add support for a fixed number of proxies that are *always* used

e.g. for having tor fixed as first proxy, then using the rest for
random selection.

src/core.c

@@ -475,7 +475,8 @@ static proxy_data *select_proxy(select_type how, proxy_data * pd, unsigned int p
 		case RANDOMLY:
 			do {
 				k++;
-				i = rand() % proxy_count;
+				i = rand() % (proxy_count-proxychains_fixed_chain);
+				i += proxychains_fixed_chain;
 			} while(pd[i].ps != PLAY_STATE && k < proxy_count * 100);
 			break;
 		case FIFOLY:
@@ -563,9 +564,38 @@ static int chain_step(int ns, proxy_data * pfrom, proxy_data * pto) {
 	return retcode;
 }
 
+static int strict_connect(
+	unsigned *alive_count,
+	unsigned *offset,
+	int *ns,
+	proxy_data **p1, proxy_data **p2,
+	unsigned proxy_count, proxy_data * pd)
+{
+	*alive_count = calc_alive(pd, proxy_count);
+	*offset = 0;
+	if(!(*p1 = select_proxy(FIFOLY, pd, proxy_count, offset))) {
+		PDEBUG("select_proxy failed\n");
+		return 0;
+	}
+	if(SUCCESS != start_chain(ns, *p1, ST)) {
+		PDEBUG("start_chain failed\n");
+		return 0;
+	}
+	while(*offset < proxy_count) {
+		if(!(*p2 = select_proxy(FIFOLY, pd, proxy_count, offset)))
+			break;
+		if(SUCCESS != chain_step(*ns, *p1, *p2)) {
+			PDEBUG("chain_step failed\n");
+			return 0;
+		}
+		*p1 = *p2;
+	}
+	return 1;
+}
+
 int connect_proxy_chain(int sock, ip_type target_ip,
 			unsigned short target_port, proxy_data * pd,
-			unsigned int proxy_count, chain_type ct, unsigned int max_chain) {
+			unsigned int proxy_count, chain_type ct) {
 	proxy_data p4;
 	proxy_data *p1, *p2, *p3;
 	int ns = -1;
@@ -575,6 +605,7 @@ int connect_proxy_chain(int sock, ip_type target_ip,
 	unsigned int curr_len = 0;
 	unsigned int looped = 0; // went back to start of list in RR mode
 	unsigned int rr_loop_max = 14;
+	unsigned int max_chain = proxychains_max_chain;
 
 	p3 = &p4;
 
@@ -583,9 +614,14 @@ int connect_proxy_chain(int sock, ip_type target_ip,
 	again:
 	rc = -1;
 	DUMP_PROXY_CHAIN(pd, proxy_count);
+	if(proxychains_fixed_chain) {
+		if(!strict_connect(&alive_count, &offset, &ns, &p1, &p2, proxychains_fixed_chain, pd))
+			goto error_strict;
+	}
 
 	switch (ct) {
 		case DYNAMIC_TYPE:
+			if(proxychains_fixed_chain) goto dyn_fixed_resume;
 			alive_count = calc_alive(pd, proxy_count);
 			offset = 0;
 			do {
@@ -601,6 +637,7 @@ int connect_proxy_chain(int sock, ip_type target_ip,
 					goto again;
 				}
 				p1 = p2;
+		dyn_fixed_resume:;
 			}
 			//proxychains_write_log(TP);
 			p3->ip = target_ip;
@@ -610,6 +647,7 @@ int connect_proxy_chain(int sock, ip_type target_ip,
 			break;
 
 		case ROUND_ROBIN_TYPE:
+			// FIXME: add support for fixed_len
 			alive_count = calc_alive(pd, proxy_count);
 			offset = proxychains_proxy_offset;
 			if(alive_count < max_chain)
@@ -660,25 +698,8 @@ int connect_proxy_chain(int sock, ip_type target_ip,
 			break;
 
 		case STRICT_TYPE:
-			alive_count = calc_alive(pd, proxy_count);
+			if(!strict_connect(&alive_count, &offset, &ns, &p1, &p2, proxy_count, pd))
-			offset = 0;
-			if(!(p1 = select_proxy(FIFOLY, pd, proxy_count, &offset))) {
-				PDEBUG("select_proxy failed\n");
 				goto error_strict;
-			}
-			if(SUCCESS != start_chain(&ns, p1, ST)) {
-				PDEBUG("start_chain failed\n");
-				goto error_strict;
-			}
-			while(offset < proxy_count) {
-				if(!(p2 = select_proxy(FIFOLY, pd, proxy_count, &offset)))
-					break;
-				if(SUCCESS != chain_step(ns, p1, p2)) {
-					PDEBUG("chain_step failed\n");
-					goto error_strict;
-				}
-				p1 = p2;
-			}
 			//proxychains_write_log(TP);
 			p3->ip = target_ip;
 			p3->port = target_port;
@@ -687,6 +708,12 @@ int connect_proxy_chain(int sock, ip_type target_ip,
 			break;
 
 		case RANDOM_TYPE:
+			if(proxychains_fixed_chain) {
+				if(alive_count < max_chain)
+					goto error_more;
+				curr_len = proxychains_fixed_chain - 1;
+				goto random_fixed_resume;
+			}
 			alive_count = calc_alive(pd, proxy_count);
 			if(alive_count < max_chain)
 				goto error_more;
@@ -695,6 +722,9 @@ int connect_proxy_chain(int sock, ip_type target_ip,
 				if(!(p1 = select_proxy(RANDOMLY, pd, proxy_count, &offset)))
 					goto error_more;
 			} while(SUCCESS != start_chain(&ns, p1, RT) && offset < max_chain);
+
+		random_fixed_resume:;
+
 			while(++curr_len < max_chain) {
 				if(!(p2 = select_proxy(RANDOMLY, pd, proxy_count, &offset)))
 					goto error_more;

src/core.h

@@ -84,8 +84,7 @@ typedef struct {
 } proxy_data;
 
 int connect_proxy_chain (int sock, ip_type target_ip, unsigned short target_port,
-			 proxy_data * pd, unsigned int proxy_count, chain_type ct,
+			 proxy_data * pd, unsigned int proxy_count, chain_type ct );
-			 unsigned int max_chain );
 
 void proxychains_write_log(char *str, ...);
 
@@ -130,6 +129,9 @@ void proxy_freeaddrinfo(struct addrinfo *res);
 void core_initialize(void);
 void core_unload(void);
 
+extern unsigned int proxychains_max_chain;
+extern unsigned int proxychains_fixed_chain;
+
 #include "debug.h"
 
 #endif

src/libproxychains.c

@@ -71,6 +71,7 @@ unsigned int proxychains_proxy_count = 0;
 unsigned int proxychains_proxy_offset = 0;
 int proxychains_got_chain_data = 0;
 unsigned int proxychains_max_chain = 1;
+unsigned int proxychains_fixed_chain = 0;
 int proxychains_quiet_mode = 0;
 enum dns_lookup_flavor proxychains_resolver = DNSLF_LIBC;
 localaddr_arg localnet_addr[MAX_LOCALNET];
@@ -438,6 +439,16 @@ inv_host:
 					}
 					len = atoi(++pc);
 					proxychains_max_chain = (len ? len : 1);
+				} else if(STR_STARTSWITH(buff, "fixed_len")) {
+					char *pc;
+					int len;
+					pc = strchr(buff, '=');
+					if(!pc) {
+						fprintf(stderr, "error: missing equals sign '=' in fixed_len directive.\n");
+						exit(1);
+					}
+					len = atoi(++pc);
+					proxychains_fixed_chain = (len ? len : 1);
 				} else if(!strcmp(buff, "quiet_mode")) {
 					proxychains_quiet_mode = 1;
 				} else if(!strcmp(buff, "proxy_dns_old")) {
@@ -520,6 +531,14 @@ inv_host:
 		fprintf(stderr, "error: no valid proxy found in config\n");
 		exit(1);
 	}
+	if(proxychains_max_chain <= proxychains_fixed_chain) {
+		fprintf(stderr, "error: fixed_len needs to be smaller than chain_len\n");
+		exit(1);
+	}
+	if(proxychains_fixed_chain > count) {
+		fprintf(stderr, "error: fixed_len > proxycount\n");
+		exit(1);
+	}
 	*proxy_count = count;
 	proxychains_got_chain_data = 1;
 	PDEBUG("proxy_dns: %s\n", rdns_resolver_string(proxychains_resolver));
@@ -630,7 +649,7 @@ int connect(int sock, const struct sockaddr *addr, unsigned int len) {
 	ret = connect_proxy_chain(sock,
 				  dest_ip,
 				  htons(port),
-				  proxychains_pd, proxychains_proxy_count, proxychains_ct, proxychains_max_chain);
+				  proxychains_pd, proxychains_proxy_count, proxychains_ct);
 
 	fcntl(sock, F_SETFL, flags);
 	if(ret != SUCCESS)

src/proxychains.conf

@@ -45,6 +45,12 @@ strict_chain
 # Make sense only if random_chain or round_robin_chain
 #chain_len = 2
 
+# use this if you want to use e.g. random_chain but always have
+# e.g. tor as first proxy. in that case only chain_len - fixed_len proxies
+# will be used for random chain.
+# currently only implemented for dynamic_chain and random_chain.
+#fixed_len = 1
+
 # Quiet mode (no output from library)
 #quiet_mode