A content digest. A digest for a given blob consists of the size of the blob
and its hash. The hash algorithm to use is defined by the server. The size
is considered to be an integral part of the digest and cannot be separated.
That is, even if the
hash field is correctly specified but
not, the server MUST reject the request. The reason for including the size
in the digest is as follows: in a great many cases, the server needs to know
the size of the blob it is about to work with prior to starting an operation
with it, such as flattening Merkle tree structures or streaming it to a
worker. Technically, the server could implement a separate metadata store,
but this results in a significantly more complicated implementation as
opposed to having the client specify the size up-front (or storing the size
along with the digest in every message where digests are embedded). This
does mean that the API leaks some implementation details of (what we
consider to be) a reasonable server implementation, but we consider this to
be a worthwhile tradeoff. When a
Digest is used to refer to a proto
message, it always refers to the message in binary encoded form. To ensure
consistent hashing, clients and servers MUST ensure that they serialize
messages according to the following rules, even if there are alternate valid
encodings for the same message: * Fields are serialized in tag order. *
There are no unknown fields. * There are no duplicate fields. * Fields are
serialized according to the default semantics for their type. Most protocol
buffer implementations will always follow these rules when serializing, but
care should be taken to avoid shortcuts. For instance, concatenating two
messages to merge them may produce duplicate fields.
- hash ↔ String
The hash. In the case of SHA-256, it will always be a lowercase hex string
exactly 64 characters long.
read / write
- hashCode → int
The hash code for this object. [...]
- runtimeType → Type
A representation of the runtime type of the object.
- sizeBytes ↔ String
The size of the blob, in bytes.
read / write