // Connection is fine, token is bad
			jsonResponse(w, APIResponse{Status: "error", Error: "Session Expired"})
			return
		}

		// If network error, discard and retry once
		pool.Discard(conn)

		// Retry with new connection
		conn, err = net.Dial("tcp", TargetTCPAddr)
		if err != nil {
			jsonResponse(w, APIResponse{Status: "error", Error: "Connection failed: 无法连接到后端节点 (127.0.0.1:9011)。请确保 Raft 服务已启动。 (" + err.Error() + ")"})
			return
		}

		err = execute(conn)
		if err != nil {
			pool.Discard(conn)
			// Return error to client
			errMsg := err.Error()
			if errMsg != "Session Expired" {
				errMsg = "Connection failed: 无法连接到后端节点。请确保 Raft 服务已启动。 (" + errMsg + ")"
			}
			jsonResponse(w, APIResponse{Status: "error", Error: errMsg})
			return
		}
		// Success on retry
		pool.Put(conn)
	} else {
		// Success on first try
		pool.Put(conn)
	}
}

func jsonResponse(w http.ResponseWriter, resp APIResponse) {
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(resp)
}