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Calculating a SHA1 hash for large files
Description
There are a number of posts on the net about SHA1 hashing in groovy but they tend to assume small data sets. This script calculates a SHA1 hash for an arbitrary size argument file using a one MB memory buffer.
Note that the script uses the File.eachByte(int, closure) method which is only available in Groovy v1.7.4 and later. You can naturally replace this construct with some other pattern, but as it fits so beautifully for the purpose, the script makes use of it.
Code
Paste the below into a file "sha1.groovy" and run with a file param, i.e.:
> groovy sha1.groovy myLargeFile.isoand now for the code:
import java.security.MessageDigest
int KB = 1024
int MB = 1024*KB
File f = new File(args[0])
if (!f.exists() || !f.isFile()) {
println "Invalid file $f provided"
println "Usage: groovy sha1.groovy <file_to_hash>"
}
def messageDigest = MessageDigest.getInstance("SHA1")
long start = System.currentTimeMillis()
f.eachByte(MB) { byte[] buf, int bytesRead ->
messageDigest.update(buf, 0, bytesRead);
}
def sha1Hex = new BigInteger(1, messageDigest.digest()).toString(16).padLeft( 40, '0' )
long delta = System.currentTimeMillis()-start
println "$sha1Hex took $delta ms to calculate"Author: Matias Bjarland, Iteego Inc
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