How to Efficiently Parse Integers from a Byte Buffer in Go?

How to Parse Integers from a Byte Buffer in Go

This code snippet outlines a method for reading and parsing integers from a byte buffer in Go.

func (fs *FileSystem) readSB() {
    // fs.f is a *os.File
    buf := make([]byte, 1024)
    fs.f.ReadAt(buf, 1024)

    // Offset: type
    var p *bytes.Buffer

    // 0: uint32
    p = bytes.NewBuffer(buf[0:])
    binary.Read(p, binary.LittleEndian, &fs.sb.inodeCount)
    // 4: uint32
    p = bytes.NewBuffer(buf[4:])
    binary.Read(p, binary.LittleEndian, &fs.sb.blockCount)
    // 20: uint32
    p = bytes.NewBuffer(buf[20:])
    binary.Read(p, binary.LittleEndian, &fs.sb.firstDataBlock)
    // 24: uint32
    p = bytes.NewBuffer(buf[24:])
    binary.Read(p, binary.LittleEndian, &fs.sb.blockSize)
    fs.sb.blockSize = 1024 << fs.sb.blockSize
    // 32: uint32
    p = bytes.NewBuffer(buf[32:])
    binary.Read(p, binary.LittleEndian, &fs.sb.blockPerGroup)
    // 40: uint32
    p = bytes.NewBuffer(buf[40:])
    binary.Read(p, binary.LittleEndian, &fs.sb.inodePerBlock)
}

While this approach is functional, there are alternative methods that may be more efficient or idiomatic.

Avoid Creating New Buffers

To avoid creating a new buffer for each read, you can use .Next() to skip the bytes you don't want to read.

var p *bytes.Buffer

// Offset: type
p = bytes.NewBuffer(buf)

// 0: uint32
binary.Read(p, binary.LittleEndian, &fs.sb.inodeCount)

// 4: uint32
binary.Read(p, binary.LittleEndian, &fs.sb.blockCount)

// Skip [8:20)
p.Next(12)

// 20: uint32
binary.Read(p, binary.LittleEndian, &fs.sb.firstDataBlock)

// 24: uint32
binary.Read(p, binary.LittleEndian, &fs.sb.blockSize)
fs.sb.blockSize = 1024 << fs.sb.blockSize

// Skip [28:32)
p.Next(4)

// 32: uint32
binary.Read(p, binary.LittleEndian, &fs.sb.blockPerGroup)

// Skip [36:40)
p.Next(4)

// 40: uint32
binary.Read(p, binary.LittleEndian, &fs.sb.inodePerBlock)

Use a Header Structure

Alternatively, you can avoid reading chunk by chunk and create a header structure which you read directly using binary.Read.

type Head struct {
    InodeCount      uint32  //  0:4
    BlockCount      uint32  //  4:8
    Unknown1        uint32  //  8:12
    Unknown2        uint32  // 12:16
    Unknown3        uint32  // 16:20
    FirstBlock      uint32  // 20:24
    BlockSize       uint32  // 24:28
    Unknown4        uint32  // 28:32
    BlocksPerGroup  uint32  // 32:36
    Unknown5        uint32  // 36:40
    InodesPerBlock  uint32  // 40:44
}

func main() {
    var header Head

    // ...
    binary.Read(file, binary.LittleEndian, &header)
    // ...
}

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