1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
|
# `stream`
[](https://godoc.org/github.com/google/go-containerregistry/pkg/v1/stream)
The `stream` package contains an implementation of
[`v1.Layer`](https://godoc.org/github.com/google/go-containerregistry/pkg/v1#Layer)
that supports _streaming_ access, i.e. the layer contents are read once and not
buffered.
## Usage
```go
package main
import (
"os"
"github.com/google/go-containerregistry/pkg/name"
"github.com/google/go-containerregistry/pkg/v1/remote"
"github.com/google/go-containerregistry/pkg/v1/stream"
)
// upload the contents of stdin as a layer to a local registry
func main() {
repo, err := name.NewRepository("localhost:5000/stream")
if err != nil {
panic(err)
}
layer := stream.NewLayer(os.Stdin)
if err := remote.WriteLayer(repo, layer); err != nil {
panic(err)
}
}
```
## Structure
This implements the layer portion of an [image
upload](/pkg/v1/remote#anatomy-of-an-image-upload). We launch a goroutine that
is responsible for hashing the uncompressed contents to compute the `DiffID`,
gzipping them to produce the `Compressed` contents, and hashing/counting the
bytes to produce the `Digest`/`Size`. This goroutine writes to an
`io.PipeWriter`, which blocks until `Compressed` reads the gzipped contents from
the corresponding `io.PipeReader`.
<p align="center">
<img src="/images/stream.dot.svg" />
</p>
## Caveats
This assumes that you have an uncompressed layer (i.e. a tarball) and would like
to compress it. Calling `Uncompressed` is always an error. Likewise, other
methods are invalid until the contents of `Compressed` have been completely
consumed and `Close`d.
Using a `stream.Layer` will likely not work without careful consideration. For
example, in the `mutate` package, we defer computing the manifest and config
file until they are actually called. This allows you to `mutate.Append` a
streaming layer to an image without accidentally consuming it. Similarly, in
`remote.Write`, if calling `Digest` on a layer fails, we attempt to upload the
layer anyway, understanding that we may be dealing with a `stream.Layer` whose
contents need to be uploaded before we can upload the config file.
Given the [structure](#structure) of how this is implemented, forgetting to
`Close` a `stream.Layer` will leak a goroutine.
|
