* Give volume.merge the needle size the target actually indexes by
needleBlobFromNeedle returned the size Append reports, which is
Size(n.DataSize) - payload bytes only. The .dat header, the needle map and
WriteNeedleBlobRequest.Size all use n.Size, which additionally covers the
flags, name, mime and lastModified fields.
Every needle volume.merge copied therefore landed with a too-small size. The
target indexed it at that length, so every later read failed the header check
in ReadBytes with a size mismatch, and on v3 the fresh AppendAtNs stamp landed
NeedleHeaderSize+DataSize+NeedleChecksumSize into the blob - exactly on the
flags byte - overwriting flags, name size, mime size and the first mime bytes
with the top of a timestamp. Needles came back with flags 0x18, no name, no
mime and a phantom TTL parsed from two arbitrary timestamp bytes; the ones
that decoded as expired 404 and vacuum would drop them. Since merge rebuilds
every replica from the merged copy, no clean replica survives.
Return n.Size, which Append fills in as it serializes, matching what the
normal write path stores via nm.Put.
* Reject needle blobs whose size disagrees with their own header
WriteNeedleBlob trusts the caller's size for two destructive things: it is
what goes into the needle map, and it is where the v3 AppendAtNs stamp is
written inside the caller's buffer. A caller passing the payload-only DataSize
convention corrupts both, and nothing surfaces until the needle is read back -
by which point every replica may already have been rebuilt from it.
Parse the blob's own header and refuse the write when the two disagree.
Mirrored in the Rust volume server.
Chris LuandGitHub
312cfe5ae1