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update png decoder to support png file with garbage trailing bytes #56

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Binary file added example/asset/issue28/issue28-1.png
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Binary file added example/asset/issue28/issue28-2.png
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114 changes: 114 additions & 0 deletions example/test/issue_028_test.dart
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Original file line number Diff line number Diff line change
@@ -0,0 +1,114 @@
import 'dart:io';

import 'package:image_size_getter/file_input.dart';
import 'package:image_size_getter/image_size_getter.dart';
import 'package:test/test.dart';

void main() {
group('PNG with trailing bytes test', () {
late List<File> pngFiles;

setUpAll(() {
final dir = Directory('asset/issue28');
pngFiles = dir
.listSync()
.whereType<File>()
.where((file) => file.path.endsWith('.png'))
.toList();

expect(pngFiles.isNotEmpty, true,
reason: 'No PNG files found in asset/issue28/');

print('Found ${pngFiles.length} PNG files to test');
});

test('all PNG files should work with non-standard mode', () {
final nonStandardDecoder = PngDecoder(isStandardPng: false);
ImageSizeGetter.registerDecoder(nonStandardDecoder);

for (final file in pngFiles) {
print('\nTesting: ${file.path}');

final fileInput = FileInput(file);
final result = ImageSizeGetter.getSizeResult(
fileInput,
);

print(' Size: ${result.size.width}x${result.size.height}');
print(' Decoded by: ${result.decoder.decoderName}');

expect(result.size.width, greaterThan(0));
expect(result.size.height, greaterThan(0));
expect(result.decoder.decoderName, 'non-standard-png');
}
});

test('PNG with trailing bytes should fail in standard mode', () {
final standardDecoder = PngDecoder(isStandardPng: true);
ImageSizeGetter.registerDecoder(standardDecoder);
// Find the bug PNG (the one with trailing bytes)
final bugPng = pngFiles.firstWhere(
(f) => f.path.contains('bug') || f.path.contains('trailing'),
orElse: () => pngFiles.last, // Assume last one is the bug
);

print('\nTesting bug PNG with standard mode: ${bugPng.path}');

// Standard mode should reject it
expect(
() => ImageSizeGetter.getSizeResult(
FileInput(bugPng),
),
throwsA(isA<UnsupportedError>()),
reason: 'Standard mode should reject PNG with trailing bytes',
);

print(' ✓ Correctly rejected by standard mode');
});

test('same PNG should succeed with non-standard mode', () {
final nonStandardDecoder = PngDecoder(isStandardPng: false);
ImageSizeGetter.registerDecoder(nonStandardDecoder);
// Find the bug PNG
final bugPng = pngFiles.firstWhere(
(f) => f.path.contains('bug') || f.path.contains('trailing'),
orElse: () => pngFiles.last,
);

print('\nTesting bug PNG with non-standard mode: ${bugPng.path}');

// Non-standard mode should accept it
final result = ImageSizeGetter.getSizeResult(
FileInput(bugPng)
);

print(' Size: ${result.size.width}x${result.size.height}');
print(' ✓ Successfully decoded');

expect(result.size.width, greaterThan(0));
expect(result.size.height, greaterThan(0));
});

test('default PngDecoder should use non-standard mode', () {
// When no parameter is passed, should default to non-standard (lenient)
final defaultDecoder = PngDecoder();
ImageSizeGetter.registerDecoder(defaultDecoder);
for (final file in pngFiles) {
final result = ImageSizeGetter.getSizeResult(
FileInput(file),
);

expect(result.size.width, greaterThan(0));
expect(result.decoder.decoderName, 'non-standard-png');
}
});

test('verify decoder names', () {
final standard = PngDecoder(isStandardPng: true);
final nonStandard = PngDecoder(isStandardPng: false);

expect(standard.decoderName, 'png');
expect(nonStandard.decoderName, 'non-standard-png');
});
});
}
43 changes: 39 additions & 4 deletions packages/image_size_getter/lib/src/decoder/impl/png_decoder.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -7,10 +7,16 @@ import 'package:image_size_getter/image_size_getter.dart';
/// {@endtemplate}
class PngDecoder extends BaseDecoder with SimpleTypeValidator {
/// {@macro image_size_getter.PngDecoder}
const PngDecoder();

const PngDecoder({
this.isStandardPng = false, // Default to lenient
});

final bool isStandardPng;

@override
String get decoderName => 'png';
String get decoderName => isStandardPng ? 'png' : 'non-standard-png';


@override
List<String> get supportedExtensions => List.unmodifiable(['png']);
Expand All @@ -36,10 +42,11 @@ class PngDecoder extends BaseDecoder with SimpleTypeValidator {
}

@override
SimpleFileHeaderAndFooter get simpleFileHeaderAndFooter => _PngHeaders();
SimpleFileHeaderAndFooter get simpleFileHeaderAndFooter =>
isStandardPng ? _StandardPngHeaders() : _NonStandardPngHeaders();
}

class _PngHeaders with SimpleFileHeaderAndFooter {
class _StandardPngHeaders with SimpleFileHeaderAndFooter {
static const sig = [
0x89,
0x50,
Expand Down Expand Up @@ -72,3 +79,31 @@ class _PngHeaders with SimpleFileHeaderAndFooter {
@override
List<int> get startBytes => sig;
}

/// Non-standard PNG Info
///
/// Some PNG files have trailing bytes after the IEND chunk.
///
/// These files are technically invalid per PNG specification, but are
/// commonly produced by various tools and should be supported for
/// interoperability with other image libraries.
class _NonStandardPngHeaders with SimpleFileHeaderAndFooter {
static const sig = [
0x89,
0x50,
0x4E,
0x47,
0x0D,
0x0A,
0x1A,
0x0A,
];

static const iend = <int>[];

@override
List<int> get endBytes => iend;

@override
List<int> get startBytes => sig;
}