diff -r dc5c210295d0 -r f466b4c7d9b1 streamlet-examples/exiftool
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/streamlet-examples/exiftool	Sat Jan 18 20:09:34 2020 +0100
@@ -0,0 +1,84 @@
+#!/bin/bash
+
+# Relational pipes
+# Copyright © 2020 František Kučera (Frantovo.cz, GlobalCode.info)
+#
+# 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, version 3 of the License.
+#
+# 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.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+
+# This streamlet provides various file metadata like EXIF or PDF. It calls the tool exiftool.
+# With no options it returns "File:MIMEType" and "exiftool_xml" attributes.
+# Specific attributes can be selected using options – e.g. --option 'attribute' '…'
+# List of available attributes can be obtained by directly calling the "exiftool -X" command on given file or from the "available_attributes" attribute.
+# Two additional attributes are provided by this streamlet:
+#  - "exiftool_xml" – all attributes provided by exiftool in form of XML
+#  - "available_attributes" – list of available attributes (each file may have different) separated by line-breaks (TODO: return as an array of strings, when this data type is implemented)
+
+
+. "$(dirname $0)/streamlet-common.sh"
+
+processMessage_WAITING_FOR_OUTPUT_ATTRIBUTES_METADATA() {
+	streamletFields=()
+
+	for (( i=0; i<${#optionNames[@]}; i++)); do
+		if [[ "x${optionNames[$i]}" == "xattribute" ]]; then
+			streamletFields+=("${optionValues[$i]}");
+		elif [[ "x${optionNames[$i]}" == "xprefix" ]]; then
+			pdfPrefix="${optionValues[$i]}";
+		else
+			echo "Unsupported option: ${optionNames[$i]}" >&2
+		fi
+	done
+
+	if [[ -z "$streamletFields" ]]; then
+		streamletFields=( "File:MIMEType" "exiftool_xml" );
+	fi
+
+	for (( i=0; i<${#streamletFields[@]}; i++)); do
+		# TODO: data type mappings (integers, booleans)
+		send OUTPUT_ATTRIBUTE_METADATA "${outputAttributeAliases[$i]-$pdfPrefix${streamletFields[$i]}}"    "string"
+	done
+
+	send WAITING_FOR_INPUT_ATTRIBUTES
+}
+
+processMessage_WAITING_FOR_OUTPUT_ATTRIBUTES() {
+	local streamletInfo streamletValid value isNull;
+
+	[[ -d "$currentFile" ]] || streamletInfo="$(exiftool -X "$currentFile")";
+	streamletValid="$?";
+
+	for (( i=0; i<${#streamletFields[@]}; i++)); do
+		if   [[ "x${streamletFields[$i]}" == "xexiftool_xml"  ]]; then value="$streamletInfo";
+		elif [[ "x${streamletFields[$i]}" == "xavailable_attributes"  ]]; then
+			value=$'available_attributes\nexiftool_xml\n'"$(echo "$streamletInfo" | relpipe-in-xmltable --relation exif --records '/*/*/*' --attribute 'name' string 'name()' | relpipe-out-nullbyte | tr \\0 \\n)";
+		else
+			value="$(echo "$streamletInfo" | relpipe-in-xmltable --relation exif --records "/*/*/*[name() = '${streamletFields[$i]}']" --attribute 'value' string '.' | relpipe-out-nullbyte | tr -d \\0)";
+			# TODO: parse the XML only once
+			# TODO: validate parameter or use parametrized XPath
+			# TODO: use real namespaces
+		fi
+
+		# n.b. for some files exiftools returns exit code, however it provides some basic properties like file timestamps and <ExifTool:Error>Unknown file type</ExifTool:Error> which is also valid XML and might be useful
+		if   [[ ! "x$streamletValid" == "x0" ]] && [[ "x$value" == "x" ]]; then value="";  isNull="true";
+		else                                                                               isNull="false";
+		fi
+
+		send OUTPUT_ATTRIBUTE "$value"    "$isNull";
+	done
+	
+	send WAITING_FOR_INPUT_ATTRIBUTES;
+}
+
+initialize
+processMessages