https://stackoverflow.com/q/68469752/447503 svnsync cannot recover from source idle disconnect

hugebuf.sh

#!/bin/bash

# usage:
# socat TCP-LISTEN:3128,reuseaddr,fork EXEC:"./hugebuf.sh -p",nofork

set -e

proxymode=

case $1 in
  -p)
    proxymode=x
    ;;
esac

if [ "$proxymode" ]; then
  if [ $# -ne 1 ]; then
    >&2 echo "No extra arguments expected in proxy mode"
    exit 1
  fi
else
  host=${1:?}
  port=${2:?}
fi


WAITCMD=
NAME="<"

fn_log() {
  >&2 printf '%(%c)T %s\n' -1 "$*"
}

fn_cleanup() {
  fn_log "$NAME cleanup"
  exec 4>&-
  $WAITCMD
  fn_log "$NAME exiting"
}

fn_wait_graceful() {
  fn_log "$NAME received EOF from upstream; waiting for the other side: ${OTHERPID:?}"
  sleep 60 &
  #fn_log "$NAME" wait -n ${OTHERPID:?} $!
  wait -n -p DEADPID ${OTHERPID:?} $!
  if [ x"$DEADPID" != x"${OTHERPID:?}" ]; then
    fn_log "$NAME killing the other side: ${OTHERPID:?}"
    kill -KILL ${OTHERPID:?} $! 2>/dev/null || true
  fi
}

# TODO: do not use -KILL, otherwise a grandchild may survive
fn_kill() {
  fn_log "$NAME read failed; killing the other side"
  kill -KILL ${OTHERPID:?} 2>/dev/null || true
}

# parent process is upstream reader, it pumps data with `pv`
# child process is upstream writer, it pumps data with `socat`
# '>' prefixes upstream writer logs or HTTP proxy request 
# '<' prefixes upstream reader logs or HTTP proxy response

if [ "$proxymode" ]; then
  fn_log "reading CONNECT request..."
  <&0 read -r line
  line=${line%$'\r'}
  fn_log "> $line"
  case $line in
    'CONNECT '*' HTTP'*)
      x=${line#* }
      hostport=${x%% *}
      host=${hostport%:*}
      port=${hostport:${#host}}
      port=${port#:}
      ;;
    *)
      fn_log "invalid request"
      ;;
  esac
  while true; do
    <&0 read -r line
    line=${line%$'\r'}
    fn_log "> $line"
    [ -n "$line" ] || break
  done
  #
fi

fn_log "upstream reader pid: $$"

OTHERPID=$$

socketpeerhost=$host
socketpeerport=$port

# Since 2024-03-05 Mendix Team Server blocks connections from Russia
parentproxyhost=basin
parentproxyport=3130

#parentproxyhost=

if [ x"$parentproxyhost" != x"" ]; then
  socketpeerhost=${parentproxyhost}
  socketpeerport=${parentproxyport}
fi

fn_log "connecting to ${socketpeerhost:?}:${socketpeerport}"
exec 4>"/dev/tcp/${socketpeerhost:?}/${socketpeerport}"

if [ x"$parentproxyhost" != x"" ]; then
  >&4 printf 'CONNECT %s:%s HTTP/1.1\r\n' "${host:?}" "${port:?}"
  >&4 printf '\r\n'
  while true; do
    <&4 read -r line
    line=${line%$'\r'}
    #fn_log "> $line"
    [ -n "$line" ] || break
  done
fi

if [ "$proxymode" ]; then
  fn_proxyresponseline() {
    fn_log "< $1"
    >&1 printf '%s\r\n' "$1"
  }
  fn_proxyresponseline "HTTP/1.0 200 Connection Established"
  fn_proxyresponseline "Proxy-agent: hugebuf.sh"
  fn_proxyresponseline ""
fi

# TODO: do not use `wait`, use coproc and read with timeout to confirm the other side death
{
  trap 'fn_cleanup' EXIT
  NAME=">"
  WAITCMD=fn_kill

  # override graceful wait command because we can't POSIX wait for parent
  fn_wait_graceful() {
    fn_log "$NAME received EOF from my client; waiting for the other side: ${OTHERPID:?}"
    for ((i=0;i<60;i++)); do
      # check OTHERPID still exists
      kill -0 ${OTHERPID:?} 2>/dev/null || {
        fn_log "$NAME the other side no longer exists: ${OTHERPID:?}, exiting"
        return
      }
      sleep 1
    done
    fn_log "$NAME killing the other side: ${OTHERPID:?}"
    kill -KILL ${OTHERPID:?} 2>/dev/null || true
  }

  # unlike cat socat will hopefully shutdown the socket instead of closing it
  fn_log "$NAME upstream writer started"
  socat -u FD:0 FD:1,shut-down <&0 >&4

  # closing the FDs won't terminate the connection because the parent process has same FDs
  # but we need to close them so they're not inherited by the killer
  exec 0<&- 4>&-

  # start killer
  {
    # EXIT trap is not inherited
    WAITCMD=fn_wait_graceful
    fn_cleanup
  } &

  # no error
  trap '' EXIT
} <&0 &
OTHERPID=$!

fn_log "upstream writer pid: ${OTHERPID:?}"

trap 'fn_cleanup' EXIT

WAITCMD=fn_kill

fn_log "$NAME upstream reader started"
pv --force -C -B8G -N $'\nabcdefgh' -F '%N %t %T %b' <&4
socat -u FD:0 FD:1,shut-down </dev/null
WAITCMD=fn_wait_graceful