Pass file mode to output data command

We can expect file mode to be provided to outputData function instead of
the boolen value. We don't need to check if the file exists before
writing to it as access permissions of the file will prevent us from
overwriting it if configured properly.

Author: nkuba

cmd/signing.go

@@ -112,7 +112,7 @@ func DecryptKeyShare(c *cli.Context) error {
 		)
 	}
 
-	return outputData(c, signerBytes, false)
+	return outputData(c, signerBytes, 0444) // store to read-only file
 }
 
 // SignDigest signs a given digest using key shares from the provided directory.
@@ -262,23 +262,12 @@ func SignDigest(c *cli.Context) error {
 	return nil
 }
 
-func outputData(c *cli.Context, data []byte, overwrite bool) error {
+// If `output-file` flag is provided stores the output in a file.
+// `fileMode` determines the access permission for the output file. Sample values:
+// 	0444 - read-only for all
+// 	0644 - readable for all, but writeable only for the user (owner)
+func outputData(c *cli.Context, data []byte, fileMode os.FileMode) error {
 	if outputFilePath := c.String("output-file"); len(outputFilePath) > 0 {
-		var fileMode os.FileMode
-
-		if !overwrite {
-			if _, err := os.Stat(outputFilePath); !os.IsNotExist(err) {
-				return fmt.Errorf(
-					"could not write output to a file; file [%s] already exists",
-					outputFilePath,
-				)
-			}
-
-			fileMode = 0444 // read-only
-		} else {
-			fileMode = 0644 // user writable
-		}
-
 		err := ioutil.WriteFile(outputFilePath, data, fileMode)
 		if err != nil {
 			return fmt.Errorf(

cmd/signing_ethereum.go

@@ -153,7 +153,7 @@ func EthereumSign(c *cli.Context) error {
 		return fmt.Errorf("failed to marshal ethereum signature: [%v]", err)
 	}
 
-	return outputData(c, marshaledSignature, true)
+	return outputData(c, marshaledSignature, 0644) // store to user writeable file
 }
 
 // EthereumVerify verifies if a signature was calculated by a signer with the