OpenSSL::SSL::SSLSocket#export_keying_material

static VALUE
ossl_ssl_export_keying_material(int argc, VALUE *argv, VALUE self)
{
    SSL *ssl;
    VALUE str;
    VALUE label;
    VALUE length;
    VALUE context;
    unsigned char *p;
    size_t len;
    int use_ctx = 0;
    unsigned char *ctx = NULL;
    size_t ctx_len = 0;
    int ret;

    rb_scan_args(argc, argv, "21", &label, &length, &context);
    StringValue(label);

    GetSSL(self, ssl);

    len = (size_t)NUM2LEN(length);
    str = rb_str_new(0, len);
    p = (unsigned char *)RSTRING_PTR(str);
    if (!NIL_P(context)) {
        use_ctx = 1;
        StringValue(context);
        ctx = (unsigned char *)RSTRING_PTR(context);
        ctx_len = RSTRING_LEN(context);
    }
    ret = SSL_export_keying_material(ssl, p, len, (char *)RSTRING_PTR(label),
                                     RSTRING_LENINT(label), ctx, ctx_len, use_ctx);
    if (ret == 0 || ret == -1) {
        ossl_raise(eSSLError, "SSL_export_keying_material");
    }
    return str;
}