fix: avoid max read size reached error when cmp imported files (#618)

The equalfile golang package defaults to max read size of 10**10
bytes unless both files use io.LimitedReader to set an upper bound
on the read.  In stacker import we already stat the two files being
compared and know the actual file size.  This PR constructs two
io.LimitedReader's for each file being compared.

Fixes: #617

Signed-off-by: Ryan Harper <[email protected]>

pkg/stacker/import.go

@@ -1,6 +1,7 @@
 package stacker
 
 import (
+	"io"
 	"io/fs"
 	"os"
 	"path"
@@ -59,7 +60,11 @@ func filesDiffer(p1 string, info1 os.FileInfo, p2 string, info2 os.FileInfo) (bo
 	}
 	defer f2.Close()
 
-	eq, err := equalfile.New(nil, equalfile.Options{}).CompareReader(f1, f2)
+	// use limited reader to prevent the default cap of 10**10 max file size
+	limf1R := io.LimitReader(f1, info1.Size())
+	limf2R := io.LimitReader(f2, info2.Size())
+
+	eq, err := equalfile.New(nil, equalfile.Options{}).CompareReader(limf1R, limf2R)
 	if err != nil {
 		return false, err
 	}