Request: tools::md5sum should accept connections and finally in-memory objects
On 5/1/20 11:35 PM, Duncan Murdoch wrote:
The tools package is not for users, it's for functions that R uses in installing packages, checking them, etc.
I think the target group for this functionality is the group of R developers, not regular R users.
If you want a function for users, it would belong in utils.? But what's wrong with the digest package?? What's the argument that R Core should take this on?
There is nothing wrong with the digest package except for being an extra dependency which could be avoided if an already implemented C function were available at the R level. I do understand that given the load on R Core, they do include new features and the related burden of maintenance only if it is absolutely necessary. This is why I asked first whether there is a particular reason not to expose an already existing (base-R) implementation. I think it is reasonable to assume that 'md5_buffer' exists for a reason - but probably there is a reason why it never became part of any exported function. Now I checked the history of the md5.c file; it was last edited 8 years ago. Somewhat surprisingly, md5_buffer was already included in the original file (created 17 years ago), but marked as UNUSED 12 years ago. Just to clarify: I do not want suggest that R Core team should take over all functionalities of the digest package. I do really focus on computing MD5 digests, which is already possible for files. My suggestion for a more general function was meant for keeping potential further enhancements in mind.
Duncan Murdoch On 01/05/2020 5:00 p.m., D?nes T?th wrote:
AFAIK there is no hashing utility in base R which can create hash
digests of arbitrary R objects. However, as also described by Henrik
Bengtsson in [1], we have tools::md5sum() which calculates MD5 hashes of
files. Calculating hashes of in-memory objects is a very common task in
several areas, as demonstrated by the popularity of the 'digest' package
(~850.000 downloads/month).
Upon the inspection of the relevant files in the R-source (e.g., [2] and
[3]), it seems all building blocks have already been implemented so that
hashing should not be restricted to files. I would like to ask:
1) Why is md5_buffer unused?:
In src/library/tools/src/md5.c [see 2], md5_buffer is implemented which
seems to be the counterpart of md5_stream for non-file inputs:
---
#ifdef UNUSED
/* Compute MD5 message digest for LEN bytes beginning at BUFFER.? The
???? result is always in little endian byte order, so that a byte-wise
???? output yields to the wanted ASCII representation of the message
???? digest.? */
static void *
md5_buffer (const char *buffer, size_t len, void *resblock)
{
??? struct md5_ctx ctx;
??? /* Initialize the computation context.? */
??? md5_init_ctx (&ctx);
??? /* Process whole buffer but last len % 64 bytes.? */
??? md5_process_bytes (buffer, len, &ctx);
??? /* Put result in desired memory area.? */
??? return md5_finish_ctx (&ctx, resblock);
}
#endif
---
2) How can the R-community help so that this feature becomes available
in package 'tools'?
Suggestions:
As a first step, it would be great if tools::md5sum would support
connections (credit goes to Henrik for the idea). E.g., instead of the
signature tools::md5sum(files), we could have tools::md5sum(files, conn
= NULL), which would allow:
x <- runif(10)
tools::md5sum(conn = rawConnection(serialize(x, NULL)))
To avoid the inconsistency between 'files' (which computes the hash
digests in a vectorized manner, that is, one for each file) and 'conn'
(which expects a single connection), and to make it easier to extend the
hashing for other algorithms without changing the main R interface, a
more involved solution would be to introduce tools::hash and
tools::hashes, in a similar vein to digest::digest and
digest::getVDigest.
Regards,
Denes
[1]: https://github.com/HenrikBengtsson/Wishlist-for-R/issues/21
[2]:
https://github.com/wch/r-source/blob/5a156a0865362bb8381dcd69ac335f5174a4f60c/src/library/tools/src/md5.c#L172
[3]:
https://github.com/wch/r-source/blob/5a156a0865362bb8381dcd69ac335f5174a4f60c/src/library/tools/src/Rmd5.c#L27
______________________________________________ R-devel at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel