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replace strings.Split(N) for strings.Cut() or alternatives

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Go 1.18 and up now provides a strings.Cut() which is better suited for
splitting key/value pairs (and similar constructs), and performs better:

```go
func BenchmarkSplit(b *testing.B) {
        b.ReportAllocs()
        data := []string{"12hello=world", "12hello=", "12=hello", "12hello"}
        for i := 0; i < b.N; i++ {
                for _, s := range data {
                        _ = strings.SplitN(s, "=", 2)[0]
                }
        }
}

func BenchmarkCut(b *testing.B) {
        b.ReportAllocs()
        data := []string{"12hello=world", "12hello=", "12=hello", "12hello"}
        for i := 0; i < b.N; i++ {
                for _, s := range data {
                        _, _, _ = strings.Cut(s, "=")
                }
        }
}
```

    BenchmarkSplit
    BenchmarkSplit-10            8244206               128.0 ns/op           128 B/op          4 allocs/op
    BenchmarkCut
    BenchmarkCut-10             54411998                21.80 ns/op            0 B/op          0 allocs/op

While looking at occurrences of `strings.Split()`, I also updated some for alternatives,
or added some constraints; for cases where an specific number of items is expected, I used `strings.SplitN()`
with a suitable limit. This prevents (theoretical) unlimited splits.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
This commit is contained in:
Sebastiaan van Stijn
2022-11-04 09:05:39 +01:00
parent f90219d472
commit eaedadbed0
19 changed files with 96 additions and 106 deletions
Download Patch File Download Diff File Expand all files Collapse all files

31
images/mediatypes.go
View File

@@ -38,7 +38,9 @@ const (
MediaTypeDockerSchema2Config = "application/vnd.docker.container.image.v1+json"
MediaTypeDockerSchema2Manifest = "application/vnd.docker.distribution.manifest.v2+json"
MediaTypeDockerSchema2ManifestList = "application/vnd.docker.distribution.manifest.list.v2+json"
// Checkpoint/Restore Media Types
MediaTypeContainerd1Checkpoint = "application/vnd.containerd.container.criu.checkpoint.criu.tar"
MediaTypeContainerd1CheckpointPreDump = "application/vnd.containerd.container.criu.checkpoint.predump.tar"
MediaTypeContainerd1Resource = "application/vnd.containerd.container.resource.tar"
@@ -47,9 +49,12 @@ const (
MediaTypeContainerd1CheckpointOptions = "application/vnd.containerd.container.checkpoint.options.v1+proto"
MediaTypeContainerd1CheckpointRuntimeName = "application/vnd.containerd.container.checkpoint.runtime.name"
MediaTypeContainerd1CheckpointRuntimeOptions = "application/vnd.containerd.container.checkpoint.runtime.options+proto"
// Legacy Docker schema1 manifest
// MediaTypeDockerSchema1Manifest is the legacy Docker schema1 manifest
MediaTypeDockerSchema1Manifest = "application/vnd.docker.distribution.manifest.v1+prettyjws"
// Encypted media types
// Encrypted media types
MediaTypeImageLayerEncrypted = ocispec.MediaTypeImageLayer + "+encrypted"
MediaTypeImageLayerGzipEncrypted = ocispec.MediaTypeImageLayerGzip + "+encrypted"
)
@@ -93,16 +98,23 @@ func DiffCompression(ctx context.Context, mediaType string) (string, error) {
// parseMediaTypes splits the media type into the base type and
// an array of sorted extensions
func parseMediaTypes(mt string) (string, []string) {
func parseMediaTypes(mt string) (mediaType string, suffixes []string) {
if mt == "" {
return "", []string{}
}
mediaType, ext, ok := strings.Cut(mt, "+")
if !ok {
return mediaType, []string{}
}
s := strings.Split(mt, "+")
ext := s[1:]
sort.Strings(ext)
return s[0], ext
// Splitting the extensions following the mediatype "(+)gzip+encrypted".
// We expect this to be a limited list, so add an arbitrary limit (50).
//
// Note that DiffCompression is only using the last element, so perhaps we
// should split on the last "+" only.
suffixes = strings.SplitN(ext, "+", 50)
sort.Strings(suffixes)
return mediaType, suffixes
}
// IsNonDistributable returns true if the media type is non-distributable.
@@ -118,8 +130,7 @@ func IsLayerType(mt string) bool {
}
// Parse Docker media types, strip off any + suffixes first
base, _ := parseMediaTypes(mt)
switch base {
switch base, _ := parseMediaTypes(mt); base {
case MediaTypeDockerSchema2Layer, MediaTypeDockerSchema2LayerGzip,
MediaTypeDockerSchema2LayerForeign, MediaTypeDockerSchema2LayerForeignGzip:
return true