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+#!/usr/bin/env bash
+
+# This script is a wrapper to the other download backends.
+# Its role is to ensure atomicity when saving downloaded files
+# back to BR2_DL_DIR, and not clutter BR2_DL_DIR with partial,
+# failed downloads.
+#
+# Call it with -h to see some help.
+
+# To avoid cluttering BR2_DL_DIR, we download to a trashable
+# location, namely in $(BUILD_DIR).
+# Then, we move the downloaded file to a temporary file in the
+# same directory as the final output file.
+# This allows us to finally atomically rename it to its final
+# name.
+# If anything goes wrong, we just remove all the temporaries
+# created so far.
+
+# We want to catch any unexpected failure, and exit immediately.
+set -e
+
+main() {
+ local OPT OPTARG
+ local backend output
+
+ # Parse our options; anything after '--' is for the backend
+ while getopts :hb:o: OPT; do
+ case "${OPT}" in
+ h) help; exit 0;;
+ b) backend="${OPTARG}";;
+ o) output="${OPTARG}";;
+ :) error "option '%s' expects a mandatory argument\n" "${OPTARG}";;
+ \?) error "unknown option '%s'\n" "${OPTARG}";;
+ esac
+ done
+ # Forget our options, and keep only those for the backend
+ shift $((OPTIND-1))
+
+ if [ -z "${backend}" ]; then
+ error "no backend specified, use -b\n"
+ fi
+ if [ -z "${output}" ]; then
+ error "no output specified, use -o\n"
+ fi
+
+ # tmpd is a temporary directory in which backends may store intermediate
+ # by-products of the download.
+ # tmpf is the file in which the backends should put the downloaded content.
+ # tmpd is located in $(BUILD_DIR), so as not to clutter the (precious)
+ # $(BR2_DL_DIR)
+ # We let the backends create tmpf, so they are able to set whatever
+ # permission bits they want (although we're only really interested in
+ # the executable bit.)
+ tmpd="$(mktemp -d "${BUILD_DIR}/.${output##*/}.XXXXXX")"
+ tmpf="${tmpd}/output"
+
+ # Helpers expect to run in a directory that is *really* trashable, so
+ # they are free to create whatever files and/or sub-dirs they might need.
+ # Doing the 'cd' here rather than in all backends is easier.
+ cd "${tmpd}"
+
+ # If the backend fails, we can just remove the temporary directory to
+ # remove all the cruft it may have left behind. Then we just exit in
+ # error too.
+ if ! "${OLDPWD}/support/download/${backend}" "${tmpf}" "${@}"; then
+ rm -rf "${tmpd}"
+ exit 1
+ fi
+
+ # cd back to free the temp-dir, so we can remove it later
+ cd "${OLDPWD}"
+
+ # tmp_output is in the same directory as the final output, so we can
+ # later move it atomically.
+ tmp_output="$(mktemp "${output}.XXXXXX")"
+
+ # 'mktemp' creates files with 'go=-rwx', so the files are not accessible
+ # to users other than the one doing the download (and root, of course).
+ # This can be problematic when a shared BR2_DL_DIR is used by different
+ # users (e.g. on a build server), where all users may write to the shared
+ # location, since other users would not be allowed to read the files
+ # another user downloaded.
+ # So, we restore the 'go' access rights to a more sensible value, while
+ # still abiding by the current user's umask. We must do that before the
+ # final 'mv', so just do it now.
+ # Some backends (cp and scp) may create executable files, so we need to
+ # carry the executable bit if needed.
+ [ -x "${tmpf}" ] && new_mode=755 || new_mode=644
+ new_mode=$(printf "%04o" $((0${new_mode} & ~0$(umask))))
+ chmod ${new_mode} "${tmp_output}"
+
+ # We must *not* unlink tmp_output, otherwise there is a small window
+ # during which another download process may create the same tmp_output
+ # name (very, very unlikely; but not impossible.)
+ # Using 'cp' is not reliable, since 'cp' may unlink the destination file
+ # if it is unable to open it with O_WRONLY|O_TRUNC; see:
+ # http://pubs.opengroup.org/onlinepubs/9699919799/utilities/cp.html
+ # Since the destination filesystem can be anything, it might not support
+ # O_TRUNC, so 'cp' would unlink it first.
+ # Use 'cat' and append-redirection '>>' to save to the final location,
+ # since that is the only way we can be 100% sure of the behaviour.
+ if ! cat "${tmpf}" >>"${tmp_output}"; then
+ rm -rf "${tmpd}" "${tmp_output}"
+ exit 1
+ fi
+ rm -rf "${tmpd}"
+
+ # tmp_output and output are on the same filesystem, so POSIX guarantees
+ # that 'mv' is atomic, because it then uses rename() that POSIX mandates
+ # to be atomic, see:
+ # http://pubs.opengroup.org/onlinepubs/9699919799/functions/rename.html
+ if ! mv -f "${tmp_output}" "${output}"; then
+ rm -f "${tmp_output}"
+ exit 1
+ fi
+}
+
+help() {
+ cat <<_EOF_
+NAME
+ ${my_name} - download wrapper for Buildroot
+
+SYNOPSIS
+ ${my_name} [OPTION]... -- [BACKEND OPTION]...
+
+DESCRIPTION
+ Wrapper script around different download mechanisms. Ensures that
+ concurrent downloads do not conflict, that partial downloads are
+ properly evicted without leaving temporary files, and that access
+ rights are maintained.
+
+ -h This help text.
+
+ -b BACKEND
+ Wrap the specified BACKEND. Known backends are:
+ bzr Bazaar
+ cp Local files
+ cvs Concurrent Versions System
+ git Git
+ hg Mercurial
+ scp Secure copy
+ svn Subversion
+ wget HTTP download
+
+ -o FILE
+ Store the downloaded archive in FILE.
+
+ Exit status:
+ 0 if OK
+ !0 in case of error
+
+ENVIRONMENT
+
+ BUILD_DIR
+ The path to Buildroot's build dir
+_EOF_
+}
+
+trace() { local msg="${1}"; shift; printf "%s: ${msg}" "${my_name}" "${@}"; }
+warn() { trace "${@}" >&2; }
+errorN() { local ret="${1}"; shift; warn "${@}"; exit ${ret}; }
+error() { errorN 1 "${@}"; }
+
+my_name="${0##*/}"
+main "${@}"