QUIC: refactored packet creation.

The "min" and "max" arguments refer to UDP datagram size.  Generating payload
requires to account properly for header size, which is variable and depends on
payload size and packet number.

1 files changed, 45 insertions, 7 deletions

diff --git a/src/event/quic/ngx_event_quic_transport.c b/src/event/quic/ngx_event_quic_transport.c
index 16ae9c37c..6bc188b59 100644
--- a/src/event/quic/ngx_event_quic_transport.c
+++ b/src/event/quic/ngx_event_quic_transport.c
@@ -94,7 +94,7 @@ static ngx_int_t ngx_quic_supported_version(uint32_t version);
 static ngx_int_t ngx_quic_parse_long_header_v1(ngx_quic_header_t *pkt);
 
 static size_t ngx_quic_create_long_header(ngx_quic_header_t *pkt, u_char *out,
-    size_t pkt_len, u_char **pnp);
+    u_char **pnp);
 static size_t ngx_quic_create_short_header(ngx_quic_header_t *pkt, u_char *out,
     u_char **pnp);
 
@@ -613,25 +613,63 @@ ngx_quic_create_version_negotiation(ngx_quic_header_t *pkt, u_char *out)
 }
 
 
+/* returns the amount of payload quic packet of "pkt_len" size may fit or 0 */
 size_t
-ngx_quic_create_header(ngx_quic_header_t *pkt, u_char *out, size_t pkt_len,
-    u_char **pnp)
+ngx_quic_payload_size(ngx_quic_header_t *pkt, size_t pkt_len)
+{
+    size_t  len;
+
+    if ngx_quic_short_pkt(pkt->flags) {
+
+        len = 1 + pkt->dcid.len + pkt->num_len + EVP_GCM_TLS_TAG_LEN;
+        if (len > pkt_len) {
+            return 0;
+        }
+
+        return pkt_len - len;
+    }
+
+    /* flags, version, dcid and scid with lengths and zero-length token */
+    len = 5 + 2 + pkt->dcid.len + pkt->scid.len
+           + (pkt->level == ssl_encryption_initial ? 1 : 0);
+
+    if (len > pkt_len) {
+        return 0;
+    }
+
+    /* (pkt_len - len) is 'remainder' packet length (see RFC 9000, 17.2) */
+    len += ngx_quic_varint_len(pkt_len - len)
+           + pkt->num_len + EVP_GCM_TLS_TAG_LEN;
+
+    if (len > pkt_len) {
+        return 0;
+    }
+
+    return pkt_len - len;
+}
+
+
+size_t
+ngx_quic_create_header(ngx_quic_header_t *pkt, u_char *out, u_char **pnp)
 {
     return ngx_quic_short_pkt(pkt->flags)
            ? ngx_quic_create_short_header(pkt, out, pnp)
-           : ngx_quic_create_long_header(pkt, out, pkt_len, pnp);
+           : ngx_quic_create_long_header(pkt, out, pnp);
 }
 
 
 static size_t
 ngx_quic_create_long_header(ngx_quic_header_t *pkt, u_char *out,
-    size_t pkt_len, u_char **pnp)
+    u_char **pnp)
 {
+    size_t   rem_len;
     u_char  *p, *start;
 
+    rem_len = pkt->num_len + pkt->payload.len + EVP_GCM_TLS_TAG_LEN;
+
     if (out == NULL) {
         return 5 + 2 + pkt->dcid.len + pkt->scid.len
-               + ngx_quic_varint_len(pkt_len + pkt->num_len) + pkt->num_len
+               + ngx_quic_varint_len(rem_len) + pkt->num_len
                + (pkt->level == ssl_encryption_initial ? 1 : 0);
     }
 
@@ -651,7 +689,7 @@ ngx_quic_create_long_header(ngx_quic_header_t *pkt, u_char *out,
         ngx_quic_build_int(&p, 0);
     }
 
-    ngx_quic_build_int(&p, pkt_len + pkt->num_len);
+    ngx_quic_build_int(&p, rem_len);
 
     *pnp = p;