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69 lines
2.3 KiB
69 lines
2.3 KiB
1 year ago
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# `stream`
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[](https://godoc.org/github.com/google/go-containerregistry/pkg/v1/stream)
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The `stream` package contains an implementation of
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[`v1.Layer`](https://godoc.org/github.com/google/go-containerregistry/pkg/v1#Layer)
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that supports _streaming_ access, i.e. the layer contents are read once and not
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buffered.
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## Usage
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```go
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package main
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import (
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"os"
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"github.com/google/go-containerregistry/pkg/name"
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"github.com/google/go-containerregistry/pkg/v1/remote"
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"github.com/google/go-containerregistry/pkg/v1/stream"
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)
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// upload the contents of stdin as a layer to a local registry
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func main() {
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repo, err := name.NewRepository("localhost:5000/stream")
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if err != nil {
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panic(err)
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}
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layer := stream.NewLayer(os.Stdin)
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if err := remote.WriteLayer(repo, layer); err != nil {
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panic(err)
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}
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}
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```
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## Structure
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This implements the layer portion of an [image
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upload](/pkg/v1/remote#anatomy-of-an-image-upload). We launch a goroutine that
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is responsible for hashing the uncompressed contents to compute the `DiffID`,
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gzipping them to produce the `Compressed` contents, and hashing/counting the
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bytes to produce the `Digest`/`Size`. This goroutine writes to an
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`io.PipeWriter`, which blocks until `Compressed` reads the gzipped contents from
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the corresponding `io.PipeReader`.
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<p align="center">
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<img src="/images/stream.dot.svg" />
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</p>
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## Caveats
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This assumes that you have an uncompressed layer (i.e. a tarball) and would like
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to compress it. Calling `Uncompressed` is always an error. Likewise, other
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methods are invalid until the contents of `Compressed` have been completely
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consumed and `Close`d.
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Using a `stream.Layer` will likely not work without careful consideration. For
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example, in the `mutate` package, we defer computing the manifest and config
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file until they are actually called. This allows you to `mutate.Append` a
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streaming layer to an image without accidentally consuming it. Similarly, in
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`remote.Write`, if calling `Digest` on a layer fails, we attempt to upload the
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layer anyway, understanding that we may be dealing with a `stream.Layer` whose
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contents need to be uploaded before we can upload the config file.
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Given the [structure](#structure) of how this is implemented, forgetting to
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`Close` a `stream.Layer` will leak a goroutine.
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