tar.R

# This file was pulled from the R code base as of
# Thursday, November 22, 2012 at 6:24:55 AM UTC
# and edited to remove everything but the copyright
# header and untar2, and to make untar2 more tolerant
# of the 'x' and 'g' extended block indicators, the
# latter of which is used in tar files generated by
# GitHub.


#  File src/library/utils/R/tar.R
#  Part of the R package, http://www.R-project.org
#
#  Copyright (C) 1995-2012 The R Core Team
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  A copy of the GNU General Public License is available at
#  http://www.r-project.org/Licenses/

untar2 <- function(tarfile, files = NULL, list = FALSE, exdir = ".")
{
    getOct <- function(x, offset, len)
    {
        x <- 0L
        for(i in offset + seq_len(len)) {
            z <- block[i]
            if(!as.integer(z)) break; # terminate on nul
            switch(rawToChar(z),
                   " " = {},
                   "0"=,"1"=,"2"=,"3"=,"4"=,"5"=,"6"=,"7"=
                   {x <- 8*x + (as.integer(z)-48)},
                   stop("invalid octal digit")
                   )
        }
        x
    }

    mydir.create <- function(path, ...) {
        ## for Windows' sake
        path <- sub("[\\/]$", "", path)
        if(file_test("-d", path)) return()
        if(!dir.create(path, showWarnings = TRUE, recursive = TRUE, ...))
           stop(gettextf("failed to create directory %s", sQuote(path)),
                domain = NA)
    }

    warn1 <- character()

    ## A tar file is a set of 512 byte records,
    ## a header record followed by file contents (zero-padded).
    ## See http://en.wikipedia.org/wiki/Tar_%28file_format%29
    if(is.character(tarfile) && length(tarfile) == 1L) {
        con <- gzfile(path.expand(tarfile), "rb") # reads compressed formats
        on.exit(close(con))
    } else if(inherits(tarfile, "connection")) con <- tarfile
    else stop("'tarfile' must be a character string or a connection")
    if (!missing(exdir)) {
        mydir.create(exdir)
        od <- setwd(exdir)
        on.exit(setwd(od), add = TRUE)
    }
    contents <- character()
    llink <- lname <- NULL
    repeat{
        block <- readBin(con, "raw", n = 512L)
        if(!length(block)) break
        if(length(block) < 512L) stop("incomplete block on file")
        if(all(block == 0)) break
        ns <- max(which(block[1:100] > 0))
        name <- rawToChar(block[seq_len(ns)])
        magic <- rawToChar(block[258:262])
        if ((magic == "ustar") && block[346] > 0) {
            ns <- max(which(block[346:500] > 0))
            prefix <- rawToChar(block[345+seq_len(ns)])
            name <- file.path(prefix, name)
        }
        ## mode zero-padded 8 bytes (including nul) at 101
        ## Aargh: bsdtar has this one incorrectly with 6 bytes+space
        mode <- as.octmode(getOct(block, 100, 8))
        size <- getOct(block, 124, 12)
        ts <- getOct(block, 136, 12)
        ft <- as.POSIXct(as.numeric(ts), origin="1970-01-01", tz="UTC")
        csum <- getOct(block, 148, 8)
        block[149:156] <- charToRaw(" ")
        xx <- as.integer(block)
        checksum <- sum(xx) %% 2^24 # 6 bytes
        if(csum != checksum) {
            ## try it with signed bytes.
            checksum <- sum(ifelse(xx > 127, xx - 128, xx)) %% 2^24 # 6 bytes
            if(csum != checksum)
                warning(gettextf("checksum error for entry '%s'", name),
                        domain = NA)
        }
        type <- block[157L]
        ctype <- rawToChar(type)
        if(type == 0L || ctype == "0") {
            if(!is.null(lname)) {name <- lname; lname <- NULL}
            contents <- c(contents, name)
            remain <- size
            dothis <- !list
            if(dothis && length(files)) dothis <- name %in% files
            if(dothis) {
                mydir.create(dirname(name))
                out <- file(name, "wb")
            }
            for(i in seq_len(ceiling(size/512L))) {
                block <- readBin(con, "raw", n = 512L)
                if(length(block) < 512L)
                    stop("incomplete block on file")
                if (dothis) {
                    writeBin(block[seq_len(min(512L, remain))], out)
                    remain <- remain - 512L
                }
            }
            if(dothis) {
                close(out)
                Sys.chmod(name, mode, FALSE) # override umask
                Sys.setFileTime(name, ft)
            }
        } else if(ctype %in% c("1", "2")) { # hard and symbolic links
            contents <- c(contents, name)
            ns <- max(which(block[158:257] > 0))
            name2 <- rawToChar(block[157L + seq_len(ns)])
            if(!is.null(lname)) {name <- lname; lname <- NULL}
            if(!is.null(llink)) {name2 <- llink; llink <- NULL}
            if(!list) {
                if(ctype == "1") {
                    if (!file.link(name2, name)) { # will give a warning
                        ## link failed, so try a file copy
                        if(file.copy(name2, name))
                             warn1 <- c(warn1, "restoring hard link as a file copy")
                        else
                            warning(gettextf("failed to copy %s to %s", sQuote(name2), sQuote(name)), domain = NA)
                    }
                } else {
                    if(isWindows()) {
                        ## this will not work for links to dirs
                        from <- file.path(dirname(name), name2)
                        if (!file.copy(from, name))
                            warning(gettextf("failed to copy %s to %s", sQuote(from), sQuote(name)), domain = NA)
                        else
                            warn1 <- c(warn1, "restoring symbolic link as a file copy")
                   } else {
                       if(!file.symlink(name2, name)) { # will give a warning
                        ## so try a file copy: will not work for links to dirs
                        from <- file.path(dirname(name), name2)
                        if (file.copy(from, name))
                            warn1 <- c(warn1, "restoring symbolic link as a file copy")
                           else
                               warning(gettextf("failed to copy %s to %s", sQuote(from), sQuote(name)), domain = NA)
                       }
                   }
                }
            }
        } else if(ctype == "5") {
            contents <- c(contents, name)
            if(!list) {
                mydir.create(name)
                Sys.chmod(name, mode, TRUE) # FIXME: check result
                ## no point is setting time, as dir will be populated later.
            }
        } else if(ctype %in% c("L", "K")) {
            ## This is a GNU extension that should no longer be
            ## in use, but it is.
            name_size <- 512L * ceiling(size/512L)
            block <- readBin(con, "raw", n = name_size)
            if(length(block) < name_size)
                stop("incomplete block on file")
            ns <- max(which(block > 0)) # size on file may or may not include final nul
            if(ctype == "L")
                lname <- rawToChar(block[seq_len(ns)])
            else
                llink <- rawToChar(block[seq_len(ns)])
        } else if(ctype %in% c("x", "g")) {
            readBin(con, "raw", n = 512L*ceiling(size/512L))
        } else stop("unsupported entry type ", sQuote(ctype))
    }
    if(length(warn1)) {
        warn1 <- unique(warn1)
        for (w in warn1) warning(w, domain = NA)
    }
    if(list) contents else invisible(0L)
}