1 files changed, 94 insertions, 0 deletions
diff --git a/utils/rebind.c b/utils/rebind.c
new file mode 100644
index 0000000..c7e83de
--- /dev/null
+++ b/utils/rebind.c
@@ -0,0 +1,94 @@
+/*
+ * rebind: Intercept bind calls and bind to a different port
+ * Copyright 2010 Joel Martin
+ * Licensed under LGPL version 3 (see docs/LICENSE.LGPL-3)
+ *
+ * Overload (LD_PRELOAD) bind system call. If REBIND_PORT_OLD and
+ * REBIND_PORT_NEW environment variables are set then bind on the new
+ * port (of localhost) instead of the old port. 
+ *
+ * This allows a proxy (such as wsproxy) to run on the old port and translate
+ * traffic to/from the new port.
+ *
+ * Usage:
+ *     LD_PRELOAD=./rebind.so \
+ *     REBIND_PORT_OLD=23 \
+ *     REBIND_PORT_NEW=2023 \
+ *     program
+ */
+
+//#define DO_DEBUG 1
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define __USE_GNU 1  // Pull in RTLD_NEXT
+#include <dlfcn.h>
+
+#include <string.h>
+#include <netinet/in.h>
+
+
+#if defined(DO_DEBUG)
+#define DEBUG(...) \
+    fprintf(stderr, "wswrapper: "); \
+    fprintf(stderr, __VA_ARGS__);
+#else
+#define DEBUG(...)
+#endif
+
+
+int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen)
+{
+    static void * (*func)();
+    int do_move = 0;
+    struct sockaddr_in * addr_in = (struct sockaddr_in *)addr;
+    struct sockaddr_in addr_tmp;
+    socklen_t addrlen_tmp;
+    char * PORT_OLD, * PORT_NEW, * end1, * end2;
+    int ret, oldport, newport, askport = htons(addr_in->sin_port);
+    uint32_t askaddr = htons(addr_in->sin_addr.s_addr);
+    if (!func) func = (void *(*)()) dlsym(RTLD_NEXT, "bind");
+
+    DEBUG(">> bind(%d, _, %d), askaddr %d, askport %d\n",
+          sockfd, addrlen, askaddr, askport);
+
+    /* Determine if we should move this socket */
+    if (addr_in->sin_family == AF_INET) {
+        // TODO: support IPv6
+        PORT_OLD = getenv("REBIND_OLD_PORT");
+        PORT_NEW = getenv("REBIND_NEW_PORT");
+        if (PORT_OLD && (*PORT_OLD != '\0') &&
+            PORT_NEW && (*PORT_NEW != '\0')) {
+            oldport = strtol(PORT_OLD, &end1, 10);
+            newport = strtol(PORT_NEW, &end2, 10);
+            if (oldport && (*end1 == '\0') &&
+                newport && (*end2 == '\0') &&
+                (oldport == askport)) {
+                do_move = 1;
+            }
+        }
+    }
+
+    if (! do_move) {
+        /* Just pass everything right through to the real bind */
+        ret = (int) func(sockfd, addr, addrlen);
+        DEBUG("<< bind(%d, _, %d) ret %d\n", sockfd, addrlen, ret);
+        return ret;
+    }
+
+    DEBUG("binding fd %d on localhost:%d instead of 0x%x:%d\n",
+        sockfd, newport, ntohl(addr_in->sin_addr.s_addr), oldport);
+
+    /* Use a temporary location for the new address information */
+    addrlen_tmp = sizeof(addr_tmp);
+    memcpy(&addr_tmp, addr, addrlen_tmp);
+
+    /* Bind to other port on the loopback instead */
+    addr_tmp.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+    addr_tmp.sin_port = htons(newport);
+    ret = (int) func(sockfd, &addr_tmp, addrlen_tmp);
+
+    DEBUG("<< bind(%d, _, %d) ret %d\n", sockfd, addrlen, ret);
+    return ret;
+}