Sockaddr IPv4 & Port Extractor

Challenge

BSD socket network programs receive generic struct sockaddr pointers that must be inspected for address family (AF_INET), cast to struct sockaddr_in, and converted to human-readable IP strings.

Your Task

Implement:

#include <netinet/in.h>

int extract_ipv4_and_port(const struct sockaddr *addr, char *ip_buf, size_t ip_cap, uint16_t *out_port);

Rules

1. If addr == NULL, ip_buf == NULL, out_port == NULL, or ip_cap < 16, return -1.
2. Verify addr->sa_family == AF_INET. If not IPv4, return -1.
3. Cast addr to const struct sockaddr_in *.
4. Extract port using ntohs(sin->sin_port) and write to *out_port.
5. Convert sin->sin_addr.s_addr to dotted-decimal format ("A.B.C.D") into ip_buf.
6. Return 0 on success.

Example

struct sockaddr_in sin = {0};
sin.sin_family = AF_INET;
sin.sin_port = htons(8080);
sin.sin_addr.s_addr = htonl(0x7F000001); // 127.0.0.1
char ip[16]; uint16_t port;
extract_ipv4_and_port((struct sockaddr *)&sin, ip, sizeof(ip), &port); // ip=="127.0.0.1", port==8080

Input format

addr: generic sockaddr pointer; ip_buf: buffer of at least 16 bytes; out_port: uint16_t pointer.

Output format

Returns 0 on success, or -1 on non-AF_INET or NULL args.

Constraints

Must use ntohs and extract 4 octets. Buffer must be >= 16.

Starter code

#include <stddef.h>
#include <stdint.h>
#include <netinet/in.h>

int extract_ipv4_and_port(const struct sockaddr *addr, char *ip_buf, size_t ip_cap, uint16_t *out_port) {
    (void)addr; (void)ip_buf; (void)ip_cap; (void)out_port;
    return -1;
}

Common mistakes

Forgetting ntohs on port; insufficient buffer capacity; buffer overrun on snprintf.

Edge cases to handle

AF_INET6 or other family returns -1; 0.0.0.0 and 255.255.255.255 formatted accurately.

Background lessons

• struct sockaddr_in — addresses for IPv4
• htons(), htonl(), inet_pton() — network byte order