internal/pkg: expose underlying reader

This will be fully implemented in httpArtifact in a future commit.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/file.go

@@ -1,9 +1,11 @@
 package pkg
 
 import (
+	"bytes"
 	"context"
 	"crypto/sha512"
 	"fmt"
+	"io"
 )
 
 // A fileArtifact is an [Artifact] that cures into data known ahead of time.
@@ -24,10 +26,10 @@ var _ KnownChecksum = new(fileArtifactNamed)
 // String returns the caller-supplied reporting name.
 func (a *fileArtifactNamed) String() string { return a.name }
 
-// NewFile returns a [File] that cures into a caller-supplied byte slice.
+// NewFile returns a [FileArtifact] that cures into a caller-supplied byte slice.
 //
 // Caller must not modify data after NewFile returns.
-func NewFile(name string, data []byte) File {
+func NewFile(name string, data []byte) FileArtifact {
 	f := fileArtifact(data)
 	if name != "" {
 		return &fileArtifactNamed{f, name}
@@ -52,4 +54,6 @@ func (a *fileArtifact) Checksum() Checksum {
 }
 
 // Cure returns the caller-supplied data.
-func (a *fileArtifact) Cure(context.Context) ([]byte, error) { return *a, nil }
+func (a *fileArtifact) Cure(context.Context) (io.ReadCloser, error) {
+	return io.NopCloser(bytes.NewReader(*a)), nil
+}