On a range request Azure returns the whole-blob MD5 in the
x-ms-blob-content-md5 header (BlobContentMD5) and leaves Content-MD5
empty. The download metadata decoder only read Content-MD5, so every
ranged read overwrote the object's MD5 with an empty string.
With --vfs-cache-mode full this changed the object's fingerprint between
opens, so the VFS cache judged every reopened file as stale and
re-downloaded it, defeating the cache and inflating egress. Prefer
BlobContentMD5 and never overwrite a known hash with an empty one.
Nick Craig-Wood
70c815d1b7