http_xsltproc.sh

#!/bin/bash

#######################################################################
# Copyright 2016 Internet2
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#######################################################################

#######################################################################
# Help message
#######################################################################

display_help () {
/bin/cat <<- HELP_MSG
	This script is a wrapper around the xsltproc command-line tool.
	Like xsltproc, this script applies an XSL stylesheet to an XML
	document and outputs the resulting transformed document on stdout.
	Unlike xsltproc, this script fetches the target XML document
	from an HTTP server. 
	
	Usage: ${0##*/} [-hv] [-F | -C] [-o OUT_FILE] STYLESHEET URL
	
	This script takes two command-line arguments. The STYLESHEET
	argument is the absolute path to an XSL document in the local
	file system. The URL argument is the absolute URL of an XML 
	document. The script fetches the XML document at the given 
	URL using HTTP Conditional GET [RFC 7232]. If the server 
	responds with 200, the document in the response body is used. 
	If the server responds with 304, the document in the cache is
	used instead.
	
	This script requires two environment variables. CACHE_DIR is
	the absolute path to the cache directory (which may or may not
	exist) whereas LIB_DIR specifies a directory containing various 
	helper scripts.

	Options:
	   -h      Display this help message
	   -v      Write verbose messages to stdout
	   -F      Enables "Force Output Mode"
	   -C      Enables "Cache Only Mode"
	   -o      Output the transformed document to OUT_FILE

	Option -h is mutually exclusive of all other options.
	
	The default behavior of the script may be modified by using 
	option -F or -C, which are mutually exclusive. Force Output 
	Mode (option -F) forces the return of a fresh resource. The 
	resource is output on stdout if and only if the server 
	responds with 200. If the response is 304, the script silently
	fails with exit code 1.
	 
	Cache Only Mode (option -C) bypasses the GET request altogether 
	and goes directly to cache. If the resource resides in cache, 
	it is output on stdout, otherwise the script silently fails
	with exit code 1.
	
	Option -o specifies an output file in the local file system.
	If option -o is omitted, the transformed document is written
	to stdout.

	LIBRARY
	
	Environment variable LIB_DIR specifies a directory containing at
	least the following library files, which act as helper scripts for 
	${0##*/}:
	
	$LIB_FILENAMES

	EXAMPLES

	  stylesheet=/path/to/stylesheets/style.xsl
	  url=http://md.incommon.org/InCommon/InCommon-metadata.xml
	  out_file=/tmp/output.txt
	  ${0##*/} \$stylesheet \$url
	  ${0##*/} -o \$out_file \$stylesheet \$url
	  ${0##*/} -F \$stylesheet \$url
	  ${0##*/} -C \$stylesheet \$url
HELP_MSG
}

#######################################################################
# Bootstrap
#######################################################################

script_name=${0##*/}  # equivalent to basename $0

# library filenames
LIB_FILENAMES="core_lib.sh
http_tools.sh"

#######################################################################
# Process command-line options and arguments
#######################################################################

help_mode=false; verbose_mode=false; local_opts=
force_get_mode=false; cache_only_mode=false
while getopts ":hvFCo:" opt; do
	case $opt in
		h)
			help_mode=true
			;;
		v)
			verbose_mode=true
			local_opts="$local_opts -$opt"
			;;
		F)
			force_get_mode=true
			cache_only_mode=false
			local_opts="$local_opts -$opt"
			;;
		C)
			cache_only_mode=true
			force_get_mode=false
			local_opts="$local_opts -$opt"
			;;
		o)
			out_file="$OPTARG"
			;;
		\?)
			echo "ERROR: $script_name: Unrecognized option: -$OPTARG" >&2
			exit 2
			;;
		:)
			echo "ERROR: $script_name: Option -$OPTARG requires an argument" >&2
			exit 2
			;;
	esac
done

if $help_mode; then
	display_help
	exit 0
fi

# check the output file
if [ -z "$out_file" ]; then
	$verbose_mode && echo "$script_name using stdout"
else
	$verbose_mode && printf "$script_name using output file: %s\n" "$out_file"
fi

# check the number of remaining arguments
shift $(( OPTIND - 1 ))
if [ "$#" -ne 2 ]; then
	echo "ERROR: $script_name found $# command-line arguments (2 required)" >&2
	exit 2
fi

# check the stylesheet
xsl_file=$1
if [ ! -f "$xsl_file" ]; then
	echo "ERROR: $script_name: file does not exist: $xsl_file" >&2
	exit 2
fi
$verbose_mode && printf "$script_name using XSL stylesheet: %s\n" "$xsl_file"

# capture the location of the XML file
xml_location=$2
$verbose_mode && printf "$script_name using XML file at location: %s\n" "$xml_location"

#######################################################################
# Initialization
#######################################################################

# determine the cache directory
if [ -z "$CACHE_DIR" ]; then
	echo "ERROR: $script_name requires env var CACHE_DIR" >&2
	exit 2
fi
if [ ! -d "$CACHE_DIR" ]; then
	/bin/mkdir "$CACHE_DIR"
	exit_code=$?
	if [ $exit_code -ne 0 ]; then
		echo "ERROR: $script_name failed to create dir $CACHE_DIR (exit code: $exit_code)" >&2
		exit 2
	fi
fi
$verbose_mode && printf "$script_name using cache directory: %s\n" "$CACHE_DIR"

# determine the source lib directory
if [ -z "$LIB_DIR" ]; then
	echo "ERROR: $script_name requires env var LIB_DIR" >&2
	exit 2
fi
if [ ! -d "$LIB_DIR" ]; then
	echo "ERROR: $script_name: directory does not exist: $LIB_DIR" >&2
	exit 2
fi
$verbose_mode && printf "$script_name using source lib directory: %s\n" "$LIB_DIR"

# source lib files (always source command_paths first)
for lib_filename in $LIB_FILENAMES; do
	lib_file="$LIB_DIR/$lib_filename"
	if [ ! -f "$lib_file" ]; then
		echo "ERROR: $script_name: file does not exist: $lib_file" >&2
		exit 2
	fi
	$verbose_mode && printf "$script_name sourcing lib file: %s\n" "$lib_file"
	source "$lib_file" >&2
	exit_code=$?
	if [ $exit_code -ne 0 ]; then
		echo "ERROR: $script_name failed to source script $lib_file (exit code: $exit_code)" >&2
		exit 2
	fi
done

# determine temporary directory
if [ -n "$TMPDIR" ] && [ -d "$TMPDIR" ]; then
	# use system temporary directory (remove trailing slash)
	TMP_DIR="${TMPDIR%%/}/${script_name%%.*}"
	$verbose_mode && printf "$script_name using temp dir: %s\n" "$TMP_DIR"
else
	# create temporary directory
	tmp_dir="$( make_temp_file -d )"
	if [ ! -d "$tmp_dir" ] ; then
		printf "ERROR: $script_name unable to create temporary dir\n" >&2
		exit 2
	fi
	# use temporary directory (remove trailing slash)
	TMP_DIR="${tmp_dir%%/}/${script_name%%.*}"
	$verbose_mode && printf "$script_name creating temp dir: %s\n" "$TMP_DIR"
fi
# create a subdirectory
if [ ! -d "$TMP_DIR" ]; then
	/bin/mkdir "$TMP_DIR"
	exit_code=$?
	if [ $exit_code -ne 0 ]; then
		echo "ERROR: $script_name failed to create dir $TMP_DIR (exit code: $exit_code)" >&2
		exit 2
	fi
fi

# temporary files
xml_file="${TMP_DIR}/http_resource_$$.xml"
xsltproc_out_file="${TMP_DIR}/xsltproc_output_$$"

#######################################################################
# Main processing
#######################################################################

# GET the XML document
$verbose_mode && printf "$script_name requesting resource: %s\n" "$xml_location"
conditional_get $local_opts -d "$CACHE_DIR" -T "$TMP_DIR" "$xml_location" > "$xml_file"
exit_code=$?
if [ $exit_code -ne 0 ]; then
	if [ $exit_code -gt 1 ]; then
		echo "ERROR: $script_name failed to get resource: $location" >&2
		printf "See output log: %s\n" "$TMP_DIR/$conditional_get_log" >&2
	fi
	exit $exit_code
fi
$verbose_mode && printf "$script_name successfully obtained XML file: %s\n" "$xml_file"

# transform the XML document
$verbose_mode && printf "$script_name writing xsltproc output to file: %s\n" "$xsltproc_out_file"
/usr/bin/xsltproc --output "$xsltproc_out_file" "$xsl_file" "$xml_file"
exit_code=$?
if [ $exit_code -ne 0 ]; then
	echo "ERROR: ${script_name}: xsltproc failed with status code: $exit_code" >&2
	exit 3
fi
$verbose_mode && printf "$script_name successfully executed xsltproc\n"

# output the transformed document
if [ -z "$out_file" ]; then
	/bin/cat "$xsltproc_out_file"
	exit_code=$?
	if [ $exit_code -ne 0 ]; then
		echo "ERROR: ${script_name} unable to cat output with status code: $exit_code" >&2
		exit 3
	fi
else
	$verbose_mode && printf "$script_name writing output to file: %s\n" "$out_file"
	/bin/cp "$xsltproc_out_file" "$out_file"
	exit_code=$?
	if [ $exit_code -ne 0 ]; then
		echo "ERROR: ${script_name} unable to copy output to file $out_file (exit code: $exit_code)" >&2
		exit 3
	fi
fi

exit 0