fix incorrect config key

README.md

@@ -2,41 +2,58 @@
 
 _A round-robin load balancer for HTTP proxies._
 
-This is a simple proxy load balancer that will route requests to a cluster of proxy backends in a round-robin fashion. This makes it easy to connect your clients to a large number of proxy servers without worrying about implementing anything special clientside.
+This is a simple proxy load balancer that will route requests to a cluster of proxy backends in a round-robin fashion.
+This makes it easy to connect your clients to a large number of proxy servers without worrying about implementing
+anything special client-side.
 
-This proxy server will transparently forward HTTPS requests without terminating them, meaning a self-signed certificate is not required. Downstream HTTPS proxy servers are not supported.
+This proxy server will transparently forward HTTPS requests without terminating them, meaning a self-signed certificate
+is not required. Downstream HTTPS proxy servers are not supported.
 
 Memory usage sits at around 25M under load.
 
 ## Install
 
-1.  Download the latest release from [/releases](https://git.evulid.cc/cyberes/proxy-loadbalancer/releases) or run `./build.sh` to build the program locally.
+1. Download the latest release from [/releases](https://git.evulid.cc/cyberes/proxy-loadbalancer/releases) or
-2.  `cp config.example.yml config.yml`
+   run `./build.sh` to build the program locally.
-3.  Edit the config.
+2. `cp config.example.yml config.yml`
-4.  Start the loadbalancer with `./proxy-loadbalancer --config [path to your config.yml]`
+3. Edit the config.
+4. Start the loadbalancer with `./proxy-loadbalancer --config [path to your config.yml]`
+
+The load balancer has experimental support for using [curl-impersonate](https://github.com/lwthiker/curl-impersonate) to masquerade as the Chrome browser when
+performing proxy checks.
+
+1. Download `*.x86_64-linux-gnu.tar.gz ` from https://github.com/lwthiker/curl-impersonate/releases
+2. Set `proxy_check_impersonate_chrome: true`
+3. Enter the path to the `curl_chrome116` binary in `proxy_check_impersonate_chrome_binary`
 
 ## Use
 
-You can run your own "public IP delivery server" `canihazip` <https://git.evulid.cc/cyberes/canihazip> or use the default `api.ipify.org`
+You can run your own "public IP delivery server" `canihazip` <https://git.evulid.cc/cyberes/canihazip> or use the
+default `api.ipify.org`
 
 An example systemd service `loadbalancer.service` is provided.
 
 The server displays health, stats, info at `/json`.
 
+Use `--log-third-party-test-failures` along with `--debug` when you want extra info on the third-party proxy tests. This
+can get very noisy if you have lots of third-party proxies so it's hidden behind an extra flag.
+
 ```
 === Proxy Load Balancer ===
-Usage of ./proxy-loadbalancer:
+Usage of /tmp/go-build1714785557/b001/exe/proxy-loadbalancer:
   --config [string]
-               Path to the config file
+        Path to the config file
-  -d, --debug  
+  -d, --debug
-               Enable debug mode
+        Enable debug mode
-  --v          Print version and exit
+  -l, --log-third-party-test-failures
-  -h, --help   Print this help message
+        Log third-party test debug info
+  -v    Print version and exit
 ```
 
 ## Special Headers
 
 The load balancer accepts special headers to control its behavior:
 
--   `Thirdparty-Bypass`: don't use any third-party endpoints for this request.
+- `Thirdparty-Bypass`: don't use any third-party endpoints for this request.
--   `Thirdparty-Include-Broken`: use all online endpoints for this request, including third-party ones that failed the special test.
+- `Thirdparty-Include-Broken`: use all online endpoints for this request, including third-party ones that failed the
+  special test.

config.example.yml

@@ -1,17 +1,25 @@
 # Port to run on.
-http_port:                 9000
+http_port:                             9000
 
 # How many proxies will be checked at once?
-proxy_checkers:            50
+proxy_checkers:                        50
 
 # The interval between proxy checks in seconds.
-proxy_check_interval:      60
+proxy_check_interval:                  60
 
 # URL to get a proxy's IP.
-ip_checker_url:            https://api.ipify.org
+ip_checker_url:                        https://api.ipify.org
 
 # Connection timeout for the proxies in seconds.
-proxy_connect_timeout:     60
+proxy_connect_timeout:                 60
+
+# How many times to retry a proxy connection.
+# On each retry a new proxy will be chosen.
+proxy_connect_retries:                   3
+
+# Use `curl-impersonate` to pretend to be Chrome when testing proxies.
+proxy_check_impersonate_chrome:        false
+proxy_check_impersonate_chrome_binary: ./curl_chrome116
 
 # Your proxies.
 proxy_pool_ours:
@@ -34,7 +42,7 @@ thirdparty_bypass_domains:
 
 # Shuffle the proxy lists whenever the background thread refreshes them.
 # If false, round-robin on default order.
-shuffle_proxies:           false
+shuffle_proxies:                       false
 
 # Don't allow requests to these domains through the proxy.
 blocked_domains:
@@ -43,4 +51,4 @@ blocked_domains:
 # Resolve specific domains through specific proxies.
 # Proxies here are not validated.
 resolve_through:
-  github.com:              http://1.2.3.4:3128
+  github.com:                          http://1.2.3.4:3128

src/config/config.go

@@ -2,7 +2,10 @@ package config
 
 import (
 	"errors"
+	"fmt"
 	"github.com/spf13/viper"
+	"os"
+	"os/exec"
 	"time"
 )
 
@@ -10,18 +13,21 @@ import (
 var cfg *Config
 
 type Config struct {
-	HTTPPort                string
+	HTTPPort                          string
-	IpCheckerURL            string
+	IpCheckerURL                      string
-	MaxProxyCheckers        int
+	MaxProxyCheckers                  int
-	ProxyConnectTimeout     time.Duration
+	ProxyConnectTimeout               time.Duration
-	ProxyPoolOurs           []string
+	ProxyPoolOurs                     []string
-	ProxyPoolThirdparty     []string
+	ProxyPoolThirdparty               []string
-	ThirdpartyTestUrls      []string
+	ThirdpartyTestUrls                []string
-	ThirdpartyBypassDomains []string
+	ThirdpartyBypassDomains           []string
-	ShuffleProxies          bool
+	ShuffleProxies                    bool
-	BlockedDomains          []string
+	BlockedDomains                    []string
-	ResolveThrough          map[string]string
+	ResolveThrough                    map[string]string
-	ProxyCheckInterval      int
+	ProxyCheckInterval                int
+	ProxyCheckImpersonateChrome       bool
+	ProxyCheckImpersonateChromeBinary string
+	ProxyConnectRetries               int
 }
 
 func SetConfig(configFile string) (*Config, error) {
@@ -42,6 +48,9 @@ func SetConfig(configFile string) (*Config, error) {
 	viper.SetDefault("blocked_domains", make([]string, 0))
 	viper.SetDefault("resolve_through", make(map[string]string))
 	viper.SetDefault("proxy_check_interval", 60)
+	viper.SetDefault("proxy_check_impersonate_chrome", false)
+	viper.SetDefault("proxy_check_impersonate_chrome_binary", nil)
+	viper.SetDefault("proxy_connect_retries", 3)
 
 	err := viper.ReadInConfig()
 	if err != nil {
@@ -49,17 +58,20 @@ func SetConfig(configFile string) (*Config, error) {
 	}
 
 	config := &Config{
-		HTTPPort:                viper.GetString("http_port"),
+		HTTPPort:                          viper.GetString("http_port"),
-		IpCheckerURL:            viper.GetString("ip_checker_url"),
+		IpCheckerURL:                      viper.GetString("ip_checker_url"),
-		MaxProxyCheckers:        viper.GetInt("proxy_checkers"),
+		MaxProxyCheckers:                  viper.GetInt("proxy_checkers"),
-		ProxyPoolOurs:           viper.GetStringSlice("proxy_pool_ours"),
+		ProxyPoolOurs:                     viper.GetStringSlice("proxy_pool_ours"),
-		ProxyPoolThirdparty:     viper.GetStringSlice("proxy_pool_thirdparty"),
+		ProxyPoolThirdparty:               viper.GetStringSlice("proxy_pool_thirdparty"),
-		ThirdpartyTestUrls:      viper.GetStringSlice("thirdparty_test_urls"),
+		ThirdpartyTestUrls:                viper.GetStringSlice("thirdparty_test_urls"),
-		ThirdpartyBypassDomains: viper.GetStringSlice("thirdparty_bypass_domains"),
+		ThirdpartyBypassDomains:           viper.GetStringSlice("thirdparty_bypass_domains"),
-		ShuffleProxies:          viper.GetBool("shuffle_proxies"),
+		ShuffleProxies:                    viper.GetBool("shuffle_proxies"),
-		BlockedDomains:          viper.GetStringSlice("blocked_domains"),
+		BlockedDomains:                    viper.GetStringSlice("blocked_domains"),
-		ResolveThrough:          viper.GetStringMapString("resolve_through"),
+		ResolveThrough:                    viper.GetStringMapString("resolve_through"),
-		ProxyCheckInterval:      viper.GetInt("proxy_check_interval"),
+		ProxyCheckInterval:                viper.GetInt("proxy_check_interval"),
+		ProxyCheckImpersonateChrome:       viper.GetBool("proxy_check_impersonate_chrome"),
+		ProxyCheckImpersonateChromeBinary: viper.GetString("proxy_check_impersonate_chrome_binary"),
+		ProxyConnectRetries:               viper.GetInt("proxy_connect_retries"),
 	}
 
 	if len(config.ProxyPoolOurs) == 0 && len(config.ProxyPoolThirdparty) == 0 {
@@ -86,6 +98,21 @@ func SetConfig(configFile string) (*Config, error) {
 		return nil, proxyPoolThirdpartyErr
 	}
 
+	if config.ProxyCheckImpersonateChrome {
+		if _, err := os.Stat(config.ProxyCheckImpersonateChromeBinary); os.IsNotExist(err) {
+			return nil, errors.New(fmt.Sprintf(`curl-impersonate-chrome binary does not exist: "%s"`, config.ProxyCheckImpersonateChromeBinary))
+		}
+		cmd := exec.Command(config.ProxyCheckImpersonateChromeBinary, "--help")
+		err = cmd.Run()
+		if err != nil {
+			return nil, errors.New(fmt.Sprintf(`curl-impersonate-chrome binary failed to run: %s`, err))
+		}
+	}
+
+	if config.ProxyConnectRetries <= 0 {
+		return nil, errors.New("proxy_connect_retries must be greater than 0")
+	}
+
 	cfg = config
 	return config, nil
 }

src/config/flags.go

@@ -0,0 +1,27 @@
+package config
+
+import "flag"
+
+var CliArgs *CliConfig
+
+type CliConfig struct {
+	ConfigFile        string
+	Debug             bool
+	Help              bool
+	Version           bool
+	LogThirdPartyTest bool
+}
+
+func ParseArgs() {
+	if CliArgs != nil {
+		panic("already defined")
+	}
+	CliArgs = &CliConfig{}
+	flag.StringVar(&CliArgs.ConfigFile, "config", "", "Path to the config file")
+	flag.BoolVar(&CliArgs.Debug, "d", false, "Enable debug mode")
+	flag.BoolVar(&CliArgs.Debug, "debug", false, "Enable debug mode")
+	flag.BoolVar(&CliArgs.Debug, "l", false, "Log third-party test debug info")
+	flag.BoolVar(&CliArgs.Debug, "log-third-party-test-failures", false, "Log third-party test debug info")
+	flag.BoolVar(&CliArgs.Version, "v", false, "Print version and exit")
+	flag.Parse()
+}

src/proxy-loadbalancer.go

@@ -13,26 +13,17 @@ import (
 	"runtime/debug"
 )
 
-type cliConfig struct {
-	configFile         string
-	initialCrawl       bool
-	debug              bool
-	disableElasticSync bool
-	help               bool
-	version            bool
-}
-
 var Version = "development"
 var VersionDate = "not set"
 
 func main() {
 	fmt.Println("=== Proxy Load Balancer ===")
-	cliArgs := parseArgs()
+	config.ParseArgs()
-	if cliArgs.help {
+	if config.CliArgs.Help {
 		flag.Usage()
 		os.Exit(0)
 	}
-	if cliArgs.version {
+	if config.CliArgs.Version {
 		buildInfo, ok := debug.ReadBuildInfo()
 
 		if ok {
@@ -51,7 +42,7 @@ func main() {
 		os.Exit(0)
 	}
 
-	if cliArgs.debug {
+	if config.CliArgs.Debug {
 		logging.InitLogger(logrus.DebugLevel)
 	} else {
 		logging.InitLogger(logrus.InfoLevel)
@@ -59,7 +50,7 @@ func main() {
 	log := logging.GetLogger()
 	log.Debugln("Initializing...")
 
-	if cliArgs.configFile == "" {
+	if config.CliArgs.ConfigFile == "" {
 		exePath, err := os.Executable()
 		if err != nil {
 			panic(err)
@@ -70,20 +61,24 @@ func main() {
 			if _, err := os.Stat(filepath.Join(exeDir, "config.yaml")); err == nil {
 				log.Fatalln("Both config.yml and config.yaml exist in the executable directory. Please specify one with the --config flag.")
 			}
-			cliArgs.configFile = filepath.Join(exeDir, "config.yml")
+			config.CliArgs.ConfigFile = filepath.Join(exeDir, "config.yml")
 		} else if _, err := os.Stat(filepath.Join(exeDir, "config.yaml")); err == nil {
-			cliArgs.configFile = filepath.Join(exeDir, "config.yaml")
+			config.CliArgs.ConfigFile = filepath.Join(exeDir, "config.yaml")
 		} else {
 			log.Fatalln("No config file found in the executable directory. Please provide one with the --config flag.")
 		}
 	}
-	configData, err := config.SetConfig(cliArgs.configFile)
+	configData, err := config.SetConfig(config.CliArgs.ConfigFile)
 	if err != nil {
 		log.Fatalf(`Failed to load config: %s`, err)
 	}
 
 	log.Debugf(`Proxy check interval: %d sec`, config.GetConfig().ProxyCheckInterval)
 
+	if config.GetConfig().ProxyCheckImpersonateChrome {
+		log.Debugf(`Using curl-impersonate binary: %s`, config.GetConfig().ProxyCheckImpersonateChromeBinary)
+	}
+
 	proxyCluster := proxy.NewForwardProxyCluster()
 	go func() {
 		log.Fatal(http.ListenAndServe(":"+configData.HTTPPort, proxyCluster))
@@ -96,13 +91,3 @@ func main() {
 
 	select {}
 }
-
-func parseArgs() cliConfig {
-	var cliArgs cliConfig
-	flag.StringVar(&cliArgs.configFile, "config", "", "Path to the config file")
-	flag.BoolVar(&cliArgs.debug, "d", false, "Enable debug mode")
-	flag.BoolVar(&cliArgs.debug, "debug", false, "Enable debug mode")
-	flag.BoolVar(&cliArgs.version, "v", false, "Print version and exit")
-	flag.Parse()
-	return cliArgs
-}

src/proxy/checkProxy.go

@@ -1,11 +1,17 @@
 package proxy
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"main/config"
 	"net/http"
 	"net/url"
+	"os"
+	"os/exec"
+	"regexp"
+	"strconv"
+	"strings"
 )
 
 func sendRequestThroughProxy(pxy string, targetURL string) (string, error) {
@@ -17,43 +23,128 @@ func sendRequestThroughProxy(pxy string, targetURL string) (string, error) {
 	if proxyUser != "" && proxyPass != "" {
 		parsedProxyUrl.User = url.UserPassword(proxyUser, proxyPass)
 	}
-	transport := &http.Transport{
-		Proxy: http.ProxyURL(parsedProxyUrl),
-	}
-	client := &http.Client{
-		Transport: transport,
-		Timeout:   config.GetConfig().ProxyConnectTimeout,
-	}
 
-	req, err := http.NewRequest("GET", targetURL, nil)
+	if !config.GetConfig().ProxyCheckImpersonateChrome {
-	if err != nil {
+		transport := &http.Transport{
-		return "", err
+			Proxy: http.ProxyURL(parsedProxyUrl),
-	}
+		}
+		client := &http.Client{
+			Transport: transport,
+			Timeout:   config.GetConfig().ProxyConnectTimeout,
+		}
 
-	req.Header.Set("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7")
+		req, err := http.NewRequest("GET", targetURL, nil)
-	req.Header.Set("Accept-Language", "en-US,en;q=0.9")
-	req.Header.Set("Priority", "u=0, i")
-	req.Header.Set("Sec-Ch-Ua", `"Chromium";v="124", "Google Chrome";v="124", "Not-A.Brand";v="99"`)
-	req.Header.Set("Sec-Ch-Ua-Mobile", "?0")
-	req.Header.Set("Sec-Ch-Ua-Platform", `"Windows"`)
-	req.Header.Set("Sec-Fetch-Dest", "document")
-	req.Header.Set("Sec-Fetch-Mode", "navigate")
-	req.Header.Set("Sec-Fetch-Site", "cross-site")
-	req.Header.Set("Sec-Fetch-User", "?1")
-	req.Header.Set("Upgrade-Insecure-Requests", "1")
-	req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36")
-
-	resp, err := client.Do(req)
-	if err != nil {
-		return "", err
-	}
-	defer resp.Body.Close()
-	if resp.StatusCode == http.StatusOK {
-		bodyBytes, err := io.ReadAll(resp.Body)
 		if err != nil {
 			return "", err
 		}
-		return string(bodyBytes), nil
+
+		req.Header.Set("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7")
+		req.Header.Set("Accept-Language", "en-US,en;q=0.9")
+		req.Header.Set("Priority", "u=0, i")
+		req.Header.Set("Sec-Ch-Ua", `Chromium";v="116", "Not)A;Brand";v="24", "Google Chrome";v="116"`)
+		req.Header.Set("Sec-Ch-Ua-Mobile", "?0")
+		req.Header.Set("Sec-Ch-Ua-Platform", `"Windows"`)
+		req.Header.Set("Sec-Fetch-Dest", "document")
+		req.Header.Set("Sec-Fetch-Mode", "navigate")
+		req.Header.Set("Sec-Fetch-Site", "none")
+		req.Header.Set("Sec-Fetch-User", "?1")
+		req.Header.Set("Upgrade-Insecure-Requests", "1")
+		req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/116.0.0.0 Safari/537.36")
+
+		resp, err := client.Do(req)
+		if err != nil {
+			return "", err
+		}
+		defer resp.Body.Close()
+		if resp.StatusCode == http.StatusOK {
+			bodyBytes, err := io.ReadAll(resp.Body)
+			if err != nil {
+				return "", err
+			}
+			return string(bodyBytes), nil
+		}
+		return "", fmt.Errorf("bad response code %d", resp.StatusCode)
+	} else {
+		tmpfile, err := os.CreateTemp("", "response")
+		if err != nil {
+			log.Fatal(err)
+		}
+		defer os.Remove(tmpfile.Name()) // clean up
+
+		cmd := exec.Command(
+			config.GetConfig().ProxyCheckImpersonateChromeBinary,
+			"--proxy",
+			parsedProxyUrl.String(),
+			"-o",
+			tmpfile.Name(),
+			"-w",
+			"%{http_code}",
+			"--ciphers",
+			"TLS_AES_128_GCM_SHA256,TLS_AES_256_GCM_SHA384,TLS_CHACHA20_POLY1305_SHA256,ECDHE-ECDSA-AES128-GCM-SHA256,ECDHE-RSA-AES128-GCM-SHA256,ECDHE-ECDSA-AES256-GCM-SHA384,ECDHE-RSA-AES256-GCM-SHA384,ECDHE-ECDSA-CHACHA20-POLY1305,ECDHE-RSA-CHACHA20-POLY1305,ECDHE-RSA-AES128-SHA,ECDHE-RSA-AES256-SHA,AES128-GCM-SHA256,AES256-GCM-SHA384,AES128-SHA,AES256-SHA",
+			"-H",
+			`sec-ch-ua: "Chromium";v="116", "Not)A;Brand";v="24", "Google Chrome";v="116"`,
+			"-H",
+			`sec-ch-ua-mobile: ?0`,
+			"-H",
+			`sec-ch-ua-platform: "Windows"`,
+			"-H",
+			`Upgrade-Insecure-Requests: 1`,
+			"-H",
+			`User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/116.0.0.0 Safari/537.36`,
+			"-H",
+			`Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7`,
+			"-H",
+			`Sec-Fetch-Site: none`,
+			"-H",
+			`Sec-Fetch-Mode: navigate`,
+			"-H",
+			`Sec-Fetch-User: ?1`,
+			"-H",
+			`Sec-Fetch-Dest: document`,
+			"-H",
+			`Accept-Encoding: gzip, deflate, br`,
+			"-H",
+			`Accept-Language: en-US,en;q=0.9`,
+			"--http2",
+			"--http2-no-server-push",
+			"--compressed",
+			"--tlsv1.2",
+			"--alps",
+			"--tls-permute-extensions",
+			"--cert-compression",
+			"brotli",
+			targetURL,
+		)
+
+		output, err := cmd.Output()
+		if err != nil {
+			var exitError *exec.ExitError
+			if errors.As(err, &exitError) {
+				return "", fmt.Errorf("command exited with code %d: %s", exitError.ExitCode(), exitError.Stderr)
+			}
+			return "", err
+		}
+
+		outputStr := strings.TrimSpace(string(output))
+		match, _ := regexp.MatchString(`^\d{3}$`, outputStr)
+		if !match {
+			return "", fmt.Errorf("unexpected output from curl command: %s", outputStr)
+		}
+
+		statusCode, err := strconv.Atoi(outputStr)
+		if err != nil {
+			return "", err
+		}
+
+		if statusCode != http.StatusOK {
+			return "", fmt.Errorf("bad response code %d", statusCode)
+		}
+
+		body, err := os.ReadFile(tmpfile.Name())
+		if err != nil {
+			return "", err
+		}
+
+		return string(body), nil
 	}
-	return "", fmt.Errorf("bad response code %d", resp.StatusCode)
 }

src/proxy/handleConnect.go

@@ -90,7 +90,6 @@ func (p *ForwardProxyCluster) validateRequestAndGetProxy(w http.ResponseWriter,
 	}
 
 	return selectedProxy, proxyUser, proxyPass, proxyHost, parsedProxyUrl, nil
-
 }
 
 func (p *ForwardProxyCluster) proxyHttpConnect(w http.ResponseWriter, req *http.Request) {
@@ -98,7 +97,6 @@ func (p *ForwardProxyCluster) proxyHttpConnect(w http.ResponseWriter, req *http.
 	remoteAddr, _, _ := net.SplitHostPort(req.RemoteAddr)
 	_, proxyUser, proxyPass, proxyHost, parsedProxyUrl, err := p.validateRequestAndGetProxy(w, req)
 	if err != nil {
-		// Error has already been handled, just log and return.
 		if proxyHost == "" {
 			proxyHost = "none"
 		}
@@ -106,7 +104,6 @@ func (p *ForwardProxyCluster) proxyHttpConnect(w http.ResponseWriter, req *http.
 		return
 	}
 
-	// Variables for later
 	var returnCode *int
 	returnCode = new(int)
 	*returnCode = -1
@@ -136,18 +133,25 @@ func (p *ForwardProxyCluster) proxyHttpConnect(w http.ResponseWriter, req *http.
 	copyHeader(proxyReq.Header, req.Header)
 	proxyReq.Header.Set("X-Forwarded-For", req.RemoteAddr)
 
-	resp, err := client.Do(proxyReq)
+	for i := 0; i < config.GetConfig().ProxyConnectRetries; i++ { // Retry mechanic
-	if err != nil {
+		resp, err := client.Do(proxyReq)
-		*errorMsg = fmt.Sprintf(`Failed to execute %s request to "%s": %s`, req.Method, req.URL.String(), err)
+		if err != nil {
-		http.Error(w, "failed to execute request to downstream", http.StatusServiceUnavailable)
+			*errorMsg = fmt.Sprintf(`Failed to execute %s request to "%s" - attempt %d/%d - %s`, req.Method, req.URL.String(), i+1, config.GetConfig().ProxyConnectRetries, err)
-		return
+			if i < config.GetConfig().ProxyConnectRetries-1 {
+				continue
+			} else {
+				http.Error(w, "failed to execute request to downstream", http.StatusServiceUnavailable)
+				return
+			}
+		} else {
+			defer resp.Body.Close()
+			*returnCode = resp.StatusCode
+			copyHeader(w.Header(), resp.Header)
+			w.WriteHeader(resp.StatusCode)
+			io.Copy(w, resp.Body)
+			break
+		}
 	}
-	defer resp.Body.Close()
-	*returnCode = resp.StatusCode
-
-	copyHeader(w.Header(), resp.Header)
-	w.WriteHeader(resp.StatusCode)
-	io.Copy(w, resp.Body)
 }
 
 func (p *ForwardProxyCluster) proxyHttpsConnect(w http.ResponseWriter, req *http.Request) {
@@ -156,7 +160,6 @@ func (p *ForwardProxyCluster) proxyHttpsConnect(w http.ResponseWriter, req *http
 	targetHost, _, _ := net.SplitHostPort(req.Host)
 	_, proxyUser, proxyPass, proxyHost, _, err := p.validateRequestAndGetProxy(w, req)
 	if err != nil {
-		// Error has already been handled, just log and return.
 		if proxyHost == "" {
 			proxyHost = "none"
 		}
@@ -171,12 +174,21 @@ func (p *ForwardProxyCluster) proxyHttpsConnect(w http.ResponseWriter, req *http
 	*errorMsg = ""
 	defer logProxyRequest(remoteAddr, proxyHost, targetHost, returnCode, "CONNECT", requestStartTime, errorMsg)
 
-	// Start a connection to the downstream proxy server.
+	var proxyConn net.Conn
-	proxyConn, err := net.DialTimeout("tcp", proxyHost, config.GetConfig().ProxyConnectTimeout)
+	for i := 0; i < config.GetConfig().ProxyConnectRetries; i++ {
-	if err != nil {
+		// Start a connection to the downstream proxy server.
-		*errorMsg = fmt.Sprintf(`Failed to dial proxy %s - %s`, proxyHost, err)
+		proxyConn, err = net.DialTimeout("tcp", proxyHost, config.GetConfig().ProxyConnectTimeout)
-		http.Error(w, "failed to make request to downstream", http.StatusServiceUnavailable)
+		if err != nil {
-		return
+			*errorMsg = fmt.Sprintf(`Failed to dial proxy %s - attempt %d/%d - %s`, proxyHost, i+1, config.GetConfig().ProxyConnectRetries, err)
+			if i < config.GetConfig().ProxyConnectRetries-1 {
+				continue
+			} else {
+				http.Error(w, "failed to make request to downstream", http.StatusServiceUnavailable)
+				return
+			}
+		} else {
+			break
+		}
 	}
 
 	// Proxy authentication

src/proxy/threads.go

@@ -10,6 +10,8 @@ import (
 	"time"
 )
 
+// TODO: fix 503 errors returned during proxy checking process
+
 func (p *ForwardProxyCluster) ValidateProxiesThread() {
 	log.Infoln("Doing initial backend check, please wait...")
 	started := false
@@ -58,10 +60,13 @@ func (p *ForwardProxyCluster) ValidateProxiesThread() {
 				// Test the proxy.
 				ipAddr, testErr := sendRequestThroughProxy(pxy, config.GetConfig().IpCheckerURL)
 				if testErr != nil {
-					log.Debugf("Validate - %s failed: %s", proxyHost, testErr)
 					if isThirdparty(pxy) {
+						if config.CliArgs.LogThirdPartyTest {
+							log.Debugf("Validate - %s failed: %s", proxyHost, testErr)
+						}
 						newThirdpartyOfflineProxies = append(newThirdpartyOfflineProxies, pxy)
 					} else {
+						log.Debugf("Validate - %s failed: %s", proxyHost, testErr)
 						newOurOfflineProxies = append(newOurOfflineProxies, pxy)
 					}
 					return
@@ -85,7 +90,9 @@ func (p *ForwardProxyCluster) ValidateProxiesThread() {
 						if bv3hiErr != nil {
 							okToAdd = false
 							newThirdpartyBrokenProxies = append(newThirdpartyBrokenProxies, pxy)
-							log.Debugf("Validate - %s failed third-party test: %s", proxyHost, bv3hiErr)
+							if config.CliArgs.LogThirdPartyTest {
+								log.Debugf(`%s failed third-party test for URL "%s" -- %s`, proxyHost, d, bv3hiErr)
+							}
 							break
 						}
 					}