add SOCKS upstream proxy support (socks4/socks5)

original patch submitted in 2006 to debian mailing list:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=392848%29#12

this version was rebased to git and updated by Russ Dill <russ.dill@gmail.com>
in 2015 (the original patch used a different config file format).

as discussed in #40.

commit message by @rofl0r.

src/conf.c

@@ -160,6 +160,8 @@ static HANDLE_FUNC (handle_xtinyproxy);
 
 #ifdef UPSTREAM_SUPPORT
 static HANDLE_FUNC (handle_upstream);
+static HANDLE_FUNC (handle_upstream4);
+static HANDLE_FUNC (handle_upstream5);
 static HANDLE_FUNC (handle_upstream_no);
 #endif
 
@@ -257,6 +259,14 @@ struct {
                 BEGIN "(upstream)" WS "(" IP "|" ALNUM ")" ":" INT "(" WS STR
                       ")?" END, handle_upstream, NULL
         },
+        {
+                BEGIN "(upstream4)" WS "(" IP "|" ALNUM ")" ":" INT "(" WS STR
+                      ")?" END, handle_upstream4, NULL
+        },
+        {
+                BEGIN "(upstream5)" WS "(" IP "|" ALNUM ")" ":" INT "(" WS STR
+                      ")?" END, handle_upstream5, NULL
+        },
 #endif
         /* loglevel */
         STDCONF ("loglevel", "(critical|error|warning|notice|connect|info)",
@@ -1066,7 +1076,8 @@ static HANDLE_FUNC (handle_reversepath)
 #endif
 
 #ifdef UPSTREAM_SUPPORT
-static HANDLE_FUNC (handle_upstream)
+static int _handle_upstream(struct config_s* conf, const char* line,
+           regmatch_t match[], proxy_type type)
 {
         char *ip;
         int port;
@@ -1080,11 +1091,11 @@ static HANDLE_FUNC (handle_upstream)
         if (match[10].rm_so != -1) {
                 domain = get_string_arg (line, &match[10]);
                 if (domain) {
-                        upstream_add (ip, port, domain, &conf->upstream_list);
+                        upstream_add (ip, port, domain, type, &conf->upstream_list);
                         safefree (domain);
                 }
         } else {
-                upstream_add (ip, port, NULL, &conf->upstream_list);
+                upstream_add (ip, port, NULL, type, &conf->upstream_list);
         }
 
         safefree (ip);
@@ -1092,6 +1103,21 @@ static HANDLE_FUNC (handle_upstream)
         return 0;
 }
 
+static HANDLE_FUNC (handle_upstream)
+{
+	return _handle_upstream(conf, line, match, HTTP_TYPE);
+}
+
+static HANDLE_FUNC (handle_upstream4)
+{
+	return _handle_upstream(conf, line, match, SOCKS4_TYPE);
+}
+
+static HANDLE_FUNC (handle_upstream5)
+{
+	return _handle_upstream(conf, line, match, SOCKS5_TYPE);
+}
+
 static HANDLE_FUNC (handle_upstream_no)
 {
         char *domain;
@@ -1100,7 +1126,7 @@ static HANDLE_FUNC (handle_upstream_no)
         if (!domain)
                 return -1;
 
-        upstream_add (NULL, 0, domain, &conf->upstream_list);
+        upstream_add (NULL, 0, domain, HTTP_TYPE, &conf->upstream_list);
         safefree (domain);
 
         return 0;

src/reqs.c

@@ -61,9 +61,11 @@
 #ifdef UPSTREAM_SUPPORT
 #  define UPSTREAM_CONFIGURED() (config.upstream_list != NULL)
 #  define UPSTREAM_HOST(host) upstream_get(host, config.upstream_list)
+#  define UPSTREAM_IS_HTTP(conn) (conn->upstream_proxy != NULL && conn->upstream_proxy->type == HTTP_TYPE)
 #else
 #  define UPSTREAM_CONFIGURED() (0)
 #  define UPSTREAM_HOST(host) (NULL)
+#  define UPSTREAM_IS_HTTP(up) (0)
 #endif
 
 /*
@@ -853,10 +855,10 @@ process_client_headers (struct conn_s *connptr, hashmap_t hashofheaders)
         /*
          * Don't send headers if there's already an error, if the request was
          * a stats request, or if this was a CONNECT method (unless upstream
-         * proxy is in use.)
+         * http proxy is in use.)
          */
         if (connptr->server_fd == -1 || connptr->show_stats
-            || (connptr->connect_method && (connptr->upstream_proxy == NULL))) {
+            || (connptr->connect_method && ! UPSTREAM_IS_HTTP(connptr))) {
                 log_message (LOG_INFO,
                              "Not sending client headers to remote machine");
                 return 0;
@@ -1265,6 +1267,88 @@ static void relay_connection (struct conn_s *connptr)
         return;
 }
 
+static int
+connect_to_upstream_proxy(struct conn_s *connptr, struct request_s *request)
+{
+	int len;
+	char buff[512]; /* won't use more than 7 + 255 */
+	unsigned short port;
+	struct hostent *host;
+	struct upstream *cur_upstream = connptr->upstream_proxy;
+
+	log_message(LOG_CONN,
+		    "Established connection to %s proxy \"%s\" using file descriptor %d.",
+		    proxy_type_name(cur_upstream->type), cur_upstream->host, connptr->server_fd);
+
+	if (cur_upstream->type == SOCKS4_TYPE) {
+
+		buff[0] = 4; /* socks version */
+		buff[1] = 1; /* connect command */
+		port = htons(request->port);
+		memcpy(&buff[2], &port, 2); /* dest port */
+		host = gethostbyname(request->host);
+		memcpy(&buff[4], host->h_addr_list[0], 4); /* dest ip */
+		buff[8] = 0; /* user */
+		if (9 != safe_write(connptr->server_fd, buff, 9))
+			return -1;
+		if (8 != safe_read(connptr->server_fd, buff, 8))
+			return -1;
+		if (buff[0]!=0 || buff[1]!=90)
+			return -1;
+
+	} else if (cur_upstream->type == SOCKS5_TYPE) {
+
+		/* init */
+		buff[0] = 5; /* socks version */
+		buff[1] = 1; /* number of methods  */
+		buff[2] = 0; /* no auth method */
+		if (3 != safe_write(connptr->server_fd, buff, 3))
+			return -1;
+		if (2 != safe_read(connptr->server_fd, buff, 2))
+			return -1;
+		if (buff[0]!=5 || buff[1]!=0)
+			return -1;
+		/* connect */
+		buff[0] = 5; /* socks version */
+		buff[1] = 1; /* connect */
+		buff[2] = 0; /* reserved */
+		buff[3] = 3; /* domainname */
+		len=strlen(request->host);
+		if(len>255)
+			return -1;
+		buff[4] = len; /* length of domainname */
+		memcpy(&buff[5], request->host, len); /* dest ip */
+		port = htons(request->port);
+		memcpy(&buff[5+len], &port, 2); /* dest port */
+		if (7+len != safe_write(connptr->server_fd, buff, 7+len))
+			return -1;
+		if (4 != safe_read(connptr->server_fd, buff, 4))
+			return -1;
+		if (buff[0]!=5 || buff[1]!=0)
+			return -1;
+		switch(buff[3]) {
+			case 1: len=4; break; /* ip v4 */
+			case 4: len=16; break; /* ip v6 */
+			case 3: /* domainname */
+				if (1 != safe_read(connptr->server_fd, buff, 1))
+					return -1;
+				len = buff[0]; /* max = 255 */
+				break;
+			default: return -1;
+		}
+		if (2+len != safe_read(connptr->server_fd, buff, 2+len))
+			return -1;
+	} else {
+		return -1;
+	}
+
+	if (connptr->connect_method)
+		return 0;
+
+	return establish_http_connection(connptr, request);
+}
+
+
 /*
  * Establish a connection to the upstream proxy server.
  */
@@ -1308,6 +1392,9 @@ connect_to_upstream (struct conn_s *connptr, struct request_s *request)
                 return -1;
         }
 
+	if (cur_upstream->type != HTTP_TYPE)
+		return connect_to_upstream_proxy(connptr, request);
+
         log_message (LOG_CONN,
                      "Established connection to upstream proxy \"%s\" "
                      "using file descriptor %d.",
@@ -1527,7 +1614,7 @@ void handle_connection (int fd)
                 goto fail;
         }
 
-        if (!(connptr->connect_method && (connptr->upstream_proxy == NULL))) {
+        if (!connptr->connect_method || UPSTREAM_IS_HTTP(connptr)) {
                 if (process_server_headers (connptr) < 0) {
                         update_stats (STAT_BADCONN);
                         goto fail;

src/upstream.c

@@ -29,10 +29,22 @@
 #include "log.h"
 
 #ifdef UPSTREAM_SUPPORT
+const char *
+proxy_type_name(proxy_type type)
+{
+    switch(type) {
+        case HTTP_TYPE: return "http";
+        case SOCKS4_TYPE: return "socks4";
+        case SOCKS5_TYPE: return "socks5";
+        default: return "unknown";
+    }
+}
+
 /**
  * Construct an upstream struct from input data.
  */
-static struct upstream *upstream_build (const char *host, int port, const char *domain)
+static struct upstream *upstream_build (const char *host, int port, const char *domain,
+			proxy_type type)
 {
         char *ptr;
         struct upstream *up;
@@ -44,6 +56,7 @@ static struct upstream *upstream_build (const char *host, int port, const char *
                 return NULL;
         }
 
+        up->type = type;
         up->host = up->domain = NULL;
         up->ip = up->mask = 0;
 
@@ -57,8 +70,8 @@ static struct upstream *upstream_build (const char *host, int port, const char *
                 up->host = safestrdup (host);
                 up->port = port;
 
-                log_message (LOG_INFO, "Added upstream %s:%d for [default]",
+                log_message (LOG_INFO, "Added upstream %s %s:%d for [default]",
-                             host, port);
+                             proxy_type_name(type), host, port);
         } else if (host == NULL) {
                 if (!domain || domain[0] == '\0') {
                         log_message (LOG_WARNING,
@@ -101,8 +114,8 @@ static struct upstream *upstream_build (const char *host, int port, const char *
                 up->port = port;
                 up->domain = safestrdup (domain);
 
-                log_message (LOG_INFO, "Added upstream %s:%d for %s",
+                log_message (LOG_INFO, "Added upstream %s %s:%d for %s",
-                             host, port, domain);
+                             proxy_type_name(type), host, port, domain);
         }
 
         return up;
@@ -119,11 +132,11 @@ fail:
  * Add an entry to the upstream list
  */
 void upstream_add (const char *host, int port, const char *domain,
-                   struct upstream **upstream_list)
+                   proxy_type type, struct upstream **upstream_list)
 {
         struct upstream *up;
 
-        up = upstream_build (host, port, domain);
+        up = upstream_build (host, port, domain, type);
         if (up == NULL) {
                 return;
         }
@@ -202,8 +215,8 @@ struct upstream *upstream_get (char *host, struct upstream *up)
                 up = NULL;
 
         if (up)
-                log_message (LOG_INFO, "Found upstream proxy %s:%d for %s",
+                log_message (LOG_INFO, "Found upstream proxy %s %s:%d for %s",
-                             up->host, up->port, host);
+                             proxy_type_name(up->type), up->host, up->port, host);
         else
                 log_message (LOG_INFO, "No upstream proxy for %s", host);
 

src/upstream.h

@@ -31,17 +31,20 @@
  * Even if upstream support is not compiled into tinyproxy, this
  * structure still needs to be defined.
  */
+typedef enum {HTTP_TYPE, SOCKS4_TYPE, SOCKS5_TYPE} proxy_type;
 struct upstream {
         struct upstream *next;
         char *domain;           /* optional */
         char *host;
         int port;
         in_addr_t ip, mask;
+        proxy_type type;
 };
 
 #ifdef UPSTREAM_SUPPORT
+const char *proxy_type_name(proxy_type type);
 extern void upstream_add (const char *host, int port, const char *domain,
-                          struct upstream **upstream_list);
+                          proxy_type type, struct upstream **upstream_list);
 extern struct upstream *upstream_get (char *host, struct upstream *up);
 extern void free_upstream_list (struct upstream *up);
 #endif /* UPSTREAM_SUPPORT */