Fixed error when requesting resize of a blank image

closes https://github.com/TryGhost/Team/issues/819

- adds guard for an empty buffer when reading file from storage for resizing, if a blank image is loaded then redirect to the original file

core/server/web/site/middleware/handle-image-sizes.js

@@ -1,5 +1,6 @@
 const _ = require('lodash');
 const path = require('path');
+const {GhostError} = require('@tryghost/errors');
 const imageTransform = require('@tryghost/image-transform');
 const storage = require('../../../adapters/storage');
 const activeTheme = require('../../../../frontend/services/theme-engine/active');
@@ -100,6 +101,12 @@ module.exports = function (req, res, next) {
                 return storageInstance.read({path: storagePath});
             })
             .then((originalImageBuffer) => {
+                if (originalImageBuffer.length <= 0) {
+                    throw new GhostError({
+                        errorType: 'NoContentError',
+                        statusCode: 204
+                    });
+                }
                 return imageTransform.resizeFromBuffer(originalImageBuffer, imageDimensionConfig);
             })
             .then((resizedImageBuffer) => {
@@ -108,7 +115,7 @@ module.exports = function (req, res, next) {
     }).then(() => {
         next();
     }).catch(function (err) {
-        if (err.code === 'SHARP_INSTALLATION') {
+        if (err.code === 'SHARP_INSTALLATION' || err.errorType === 'NoContentError') {
             return redirectToOriginal();
         }
         next(err);

test/unit/web/site/middleware/handle-image-sizes.test.js

@@ -1,4 +1,7 @@
 const should = require('should');
+const sinon = require('sinon');
+const storage = require('../../../../../core/server/adapters/storage');
+const activeTheme = require('../../../../../core/frontend/services/theme-engine/active');
 const handleImageSizes = require('../../../../../core/server/web/site/middleware/handle-image-sizes.js');
 
 // @TODO make these tests lovely and non specific to implementation
@@ -41,4 +44,73 @@ describe('handleImageSizes middleware', function () {
             done();
         });
     });
+
+    describe('file handling', function () {
+        let dummyStorage;
+        let dummyTheme;
+
+        this.beforeEach(function () {
+            dummyStorage = {
+                async exists() {
+                    return true;
+                },
+
+                read() {
+                    return Buffer.from([]);
+                },
+
+                async saveRaw(buf, url) {
+                    return url;
+                }
+            };
+
+            dummyTheme = {
+                config(key) {
+                    if (key === 'image_sizes') {
+                        return {
+                            l: {
+                                width: 1000
+                            }
+                        };
+                    }
+                }
+            };
+
+            sinon.stub(storage, 'getStorage').returns(dummyStorage);
+            sinon.stub(activeTheme, 'get').returns(dummyTheme);
+        });
+
+        this.afterEach(function () {
+            sinon.restore();
+        });
+
+        it('returns original URL if file is empty', function (done) {
+            dummyStorage.exists = async function (path) {
+                if (path === '/blank_o.png') {
+                    return true;
+                }
+                if (path === '/size/w1000/blank.png') {
+                    return false;
+                }
+            };
+
+            const fakeReq = {
+                url: '/size/w1000/blank.png',
+                originalUrl: '/size/w1000/blank.png'
+            };
+            const fakeRes = {
+                redirect(url) {
+                    url.should.equal('/blank.png');
+                    done();
+                }
+            };
+
+            handleImageSizes(fakeReq, fakeRes, function next(err) {
+                if (err) {
+                    return done(err);
+                }
+                done(new Error('Should not have called next'));
+            });
+        });
+    });
 });