fix(gridfs-stream): honor chunk size

Fixes NODE-1219

Author: kvwalker

lib/gridfs-stream/download.js

@@ -234,13 +234,12 @@ function doRead(_this) {
       _this.s.bytesToSkip = 0;
     }
 
-    if (expectedN === _this.s.expectedEnd && _this.s.bytesToTrim != null) {
-      sliceEnd = _this.s.bytesToTrim;
-    }
-
-    // If the remaining amount of data left is < chunkSize read the right amount of data
-    if (_this.s.options.end && _this.s.options.end - _this.s.bytesToSkip < buf.length) {
-      sliceEnd = _this.s.options.end - _this.s.bytesToSkip;
+    const atEndOfStream = expectedN === _this.s.expectedEnd - 1;
+    const bytesLeftToRead = _this.s.options.end - _this.s.bytesToSkip;
+    if (atEndOfStream && _this.s.bytesToTrim != null) {
+      sliceEnd = _this.s.file.chunkSize - _this.s.bytesToTrim;
+    } else if (_this.s.options.end && bytesLeftToRead < doc.data.length()) {
+      sliceEnd = bytesLeftToRead;
     }
 
     if (sliceStart != null || sliceEnd != null) {

test/functional/gridfs_stream_tests.js

@@ -1,5 +1,6 @@
 'use strict';
 
+const stream = require('stream');
 const crypto = require('crypto'),
   EJSON = require('mongodb-extjson'),
   fs = require('fs'),
@@ -1036,6 +1037,47 @@ describe('GridFS Stream', function() {
     }
   });
 
+  it('should use chunkSize for download', {
+    metadata: { requires: { topology: ['single'] } },
+
+    // The actual test we wish to run
+    test: function(done) {
+      if (typeof stream.pipeline !== 'function') {
+        this.skip();
+      }
+
+      const configuration = this.configuration;
+      const GridFSBucket = configuration.require.GridFSBucket;
+
+      const client = configuration.newClient(configuration.writeConcernMax(), { poolSize: 1 });
+      client.connect(function(err, client) {
+        const db = client.db(configuration.db);
+        const bucket = new GridFSBucket(db, { bucketName: 'gridfs' });
+
+        const uploadStream = bucket.openUploadStream('test');
+        uploadStream.end(Buffer.alloc(40 * 1024 * 1024), err => {
+          expect(err).to.be.null;
+          const range = {
+            start: 35191617,
+            end: 35192831
+          };
+          const downloadStream = bucket.openDownloadStreamByName('test', range);
+          const outputStream = fs.createWriteStream('output');
+          stream.pipeline(downloadStream, outputStream, err => {
+            expect(err).to.not.exist;
+            client.close(() => {
+              fs.stat('output', (err, stats) => {
+                expect(err).to.be.null;
+                expect(range.end - range.start).to.equal(stats.size);
+                done();
+              });
+            });
+          });
+        });
+      });
+    }
+  });
+
   var UPLOAD_SPEC = require('./spec/gridfs/gridfs-upload.json');
   UPLOAD_SPEC.tests.forEach(function(specTest) {
     (function(testSpec) {