sparse

README

Golang implementation of simg2img

Overview

A go (golang) library for decoding android sparse image formatted files into raw images.

Examples

For a full example see example utility in ./cmd/

Using the writer. The performance of the writer is much better than the performance of the reader, as we can seek-past any "don't care" chunks in the sparse format, instead of writing random data.

func simg2img(in_filename, out_filename string) error {
    in, err := os.Open(in_filename)
    if err != nil {
        return err
    }
    defer in.Close()

    out, err := os.OpenFile(out_filename, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
    if err != nil {
        return err
    }
    defer out.Close()

    writer := sparse.Simg2imgWriter(out)
    _, err = io.Copy(writer, in)
    return err
}

Using the reader (slower!! Read Above!)

func simg2img_alt(in_filename, out_filename string) error {
    in, err := os.Open(in_filename)
    if err != nil {
        return err
    }
    defer in.Close()

    out, err := os.OpenFile(out_filename, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
    if err != nil {
        return err
    }
    defer out.Close()

    reader, err := sparse.Simg2imgReader(in)
    if err != nil {
        return err
    }

    _, err = io.Copy(out, reader)
    return err
}

License

See LICENSE file.

Documentation

Index

• func Simg2imgReader(input io.Reader) (io.Reader, error)
• func Simg2imgWriter(output io.WriteSeeker) io.Writer
• type ChunkHeader
• type SparseHeader

Functions

func Simg2imgReader

func Simg2imgReader(input io.Reader) (io.Reader, error)

func Simg2imgWriter

func Simg2imgWriter(output io.WriteSeeker) io.Writer

Types

type ChunkHeader

type ChunkHeader struct {
	ChunkType uint16 // 0xCAC1 -> raw; 0xCAC2 -> fill; 0xCAC3 -> don't care
	Reserved  uint16
	ChunkSize uint32 // in blocks in output image
	TotalSize uint32 // in bytes of chunk input file including chunk header and data
}

type SparseHeader

type SparseHeader struct {
	Magic           uint32 // 0xed26ff3a
	MajorVersion    uint16 // (0x1) - reject images with higher major versions
	MinorVersion    uint16 // (0x0) - allow images with higer minor versions
	FileHeaderSize  uint16 // 28 bytes for first revision of the file format
	ChunkHeaderSize uint16 // 12 bytes for first revision of the file format
	BlockSize       uint32 // block size in bytes, must be a multiple of 4 (4096)
	TotalBlocks     uint32 // total blocks in the non-sparse output image
	TotalChunks     uint32 // total chunks in the sparse input image
	ImageChecksum   uint32 // CRC32 checksum of the original data, counting "don't care"
}