Parse a TLS record header

Challenge

A TLS record begins with a 5-byte header: content type (1 byte), protocol version (2 bytes: major, minor), and length (2 bytes, big-endian). Implement

int tls_parse(const unsigned char *b, size_t n, int *type, int *major, int *minor, int *length)

returning 0 on success (writing the four fields), or -1 if n < 5. Parse from a fixed byte buffer — no network.

Starter code

#include <stddef.h>

int tls_parse(const unsigned char *b, size_t n,
              int *type, int *major, int *minor, int *length) {
    /* TODO: need at least 5 bytes. type=b[0], version=b[1].b[2],
       length = big-endian b[3..4]. Return 0, or -1 if too short. */
    (void)b;(void)n;(void)type;(void)major;(void)minor;(void)length;
    return -1;
}

Common mistakes

Reading before the length check; little-endian length; sign-extending bytes.

Edge cases to handle

Exactly 5 bytes (minimum). Length 0x0100 = 256. Buffer shorter than 5.

Complexity

O(1).

Background lessons

• TLS, certificates, and digital signatures
• Reading packet captures with Wireshark