src/first-free-port.c

@@ -6,12 +6,12 @@
 #include <errno.h>
 
 #define MIN_TCP_PORT 1
-#define TCP_TABLE_PATH "/proc/net/tcp"
+#define TCP_TABLE "/proc/net/tcp"
 #define TCP_TABLE_LINE_LENGTH 151
-#define LOCALHOSTIP_HEX "0100007F"
-#define WILDCARDIP_HEX "00000000"
+#define LOCALHOST_HEX "0100007F"
+#define WILDCARD_HEX "00000000"
 #define LISTENING_HEX "0A"
-#define BLOCKS_TO_ALLOC 4
+#define PORTS_BLOCKS_TO_ALLOW 4
 
 /**
  * Print a nice error message
@@ -23,15 +23,14 @@ static void print_error(char *name, const char *message) {
 /**
  * Get all the listening TCP ports
  */
-static unsigned short *get_listening_ports(FILE *tcp_table_fptr) {
-    unsigned short *listening_ports = malloc(BLOCKS_TO_ALLOC * sizeof(short));
+static unsigned short *get_listening_ports(unsigned short *listening_ports, FILE *tcp_table_fptr) {
     char line[TCP_TABLE_LINE_LENGTH];
     char delimiter[] = " ";
     unsigned short len = 0;
     char *address;
     char *state;
     char *field;
-    size_t blocks_allocated = BLOCKS_TO_ALLOC;
+    size_t allowed_for_ports = PORTS_BLOCKS_TO_ALLOW;
 
     // Skip first line (header)
     fgets(line, sizeof(line), tcp_table_fptr);
@@ -49,18 +48,19 @@ static unsigned short *get_listening_ports(FILE *tcp_table_fptr) {
             field = strtok(NULL, delimiter);
         }
 
-        if ((!strncmp(address, LOCALHOSTIP_HEX, 8) || !strncmp(address, WILDCARDIP_HEX, 8)) && !strncmp(state, LISTENING_HEX, 2)) {
-            if (len == blocks_allocated) {
-                blocks_allocated = blocks_allocated + BLOCKS_TO_ALLOC;
-                listening_ports = realloc(listening_ports, blocks_allocated * sizeof(short));
+        if ((!strncmp(address, LOCALHOST_HEX, 8) || !strncmp(address, WILDCARD_HEX, 8)) && !strncmp(state, LISTENING_HEX, 2)) {
+            if (len == allowed_for_ports) {
+                allowed_for_ports = allowed_for_ports + PORTS_BLOCKS_TO_ALLOW;
+                listening_ports = realloc(listening_ports, allowed_for_ports * sizeof(unsigned short));
             }
             listening_ports[len] = strtol(address + strlen(address) - 4, NULL, 16);
             len++;
         }
     }
 
-    if (len == blocks_allocated) {
-        listening_ports = realloc(listening_ports, blocks_allocated + 1);
+    if (len == allowed_for_ports) {
+        allowed_for_ports = allowed_for_ports + PORTS_BLOCKS_TO_ALLOW;
+        listening_ports = realloc(listening_ports, allowed_for_ports * sizeof(unsigned short));
     }
     listening_ports[len] = 0;
 
@@ -94,13 +94,14 @@ int main(int argc, char *argv[]) {
     }
 
     // Open TCP table
-    FILE *tcp_table_fptr = fopen(TCP_TABLE_PATH, "r");
+    FILE *tcp_table_fptr = fopen(TCP_TABLE, "r");
     if (tcp_table_fptr == NULL) {
         print_error(argv[0], "error opening the TCP table.");
         return errno;
     }
 
-    unsigned short *listening_ports = get_listening_ports(tcp_table_fptr);
+    unsigned short *listening_ports = malloc(PORTS_BLOCKS_TO_ALLOW * sizeof(unsigned short));
+    listening_ports = get_listening_ports(listening_ports, tcp_table_fptr);
 
     if (fclose(tcp_table_fptr) != 0) {
         print_error(argv[0], "can't close the TCP table.");