dockerTools: nix functions for manipulating docker images

pkgs/build-support/docker/tarsum.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+    "tarsum"
+    "io"
+    "io/ioutil"
+    "fmt"
+    "os"
+)
+
+func main() {
+    ts, err := tarsum.NewTarSum(os.Stdin, false, tarsum.Version1)
+    if err != nil {
+        fmt.Println(err)
+        os.Exit(1)
+    }
+
+    if _, err = io.Copy(ioutil.Discard, ts); err != nil {
+        fmt.Println(err)
+        os.Exit(1)
+    }
+
+    fmt.Println(ts.Sum(nil))
+}