These snippets should be useful to read RAR archives with store compression (which means none compression is used). Feel free to edit/add source-codes if you have faster/better/new language implementation.

Links:

• ​http://www.unrarlib.org/
• ​http://www.rarlab.com/rar_add.htm
• ​http://github.com/jphastings/unrar/ (in Ruby)

Python

#(c)Kamil Dzióbek turbos11(at)gmail.com
#   BSD License

from struct import *

def getlastsplit(firsrarfile,x):
    if firsrarfile[-3:]=='001':
        return firsrarfile[:-3]+('%03d' %(x+1))
    if firsrarfile[-11:-6]=='.part':
        return firsrarfile[0:-6]+('%02d' % (x+1))+firsrarfile[-4:]
    if firsrarfile[-10:-5]=='.part':
        return firsrarfile[0:-5]+('%1d' % (x+1))+firsrarfile[-4:]
    return firsrarfile[0:-2]+('%02d' %(x-1) )

def addfilehash(name,hash,seek):
    f=open(name, 'rb')
    f.seek(seek)
    for i in range(8192):
        hash+=unpack('<q', f.read(8))[0]
        hash =hash & 0xffffffffffffffff
    return hash


def OpensubtitlesHashRar(firsrarfile):
    """Hash file in rar split archive. -> (size,hash)"""
    if not(firsrarfile.lower().endswith('.rar') | firsrarfile.endswith('.001')):
        raise Exception('Bad file suffix. Only .rar and .001 support.')
    if firsrarfile[-11:-6]=='.part':
        firsrarfile=firsrarfile[0:-6]+'01'+firsrarfile[-4:]
    f=open(firsrarfile, 'rb')
    a=f.read(4)
    if a!='Rar!':
        raise Exception('ERROR: This is not rar file.')
    seek=0
    for i in range(4):
        f.seek(seek)
        a=f.read(100)
        type,flag,size=unpack( '<BHH', a[2:2+5]) 
        if 0x74==type:
            if 0x30!=unpack( '<B', a[25:25+1])[0]:
                raise Exception('Bad compression method! Work only for "store".')            
            s_partiizebodystart=seek+size
            s_partiizebody,s_unpacksize=unpack( '<II', a[7:7+2*4])
            if (flag & 0x0100):
                s_unpacksize=(unpack( '<I', a[36:36+4])[0] <<32 )+s_unpacksize
                print 'Hash untested for files biger that 2gb. May work or may generate bad hash.'
            lastrarfile=getlastsplit(firsrarfile,(s_unpacksize-1)/s_partiizebody)
            hash=addfilehash(firsrarfile,s_unpacksize,s_partiizebodystart)
            hash=addfilehash(lastrarfile,hash,(s_unpacksize%s_partiizebody)+s_partiizebodystart-65536)
            return (s_unpacksize,"%016x" % hash )
        seek+=size
    raise Exception('ERROR: Not Body part in rar file.')

#example
firsrarsplitfile='I:\\test.rar'
size,hash=OpensubtitlesHashRar(firsrarsplitfile)
print 'use this valuse on opensubtiles.com\n\tsize is: %d\n\thash is: %s' % (size,hash)

Ruby

Noncomplete translation of Python-code.

def getlastsplit(firsrarfile, x)
    return firsrarfile[0..-3] + ('%03d' % (x+1)) if firsrarfile[-3..-1] == '001'
    return firsrarfile[0..-6] + ('%02d' % (x+1)) + firsrarfile[-4..-1] if firsrarfile[-11..-6] == '.part'
    return firsrarfile[0..-5] + ('%1d' % (x+1)) + firsrarfile[-4..-1] if firsrarfile[-10..-5] == '.part'
    return firsrarfile[0..-2] + ('%02d' % (x-1))
end

def addfilehash(name, hash, seek)
    f = File.open(name, 'rb')
    f.seek(seek)
    8192.times do |i|
        hash += f.read(8).unpack('q')[0]
        hash = hash & 0xffffffffffffffff
    end
    return hash
end

# Hash file in rar split archive. -> (size,hash)
def OpensubtitlesHashRar(firsrarfile)
    raise 'Bad file suffix. Only .rar and .001 support.' unless firsrarfile.downcase =~ /\.rar$/ || firsrarfile  =~ /\.001$/
        
    firsrarfile = firsrarfile[0..-6] + '01' + firsrarfile[-4..-1] if firsrarfile[-11..-6] == '.part'
        
    f = File.open(firsrarfile, 'rb')
    a = f.read(4)
    raise 'ERROR: This is not rar file.' if a != 'Rar!'
        
    seek = 0
    4.times do |i|
        f.seek(seek)
        a = f.read(100)
        type, flag, size = a[2..7].unpack('Cvv') 
	puts [type, flag, size].inspect
        if 0x74 == type
            raise 'Bad compression method! Work only for "store".' if 0x30 != a[25..26].unpack('C')[0]
                
            s_partiizebodystart = seek + size
            s_partiizebody, s_unpacksize = a[7..15].unpack('<II')
            if flag & 0x0100
                s_unpacksize = (a[36..40].unpack('<I')[0] << 32) + s_unpacksize
                puts 'Hash untested for files biger that 2gb. May work or may generate bad hash.'
            end
            lastrarfile = getlastsplit(firsrarfile, (s_unpacksize-1) / s_partiizebody)
            hash = addfilehash(firsrarfile, s_unpacksize, s_partiizebodystart)
            hash = addfilehash(lastrarfile, hash, (s_unpacksize % s_partiizebody) + s_partiizebodystart - 65536)
            return [s_unpacksize, "%016x" % hash]
        end
        seek += size
    end
    raise 'ERROR: Not Body part in rar file.'
end

#example
firsrarsplitfile=ARGV[0]
size, hash = OpensubtitlesHashRar(firsrarsplitfile)
puts('use this valuse on opensubtiles.com\n\tsize is: %d\n\thash is: %s' % [size, hash])