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# file : libbutl/manifest-parser.bash.in
# license : MIT; see accompanying LICENSE file
if [ "$butl_manifest_parser" ]; then
return 0
else
butl_manifest_parser=true
fi
@import libbutl.bash/utility@
# Parse the manifest reading from stdin and writing the binary representation
# to stdout.
#
# Normally you would use the start/finish functions below. But if you don't
# care about errors, the following would be the typical usage:
#
# while IFS=: read -r -d '' n v; do
# ...
# done < <(butl_parse_manifest)
#
function butl_parse_manifest ()
{
"$(butl_path)/manifest" parse
}
# Start the manifest parsing co-process setting the following "return"
# variables:
#
# butl_manifest_parser_ofd
# butl_manifest_parser_ifd
# butl_manifest_parser_pid
#
# If <file> is not specified, then read from stdin.
#
# The typical usage:
#
# butl_manifest_parser_start
#
# while IFS=: read -ru "$butl_manifest_parser_ofd" -d '' n v; do
# ...
# done
#
# butl_manifest_parser_finish
#
function butl_manifest_parser_start () # [<file>]
{
if [ "$#" -gt 0 ]; then
exec {butl_manifest_parser_ifd}<"$1"
else
exec {butl_manifest_parser_ifd}<&0
fi
# Note that bash co-process facility is racy: as soon as the process
# finishes, bash unsets COPROC/COPROC_PID (my guess would be it checks after
# each command in the script). This specific sequence of steps (and the one
# in *_finish()) seems to work reliably at least from bash 4.3.30 and
# up. See the following resources for details:
#
# http://wiki.bash-hackers.org/syntax/keywords/coproc
# http://tldp.org/LDP/abs/html/bashver4.html (coproc section)
# https://lists.gnu.org/archive/html/bug-bash/2014-02/msg00017.html
# https://lists.gnu.org/archive/html/bug-bash/2012-12/msg00069.html
# https://lists.gnu.org/archive/html/bug-bash/2012-10/msg00027.html
#
# Also note that the bash bug (still present in 5.0) prevents running
# multiple coprocesses at a time (see the BUGS section of bash(1) man page
# for details).
#
# An update: it turns out that we still can end up with an unset COPROC if
# the process finishes too early. To avoid that we suspend the subshell
# before executing the parser process and resume it after querying the
# COPROC value. Note that we need to be careful not to attempt to resume the
# process that hasn't suspended itself (see butl_resume_process() for
# details).
#
# Note that the suspend builtin doesn't work in subshells by default since
# there is no job control enabled for them. Also when it is enabled (via
# `set -m`), the builtin stops subshells recursively up to the command being
# run from the interactive shell, which is not what we want. That's why we
# use kill which is also a builtin and thus presumably is not slower than
# suspend.
#
coproc { kill -SIGSTOP $BASHPID; exec "$(butl_path)/manifest" parse; } \
<&"$butl_manifest_parser_ifd"
exec {butl_manifest_parser_ofd}<&"${COPROC[0]}"
butl_manifest_parser_pid="$COPROC_PID"
butl_resume_process "$butl_manifest_parser_pid"
}
# Finish the manifest parsing co-process.
#
function butl_manifest_parser_finish ()
{
exec {butl_manifest_parser_ofd}<&-
wait "$butl_manifest_parser_pid"
exec {butl_manifest_parser_ifd}<&-
}
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