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MediaFile: replace APNGInspector with ExifTool.

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Replace our own handwritten APNG parser with ExifTool. This makes
ExifTool a hard requirement for handling APNGs.
This commit is contained in:
evazion
2021-09-21 03:53:06 -05:00
parent 273be55de8
commit ae7d964bf1
5 changed files with 54 additions and 178 deletions
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113
app/logical/apng_inspector.rb
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@@ -1,113 +0,0 @@
# Parse an PNG and return whether or not it's animated.
class APNGInspector
attr_reader :frames
PNG_MAGIC_NUMBER = ["89504E470D0A1A0A"].pack('H*')
def initialize(file_path)
@file_path = file_path
@corrupted = false
@animated = false
end
# PNG file consists of 8-byte magic number, followed by arbitrary number of chunks
# Each chunk has the following structure:
# 4-byte length (unsigned int, can be zero)
# 4-byte name (ASCII string consisting of letters A-z)
# (length)-byte data
# 4-byte CRC
#
# Any data after chunk named IEND is irrelevant
# APNG frame count is inside a chunk named acTL, in first 4 bytes of data.
# This function calls associated block for each PNG chunk
# parameters passed are |chunk_name, chunk_length, file_descriptor|
# returns true if file is read succesfully from start to IEND,
# or if 100 000 chunks are read; returns false otherwise.
def each_chunk
iend_reached = false
File.open(@file_path, 'rb') do |file|
# check if file is not PNG at all
return false if file.read(8) != PNG_MAGIC_NUMBER
chunks = 0
# We could be dealing with large number of chunks,
# so the code should be optimized to create as few objects as possible.
# All literal strings are frozen and read() function uses string buffer.
chunkheader = ''
while file.read(8, chunkheader)
# ensure that first 8 bytes from chunk were read properly
if chunkheader.nil? || chunkheader.length < 8
return false
end
current_pos = file.tell
chunk_len, chunk_name = chunkheader.unpack("Na4".freeze)
return false if chunk_name =~ /[^A-Za-z]/
yield chunk_name, chunk_len, file
# no need to read further if IEND is reached
if chunk_name == "IEND".freeze
iend_reached = true
break
end
# check if we processed too many chunks already
# if we did, file is probably maliciously formed
# fail gracefully without marking the file as corrupt
chunks += 1
if chunks > 100_000
iend_reached = true
break
end
# jump to the next chunk - go forward by chunk length + 4 bytes CRC
file.seek(current_pos + chunk_len + 4, IO::SEEK_SET)
end
end
iend_reached
end
def inspect!
actl_corrupted = false
read_success = each_chunk do |name, len, file|
if name == 'acTL'.freeze
framecount = parse_actl(len, file)
if framecount < 1
actl_corrupted = true
else
@animated = true
@frames = framecount
end
end
end
@corrupted = !read_success || actl_corrupted
self
end
def corrupted?
@corrupted
end
def animated?
!@corrupted && @animated
end
private
# return number of frames in acTL or -1 on failure
def parse_actl(len, file)
return -1 if len != 8
framedata = file.read(4)
if framedata.nil? || framedata.length != 4
return -1
end
framedata.unpack1("N".freeze)
end
end

2
app/logical/media_file/image.rb
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@@ -80,7 +80,7 @@ class MediaFile::Image < MediaFile
end
def is_animated_png?
file_ext == :png && APNGInspector.new(file.path).inspect!.animated?
file_ext == :png && metadata.fetch("PNG:AnimationFrames", 1) > 1
end
# @return [Vips::Image] the Vips image object for the file

1
config/initializers/zeitwerk.rb
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@@ -1,6 +1,5 @@
Rails.autoloaders.each do |autoloader|
autoloader.inflector.inflect(
"apng_inspector" => "APNGInspector",
"sftp" => "SFTP"
)
end

63
test/unit/apng_inspector_test.rb
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@@ -1,63 +0,0 @@
require "test_helper"
class APNGInspectorTest < ActiveSupport::TestCase
def inspect(filename)
apng = APNGInspector.new("#{Rails.root}/test/files/apng/#{filename}")
apng.inspect!
apng
end
context "APNG inspector" do
should "correctly parse normal APNG file" do
apng = inspect('normal_apng.png')
assert_equal(3, apng.frames)
assert_equal(true, apng.animated?)
assert_equal(false, apng.corrupted?)
end
should "recognize 1-frame APNG as animated" do
apng = inspect('single_frame.png')
assert_equal(1, apng.frames)
assert_equal(true, apng.animated?)
assert_equal(false, apng.corrupted?)
end
should "correctly parse normal PNG file" do
apng = inspect('not_apng.png')
assert_equal(false, apng.animated?)
assert_equal(false, apng.corrupted?)
end
should "handle empty file" do
apng = inspect('empty.png')
assert_equal(false, apng.animated?)
assert_equal(true, apng.corrupted?)
end
should "handle corrupted files" do
apng = inspect('iend_missing.png')
assert_equal(false, apng.animated?)
assert_equal(true, apng.corrupted?)
apng = inspect('misaligned_chunks.png')
assert_equal(false, apng.animated?)
assert_equal(true, apng.corrupted?)
apng = inspect('broken.png')
assert_equal(false, apng.animated?)
assert_equal(true, apng.corrupted?)
end
should "handle incorrect acTL chunk" do
apng = inspect('actl_wronglen.png')
assert_equal(false, apng.animated?)
assert_equal(true, apng.corrupted?)
apng = inspect('actl_zero_frames.png')
assert_equal(false, apng.animated?)
assert_equal(true, apng.corrupted?)
end
should "handle non-png files" do
apng = inspect('jpg.png')
assert_equal(false, apng.animated?)
assert_equal(true, apng.corrupted?)
end
end
end

53
test/unit/media_file_test.rb
View File

@@ -190,6 +190,59 @@ class MediaFileTest < ActiveSupport::TestCase
end
end
context "a PNG file" do
context "that is not animated" do
should "not be detected as animated" do
file = MediaFile.open("test/files/apng/not_apng.png")
assert_equal(false, file.is_corrupt?)
assert_equal(false, file.is_animated?)
end
end
context "that is animated" do
should "be detected as animated" do
file = MediaFile.open("test/files/apng/normal_apng.png")
assert_equal(false, file.is_corrupt?)
assert_equal(true, file.is_animated?)
end
end
context "that is animated but with only one frame" do
should "not be detected as animated" do
file = MediaFile.open("test/files/apng/single_frame.png")
assert_equal(false, file.is_corrupt?)
assert_equal(false, file.is_animated?)
end
end
context "that is animated but malformed" do
should "be handled correctly" do
file = MediaFile.open("test/files/apng/iend_missing.png")
assert_equal(false, file.is_corrupt?)
assert_equal(true, file.is_animated?)
file = MediaFile.open("test/files/apng/misaligned_chunks.png")
assert_equal(true, file.is_corrupt?)
assert_equal(true, file.is_animated?)
file = MediaFile.open("test/files/apng/broken.png")
assert_equal(true, file.is_corrupt?)
assert_equal(true, file.is_animated?)
file = MediaFile.open("test/files/apng/actl_wronglen.png")
assert_equal(false, file.is_corrupt?)
assert_equal(true, file.is_animated?)
file = MediaFile.open("test/files/apng/actl_zero_frames.png")
assert_equal(false, file.is_corrupt?)
assert_equal(false, file.is_animated?)
end
end
end
context "a corrupt GIF" do
should "still read the metadata" do
@file = MediaFile.open("test/files/test-corrupt.gif")