Clarify the canModifyBlob condition in copyBlobFromStream

The copyConfig caller already sets canModifyBlob to false, set
it explicitly inside the function just to make the relationship
easier to follow.

Also fix some comments.

Signed-off-by: Miloslav Trmač <[email protected]>

copy/copy.go

@@ -1049,7 +1049,7 @@ type diffIDResult struct {
 	err    error
 }
 
-// copyLayer copies a layer with srcInfo (with known Digest and Annotations and possibly known Size) in src to dest, perhaps compressing it if canCompress,
+// copyLayer copies a layer with srcInfo (with known Digest and Annotations and possibly known Size) in src to dest, perhaps (de/re/)compressing it,
 // and returns a complete blobInfo of the copied layer, and a value for LayerDiffIDs if diffIDIsNeeded
 func (ic *imageCopier) copyLayer(ctx context.Context, srcInfo types.BlobInfo, toEncrypt bool, pool *mpb.Progress) (types.BlobInfo, digest.Digest, error) {
 	cachedDiffID := ic.c.blobInfoCache.UncompressedDigest(srcInfo.Digest) // May be ""
@@ -1115,7 +1115,7 @@ func (ic *imageCopier) copyLayer(ctx context.Context, srcInfo types.BlobInfo, to
 
 // copyLayerFromStream is an implementation detail of copyLayer; mostly providing a separate “defer” scope.
 // it copies a blob with srcInfo (with known Digest and Annotations and possibly known Size) from srcStream to dest,
-// perhaps compressing the stream if canCompress,
+// perhaps (de/re/)compressing the stream,
 // and returns a complete blobInfo of the copied blob and perhaps a <-chan diffIDResult if diffIDIsNeeded, to be read by the caller.
 func (ic *imageCopier) copyLayerFromStream(ctx context.Context, srcStream io.Reader, srcInfo types.BlobInfo,
 	diffIDIsNeeded bool, toEncrypt bool, bar *mpb.Bar) (types.BlobInfo, <-chan diffIDResult, error) {
@@ -1191,11 +1191,15 @@ func (r errorAnnotationReader) Read(b []byte) (n int, err error) {
 
 // copyBlobFromStream copies a blob with srcInfo (with known Digest and Annotations and possibly known Size) from srcStream to dest,
 // perhaps sending a copy to an io.Writer if getOriginalLayerCopyWriter != nil,
-// perhaps compressing it if canCompress,
+// perhaps (de/re/)compressing it if canModifyBlob,
 // and returns a complete blobInfo of the copied blob.
 func (c *copier) copyBlobFromStream(ctx context.Context, srcStream io.Reader, srcInfo types.BlobInfo,
 	getOriginalLayerCopyWriter func(decompressor compression.DecompressorFunc) io.Writer,
 	canModifyBlob bool, isConfig bool, toEncrypt bool, bar *mpb.Bar) (types.BlobInfo, error) {
+	if isConfig { // This is guaranteed by the caller, but set it here to be explicit.
+		canModifyBlob = false
+	}
+
 	// The copying happens through a pipeline of connected io.Readers.
 	// === Input: srcStream
 
@@ -1371,7 +1375,7 @@ func (c *copier) copyBlobFromStream(ctx context.Context, srcStream io.Reader, sr
 
 	uploadedInfo.CompressionOperation = compressionOperation
 	// If we can modify the layer's blob, set the desired algorithm for it to be set in the manifest.
-	if canModifyBlob && !isConfig {
+	if canModifyBlob {
 		uploadedInfo.CompressionAlgorithm = &desiredCompressionFormat
 	}
 	if decrypted {

go.sum

@@ -352,6 +352,7 @@ github.com/stretchr/testify v1.6.0 h1:jlIyCplCJFULU/01vCkhKuTyc3OorI3bJFuw6obfgh
 github.com/stretchr/testify v1.6.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.6.1 h1:hDPOHmpOpP40lSULcqw7IrRb/u7w6RpDC9399XyoNd0=
 github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/syndtr/gocapability v0.0.0-20170704070218-db04d3cc01c8/go.mod h1:hkRG7XYTFWNJGYcbNJQlaLq0fg1yr4J4t/NcTQtrfww=
 github.com/syndtr/gocapability v0.0.0-20180916011248-d98352740cb2 h1:b6uOv7YOFK0TYG7HtkIgExQo+2RdLuwRft63jn2HWj8=