ref: 059f9a658d20e467bba3f42e574ed381ef0c99d7
dir: /tarsum.fnl/
#!/usr/bin/env fennel
;; vim: set filetype=scheme :
(fn usage []
(io.stderr:write "Usage: tarsum <filename>\n")
(os.exit 1))
(if (< (# arg) 1) (usage))
;; (local tarball (io.open (. arg 1) "r+b"))
(with-open (tarball (io.open (. arg 1) "r+b"))
(let [header (tarball:read 0x132) headertbl {}]
(if (= header fail) (error "Unable to read file."))
(if (~= (# header) 0x132) (error "Invalid header! (Is this really a tarball?)"))
(for [i 1 (# header) 1] (table.insert headertbl (string.sub header i i)))
(for [i 0x94 0x9b 1] (tset headertbl i " "))
(var header "")
(each [k v (ipairs headertbl)] (set header (.. header v)))
(var sum 0)
(for [i 1 (# header) 1] (set sum (+ sum (string.byte header i))))
(print (string.format "Checksum: %.7o\n" sum))
(if (~= (tarball:seek "set" 0x94) 0x94) (error "Could not seek to 0x94"))
(tarball:write (string.format "%.7o" sum))
(if (~= (tarball:seek "set" 0x9b) 0x9b) (error "Could not seek to 0x9b"))
(tarball:write (string.format "%c" 0))
(tarball:flush)
0
))