fixup! sys/net/nanocoap: implement CoAP over TCP

sys/net/application_layer/nanocoap/sock.c

@@ -1683,17 +1683,23 @@ static int _nanocoap_server_send_separate_udp(const nanocoap_server_response_ctx
     return sock_udp_sendv_aux(NULL, &head, remote, aux_out_ptr);
 }
 
-static int _tcp_send_all(sock_tcp_t *sock, const void *_data, size_t len)
+/* TODO: Implement sock_tcp_writev() to avoid sending the CoAP header and
+ * payload in separate TCP segments even if they would fit in a single one. */
+static int _tcp_writev(sock_tcp_t *sock, const iolist_t *iol)
 {
-    const uint8_t *data = _data;
-    ssize_t tmp;
-    while (len) {
-        tmp = sock_tcp_write(sock, data, len);
-        if (tmp < 0) {
-            return tmp;
+    while (iol) {
+        const uint8_t *data = iol->iol_base;
+        size_t len = iol->iol_len;
+        while (len) {
+            ssize_t tmp = sock_tcp_write(sock, data, len);
+            if (tmp < 0) {
+                return tmp;
+            }
+            data += tmp;
+            len -= tmp;
         }
-        data += tmp;
-        len -= tmp;
+
+        iol = iol->iol_next;
     }
 
     return 0;
@@ -1713,17 +1719,29 @@ static int _nanocoap_server_send_separate_tcp(const nanocoap_server_response_ctx
 
     ssize_t rbuf_len = coap_build_tcp_hdr(rbuf, sizeof(rbuf), ctx->token, ctx->tkl, code);
 
+    size_t data_len = (len > 0) ? (len + 1) : 0;
+    size_t shrunk = coap_finalize_tcp_header(rbuf, data_len);
+
     if (rbuf_len < 0) {
         return rbuf_len;
     }
 
-    size_t shrunk = coap_finalize_tcp_header(rbuf, len);
-
-    int retval = _tcp_send_all(sock, rbuf + shrunk, rbuf_len - shrunk);
-    if (retval) {
-        return retval;
+    if (len) {
+        rbuf[rbuf_len++] = 0xff; /*payload marker */
     }
-    return _tcp_send_all(sock, payload, len);
+
+    iolist_t data = {
+        .iol_base = (void *)payload,
+        .iol_len  = len,
+    };
+
+    iolist_t head = {
+        .iol_next = &data,
+        .iol_base = rbuf + shrunk,
+        .iol_len = rbuf_len - shrunk,
+    };
+
+    return _tcp_writev(sock, &head);
 }
 
 int nanocoap_server_send_separate(const nanocoap_server_response_ctx_t *ctx,