util: added checksum-stream

lib/util/checksum-stream.js

@@ -0,0 +1,24 @@
+var crypto = require('crypto')
+var through = require('mississippi').through
+
+module.exports = checksumStream
+function checksumStream (digest, algorithm) {
+  var hash = crypto.createHash(algorithm || 'sha1')
+  var stream = through(function (chunk, enc, cb) {
+    hash.update(chunk, enc)
+    cb(null, chunk, enc)
+  }, function (cb) {
+    var streamDigest = hash.digest('hex')
+    if (digest && streamDigest !== digest) {
+      var err = new Error('checksum failed')
+      err.code = 'EBADCHECKSUM'
+      err.expected = digest
+      err.found = streamDigest
+      return cb(err)
+    } else {
+      stream.emit('digest', streamDigest)
+      cb()
+    }
+  })
+  return stream
+}