#!/bin/sh

# retrieve a WAL file from a pg_receivewal archive
#
# Copyright (C) 2021-2022 Christoph Berg <myon@debian.org>
#
#  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.

set -eu

binroot="/usr/lib/postgresql/"
#redhat# binroot="/usr/pgsql-"

if [ -z "${2:-}" ]; then
    echo "Syntax: $0 /path/to/wal/%f %p" >&2
    exit 1
fi

file="$1"
path="$2"

# sanity-check the first argument
waldir="$(dirname $file)"
if ! [ -d "$waldir" ]; then
    echo "$0: $waldir is not a directory" >&2
    exit 129
fi

if [ -f "$file.gz" ]; then
    gunzip < "$file.gz" > "$path" || exit 129

elif [ -f "$file.lz4" ]; then
    unlz4 < "$file.lz4" > "$path" || exit 129

elif [ -f "$file" ]; then
    cp "$file" "$path" || exit 129

elif [ -f "$file.gz.partial" ] || [ -f "$file.lz4.partial" ]; then
    if [ -s "$file.gz.partial" ]; then
        gunzip < "$file.gz.partial" > "$path" || exit 129
    elif [ -s "$file.lz4.partial" ]; then
        unlz4 < "$file.lz4.partial" > "$path" || exit 129
    else
        # .gz.partial starts completely empty, gunzip doesn't like that
        touch "$path" || exit 129
    fi

    # expand file to original size
    version=$(cat PG_VERSION) || exit 129
    wal_file_size=$(LC_ALL=C "$binroot$version/bin/pg_controldata" . | awk '/^Bytes per WAL segment:/ { print $5 }') || exit 129
    [ "$wal_file_size" -gt 0 ] || exit 129
    truncate --size="$wal_file_size" "$path" || exit 129

elif [ -f "$file.partial" ]; then
    cp "$file.partial" "$path" || exit 129

else
    # file not found, exit silently in order not to spam the server log with errors
    exit 1
fi

exit 0

: <<=cut

=head1 NAME

pg_getwal - retrieve a WAL file from a pg_receivewal archive

=head1 SYNOPSIS

B<pg_getwal> I</path/to/wal/%f> I<%p>

=head1 DESCRIPTION

B<pg_getwal> retrieves and decompresses files from a WAL archive maintained by
B<pg_receivewal> and B<pg_backupcluster>. It is put into PostgreSQL's
B<restore_command> by B<pg_restorecluster>.

=head1 SEE ALSO

L<pg_restorecluster(1)>, L<pg_backupcluster(1)>.

=head1 AUTHOR

Christoph Berg L<E<lt>myon@debian.orgE<gt>>

=cut