add receiver loop, service multiplexing, common.h

* Service multiplexing

  Broadcaster call signature is changed to

  broadcaster host service [message]

  to acommodate multiple sevices listening on the same port for
  broadcast information.

* Receiver Loop

  Listener now loops infinitely instead of returning after the first
  packet. For each packet with the content service[,message] the
  programm

  service [message]

  will be executed. Upward directory traversal is prohibited (and
  detected).

  To prevent DoS only one service program runs concurrently.

* Common.h

  Port numbers and maximum message sizes are now stored in
  common.h. Broascaster respects max. message size.

3 files changed, 54 insertions, 18 deletions

diff --git a/broadcaster.c b/broadcaster.c
index 0e4eef5..4160b93 100644
--- a/broadcaster.c
+++ b/broadcaster.c
@@ -14,7 +14,7 @@
 #include <arpa/inet.h>
 #include <netdb.h>
 
-#define SERVERPORT 4950    // the port users will be connecting to
+#include "common.h"
 
 int main(int argc, char *argv[])
 {
@@ -23,12 +23,24 @@ int main(int argc, char *argv[])
     struct hostent *he;
     int numbytes;
     int broadcast = 1;
-    //char broadcast = '1'; // if that doesn't work, try this
 
-    if (argc != 3) {
-        fprintf(stderr,"usage: broadcaster hostname message\n");
+    // assemble packet
+    if (argc < 3 || argc > 4) {
+        fprintf(stderr,"usage: broadcaster hostname task [message]\n");
         exit(1);
     }
+    char buf[MAXBUFLEN],
+      *task = argv[2],
+      *message = (argc == 4) ? argv[3] : NULL;
+    int task_len = strlen(task),
+      total_len = task_len + 1 + strlen(message);
+    if (total_len > MAXBUFLEN) {
+      fprintf(stderr,"payload to long: max %d bytes, was %d\n", MAXBUFLEN, total_len);
+      exit(-1);
+    }
+    strcpy(buf, task);
+    buf[task_len] = 0;
+    strcpy(buf + 1 + task_len, message);
 
     if ((he=gethostbyname(argv[1])) == NULL) {  // get the host info
         perror("gethostbyname");
@@ -52,7 +64,7 @@ int main(int argc, char *argv[])
     their_addr.sin_addr = *((struct in_addr *)he->h_addr);
     memset(their_addr.sin_zero, '\0', sizeof their_addr.sin_zero);
 
-    if ((numbytes=sendto(sockfd, argv[2], strlen(argv[2]), 0,
+    if ((numbytes=sendto(sockfd, buf, total_len, 0,
              (struct sockaddr *)&their_addr, sizeof their_addr)) == -1) {
         perror("sendto");
         exit(1);
diff --git a/common.h b/common.h
new file mode 100644
index 0000000..c64c764
--- /dev/null
+++ b/common.h
@@ -0,0 +1,8 @@
+#ifndef UDP_BROADCAST_COMMON
+#define UDP_BROADCAST_COMMON
+
+#define SERVERPORT 4950    // the port users will be connecting to
+#define SERVERPORT_S "4950"
+#define MAXBUFLEN 100
+
+#endif // UDP_BROADCAST_COMMON
diff --git a/listener.c b/listener.c
index fa9f0c1..2fa6666 100644
--- a/listener.c
+++ b/listener.c
@@ -13,9 +13,7 @@
 #include <arpa/inet.h>
 #include <netdb.h>
 
-#define MYPORT "4950"    // the port users will be connecting to
-
-#define MAXBUFLEN 100
+#include "common.h"
 
 // get sockaddr, IPv4 or IPv6:
 void *get_in_addr(struct sockaddr *sa)
@@ -27,7 +25,7 @@ void *get_in_addr(struct sockaddr *sa)
     return &(((struct sockaddr_in6*)sa)->sin6_addr);
 }
 
-int main(void)
+int main(int argc, char *argv[], char *envp[])
 {
     int sockfd;
     struct addrinfo hints, *servinfo, *p;
@@ -43,7 +41,7 @@ int main(void)
     hints.ai_socktype = SOCK_DGRAM;
     hints.ai_flags = AI_PASSIVE; // use my IP
 
-    if ((rv = getaddrinfo(NULL, MYPORT, &hints, &servinfo)) != 0) {
+    if ((rv = getaddrinfo(NULL, SERVERPORT_S, &hints, &servinfo)) != 0) {
         fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
         return 1;
     }
@@ -74,16 +72,34 @@ int main(void)
 
 
     addr_len = sizeof their_addr;
-    if ((numbytes = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0,
-        (struct sockaddr *)&their_addr, &addr_len)) == -1) {
-        perror("recvfrom");
-        exit(1);
+    while ((numbytes = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0,
+           (struct sockaddr *)&their_addr, &addr_len)) != -1) {
+      // decode packet & launch handler
+      buf[numbytes] = '\0';
+      char *task = buf,
+	*cl_argv[3] = {buf, (strlen(task)<numbytes) ? (buf+strlen(task)+1) : NULL, NULL };
+
+      if (buf[0] == '/' || strstr(buf, "..")) {
+	fprintf(stderr, "payload tried directory traversal\n");
+	continue;
+      }
+
+      switch (fork()) {
+      case 0:
+	// TODO: clean file descriptors
+	execve(task, cl_argv, envp);
+	perror("exec");
+	exit(-1);
+      case -1:
+	perror("fork (serious!)");
+	exit(-1);
+      default:
+	wait();
+      }
     }
 
-    buf[numbytes] = '\0';
-    printf("%s\n", buf);
-
+    perror("recvfrom");
     close(sockfd);
 
-    return 0;
+    return -1;
 }