The following predicates are provided for building hashes
incrementally. This works by first creating a context with
crypto_context_new/2,
then using this context with crypto_data_context/3
to incrementally obtain further contexts, and finally extract the
resulting hash with crypto_context_hash/2.
- [det]crypto_context_new(-Context,
+Options)
- Context is unified with the empty context, taking into
account
Options. The context can be used in crypto_data_context/3.
For
Options, see crypto_data_hash/3.
| Context | is an opaque pure Prolog term that
is subject to garbage collection. |
- [det]crypto_data_context(+Data,
+Context0, -Context)
- Context0 is an existing computation context, and Context
is the new context after hashing Data in addition to the
previously hashed data. Context0 may be produced by a prior
invocation of either crypto_context_new/2
or crypto_data_context/3
itself.
This predicate allows a hash to be computed in chunks, which may be
important while working with Metalink (RFC 5854), BitTorrent or similar
technologies, or simply with big files.
- crypto_context_hash(+Context,
-Hash)
- Obtain the hash code of Context. Hash is an atom
representing the hash code that is associated with the current state of
the computation context Context.
The following hashing predicates work over streams:
- [det]crypto_open_hash_stream(+OrgStream,
-HashStream, +Options)
- Open a filter stream on OrgStream that maintains a hash. The
hash can be retrieved at any time using crypto_stream_hash/2.
Available
Options in addition to those of crypto_data_hash/3
are:
- close_parent(+Bool)
- If
true (default), closing the filter stream also closes
the original (parent) stream.
- [det]crypto_stream_hash(+HashStream,
-Hash)
- Unify Hash with a hash for the bytes sent to or read from
HashStream. Note that the hash is computed on the stream
buffers. If the stream is an output stream, it is first flushed and the
Digest represents the hash at the current location. If the stream is an
input stream the Digest represents the hash of the processed input
including the already buffered data.
