Swift 无法读取PNG文件的IHDR块
我阅读了PNG文件规范,了解到在PNG签名的前8个字节之后,我们有了IHDR块。此图像表示我们有长度为13(0x0000000D)字节的IHDR。 我已经用swift编写了一个代码来读取相同的png文件并打印字节,但这并没有给我一个长度等于png签名后块的前4个字节中13个字节的IHDR。控制台中的代码输出为Swift 无法读取PNG文件的IHDR块,swift,png,nsfilehandle,Swift,Png,Nsfilehandle,我阅读了PNG文件规范,了解到在PNG签名的前8个字节之后,我们有了IHDR块。此图像表示我们有长度为13(0x0000000D)字节的IHDR。 我已经用swift编写了一个代码来读取相同的png文件并打印字节,但这并没有给我一个长度等于png签名后块的前4个字节中13个字节的IHDR。控制台中的代码输出为 PNG Signature Bytes: 89 50 4E 47 0D 0A 1A 0A File offset: 8 IHDR length bytes: 00 00 00 04
PNG Signature Bytes: 89 50 4E 47 0D 0A 1A 0A
File offset: 8
IHDR length bytes: 00 00 00 04
File offset: 12
IHDR Chunktype bytes: 43 67 42 49
File offset: 16
IHDR Data byte: 50 00 20 02
File offset: 20
pngImageWidth: 1342185474
pngImageWidth: 20480
pngImageHeight: 8194
我是否遗漏了一些内容,或者我阅读的规范已经过时了?
前8个字节是实际PNG签名字节。IHDR字节是我无法获得预期长度和块类型的地方(IHDR的宽度、高度和其他字节对于不同的文件是可变的,但是长度和块类型应该与我的读取相同)
读取png文件的代码是直截了当的,如下所示:
enum PNGFileAnatomyConstants {
static let pngSignatureLength = 8
static let ihdrLength = 4
static let chunkTypeLength = 4
static let chunkCRCLength = 4
static let imageWidthLength = 4
static let imageHeigthLength = 4
}
func anatomyOfPNGFile() {
let bundle = Bundle.main
guard let pngFileUrl = bundle.url(forResource: "PNGFileSignature", withExtension: "png") else { fatalError() }
do {
// Signature start------------------------------------------------------------------------------------------
let readFileHandle = try FileHandle(forReadingFrom: pngFileUrl)
defer {
readFileHandle.closeFile()
}
let pngSignatureData = readFileHandle.readData(ofLength: PNGFileAnatomyConstants.pngSignatureLength)
let signatureString = pngSignatureData.hexEncodedString(options: [Data.HexEncodingOptions.upperCase])
if signatureString != "89 50 4E 47 0D 0A 1A 0A " {
fatalError(" Not a png")
}
print("PNG Signature Bytes: \(signatureString)")
print("File offset: \(readFileHandle.offsetInFile)")
// Signature ebd------------------------------------------------------------------------------------------
// IHDR Length start------------------------------------------------------------------------------------------
let ihdrLengthDataBigEndian = readFileHandle.readData(ofLength: PNGFileAnatomyConstants.ihdrLength)
let ihdrLength: UInt32
if PlatformEndianess.isLittleEndian {
ihdrLength = Data(ihdrLengthDataBigEndian.reversed()).withUnsafeBytes({ (unsafePointer: UnsafePointer<UInt32>) -> UInt32 in
return unsafePointer.pointee
})
} else {
ihdrLength = ihdrLengthDataBigEndian.withUnsafeBytes({ (unsafePointer: UnsafePointer<UInt32>) -> UInt32 in
return unsafePointer.pointee
})
}
let ihdrLengthDataBigEndianString = ihdrLengthDataBigEndian.hexEncodedString(options: [.upperCase])
print("IHDR length bytes: \(ihdrLengthDataBigEndianString)")
print("File offset: \(readFileHandle.offsetInFile)")
// IHDR Length end------------------------------------------------------------------------------------------
// IHDR chunk type start------------------------------------------------------------------------------------------
let ihdrChunkTypeData = readFileHandle.readData(ofLength: PNGFileAnatomyConstants.chunkTypeLength)
let ihdrChunkTypeDataString = ihdrChunkTypeData.hexEncodedString(options: [Data.HexEncodingOptions.upperCase])
print("IHDR Chunktype bytes: \(ihdrChunkTypeDataString)")
print("File offset: \(readFileHandle.offsetInFile)")
// IHDR chunk type end------------------------------------------------------------------------------------------
// IHDR data byte start------------------------------------------------------------------------------------------
let ihdrData = readFileHandle.readData(ofLength: Int(ihdrLength))
let ihdrDataString = ihdrData.hexEncodedString(options: [.upperCase])
print("IHDR Data byte: \(ihdrDataString)")
print("File offset: \(readFileHandle.offsetInFile)")
// IHDR data byte end------------------------------------------------------------------------------------------
do {
let pngImageWidth: UInt32
if PlatformEndianess.isLittleEndian {
pngImageWidth = Data(ihdrData.reversed()).withUnsafeBytes({ (unsafePointer: UnsafePointer<UInt32>) -> UInt32 in
return unsafePointer.pointee
})
} else {
pngImageWidth = ihdrData.withUnsafeBytes({ (unsafePointer: UnsafePointer<UInt32>) -> UInt32 in
return unsafePointer.pointee
})
}
print("pngImageWidth: \(pngImageWidth)")
}
do {
let pngImageWidth: UInt16
let widthData = Data(bytes: [ihdrData[0], ihdrData[1]])
if PlatformEndianess.isLittleEndian {
pngImageWidth = Data(widthData.reversed()).withUnsafeBytes({ (unsafePointer: UnsafePointer<UInt16>) -> UInt16 in
return unsafePointer.pointee
})
} else {
pngImageWidth = widthData.withUnsafeBytes({ (unsafePointer: UnsafePointer<UInt16>) -> UInt16 in
return unsafePointer.pointee
})
}
print("pngImageWidth: \(pngImageWidth)")//20480
let pngImageHeight: UInt16
let heightData = Data(bytes: [ihdrData[2], ihdrData[3]])
if PlatformEndianess.isLittleEndian {
pngImageHeight = Data(heightData.reversed()).withUnsafeBytes({ (unsafePointer: UnsafePointer<UInt16>) -> UInt16 in
return unsafePointer.pointee
})
} else {
pngImageHeight = heightData.withUnsafeBytes({ (unsafePointer: UnsafePointer<UInt16>) -> UInt16 in
return unsafePointer.pointee
})
}
print("pngImageHeight: \(pngImageHeight)")//20480
}
} catch {
fatalError(error.localizedDescription)
}
}
extension Data {
struct HexEncodingOptions: OptionSet {
let rawValue: Int
static let upperCase = HexEncodingOptions(rawValue: 1 << 0)
}
func hexEncodedString(options: HexEncodingOptions = []) -> String {
let hexDigits = Array((options.contains(.upperCase) ? "0123456789ABCDEF " : "0123456789abcdef ").utf16)
var chars: [unichar] = []
chars.reserveCapacity(3 * count)
for byte in self {
chars.append(hexDigits[Int(byte / 16)])
chars.append(hexDigits[Int(byte % 16)])
chars.append(hexDigits.last!)
}
return String(utf16CodeUnits: chars, count: chars.count)
}
}
class PlatformEndianess {
static var isLittleEndian: Bool = {
var integer: UInt16 = 0x0001
return withUnsafeBytes(of: &integer, { (rawBufferPointer) -> Bool in
return rawBufferPointer.first == 0x01
})
}()
}
enum PNGFileAnatomyConstants{
静态let pngSignatureLength=8
静态let ihdrLength=4
静态let chunkTypeLength=4
静态let chunkCRCLength=4
静态let imageWidthLength=4
静态let图像高度长度=4
}
func anatomyOfPNGFile(){
设bundle=bundle.main
guard let pngFileUrl=bundle.url(用于资源:“PNGFileSignature”,扩展名为:“png”)else{fatalError()}
做{
//签名开始------------------------------------------------------------------------------------------
让readFileHandle=尝试FileHandle(forReadingFrom:pngFileUrl)
推迟{
readFileHandle.closeFile()文件
}
让pngSignatureData=readFileHandle.readData(长度:PNGFileAnatomyConstants.pngSignatureLength)
让signatureString=pngSignatureData.hexEncodedString(选项:[Data.HexEncodingOptions.upperCase])
如果签名限制!=“89 50 4E 47 0D 0A 1A 0A”{
fatalError(“非png”)
}
打印(“PNG签名字节:\(签名限制)”)
打印(“文件偏移量:\(readFileHandle.offsetInFile)”)
//特征ebd------------------------------------------------------------------------------------------
//IHDR长度起始------------------------------------------------------------------------------------------
设ihdrLengthDataBigEndian=readFileHandle.readData(长度:PNGFileAnatomyConstants.ihdrLength)
让ihdrLength:UInt32
if PlatformEndianess.isLittleEndian{
ihdrLength=Data(ihdrLengthDataBigEndian.reversed())。在
返回unsafePointer.pointee
})
}否则{
ihdrLength=ihdrLengthDataBigEndian.withUnsafeBytes({(unsafePointer:unsafePointer)->UInt32 in
返回unsafePointer.pointee
})
}
让ihdrLengthDataBigEndianString=ihdrLengthDataBigEndian.hexEncodedString(选项:[.upperCase])
打印(“IHDR长度字节:\(ihdrLengthDataBigEndianString)”)
打印(“文件偏移量:\(readFileHandle.offsetInFile)”)
//IHDR长度端------------------------------------------------------------------------------------------
//IHDR块类型开始------------------------------------------------------------------------------------------
让ihdrChunkTypeData=readFileHandle.readData(长度:PNGFileAnatomyConstants.chunkTypeLength)
让ihdrChunkTypeDataString=ihdrChunkTypeData.hexEncodedString(选项:[Data.HexEncodingOptions.upperCase])
打印(“IHDR Chunktype字节:\(ihdrChunkTypeDataString)”)
打印(“文件偏移量:\(readFileHandle.offsetInFile)”)
//IHDR块类型结束------------------------------------------------------------------------------------------
//IHDR数据字节开始------------------------------------------------------------------------------------------
设ihdrData=readFileHandle.readData(of长度:Int(ihdrLength))
让ihdrDataString=ihdrData.hexEncodedString(选项:[.upperCase])
打印(“IHDR数据字节:\(ihdrDataString)”)
打印(“文件偏移量:\(readFileHandle.offsetInFile)”)
//IHDR数据字节结束------------------------------------------------------------------------------------------
做{
让pngImageWidth:UInt32
if PlatformEndianess.isLittleEndian{
pngImageWidth=Data(ihdrData.reversed())。在中包含unsafebytes({(unsafePointer:unsafePointer)->UInt32
返回unsafePointer.pointee
})
}否则{
pngImageWidth=ihdrData.withUnsafeBytes({(unsafePointer:unsafePointer)->UInt32 in
返回unsafePointer.pointee
})
}
打印(“pngImageWidth:\(pngImageWidth)”)
}
做{
让pngImageWidth:UInt16
设widthData=Data(字节:[ihdrData[0],ihdrData[1]]
if PlatformEndianess.isLittleEndian{
pngImageWidth=Data(widthData.reversed())。在
返回unsafePointer.pointee
})
}否则{
pngImageWidth=widthData.withUnsafeBytes({(unsafePointer:unsafePointer)->UInt16 in
返回unsafePointer.pointee
})
}
打印(“pngImageWidth:\(pngImageWidth)”)/20480
让pngImageHeight:UInt16
设heightData=Data(字节:[ihdrData[2],ihdrData[3]]
if PlatformEndianess.isLittleEndian{
pngImageHeight=Data(heightData.reversed())。在
返回unsafePointer.pointee
})
}否则{
pngImageHeight=heightData.withUnsafeBytes({(unsafePointer:unsafePointer)->UInt16 in
重新
PNG Signature(8 bytes): 89 50 4E 47 0D 0A 1A 0A
=======Chunk start=======
IHDR Chunk:
IHDR chunk length(4 bytes): 00 00 00 0D
IHDR chunk type(Identifies chunk type to be IHDR): 49 48 44 52
Image width in pixels(variable 4): xx xx xx xx
Image height in pixels(variable 4): xx xx xx xx
Flags in the chunk(variable 5 bytes): xx xx xx xx xx
CRC checksum(variable 4 bytes): xx xx xx xx
=======Chunk end=======
PNG Signature(8 bytes): 89 50 4E 47 0D 0A 1A 0A
=======Chunk start=======
CgBI Chunk:
CgBI chunk length(4 bytes): 00 00 00 04
CgBI chunk type(Identifies chunk type to be CgBI): 43 67 42 49
CgBI info flags(4 bytes): xx xx xx xx
CRC checksum(variable 4 bytes): xx xx xx xx
=======Chunk end=======
=======Chunk start=======
IHDR Chunk:
IHDR chunk length(4 bytes): 00 00 00 0D
IHDR chunk type(Identifies chunk type to be IHDR): 49 48 44 52
Image width in pixels(variable 4): xx xx xx xx
Image height in pixels(variable 4): xx xx xx xx
Flags in the chunk(variable 5 bytes): xx xx xx xx xx
CRC checksum(variable 4 bytes): xx xx xx xx
=======Chunk end=======