X509 CT: defer filling in the length field

This eliminates the need of precalculating the payload size, to make
it easier to adapt to new format.

Signed-off-by: Daiki Ueno <ueno@gnu.org>

diff --git a/lib/x509/x509_ext.c b/lib/x509/x509_ext.c
index a1a95cd17bb9a97cff9cb6e05de8ebaf5c5ff125..8bcf183a2f846387fd9100ee61c328d7436c83c9 100644 (file)
--- a/lib/x509/x509_ext.c
+++ b/lib/x509/x509_ext.c
@@ -3766,22 +3766,17 @@ static int _gnutls_ct_sct_add(struct ct_sct_st *sct,
 }
 
 static int _gnutls_export_ct_v1_sct(gnutls_buffer_st *buf,
-                                   const struct ct_sct_st *sct, size_t base_size)
+                                   const struct ct_sct_st *sct)
 {
        int ret;
        uint8_t tstamp_out[8], sigalg[2];
        /* There are no extensions defined for v1 */
        const uint8_t extensions[2] = { 0x00, 0x00 };
+       size_t length_offset;
 
-       /*
-        * The caller of this function will allocate 'out' so that it will always have enough room
-        * to write the requested SCT. Hence we don't need to bounds-check 'out' here.
-        * Currently this function is only called at gnutls_x509_ext_ct_export_scts().
-        */
-
-       /* Length field */
-       if ((ret = _gnutls_buffer_append_prefix(buf, 16,
-                                               base_size + sct->signature.size - sizeof(uint16_t))) < 0)
+       /* Length field; filled later */
+       length_offset = buf->length;
+       if ((ret = _gnutls_buffer_append_prefix(buf, 16, 0)) < 0)
                return gnutls_assert_val(ret);
 
        /* Version */
@@ -3818,6 +3813,10 @@ static int _gnutls_export_ct_v1_sct(gnutls_buffer_st *buf,
                                                     sct->signature.data, sct->signature.size)) < 0)
                return gnutls_assert_val(ret);
 
+       /* Fill the length */
+       _gnutls_write_uint16(buf->length - length_offset - 2,
+                            buf->data + length_offset);
+
        return 0;
 }
 
@@ -3916,34 +3915,25 @@ int gnutls_x509_ext_ct_import_scts(const gnutls_datum_t *ext, gnutls_x509_ct_sct
 int gnutls_x509_ext_ct_export_scts(const gnutls_x509_ct_scts_t scts, gnutls_datum_t *ext)
 {
        int ret;
-       size_t ttl_size;
        gnutls_buffer_st buf;
 
-       const size_t base_size = sizeof(uint16_t)  /* length of the whole part */
-                                + 1  /* version */
-                                + SCT_V1_LOGID_SIZE  /* Log ID */
-                                + sizeof(uint64_t)  /* Timestamp */
-                                + 2  /* Extensions */
-                                + 2  /* hash and signature algorithms */
-                                + sizeof(uint16_t);  /* Signature length */
-
-       ttl_size = 0;
-       for (size_t i = 0; i < scts->size; i++)
-               ttl_size += base_size + scts->scts[i].signature.size;
-
        _gnutls_buffer_init(&buf);
 
-       /* Start with the length of the whole string */
-       _gnutls_buffer_append_prefix(&buf, 16, ttl_size);
+       /* Start with the length of the whole string; the actual
+        * length is filled later */
+       _gnutls_buffer_append_prefix(&buf, 16, 0);
 
        for (size_t i = 0; i < scts->size; i++) {
                if ((ret = _gnutls_export_ct_v1_sct(&buf,
-                                                   &scts->scts[i], base_size)) < 0) {
+                                                   &scts->scts[i])) < 0) {
                        gnutls_assert();
                        goto cleanup;
                }
        }
 
+       /* Fill the length */
+       _gnutls_write_uint16(buf.length - 2, buf.data);
+
        /* DER-encode the whole thing as an opaque OCTET STRING, as the spec mandates */
        ret = _gnutls_x509_encode_string(
                ASN1_ETYPE_OCTET_STRING,