fix: file busy error while deploying through dropgz

dropgz/README.md

@@ -0,0 +1,10 @@
+### Running the dropgz locally
+
+Select the file(for example azure-ipam binary) you want to deploy using the dropgz.
+
+1. Copy the file (i.e azure-ipam) to the directory `/dropgz/pkg/embed/fs` 
+2. Add the sha of the file to the sum.txt file.(`sha256sum * > sum.txt`)
+3. You need to gzip the file, so run the cmd `gzip --verbose --best --recursive azure-ipam` and rename the output .gz file to original file name.
+4. Do the step 3 for `sum.txt` file as well.
+5. go to dropgz directory and build it. (`go build .`)
+6. You can now test the dropgz command locally. (`./dropgz deploy azure-ipam -o ./azure-ipam`)

dropgz/pkg/embed/payload.go

@@ -15,8 +15,9 @@ import (
 )
 
 const (
-	cwd        = "fs"
-	pathPrefix = cwd + string(filepath.Separator)
+	cwd           = "fs"
+	pathPrefix    = cwd + string(filepath.Separator)
+	oldFileSuffix = ".old"
 )
 
 var ErrArgsMismatched = errors.New("mismatched argument count")
@@ -86,6 +87,13 @@ func deploy(src, dest string) error {
 		return err
 	}
 	defer rc.Close()
+	// check if the file exists at dest already and rename it as an old one
+	if _, err := os.Stat(dest); err == nil {
+		oldDest := dest + oldFileSuffix
+		if err = os.Rename(dest, oldDest); err != nil {
+			return errors.Wrapf(err, "failed to rename the %s to %s", dest, oldDest)
+		}
+	}
 	target, err := os.OpenFile(dest, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0o755) //nolint:gomnd // executable file bitmask
 	if err != nil {
 		return errors.Wrapf(err, "failed to create file %s", dest)