Ajout : source du programme permettant de retourne le premier port libre

This commit is contained in:
Hippolyte Chauvin 2023-12-04 13:15:43 +01:00
parent 1da2ba12b6
commit 9a3462a2ba

112
src/first-free-port.c Normal file
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#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sysexits.h>
#include <string.h>
#define MIN_TCP_PORT 1
#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 inline unsigned char is_valid_tcp_port(const unsigned short tcp_port) {
return tcp_port >= MIN_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));
listening_ports = 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;
}
}