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src/commonMain/kotlin/com/ashampoo/kim/format/jpeg/JpegSegmentAnalyzer.kt
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,158 @@ | ||
| /* | ||
| * Copyright 2023 Ashampoo GmbH & Co. KG | ||
| * | ||
| * 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. | ||
| */ | ||
| package com.ashampoo.kim.format.jpeg | ||
|
|
||
| import com.ashampoo.kim.common.ImageReadException | ||
| import com.ashampoo.kim.common.toSingleNumberHexes | ||
| import com.ashampoo.kim.common.toUInt16 | ||
| import com.ashampoo.kim.common.tryWithImageReadException | ||
| import com.ashampoo.kim.format.ImageFormatMagicNumbers | ||
| import com.ashampoo.kim.format.jpeg.JpegConstants.EOI_MARKER | ||
| import com.ashampoo.kim.format.jpeg.JpegConstants.JPEG_APP1_MARKER | ||
| import com.ashampoo.kim.format.jpeg.JpegConstants.JPEG_BYTE_ORDER | ||
| import com.ashampoo.kim.format.jpeg.JpegConstants.SOI_MARKER | ||
| import com.ashampoo.kim.format.jpeg.JpegConstants.markerDescription | ||
| import com.ashampoo.kim.format.jpeg.JpegMetadataExtractor.SEGMENT_IDENTIFIER | ||
| import com.ashampoo.kim.format.jpeg.JpegMetadataExtractor.SEGMENT_START_OF_SCAN | ||
| import com.ashampoo.kim.input.ByteReader | ||
|
|
||
| /** | ||
| * Algorithm to find segment offsets, types and lengths | ||
| */ | ||
| object JpegSegmentAnalyzer { | ||
|
|
||
| @OptIn(ExperimentalStdlibApi::class) | ||
| @Throws(ImageReadException::class) | ||
| @Suppress("ComplexMethod") | ||
| fun findSegmentInfos( | ||
| byteReader: ByteReader | ||
| ): List<JpegSegmentInfo> = tryWithImageReadException { | ||
|
|
||
| val soiMarker = byteReader.read2BytesAsInt("SOI", JPEG_BYTE_ORDER) | ||
|
|
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| require(soiMarker == SOI_MARKER) { | ||
| "JPEG magic number mismatch: ${soiMarker.toHexString()}" | ||
| } | ||
|
|
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| val segmentInfos = mutableListOf<JpegSegmentInfo>() | ||
|
|
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| segmentInfos.add( | ||
| JpegSegmentInfo( | ||
| offset = 0, | ||
| marker = SOI_MARKER, | ||
| length = 2 | ||
| ) | ||
| ) | ||
|
|
||
| var positionCounter: Long = ImageFormatMagicNumbers.jpeg.size.toLong() | ||
|
|
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| @Suppress("LoopWithTooManyJumpStatements") | ||
| do { | ||
|
|
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| var segmentIdentifier = byteReader.readByte() ?: break | ||
| var segmentType = byteReader.readByte() ?: break | ||
|
|
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| positionCounter += 2 | ||
|
|
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| /* | ||
| * Find the segment marker. Markers are zero or more 0xFF bytes, followed by | ||
| * a 0xFF and then a byte not equal to 0x00 or 0xFF. | ||
| */ | ||
| while ( | ||
| segmentIdentifier != SEGMENT_IDENTIFIER || | ||
| segmentType == SEGMENT_IDENTIFIER || | ||
| segmentType.toInt() == 0 | ||
| ) { | ||
|
|
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| segmentIdentifier = segmentType | ||
|
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| val nextSegmentType = byteReader.readByte() ?: break | ||
|
|
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| positionCounter++ | ||
|
|
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| segmentType = nextSegmentType | ||
| } | ||
|
|
||
| if (segmentType == SEGMENT_START_OF_SCAN) { | ||
|
|
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| val remainingBytesCount = byteReader.contentLength - positionCounter | ||
|
|
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| segmentInfos.add( | ||
| JpegSegmentInfo( | ||
| offset = positionCounter - 2, | ||
| marker = byteArrayOf(segmentIdentifier, segmentType).toUInt16(JPEG_BYTE_ORDER), | ||
| length = remainingBytesCount.toInt() | ||
| ) | ||
| ) | ||
|
|
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| byteReader.skipBytes("image bytes", remainingBytesCount - 2) | ||
|
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| positionCounter += remainingBytesCount | ||
|
|
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| val eoiMarker = byteReader.read2BytesAsInt("EOI", JPEG_BYTE_ORDER) | ||
|
|
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| if (eoiMarker == EOI_MARKER) { | ||
|
|
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| /* Write the EOI marker if it's really there. */ | ||
|
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| segmentInfos.add( | ||
| JpegSegmentInfo( | ||
| offset = positionCounter - 2, | ||
| marker = EOI_MARKER, | ||
| length = 2 | ||
| ) | ||
| ) | ||
| } | ||
|
|
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| break | ||
| } | ||
|
|
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| /* Note: Segment length includes size bytes */ | ||
| val remainingSegmentLength = | ||
| byteReader.read2BytesAsInt("segmentLength", JPEG_BYTE_ORDER) - 2 | ||
|
|
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| segmentInfos.add( | ||
| JpegSegmentInfo( | ||
| offset = positionCounter - 2, | ||
| marker = byteArrayOf(segmentIdentifier, segmentType).toUInt16(JPEG_BYTE_ORDER), | ||
| length = remainingSegmentLength + 4 | ||
| ) | ||
| ) | ||
|
|
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| positionCounter += 2 | ||
|
|
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| if (remainingSegmentLength <= 0) | ||
| throw ImageReadException("Illegal JPEG segment length: $remainingSegmentLength") | ||
|
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| byteReader.skipBytes("skip segment", remainingSegmentLength.toLong()) | ||
|
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| positionCounter += remainingSegmentLength | ||
|
|
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| } while (true) | ||
|
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| return segmentInfos | ||
| } | ||
|
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| data class JpegSegmentInfo( | ||
| val offset: Long, | ||
| val marker: Int, | ||
| val length: Int | ||
| ) { | ||
|
|
||
| override fun toString(): String = | ||
| "$offset = ${markerDescription(marker)} [$length bytes]" | ||
| } | ||
| } |
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