go implementation

2025-12-11 16:52:13 +03:00
parent c04ab283a6
commit 8f5b9a5cd1
20 changed files with 4146 additions and 1 deletions
@@ -0,0 +1,320 @@
+// Package proxy provides reverse proxy functionality for Konduktor
+package proxy
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"github.com/konduktor/konduktor/internal/logging"
+)
+
+type Config struct {
+	// Target is the backend server URL
+	Target string
+
+	// Timeout is the request timeout (default: 30s)
+	Timeout time.Duration
+
+	// Headers are additional headers to add to requests
+	Headers map[string]string
+
+	// StripPrefix removes this prefix from the request path
+	StripPrefix string
+
+	// PreserveHost keeps the original Host header
+	PreserveHost bool
+}
+
+type ReverseProxy struct {
+	config     *Config
+	targetURL  *url.URL
+	httpClient *http.Client
+	logger     *logging.Logger
+}
+
+func New(cfg *Config, logger *logging.Logger) (*ReverseProxy, error) {
+	if cfg.Target == "" {
+		return nil, fmt.Errorf("proxy target is required")
+	}
+
+	targetURL, err := url.Parse(cfg.Target)
+	if err != nil {
+		return nil, fmt.Errorf("invalid proxy target URL: %w", err)
+	}
+
+	timeout := cfg.Timeout
+	if timeout == 0 {
+		timeout = 30 * time.Second
+	}
+
+	transport := &http.Transport{
+		Proxy: http.ProxyFromEnvironment,
+		DialContext: (&net.Dialer{
+			Timeout:   10 * time.Second,
+			KeepAlive: 30 * time.Second,
+		}).DialContext,
+		MaxIdleConns:          100,
+		MaxIdleConnsPerHost:   10,
+		IdleConnTimeout:       90 * time.Second,
+		TLSHandshakeTimeout:   10 * time.Second,
+		ExpectContinueTimeout: 1 * time.Second,
+		ResponseHeaderTimeout: timeout,
+	}
+
+	return &ReverseProxy{
+		config:    cfg,
+		targetURL: targetURL,
+		httpClient: &http.Client{
+			Transport: transport,
+			Timeout:   timeout,
+			CheckRedirect: func(req *http.Request, via []*http.Request) error {
+				return http.ErrUseLastResponse // Don't follow redirects
+			},
+		},
+		logger: logger,
+	}, nil
+}
+
+func (rp *ReverseProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	rp.ProxyRequest(w, r, nil)
+}
+
+func (rp *ReverseProxy) ProxyRequest(w http.ResponseWriter, r *http.Request, params map[string]string) {
+	ctx := r.Context()
+
+	// Build target URL
+	targetURL := rp.buildTargetURL(r)
+
+	// Create proxy request
+	proxyReq, err := rp.createProxyRequest(ctx, r, targetURL)
+	if err != nil {
+		rp.handleError(w, http.StatusInternalServerError, "Failed to create proxy request", err)
+		return
+	}
+
+	// Add custom headers with parameter substitution
+	rp.addCustomHeaders(proxyReq, r, params)
+
+	// Execute request
+	resp, err := rp.httpClient.Do(proxyReq)
+	if err != nil {
+		rp.handleProxyError(w, err)
+		return
+	}
+	defer resp.Body.Close()
+
+	// Copy response
+	rp.copyResponse(w, resp)
+}
+
+func (rp *ReverseProxy) buildTargetURL(r *http.Request) *url.URL {
+	targetURL := *rp.targetURL
+
+	// Strip prefix if configured
+	path := r.URL.Path
+	if rp.config.StripPrefix != "" {
+		path = strings.TrimPrefix(path, rp.config.StripPrefix)
+		if path == "" || path[0] != '/' {
+			path = "/" + path
+		}
+	}
+
+	// If target has a path, append request path to it
+	if rp.targetURL.Path != "" && rp.targetURL.Path != "/" {
+		targetURL.Path = singleJoiningSlash(rp.targetURL.Path, path)
+	} else {
+		targetURL.Path = path
+	}
+
+	// Preserve query string
+	targetURL.RawQuery = r.URL.RawQuery
+
+	return &targetURL
+}
+
+func (rp *ReverseProxy) createProxyRequest(ctx context.Context, r *http.Request, targetURL *url.URL) (*http.Request, error) {
+	proxyReq, err := http.NewRequestWithContext(ctx, r.Method, targetURL.String(), r.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	// Copy ContentLength
+	proxyReq.ContentLength = r.ContentLength
+
+	// Copy headers
+	for key, values := range r.Header {
+		for _, value := range values {
+			proxyReq.Header.Add(key, value)
+		}
+	}
+
+	// Set/update Host header
+	if rp.config.PreserveHost {
+		proxyReq.Host = r.Host
+	} else {
+		proxyReq.Host = targetURL.Host
+	}
+
+	// Remove hop-by-hop headers
+	removeHopByHopHeaders(proxyReq.Header)
+
+	return proxyReq, nil
+}
+
+func (rp *ReverseProxy) addCustomHeaders(proxyReq *http.Request, originalReq *http.Request, params map[string]string) {
+	// Add X-Forwarded headers
+	clientIP := getClientIP(originalReq)
+	if prior := originalReq.Header.Get("X-Forwarded-For"); prior != "" {
+		clientIP = prior + ", " + clientIP
+	}
+	proxyReq.Header.Set("X-Forwarded-For", clientIP)
+	proxyReq.Header.Set("X-Forwarded-Proto", getScheme(originalReq))
+	proxyReq.Header.Set("X-Forwarded-Host", originalReq.Host)
+
+	// Add custom headers from config
+	for key, value := range rp.config.Headers {
+		// Substitute parameters like {version}
+		substituted := value
+		for paramKey, paramValue := range params {
+			substituted = strings.ReplaceAll(substituted, "{"+paramKey+"}", paramValue)
+		}
+		// Substitute $remote_addr
+		substituted = strings.ReplaceAll(substituted, "$remote_addr", clientIP)
+		proxyReq.Header.Set(key, substituted)
+	}
+}
+
+func (rp *ReverseProxy) copyResponse(w http.ResponseWriter, resp *http.Response) {
+	// Copy headers
+	for key, values := range resp.Header {
+		for _, value := range values {
+			w.Header().Add(key, value)
+		}
+	}
+
+	// Remove hop-by-hop headers from response
+	removeHopByHopHeaders(w.Header())
+
+	// Write status code
+	w.WriteHeader(resp.StatusCode)
+
+	// Copy body
+	io.Copy(w, resp.Body)
+}
+
+func (rp *ReverseProxy) handleError(w http.ResponseWriter, status int, message string, err error) {
+	if rp.logger != nil {
+		rp.logger.Error(message, "error", err)
+	}
+	http.Error(w, message, status)
+}
+
+func (rp *ReverseProxy) handleProxyError(w http.ResponseWriter, err error) {
+	if rp.logger != nil {
+		rp.logger.Error("Proxy request failed", "error", err)
+	}
+
+	// Check for timeout
+	if err, ok := err.(net.Error); ok && err.Timeout() {
+		http.Error(w, "504 Gateway Timeout", http.StatusGatewayTimeout)
+		return
+	}
+
+	// Check for connection errors
+	if isConnectionError(err) {
+		http.Error(w, "502 Bad Gateway", http.StatusBadGateway)
+		return
+	}
+
+	// Context cancelled (client disconnected)
+	if err == context.Canceled {
+		return
+	}
+
+	http.Error(w, "502 Bad Gateway", http.StatusBadGateway)
+}
+
+// Helper functions
+
+func singleJoiningSlash(a, b string) string {
+	aslash := strings.HasSuffix(a, "/")
+	bslash := strings.HasPrefix(b, "/")
+	switch {
+	case aslash && bslash:
+		return a + b[1:]
+	case !aslash && !bslash:
+		return a + "/" + b
+	}
+	return a + b
+}
+
+func removeHopByHopHeaders(h http.Header) {
+	hopByHopHeaders := []string{
+		"Connection",
+		"Proxy-Connection",
+		"Keep-Alive",
+		"Proxy-Authenticate",
+		"Proxy-Authorization",
+		"Te",
+		"Trailer",
+		"Transfer-Encoding",
+		"Upgrade",
+	}
+
+	for _, header := range hopByHopHeaders {
+		h.Del(header)
+	}
+}
+
+func getClientIP(r *http.Request) string {
+	// Check X-Real-IP first
+	if ip := r.Header.Get("X-Real-IP"); ip != "" {
+		return ip
+	}
+
+	// Get from RemoteAddr
+	host, _, err := net.SplitHostPort(r.RemoteAddr)
+	if err != nil {
+		return r.RemoteAddr
+	}
+	return host
+}
+
+func getScheme(r *http.Request) string {
+	if r.TLS != nil {
+		return "https"
+	}
+	if scheme := r.Header.Get("X-Forwarded-Proto"); scheme != "" {
+		return scheme
+	}
+	return "http"
+}
+
+func isConnectionError(err error) bool {
+	if err == nil {
+		return false
+	}
+
+	errStr := err.Error()
+	connectionErrors := []string{
+		"connection refused",
+		"no such host",
+		"network is unreachable",
+		"connection reset",
+		"broken pipe",
+	}
+
+	for _, connErr := range connectionErrors {
+		if strings.Contains(strings.ToLower(errStr), connErr) {
+			return true
+		}
+	}
+
+	return false
+}
@@ -0,0 +1,747 @@
+package proxy
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+// ============== Test Backend Server ==============
+
+type testBackend struct {
+	server       *httptest.Server
+	requestLog   []requestLogEntry
+	mu           sync.Mutex
+	requestCount int64
+}
+
+type requestLogEntry struct {
+	Method  string
+	Path    string
+	Query   string
+	Headers http.Header
+	Body    string
+}
+
+func newTestBackend(handler http.HandlerFunc) *testBackend {
+	tb := &testBackend{
+		requestLog: make([]requestLogEntry, 0),
+	}
+
+	if handler == nil {
+		handler = tb.defaultHandler
+	}
+
+	tb.server = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		tb.logRequest(r)
+		handler(w, r)
+	}))
+
+	return tb
+}
+
+func (tb *testBackend) logRequest(r *http.Request) {
+	tb.mu.Lock()
+	defer tb.mu.Unlock()
+
+	body, _ := io.ReadAll(r.Body)
+	// Restore the body for the handler
+	r.Body = io.NopCloser(bytes.NewReader(body))
+
+	tb.requestLog = append(tb.requestLog, requestLogEntry{
+		Method:  r.Method,
+		Path:    r.URL.Path,
+		Query:   r.URL.RawQuery,
+		Headers: r.Header.Clone(),
+		Body:    string(body),
+	})
+	atomic.AddInt64(&tb.requestCount, 1)
+}
+
+func (tb *testBackend) defaultHandler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(map[string]interface{}{
+		"message": "Backend response",
+		"path":    r.URL.Path,
+		"method":  r.Method,
+	})
+}
+
+func (tb *testBackend) close() {
+	tb.server.Close()
+}
+
+func (tb *testBackend) URL() string {
+	return tb.server.URL
+}
+
+func (tb *testBackend) getRequestCount() int64 {
+	return atomic.LoadInt64(&tb.requestCount)
+}
+
+func (tb *testBackend) getLastRequest() *requestLogEntry {
+	tb.mu.Lock()
+	defer tb.mu.Unlock()
+	if len(tb.requestLog) == 0 {
+		return nil
+	}
+	return &tb.requestLog[len(tb.requestLog)-1]
+}
+
+// ============== Proxy Creation Tests ==============
+
+func TestNew_ValidConfig(t *testing.T) {
+	cfg := &Config{
+		Target:  "http://localhost:8080",
+		Timeout: 10 * time.Second,
+	}
+
+	proxy, err := New(cfg, nil)
+	if err != nil {
+		t.Fatalf("Failed to create proxy: %v", err)
+	}
+
+	if proxy == nil {
+		t.Fatal("Expected proxy instance")
+	}
+}
+
+func TestNew_EmptyTarget(t *testing.T) {
+	cfg := &Config{
+		Target: "",
+	}
+
+	_, err := New(cfg, nil)
+	if err == nil {
+		t.Error("Expected error for empty target")
+	}
+}
+
+func TestNew_InvalidTargetURL(t *testing.T) {
+	cfg := &Config{
+		Target: "://invalid-url",
+	}
+
+	_, err := New(cfg, nil)
+	if err == nil {
+		t.Error("Expected error for invalid URL")
+	}
+}
+
+func TestNew_DefaultTimeout(t *testing.T) {
+	cfg := &Config{
+		Target: "http://localhost:8080",
+	}
+
+	proxy, err := New(cfg, nil)
+	if err != nil {
+		t.Fatalf("Failed to create proxy: %v", err)
+	}
+
+	if proxy.httpClient.Timeout != 30*time.Second {
+		t.Errorf("Expected default timeout 30s, got %v", proxy.httpClient.Timeout)
+	}
+}
+
+// ============== Basic Proxy Tests ==============
+
+func TestProxy_BasicGET(t *testing.T) {
+	backend := newTestBackend(nil)
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+	req := httptest.NewRequest("GET", "/test", nil)
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Errorf("Expected status 200, got %d", rr.Code)
+	}
+
+	var response map[string]interface{}
+	json.NewDecoder(rr.Body).Decode(&response)
+
+	if response["path"] != "/test" {
+		t.Errorf("Expected path /test, got %v", response["path"])
+	}
+}
+
+func TestProxy_BasicPOST(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		body, _ := io.ReadAll(r.Body)
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(map[string]interface{}{
+			"received": string(body),
+			"method":   r.Method,
+		})
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+	req := httptest.NewRequest("POST", "/api/data", strings.NewReader(`{"key":"value"}`))
+	req.Header.Set("Content-Type", "application/json")
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Errorf("Expected status 200, got %d", rr.Code)
+	}
+
+	var response map[string]interface{}
+	json.NewDecoder(rr.Body).Decode(&response)
+
+	if response["method"] != "POST" {
+		t.Errorf("Expected method POST, got %v", response["method"])
+	}
+}
+
+func TestProxy_PUT(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		json.NewEncoder(w).Encode(map[string]string{"method": r.Method})
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+	req := httptest.NewRequest("PUT", "/resource/123", strings.NewReader(`{"name":"updated"}`))
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	var response map[string]string
+	json.NewDecoder(rr.Body).Decode(&response)
+
+	if response["method"] != "PUT" {
+		t.Errorf("Expected method PUT, got %v", response["method"])
+	}
+}
+
+func TestProxy_DELETE(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		json.NewEncoder(w).Encode(map[string]string{"method": r.Method})
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+	req := httptest.NewRequest("DELETE", "/resource/123", nil)
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	var response map[string]string
+	json.NewDecoder(rr.Body).Decode(&response)
+
+	if response["method"] != "DELETE" {
+		t.Errorf("Expected method DELETE, got %v", response["method"])
+	}
+}
+
+// ============== Header Tests ==============
+
+func TestProxy_HeadersForwarding(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]interface{}{
+			"custom_header":  r.Header.Get("X-Custom-Header"),
+			"forwarded_for":  r.Header.Get("X-Forwarded-For"),
+			"forwarded_host": r.Header.Get("X-Forwarded-Host"),
+		})
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+	req := httptest.NewRequest("GET", "/headers", nil)
+	req.Header.Set("X-Custom-Header", "test-value")
+	req.RemoteAddr = "192.168.1.100:12345"
+	req.Host = "example.com"
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	var response map[string]interface{}
+	json.NewDecoder(rr.Body).Decode(&response)
+
+	if response["custom_header"] != "test-value" {
+		t.Errorf("Expected custom header, got %v", response["custom_header"])
+	}
+
+	if response["forwarded_for"] != "192.168.1.100" {
+		t.Errorf("Expected X-Forwarded-For, got %v", response["forwarded_for"])
+	}
+
+	if response["forwarded_host"] != "example.com" {
+		t.Errorf("Expected X-Forwarded-Host, got %v", response["forwarded_host"])
+	}
+}
+
+func TestProxy_CustomHeaders(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]string{
+			"api_version": r.Header.Get("X-API-Version"),
+		})
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{
+		Target: backend.URL(),
+		Headers: map[string]string{
+			"X-API-Version": "{version}",
+		},
+	}, nil)
+
+	req := httptest.NewRequest("GET", "/api", nil)
+	rr := httptest.NewRecorder()
+
+	// Simulate parameter substitution
+	proxy.ProxyRequest(rr, req, map[string]string{"version": "2"})
+
+	var response map[string]string
+	json.NewDecoder(rr.Body).Decode(&response)
+
+	if response["api_version"] != "2" {
+		t.Errorf("Expected API version 2, got %v", response["api_version"])
+	}
+}
+
+func TestProxy_RemoteAddrSubstitution(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]string{
+			"client_ip": r.Header.Get("X-Client-IP"),
+		})
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{
+		Target: backend.URL(),
+		Headers: map[string]string{
+			"X-Client-IP": "$remote_addr",
+		},
+	}, nil)
+
+	req := httptest.NewRequest("GET", "/api", nil)
+	req.RemoteAddr = "10.0.0.1:54321"
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	var response map[string]string
+	json.NewDecoder(rr.Body).Decode(&response)
+
+	if response["client_ip"] != "10.0.0.1" {
+		t.Errorf("Expected client IP 10.0.0.1, got %v", response["client_ip"])
+	}
+}
+
+// ============== Query String Tests ==============
+
+func TestProxy_QueryStringPreservation(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]string{
+			"query": r.URL.RawQuery,
+			"param": r.URL.Query().Get("key"),
+		})
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+	req := httptest.NewRequest("GET", "/search?key=value&page=2", nil)
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	var response map[string]string
+	json.NewDecoder(rr.Body).Decode(&response)
+
+	if response["param"] != "value" {
+		t.Errorf("Expected query param 'value', got %v", response["param"])
+	}
+}
+
+// ============== Status Code Tests ==============
+
+func TestProxy_StatusCodePreservation(t *testing.T) {
+	statusCodes := []int{200, 201, 400, 404, 500}
+
+	for _, code := range statusCodes {
+		code := code // capture range variable
+		t.Run(fmt.Sprintf("Status_%d", code), func(t *testing.T) {
+			backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(code)
+				w.Write([]byte("OK"))
+			})
+			defer backend.close()
+
+			proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+			req := httptest.NewRequest("GET", "/status", nil)
+			rr := httptest.NewRecorder()
+
+			proxy.ServeHTTP(rr, req)
+
+			if rr.Code != code {
+				t.Errorf("Expected status %d, got %d", code, rr.Code)
+			}
+		})
+	}
+}
+
+// ============== Error Handling Tests ==============
+
+func TestProxy_BackendUnavailable(t *testing.T) {
+	// Use a port that's definitely not listening
+	proxy, _ := New(&Config{
+		Target:  "http://127.0.0.1:59999",
+		Timeout: 1 * time.Second,
+	}, nil)
+
+	req := httptest.NewRequest("GET", "/test", nil)
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusBadGateway {
+		t.Errorf("Expected status 502 Bad Gateway, got %d", rr.Code)
+	}
+}
+
+func TestProxy_Timeout(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		time.Sleep(2 * time.Second)
+		w.Write([]byte("OK"))
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{
+		Target:  backend.URL(),
+		Timeout: 100 * time.Millisecond,
+	}, nil)
+
+	req := httptest.NewRequest("GET", "/slow", nil)
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusGatewayTimeout {
+		t.Errorf("Expected status 504 Gateway Timeout, got %d", rr.Code)
+	}
+}
+
+// ============== Path Handling Tests ==============
+
+func TestProxy_StripPrefix(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]string{
+			"path": r.URL.Path,
+		})
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{
+		Target:      backend.URL(),
+		StripPrefix: "/api/v1",
+	}, nil)
+
+	req := httptest.NewRequest("GET", "/api/v1/users", nil)
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	var response map[string]string
+	json.NewDecoder(rr.Body).Decode(&response)
+
+	if response["path"] != "/users" {
+		t.Errorf("Expected stripped path /users, got %v", response["path"])
+	}
+}
+
+func TestProxy_TargetWithPath(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]string{
+			"path": r.URL.Path,
+		})
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{
+		Target: backend.URL() + "/backend",
+	}, nil)
+
+	req := httptest.NewRequest("GET", "/resource", nil)
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	var response map[string]string
+	json.NewDecoder(rr.Body).Decode(&response)
+
+	if response["path"] != "/backend/resource" {
+		t.Errorf("Expected path /backend/resource, got %v", response["path"])
+	}
+}
+
+// ============== Large Body Tests ==============
+
+func TestProxy_LargeRequestBody(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		body, _ := io.ReadAll(r.Body)
+		json.NewEncoder(w).Encode(map[string]int{
+			"received_bytes": len(body),
+		})
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+	// 100KB body
+	largeBody := strings.Repeat("x", 100000)
+	req := httptest.NewRequest("POST", "/upload", strings.NewReader(largeBody))
+	req.ContentLength = int64(len(largeBody))
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	var response map[string]int
+	json.NewDecoder(rr.Body).Decode(&response)
+
+	if response["received_bytes"] != 100000 {
+		t.Errorf("Expected 100000 bytes, got %d", response["received_bytes"])
+	}
+}
+
+func TestProxy_LargeResponseBody(t *testing.T) {
+	largeResponse := strings.Repeat("y", 100000)
+
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte(largeResponse))
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+	req := httptest.NewRequest("GET", "/large", nil)
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	if rr.Body.Len() != 100000 {
+		t.Errorf("Expected 100000 bytes in response, got %d", rr.Body.Len())
+	}
+}
+
+// ============== Concurrent Requests Tests ==============
+
+func TestProxy_ConcurrentRequests(t *testing.T) {
+	backend := newTestBackend(nil)
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+	const numRequests = 50
+	var wg sync.WaitGroup
+	errors := make(chan error, numRequests)
+
+	for i := 0; i < numRequests; i++ {
+		wg.Add(1)
+		go func(n int) {
+			defer wg.Done()
+
+			req := httptest.NewRequest("GET", "/concurrent", nil)
+			rr := httptest.NewRecorder()
+
+			proxy.ServeHTTP(rr, req)
+
+			if rr.Code != http.StatusOK {
+				errors <- &net.OpError{Op: "test", Err: context.DeadlineExceeded}
+			}
+		}(i)
+	}
+
+	wg.Wait()
+	close(errors)
+
+	errorCount := 0
+	for range errors {
+		errorCount++
+	}
+
+	if errorCount > 0 {
+		t.Errorf("Got %d errors in concurrent requests", errorCount)
+	}
+
+	if backend.getRequestCount() != numRequests {
+		t.Errorf("Expected %d requests at backend, got %d", numRequests, backend.getRequestCount())
+	}
+}
+
+// ============== Echo Tests ==============
+
+func TestProxy_Echo(t *testing.T) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		body, _ := io.ReadAll(r.Body)
+		w.Header().Set("Content-Type", r.Header.Get("Content-Type"))
+		w.Write(body)
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+	testData := "Hello, Proxy!"
+	req := httptest.NewRequest("POST", "/echo", strings.NewReader(testData))
+	req.Header.Set("Content-Type", "text/plain")
+	rr := httptest.NewRecorder()
+
+	proxy.ServeHTTP(rr, req)
+
+	if rr.Body.String() != testData {
+		t.Errorf("Expected echo of '%s', got '%s'", testData, rr.Body.String())
+	}
+
+	if rr.Header().Get("Content-Type") != "text/plain" {
+		t.Errorf("Expected Content-Type text/plain, got %s", rr.Header().Get("Content-Type"))
+	}
+}
+
+// ============== Helper Function Tests ==============
+
+func TestSingleJoiningSlash(t *testing.T) {
+	tests := []struct {
+		a, b, expected string
+	}{
+		{"/api", "/users", "/api/users"},
+		{"/api/", "/users", "/api/users"},
+		{"/api", "users", "/api/users"},
+		{"/api/", "users", "/api/users"},
+		{"", "/users", "/users"},
+		{"/api", "", "/api/"},
+	}
+
+	for _, tt := range tests {
+		result := singleJoiningSlash(tt.a, tt.b)
+		if result != tt.expected {
+			t.Errorf("singleJoiningSlash(%q, %q) = %q, want %q", tt.a, tt.b, result, tt.expected)
+		}
+	}
+}
+
+func TestGetClientIP(t *testing.T) {
+	tests := []struct {
+		remoteAddr string
+		xRealIP    string
+		expected   string
+	}{
+		{"192.168.1.1:1234", "", "192.168.1.1"},
+		{"192.168.1.1:1234", "10.0.0.1", "10.0.0.1"},
+		{"invalid", "", "invalid"},
+	}
+
+	for _, tt := range tests {
+		req := httptest.NewRequest("GET", "/", nil)
+		req.RemoteAddr = tt.remoteAddr
+		if tt.xRealIP != "" {
+			req.Header.Set("X-Real-IP", tt.xRealIP)
+		}
+
+		result := getClientIP(req)
+		if result != tt.expected {
+			t.Errorf("getClientIP() = %q, want %q", result, tt.expected)
+		}
+	}
+}
+
+func TestGetScheme(t *testing.T) {
+	tests := []struct {
+		name     string
+		tls      bool
+		header   string
+		expected string
+	}{
+		{"HTTP", false, "", "http"},
+		{"HTTPS from TLS", true, "", "https"},
+		{"HTTPS from header", false, "https", "https"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			req := httptest.NewRequest("GET", "/", nil)
+			if tt.header != "" {
+				req.Header.Set("X-Forwarded-Proto", tt.header)
+			}
+			// Note: httptest doesn't set TLS, so we can only test non-TLS cases fully
+
+			result := getScheme(req)
+			if !tt.tls && result != tt.expected {
+				t.Errorf("getScheme() = %q, want %q", result, tt.expected)
+			}
+		})
+	}
+}
+
+func TestIsConnectionError(t *testing.T) {
+	tests := []struct {
+		err      error
+		expected bool
+	}{
+		{nil, false},
+		{&net.OpError{Op: "dial", Err: &net.DNSError{Err: "no such host"}}, true},
+		{context.DeadlineExceeded, false},
+	}
+
+	for _, tt := range tests {
+		result := isConnectionError(tt.err)
+		if result != tt.expected {
+			t.Errorf("isConnectionError(%v) = %v, want %v", tt.err, result, tt.expected)
+		}
+	}
+}
+
+// ============== Benchmarks ==============
+
+func BenchmarkProxy_SimpleGET(b *testing.B) {
+	backend := newTestBackend(nil)
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		req := httptest.NewRequest("GET", "/bench", nil)
+		rr := httptest.NewRecorder()
+		proxy.ServeHTTP(rr, req)
+	}
+}
+
+func BenchmarkProxy_POSTWithBody(b *testing.B) {
+	backend := newTestBackend(func(w http.ResponseWriter, r *http.Request) {
+		io.Copy(io.Discard, r.Body)
+		w.WriteHeader(http.StatusOK)
+	})
+	defer backend.close()
+
+	proxy, _ := New(&Config{Target: backend.URL()}, nil)
+	body := strings.Repeat("x", 1024) // 1KB body
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		req := httptest.NewRequest("POST", "/bench", strings.NewReader(body))
+		rr := httptest.NewRecorder()
+		proxy.ServeHTTP(rr, req)
+	}
+}