/* Provenance: openssl/openssl validate_hostname_part (fixed).
 * repo: openssl/openssl
 * commit: b3a555a0a7aa0028887149f6f973af89a4937bea
 * parent: 0f3fab2eccc7c3417093a8243dd15d95b6cb472d
 * commit_url: https://github.com/openssl/openssl/commit/b3a555a0a7aa0028887149f6f973af89a4937bea
 * cve: CVE-2026-42771
 * license: Apache-2.0
 * function: validate_hostname_part
 * relpath: crypto/x509/x509_vpm.c
 */

static int validate_hostname_part(const char *name, size_t len,
    ossl_charset_t charset)
{
    size_t i, part_len;
    char c, prev;

    if (len < 2 || len > 256)
        return 0;

    part_len = 0;
    prev = '\0';
    for (i = 0; i < len; i++) {
        c = name[i];
        if (c == '.') {
            /*
             * Can not start a label with a .
             * unless it is the very first character.
             */
            if (part_len == 0 && i != 0)
                return 0;
            /* Can not end a label with a - */
            if (prev == '-')
                return 0;
            part_len = 0;
        } else {
            /* Can not start a label with a - */
            if (part_len == 0 && c == '-') {
                return 0;
            }
            if (!is_label_ok(c, charset) && c != '-')
                return 0;
            part_len++;
        }
        if (part_len > 63)
            return 0;

        prev = c;
    }
    /* Can not end with a . or a _ */
    if (prev == '.' || prev == '-')
        return 0;

    return 1;
}