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86 lines
2.1 KiB
Go
86 lines
2.1 KiB
Go
package main
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import (
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"encoding/binary"
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"hash/crc32"
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"log"
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"os"
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)
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type ChunkData struct {
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length uint32
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name string
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data []byte
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crc uint32
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raw []byte
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}
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// validates the png by reading the header of the file
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func ValidatePng(f *os.File) (bool, []byte) {
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headerBytes := make([]byte, 8)
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_, err := f.Read(headerBytes)
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if err != nil {
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log.Fatal(err)
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}
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firstByteMatch := headerBytes[0] == 0x89
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pngAsciiMatch := string(headerBytes[1:4]) == "PNG"
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dosCRLF := headerBytes[4] == 0x0d && headerBytes[5] == 0x0a
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dosEof := headerBytes[6] == 0x1a
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unixLF := headerBytes[7] == 0x0a
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return firstByteMatch && pngAsciiMatch && dosCRLF && dosEof && unixLF, headerBytes
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}
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// reads the data of one chunk
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// it is assumed that the file reader is at the beginning of the chunk when reading
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func ReadChunk(f *os.File) (ChunkData, error) {
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lengthRaw := make([]byte, 4)
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_, err := f.Read(lengthRaw)
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length := binary.BigEndian.Uint32(lengthRaw)
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crcRaw := make([]byte, 4)
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nameRaw := make([]byte, 4)
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_, _ = f.Read(nameRaw)
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name := string(nameRaw)
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data := make([]byte, length)
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_, err = f.Read(data)
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_, err = f.Read(crcRaw)
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crc := binary.BigEndian.Uint32(crcRaw)
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fullData := make([]byte, 0)
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fullData = append(fullData, lengthRaw...)
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fullData = append(fullData, nameRaw...)
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fullData = append(fullData, data...)
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fullData = append(fullData, crcRaw...)
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return ChunkData{
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length: length,
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name: name,
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data: data,
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crc: crc,
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raw: fullData,
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}, err
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}
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// creates a chunk with the given data and name
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func CreateChunk(data []byte, name string) ChunkData {
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rawLength := make([]byte, 4)
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binary.BigEndian.PutUint32(rawLength, uint32(len(data)))
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rawName := []byte(name)
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dataAndName := make([]byte, 0)
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dataAndName = append(dataAndName, rawName...)
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dataAndName = append(dataAndName, data...)
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crc := crc32.ChecksumIEEE(dataAndName)
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rawCrc := make([]byte, 4)
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binary.BigEndian.PutUint32(rawCrc, crc)
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fullData := make([]byte, 0)
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fullData = append(fullData, rawLength...)
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fullData = append(fullData, dataAndName...)
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fullData = append(fullData, rawCrc...)
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return ChunkData{
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length: uint32(len(data)),
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name: name,
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data: data,
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crc: crc,
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raw: fullData,
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}
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}
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