first-free-port : ouf celui là j'aurais galéré à le faire

src/first-free-port.c

@@ -0,0 +1,113 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <sysexits.h>
+#include <string.h>
+
+#define MIN_TCP_PORT 1
+#define MAX_TCP_PORT 65534
+#define TCP_TABLE "/proc/net/tcp"
+#define TCP_TABLE_LINE_LENGTH 151
+#define LOCALHOST_HEX "0100007F"
+#define WILDCARD_HEX "00000000"
+#define LISTENING_HEX "0A"
+#define PORTS_BLOCKS_TO_ALLOW 4
+
+/**
+ * Get all the listening TCP ports
+ */
+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 allowed_for_ports = PORTS_BLOCKS_TO_ALLOW;
+
+    // Skip first line (header)
+    fgets(line, sizeof(line), tcp_table_fptr);
+
+    // Tokenize lines one by one
+    while (fgets(line, sizeof(line), tcp_table_fptr) != NULL) {
+        strtok(line, delimiter);
+
+        address = strtok(NULL, delimiter);
+        strtok(NULL, delimiter);
+        state = strtok(NULL, delimiter);
+        field = strtok(NULL, delimiter);
+        
+        while (field != NULL) {
+            field = strtok(NULL, delimiter);
+        }
+
+        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 == 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;
+
+    return listening_ports;
+}
+
+static unsigned char is_port_available(const unsigned short port, const unsigned short *listening_ports) {
+    unsigned short i = 0;
+    while (listening_ports[i] != 0 && listening_ports[i] != port) {
+        i++;
+    }
+    return listening_ports[i] == 0;
+}
+
+static unsigned char is_valid_tcp_port(unsigned short tcp_port) {
+    return tcp_port >= MIN_TCP_PORT && tcp_port <= MAX_TCP_PORT;
+}
+
+int main(int argc, char *argv[]) {
+    unsigned short current_port;
+
+    if (argc >= 2) {
+        current_port = atoi(argv[1]);
+    } else {
+        current_port = 0;
+    }
+
+    if (!is_valid_tcp_port(current_port)) {
+        fprintf(stderr, "Provide a valid TCP port number as first argument.\n");
+        return EX_USAGE;
+    }
+
+    // Open TCP table
+    FILE *tcp_table_fptr = fopen(TCP_TABLE, "r");
+    if (tcp_table_fptr == NULL) {
+        fprintf(stderr, "Error opening the TCP table.\n");
+        return EX_OSFILE;
+    }
+
+    unsigned short *listening_ports = malloc(PORTS_BLOCKS_TO_ALLOW * sizeof(unsigned short));
+    get_listening_ports(listening_ports, tcp_table_fptr);
+
+    // Check if the current port is available, add
+    while (!is_port_available(current_port, listening_ports)) {
+        current_port++;
+    }
+
+    free(listening_ports);
+
+    if (is_valid_tcp_port(current_port)) {
+        printf("%d\n", current_port);
+        return EXIT_SUCCESS;
+    } else {
+        fprintf(stderr, "No more ports available. How did you fuck up that bad ???\n");
+        return EX_TEMPFAIL;
+    }
+}