bindata/README.md

bindata

This tool converts any file into managable Go source code. Useful for embedding binary data into a go program. The file data is optionally gzip compressed before being converted to a raw byte slice.

Usage

The simplest invocation is to pass it only the input file name. The output file and code settings are inferred from this automatically.

$ go-bindata -i testdata/gophercolor.png
[w] No output file specified. Using 'testdata/gophercolor.png.go'.
[w] No package name specified. Using 'main'.
[w] No function name specified. Using 'gophercolor_png'.
[i] Done.

This creates the testdata/gophercolor.png.go file which has a package declaration with name main a variable holding the file data in a read-only string and one function named gophercolor_png with the following signature:

func gophercolor_png() []byte

You can now simply include the new .go file in your program and call gophercolor_png() to get the uncompressed image data. The function panics if something went wrong during decompression. See the testdata directory for example input and output files for various modes.

Aternatively, you can pipe the input file data into stdin. bindata will then spit out the generated Go code to stdout. This does require explicitly naming the desired function name, as it can not be inferred from the input data. The package name will still default to 'main'.

 $ cat testdata/gophercolor.png | go-bindata -f gophercolor_png | gofmt

Invoke the program with the -h flag for more options.

Lower memory footprint

Using the -m flag, will alter the way the output file is generated. It will employ a hack that allows us to read the file data directly from the compiled program's .rodata section. This ensures that when we call call our generate function, we omit unnecessary memcopies.

The downside of this, is that it requires dependencies on the reflect and unsafe packages. These may be restricted on platforms like AppEngine and thus prevent you from using this mode.

Another disadvantage is that the byte slice we create, is strictly read-only. For most use-cases this is not a problem, but if you ever try to alter the returned byte slice, a runtime panic is thrown. Use this mode only on target platforms where memory constraints are an issue.

The default behaviour is to use the old code generation method. This prevents the two previously mentioned issues, but will employ at least one extra memcopy and thus increase memory requirements.

For instance, consider the following two examples...

This would be the default mode, using an extra memcopy but gives a safe implementation without dependencies on reflect and unsafe:

func myfile() []byte {
    return []byte{0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a}
}

Here is the same functionality, but uses the .rodata hack. The byte slice returned from this example can not be written to without generating a runtime error.

var _myfile = "\x89\x50\x4e\x47\x0d\x0a\x1a"

func myfile() []byte {
    var empty [0]byte
    sx := (*reflect.StringHeader)(unsafe.Pointer(&_myfile))
    b := empty[:]
    bx := (*reflect.SliceHeader)(unsafe.Pointer(&b))
    bx.Data = sx.Data
    bx.Len = len(_myfile)
    bx.Cap = bx.Len
    return b
}

Optional compression

When the -u flag is given, the supplied resource is not GZIP compressed before being turned into Go code. The data should still be accessed through a function call, so nothing changes in the usage of the generated file.

This feature is useful if you do not care for compression, or the supplied resource is already compressed. Doing it again would not add any value and may even increase the size of the data.

The default behaviour of the program is to use compression.