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130 lines
4.9 KiB
Go
130 lines
4.9 KiB
Go
// This work is subject to the CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
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// license. Its contents can be found at:
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// http://creativecommons.org/publicdomain/zero/1.0/
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/*
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bindata converts any file into managable Go source code. Useful for
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embedding binary data into a go program. The file data is optionally gzip
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compressed before being converted to a raw byte slice.
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The following paragraphs cover some of the customization options
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which can be specified in the Config struct, which must be passed into
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the Translate() call.
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Debug vs Release builds
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When used with the `Debug` option, the generated code does not actually include
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the asset data. Instead, it generates function stubs which load the data from
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the original file on disk. The asset API remains identical between debug and
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release builds, so your code will not have to change.
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This is useful during development when you expect the assets to change often.
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The host application using these assets uses the same API in both cases and
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will not have to care where the actual data comes from.
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An example is a Go webserver with some embedded, static web content like
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HTML, JS and CSS files. While developing it, you do not want to rebuild the
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whole server and restart it every time you make a change to a bit of
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javascript. You just want to build and launch the server once. Then just press
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refresh in the browser to see those changes. Embedding the assets with the
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`debug` flag allows you to do just that. When you are finished developing and
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ready for deployment, just re-invoke `go-bindata` without the `-debug` flag.
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It will now embed the latest version of the assets.
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Lower memory footprint
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The `NoMemCopy` option will alter the way the output file is generated.
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It will employ a hack that allows us to read the file data directly from
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the compiled program's `.rodata` section. This ensures that when we call
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call our generated function, we omit unnecessary memcopies.
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The downside of this, is that it requires dependencies on the `reflect` and
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`unsafe` packages. These may be restricted on platforms like AppEngine and
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thus prevent you from using this mode.
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Another disadvantage is that the byte slice we create, is strictly read-only.
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For most use-cases this is not a problem, but if you ever try to alter the
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returned byte slice, a runtime panic is thrown. Use this mode only on target
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platforms where memory constraints are an issue.
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The default behaviour is to use the old code generation method. This
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prevents the two previously mentioned issues, but will employ at least one
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extra memcopy and thus increase memory requirements.
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For instance, consider the following two examples:
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This would be the default mode, using an extra memcopy but gives a safe
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implementation without dependencies on `reflect` and `unsafe`:
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func myfile() []byte {
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return []byte{0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a}
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}
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Here is the same functionality, but uses the `.rodata` hack.
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The byte slice returned from this example can not be written to without
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generating a runtime error.
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var _myfile = "\x89\x50\x4e\x47\x0d\x0a\x1a"
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func myfile() []byte {
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var empty [0]byte
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sx := (*reflect.StringHeader)(unsafe.Pointer(&_myfile))
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b := empty[:]
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bx := (*reflect.SliceHeader)(unsafe.Pointer(&b))
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bx.Data = sx.Data
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bx.Len = len(_myfile)
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bx.Cap = bx.Len
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return b
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}
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Optional compression
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The NoCompress option indicates that the supplied assets are *not* GZIP
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compressed before being turned into Go code. The data should still be accessed
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through a function call, so nothing changes in the API.
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This feature is useful if you do not care for compression, or the supplied
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resource is already compressed. Doing it again would not add any value and may
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even increase the size of the data.
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The default behaviour of the program is to use compression.
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Path prefix stripping
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The keys used in the `_bindata` map are the same as the input file name
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passed to `go-bindata`. This includes the path. In most cases, this is not
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desireable, as it puts potentially sensitive information in your code base.
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For this purpose, the tool supplies another command line flag `-prefix`.
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This accepts a portion of a path name, which should be stripped off from
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the map keys and function names.
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For example, running without the `-prefix` flag, we get:
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$ go-bindata /path/to/templates/
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_bindata["/path/to/templates/foo.html"] = path_to_templates_foo_html
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Running with the `-prefix` flag, we get:
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$ go-bindata -prefix "/path/to/" /path/to/templates/
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_bindata["templates/foo.html"] = templates_foo_html
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Build tags
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With the optional Tags field, you can specify any go build tags that
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must be fulfilled for the output file to be included in a build. This
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is useful when including binary data in multiple formats, where the desired
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format is specified at build time with the appropriate tags.
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The tags are appended to a `// +build` line in the beginning of the output file
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and must follow the build tags syntax specified by the go tool.
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*/
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package bindata
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