build: bump go version

.github/workflows/build.yml

@@ -28,7 +28,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: ['1.20', '1.21']
+        go-version: ['1.21', '1.22']
       fail-fast: true
     steps:
       - name: Checkout

.github/workflows/codeql-analysis.yml

@@ -35,7 +35,7 @@ jobs:
       security-events: write
     strategy:
       matrix:
-        go-version: ['1.20', '1.21']
+        go-version: ['1.21', '1.22']
       fail-fast: false
     steps:
       - name: Checkout repository

README.md

@@ -20,7 +20,7 @@ The ORAS Go library follows [Semantic Versioning](https://semver.org/), where br
 The version `2` is actively developed in the [`main`](https://github.com/oras-project/oras-go/tree/main) branch with all new features.
 
 > [!Note]
-> The `main` branch follows [Go's Security Policy](https://github.com/golang/go/security/policy) and supports the two latest versions of Go (currently `1.20` and `1.21`).
+> The `main` branch follows [Go's Security Policy](https://github.com/golang/go/security/policy) and supports the two latest versions of Go (currently `1.21` and `1.22`).
 
 Examples for common use cases can be found below:
 

go.mod

@@ -1,6 +1,6 @@
 module oras.land/oras-go/v2
 
-go 1.20
+go 1.21
 
 require (
 	github.com/opencontainers/go-digest v1.0.0

internal/ioutil/io.go

@@ -46,13 +46,21 @@ func CopyBuffer(dst io.Writer, src io.Reader, buf []byte, desc ocispec.Descripto
 
 // nopCloserType is the type of `io.NopCloser()`.
 var nopCloserType = reflect.TypeOf(io.NopCloser(nil))
+//  nopCloserWriterToType is the type of `io.nopCloserWriterTo`
+var nopCloserWriterToType = reflect.TypeOf(io.NopCloser(struct {
+	io.Reader
+	io.WriterTo
+}{}))
 
-// UnwrapNopCloser unwraps the reader wrapped by `io.NopCloser()`.
+// UnwrapNopCloser returns the underlying reader if rc is a NopCloser
+// else it simply returns rc.
 // Similar implementation can be found in the built-in package `net/http`.
-// Reference: https://github.com/golang/go/blob/go1.17.6/src/net/http/transfer.go#L423-L425
+// Reference: https://github.com/golang/go/blob/go1.22.1/src/net/http/transfer.go#L1090-L1105
 func UnwrapNopCloser(rc io.Reader) io.Reader {
-	if reflect.TypeOf(rc) == nopCloserType {
+	switch reflect.TypeOf(rc) {
+	case nopCloserType, nopCloserWriterToType:
 		return reflect.ValueOf(rc).Field(0).Interface().(io.Reader)
+	default:
+		return rc
 	}
-	return rc
 }