gnrc, nanocoap: add optional work-arounds for buggy CoAP servers

sys/include/net/nanocoap_sock.h

@@ -175,6 +175,18 @@ extern "C" {
 #define CONFIG_NANOCOAP_SERVER_STACK_SIZE       THREAD_STACKSIZE_DEFAULT
 #endif
 
+/**
+ * @brief   Include a random token with block-wise transfers.
+ *
+ * This is a workaround for buggy CoPA implementations (e.g. go-coap) that expect
+ * to identify block-wise transfers based on the token.
+ *
+ * See https://github.com/plgd-dev/go-coap/issues/512
+ */
+#ifndef CONFIG_NANOCOAP_SOCK_BLOCK_TOKEN
+#define CONFIG_NANOCOAP_SOCK_BLOCK_TOKEN        (0)
+#endif
+
 /**
  * @brief   NanoCoAP socket types
  */

sys/net/application_layer/nanocoap/sock.c

@@ -60,6 +60,9 @@
     coap_blockwise_cb_t callback;
     void *arg;
     bool more;
+#if CONFIG_NANOCOAP_SOCK_BLOCK_TOKEN
+    uint8_t token[4];
+#endif
 } _block_ctx_t;
 
 int nanocoap_sock_dtls_connect(nanocoap_sock_t *sock, sock_udp_ep_t *local,
@@ -190,7 +193,7 @@
 
     /* random timeout, deadline for receive retries */
     uint32_t timeout = random_uint32_range((uint32_t)CONFIG_COAP_ACK_TIMEOUT_MS * US_PER_MS,
                                            (uint32_t)CONFIG_COAP_ACK_TIMEOUT_MS * CONFIG_COAP_RANDOM_FACTOR_1000);
     uint32_t deadline = _deadline_from_interval(timeout);
 
     /* check if we expect a reply */
@@ -601,7 +604,17 @@
     };
     uint16_t lastonum = 0;
 
-    buf += coap_build_hdr(pkt.hdr, COAP_TYPE_CON, NULL, 0, COAP_METHOD_GET,
+    void *token = NULL;
+    size_t token_len = 0;
+
+#if CONFIG_NANOCOAP_SOCK_BLOCK_TOKEN
+    /* HACK: go-coap always expects a token */
+    /* see https://github.com/plgd-dev/go-coap/issues/512 */
+    token = ctx->token;
+    token_len = sizeof(ctx->token);
+#endif
+
+    buf += coap_build_hdr(pkt.hdr, COAP_TYPE_CON, token, token_len, COAP_METHOD_GET,
                           nanocoap_sock_next_msg_id(sock));
     buf += coap_opt_put_uri_pathquery(buf, &lastonum, path);
     buf += coap_opt_put_uint(buf, lastonum, COAP_OPT_BLOCK2, (num << 4) | blksize);
@@ -674,6 +687,10 @@
         .more = true,
     };
 
+#if CONFIG_NANOCOAP_SOCK_BLOCK_TOKEN
+    random_bytes(ctx.token, sizeof(ctx.token));
+#endif
+
     unsigned num = 0;
     while (ctx.more) {
         DEBUG("nanocoap: fetching block %u\n", num);

sys/net/gnrc/sock/include/gnrc_sock_internal.h

@@ -55,6 +55,14 @@ extern "C" {
  */
 #define GNRC_SOCK_DYN_PORTRANGE_ERR (0)
 
+/**
+ * @brief   Check if remote address of a UDP packet matches the address the socket
+ *          is bound to.
+ */
+#ifndef CONFIG_GNRC_SOCK_UDP_CHECK_REMOTE_ADDR
+#define CONFIG_GNRC_SOCK_UDP_CHECK_REMOTE_ADDR (1)
+#endif
+
 /**
  * @brief   Structure to retrieve auxiliary data from @ref gnrc_sock_recv
  *

sys/net/gnrc/sock/udp/gnrc_sock_udp.c

@@ -231,7 +231,9 @@ static bool _accept_remote(const sock_udp_t *sock, const udp_hdr_t *hdr,
               ipv6_addr_to_str(addr_str, (ipv6_addr_t *)&sock->remote.addr, sizeof(addr_str)));
         DEBUG(", source (%s) does not match\n",
               ipv6_addr_to_str(addr_str, (ipv6_addr_t *)&remote->addr, sizeof(addr_str)));
-        return false;
+        if (CONFIG_GNRC_SOCK_UDP_CHECK_REMOTE_ADDR) {
+            return false;
+        }
     }
 
     return true;