Upper bound for CBOR-in-CBOR tag is 7 instead of 5 bytes

Apparently we sometimes generate blocks that are 65536 bytes large or more,
requiring a 7 byte CBOR-in-CBOR tag (65535 would only require 5 bytes), failing
the test added in #2481, as our upper bound assumed 5 bytes.

ouroboros-consensus-byron/src/Ouroboros/Consensus/Byron/Ledger/Block.hs

@@ -153,7 +153,14 @@ instance GetHeader ByronBlock where
             CC.ABOBBoundary blk -> recoverBytes       blk
       }
     where
-      overhead = 5 {- CBOR-in-CBOR -} + 2 {- EBB tag -}
+      -- The maximum block size is 65536, the CBOR-in-CBOR tag for this block
+      -- is:
+      --
+      -- > D8 18          # tag(24)
+      -- >    1A 00010000 # bytes(65536)
+      --
+      -- Which is 7 bytes, enough for up to 4294967295 bytes.
+      overhead = 7 {- CBOR-in-CBOR -} + 2 {- EBB tag -}
 
   -- Check if a block matches its header
   --

ouroboros-consensus-shelley/src/Ouroboros/Consensus/Shelley/Node.hs

@@ -374,7 +374,14 @@ instance ConfigSupportsNode (ShelleyBlock c) where
 instance TPraosCrypto c => RunNode (ShelleyBlock c) where
   nodeBlockFetchSize hdr = overhead + headerSize + bodySize
     where
-      overhead   = 5 {- CBOR-in-CBOR -} + 1 {- encodeListLen -}
+      -- The maximum block size is 65536, the CBOR-in-CBOR tag for this block
+      -- is:
+      --
+      -- > D8 18          # tag(24)
+      -- >    1A 00010000 # bytes(65536)
+      --
+      -- Which is 7 bytes, enough for up to 4294967295 bytes.
+      overhead   = 7 {- CBOR-in-CBOR -} + 1 {- encodeListLen -}
       bodySize   = fromIntegral . SL.bsize . SL.bhbody . shelleyHeaderRaw $ hdr
       headerSize = fromIntegral . SL.bHeaderSize . shelleyHeaderRaw $ hdr
 

ouroboros-consensus/ouroboros-consensus-mock/src/Ouroboros/Consensus/Mock/Node.hs

@@ -58,7 +58,7 @@ instance ( LedgerSupportsProtocol      (SimpleBlock SimpleMockCrypto ext)
          , RunMockBlock SimpleMockCrypto ext
          ) => RunNode (SimpleBlock SimpleMockCrypto ext) where
   nodeBlockFetchSize hdr =
-      5 {- CBOR-in-CBOR -} + 1 {- encodeListLen 2 -} + hdrSize + bodySize
+      7 {- CBOR-in-CBOR -} + 1 {- encodeListLen 2 -} + hdrSize + bodySize
     where
       hdrSize  = fromIntegral (Lazy.length (serialise hdr))
       bodySize = simpleBodySize (simpleHeaderStd hdr)