SHA-512 and CRC-32 of a file

sha512file() returns the SHA-512 digest of a file's bytes and crc32file() its CRC-32 checksum. Use the first to pin a data file for the long term and the second as a fast check that a large file arrived intact (it is the checksum zip archives record). The SHA-256 counterpart is sha256file().

Usage

sha512file(path, blkbytes = 1048576L)

crc32file(path, blkbytes = 1048576L)

Arguments

path

Path to an existing file, a single string.

blkbytes

Read size in bytes, a positive whole number (default 1048576). Affects speed only, never the result.

Value

sha512file(): a length-1 character vector, 128 lowercase hex characters. crc32file(): a length-1 numeric (double) checksum between 0 and 2^32 - 1.

Details

The file is read in blocks of blkbytes with readBin(), the blocks are joined into one raw vector, and the digest of that vector is computed with csha512() or ccrc32(). The whole file is therefore held in memory once: memory use grows with the file size. blkbytes affects only the reading, never the result. An empty file gives the digest of no bytes (cf83e135... for SHA-512, 0 for CRC-32).

Errors: path that does not name an existing file (or names a directory); blkbytes that is not a positive whole number.

Examples

p <- tempfile()
writeLines("capsule payload", p)

sha512file(p)
#> [1] "5d0664a30f586585aca8896c34269ca62f2eba708d5d7983a80925d50eaee5535116f104f245649f33054880810b4f88c542d70fd86ba95111f80342fa9bf9ba"
crc32file(p)
#> [1] 2211766739

# The block size is a speed knob and cannot change the digest.
identical(sha512file(p, 16), sha512file(p, 1048576))
#> [1] TRUE

# the same as hashing the bytes directly
identical(sha512file(p), csha512(readBin(p, "raw", file.size(p))))
#> [1] TRUE

# a missing file is an error
try(crc32file(file.path(tempdir(), "no-such-file")))
#> Error : crc32file: `path`: no such file: /tmp/RtmpZpRdcE/no-such-file
unlink(p)