[Rd] Request: tools::md5sum should accept connections and finally in-memory objects

John Mount jmount @end|ng |rom w|n-vector@com
Fri May 1 23:09:31 CEST 2020

Perhaps use the digest package? Isn't "R the R packages?"

> On May 1, 2020, at 2:00 PM, Dénes Tóth <toth.denes using kogentum.hu> 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
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John Mount
http://www.win-vector.com/ <http://www.win-vector.com/> 
Our book: Practical Data Science with R
http://practicaldatascience.com <http://practicaldatascience.com/> 

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