make rhizome over mdp block size configurable.

1K seems too big to be reliable on our prototype UHF radio links,
as CRCs fail almost all the time. #48

conf_schema.h

@@ -312,6 +312,7 @@ ATOM(int,                   enable,     1, cf_opt_int_boolean,, "If true, server
 STRING(256,                 datastore_path, "", cf_opt_absolute_path,, "Path of rhizome storage directory, absolute or relative to instance directory")
 ATOM(uint64_t,              database_size, 1000000, cf_opt_uint64_scaled,, "Size of database in bytes")
 ATOM(uint64_t,              max_internal_blob_size, 10000000000, cf_opt_uint64_scaled,, "Size of largest bundle to store internally in database.")
+ATOM(uint64_t,              rhizome_mdp_block_size, 512, cf_opt_uint64_scaled,, "Rhizome MDP block size.")
 ATOM(uint32_t,              fetch_delay_ms, 50, cf_opt_uint32_nonzero,, "Delay from receiving first bundle advert to initiating fetch")
 SUB_STRUCT(rhizome_direct,  direct,)
 SUB_STRUCT(rhizome_api,     api,)

rhizome_fetch.c

@@ -1118,7 +1118,8 @@ static int rhizome_fetch_mdp_touch_timeout(struct rhizome_fetch_slot *slot)
   // 266ms @ 1mbit (WiFi broadcast speed) = 32x1024 byte packets.
   // But on a packet radio interface at perhaps 50kbit, this is clearly
   // a bad policy.  Ideally we should know about the interface speed
-  // and adjust behaviour accordingly.
+  // and adjust behaviour accordingly. Also the packet size should be smaller
+  // on lossy links.  1K packets seem to get through only very rarely.
   // For now, we will just make the timeout 1 second from the time of the last
   // received block.
   unschedule(&slot->alarm);
@@ -1270,7 +1271,7 @@ static int rhizome_fetch_switch_to_mdp(struct rhizome_fetch_slot *slot)
 
     slot->mdpIdleTimeout=RHIZOME_IDLE_TIMEOUT; // give up if nothing received for 5 seconds
     slot->mdpRXBitmap=0x00000000; // no blocks received yet
-    slot->mdpRXBlockLength=1024;
+    slot->mdpRXBlockLength=config.rhizome.rhizome_mdp_block_size; // Rhizome over MDP block size
     rhizome_fetch_mdp_requestblocks(slot);    
   } else {
     /* We are requesting a manifest, which is stateless, except that we eventually

tests/rhizomeprotocol

@@ -283,6 +283,29 @@ test_FileTransferMultiMDP() {
    done
 }
 
+doc_FileTransferBigMDPExtBlob="Big new bundle transfers to one node via MDP, external blob file"
+setup_FileTransferBigMDPExtBlob() {
+   setup_common
+   set_instance +B
+   executeOk_servald config set rhizome.http.enable 0
+   set_instance +A
+   executeOk_servald config set rhizome.http.enable 0
+   dd if=/dev/urandom of=file1 bs=1k count=16k 2>&1
+   echo x >>file1
+   ls -l file1
+   rhizome_add_file file1
+   start_servald_instances +A +B
+   foreach_instance +A assert_peers_are_instances +B
+   foreach_instance +B assert_peers_are_instances +A
+}
+test_FileTransferBigMDPExtBlob() {
+   wait_until bundle_received_by $BID:$VERSION +B
+   set_instance +B
+   executeOk_servald rhizome list
+   assert_rhizome_list --fromhere=0 file1
+   assert_rhizome_received file1
+}
+
 doc_FileTransferMultiMDPExtBlob="New bundle transfers to four nodes via MDP, external blob files"
 setup_FileTransferMultiMDPExtBlob() {
    setup_common