IptcWriter: Followed recommendations to always write UTF8 IPTC. (#8)

There are some discussion about this topic and it looks like that it's
at least recommended to include the charset flag as otherwise readers
have to guess the right charset. Writing always UTF-8 per default should
be a good choice.

src/commonMain/kotlin/com/ashampoo/kim/format/jpeg/iptc/IptcConstants.kt

@@ -85,4 +85,5 @@ object IptcConstants {
     const val IPTC_RECORD_TAG_MARKER = 0x1c
     const val IPTC_ENVELOPE_RECORD_NUMBER = 0x01
     const val IPTC_APPLICATION_2_RECORD_NUMBER = 0x02
+    const val IPTC_RECORD_VERSION_VALUE = 4
 }

src/commonMain/kotlin/com/ashampoo/kim/format/jpeg/iptc/IptcParser.kt

@@ -19,12 +19,9 @@ package com.ashampoo.kim.format.jpeg.iptc
 import com.ashampoo.kim.common.BinaryFileParser
 import com.ashampoo.kim.common.ByteOrder
 import com.ashampoo.kim.common.ImageReadException
-import com.ashampoo.kim.common.quadsToByteArray
 import com.ashampoo.kim.common.slice
 import com.ashampoo.kim.common.startsWith
-import com.ashampoo.kim.common.toHex
 import com.ashampoo.kim.common.toInt
-import com.ashampoo.kim.common.toSingleNumberHexes
 import com.ashampoo.kim.common.toUInt16
 import com.ashampoo.kim.common.toUInt8
 import com.ashampoo.kim.format.jpeg.JpegConstants
@@ -49,8 +46,9 @@ object IptcParser : BinaryFileParser() {
 
     val DEFAULT_CHARSET = Charsets.ISO_8859_1
 
-    const val ENV_TAG_CODED_CHARACTER_SET = 90
+    const val CODED_CHARACTER_SET_IPTC_CODE = 90
 
+    /* "ESC % G" as bytes */
     val UTF8_CHARACTER_ESCAPE_SEQUENCE =
         byteArrayOf('\u001B'.code.toByte(), '%'.code.toByte(), 'G'.code.toByte())
 
@@ -123,7 +121,7 @@ object IptcParser : BinaryFileParser() {
             index += recordSize
 
             if (recordNumber == IptcConstants.IPTC_ENVELOPE_RECORD_NUMBER &&
-                recordType == ENV_TAG_CODED_CHARACTER_SET
+                recordType == CODED_CHARACTER_SET_IPTC_CODE
             ) {
                 charset = findCharset(recordData)
                 continue

src/commonMain/kotlin/com/ashampoo/kim/format/jpeg/iptc/IptcWriter.kt

@@ -22,12 +22,11 @@ import com.ashampoo.kim.format.jpeg.iptc.IptcParser.APP13_BYTE_ORDER
 import com.ashampoo.kim.output.BigEndianBinaryByteWriter
 import com.ashampoo.kim.output.BinaryByteWriter
 import com.ashampoo.kim.output.ByteArrayByteWriter
-import io.ktor.utils.io.charsets.Charsets
-import io.ktor.utils.io.core.String
 import io.ktor.utils.io.core.toByteArray
 
 object IptcWriter {
 
+    @Suppress("ThrowsCount")
     fun writePhotoshopApp13Segment(data: IptcMetadata): ByteArray {
 
         val os = ByteArrayByteWriter()
@@ -76,53 +75,37 @@ object IptcWriter {
         return os.toByteArray()
     }
 
+    /* Writes the IPTC block in UTF-8 */
     fun writeIPTCBlock(records: List<IptcRecord>): ByteArray {
 
-        var charset = IptcParser.DEFAULT_CHARSET
-
-        /*
-         * Check if the default ISO charset will work.
-         * Otherwise we need to switch to UTF8.
-         */
-        for (record in records) {
-
-            val recordData = record.value.toByteArray(charset)
-
-            val reEncodedString = String(recordData, charset = charset)
-
-            if (reEncodedString != record.value) {
-                charset = Charsets.UTF_8
-                break
-            }
-        }
-
         val byteWriter = ByteArrayByteWriter()
 
         val binaryWriter = BinaryByteWriter.createBinaryByteWriter(byteWriter, APP13_BYTE_ORDER)
 
-        if (charset != IptcParser.DEFAULT_CHARSET) {
-
-            binaryWriter.write(IptcConstants.IPTC_RECORD_TAG_MARKER)
-            binaryWriter.write(IptcConstants.IPTC_ENVELOPE_RECORD_NUMBER)
-            binaryWriter.write(IptcParser.ENV_TAG_CODED_CHARACTER_SET)
-            binaryWriter.write2Bytes(IptcParser.UTF8_CHARACTER_ESCAPE_SEQUENCE.size)
-            binaryWriter.write(IptcParser.UTF8_CHARACTER_ESCAPE_SEQUENCE)
-        }
+        /*
+         * Set the envelope for UTF-8
+         *
+         * It's recommended to use UTF-8 as a default to prevent issues with umlauts.
+         * And it's more consistent to always write data the same way.
+         */
+        binaryWriter.write(IptcConstants.IPTC_RECORD_TAG_MARKER)
+        binaryWriter.write(IptcConstants.IPTC_ENVELOPE_RECORD_NUMBER)
+        binaryWriter.write(IptcParser.CODED_CHARACTER_SET_IPTC_CODE)
+        binaryWriter.write2Bytes(IptcParser.UTF8_CHARACTER_ESCAPE_SEQUENCE.size)
+        binaryWriter.write(IptcParser.UTF8_CHARACTER_ESCAPE_SEQUENCE)
 
         /* First, right record version record */
         binaryWriter.write(IptcConstants.IPTC_RECORD_TAG_MARKER)
         binaryWriter.write(IptcConstants.IPTC_APPLICATION_2_RECORD_NUMBER)
         binaryWriter.write(IptcTypes.RECORD_VERSION.type)
         binaryWriter.write2Bytes(2) // record version record size
-        binaryWriter.write2Bytes(2) // record version value
+        binaryWriter.write2Bytes(IptcConstants.IPTC_RECORD_VERSION_VALUE)
 
-        // make a copy of the list.
         val sortedRecords: List<IptcRecord> = records.sortedWith(IptcRecord.comparator)
 
-        // write the list.
         for ((iptcType, value) in sortedRecords) {
 
-            /* Ignore the record version */
+            /* Ignore the record version, because we already wrote it. */
             if (iptcType === IptcTypes.RECORD_VERSION)
                 continue
 
@@ -134,7 +117,8 @@ object IptcWriter {
 
             binaryWriter.write(iptcType.type)
 
-            val recordData = value.toByteArray(charset)
+            val recordData = value.toByteArray()
+
             binaryWriter.write2Bytes(recordData.size)
             binaryWriter.write(recordData)
         }

src/jvmTest/kotlin/com/ashampoo/kim/format/jpeg/JpegRewriterTest.kt

@@ -107,7 +107,8 @@ class JpegRewriterTest {
             val newRecords = mutableListOf<IptcRecord>()
             newRecords.addAll(oldRecords)
 
-            newRecords.add(IptcRecord(IptcTypes.KEYWORDS, "new_keyword"))
+            /* Write a new keyword including umlauts */
+            newRecords.add(IptcRecord(IptcTypes.KEYWORDS, "Umlauts: äöüß"))
 
             val newPhotoshopData = IptcMetadata(
                 newRecords,