cmd/mbf: checksum command

This computes and encodes sha384 checksum of data streamed from standard input.

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

cmd/mbf/main.go

@@ -14,6 +14,7 @@ package main
 
 import (
 	"context"
+	"crypto/sha512"
 	"errors"
 	"fmt"
 	"io"
@@ -126,6 +127,19 @@ func main() {
 			"abstract UNIX sockets",
 	)
 
+	c.NewCommand(
+		"checksum", "Compute checksum of data read from standard input",
+		func([]string) error {
+			go func() { <-ctx.Done(); os.Exit(1) }()
+			h := sha512.New384()
+			if _, err := io.Copy(h, os.Stdin); err != nil {
+				return err
+			}
+			log.Println(pkg.Encode(pkg.Checksum(h.Sum(nil))))
+			return nil
+		},
+	)
+
 	{
 		var flagShifts int
 		c.NewCommand(