Use hash stream instead of crypto.createHash

crypto.createHash is a write stream but not a PassThrough stream!

src/backupformat/rsync.js

@@ -19,6 +19,7 @@ const assert = require('assert'),
     debug = require('debug')('box:backupformat/rsync'),
     { EncryptStream } = require('../hush.js'),
     fs = require('fs'),
+    HashStream = require('../hash-stream.js'),
     hush = require('../hush.js'),
     path = require('path'),
     paths = require('../paths.js'),
@@ -52,7 +53,7 @@ async function addFile(sourceFile, encryption, uploader, progressCallback) {
         progressCallback({ message: `Uploading ${sourceFile}: ${transferred}M@${speed}MBps` }); // 0M@0MBps looks wrong
     });
 
-    const hash = crypto.createHash('sha256');
+    const hash = new HashStream();
 
     let pipeline = null;
     if (encryption) {

src/backupformat/tgz.js

@@ -8,6 +8,7 @@ const assert = require('assert'),
     debug = require('debug')('box:backupformat/tgz'),
     { DecryptStream, EncryptStream } = require('../hush.js'),
     fs = require('fs'),
+    HashStream = require('../hash-stream.js'),
     path = require('path'),
     ProgressStream = require('../progress-stream.js'),
     promiseRetry = require('../promise-retry.js'),
@@ -141,7 +142,7 @@ async function tarPack(dataLayout, encryption, uploader, progressCallback) {
 
     const pack = tar.pack();
 
-    const hash = crypto.createHash('sha256');
+    const hash = new HashStream();
 
     let pipeline = null;
     if (encryption) {

src/hash-stream.js

@@ -0,0 +1,39 @@
+'use strict';
+
+const crypto = require('crypto'),
+    stream = require('stream'),
+    TransformStream = stream.Transform;
+
+class HashStream extends TransformStream {
+    #hasher;
+    #digest;
+    #size;
+
+    constructor() {
+        super();
+        this.#hasher = crypto.createHash('sha256');
+        this.#digest = null;
+        this.#size = 0;
+    }
+
+    digest() {
+        return this.#digest;
+    }
+
+    size() {
+        return this.#size;
+    }
+
+    _transform(chunk, encoding, callback) {
+        this.#hasher.update(chunk);
+        this.#size += chunk.length;
+        callback(null, chunk);
+    }
+
+    _flush(callback) {
+        this.#digest = this.#hasher.digest('hex');
+        callback(null);
+    }
+}
+
+exports = module.exports = HashStream;