PLT-6659 Fixed upload thumbnails that weren't properly rotated (#6816)

- Used client-side EXIF data to rotate profile picture thumbnails
- Added a small package for correctly translating EXIF orientation into CSS transforms
- Instead of displaying the image using FileReader, used URL.createObjectURL because it is faster
- For upload thumbnails, the original behavior was scaling the entire original image, without accounting for EXIF rotate. I changed this to use the thumbnail image, which does respect rotation.
- The preview image was not available when the upload request returned, because handling the preview image creation was in a goroutine. I used sync.WaitGroup to block until the preview image creation is done.

webapp/components/file_preview.jsx

@@ -3,7 +3,7 @@
 
 import ReactDOM from 'react-dom';
 import * as Utils from 'utils/utils.jsx';
-import {getFileUrl} from 'mattermost-redux/utils/file_utils';
+import {getFileThumbnailUrl} from 'mattermost-redux/utils/file_utils';
 
 import PropTypes from 'prop-types';
 
@@ -39,7 +39,7 @@ export default class FilePreview extends React.Component {
                 previewImage = (
                     <img
                         className='file-preview__image'
-                        src={getFileUrl(info.id)}
+                        src={getFileThumbnailUrl(info.id)}
                     />
                 );
             } else {

webapp/components/setting_picture.jsx

@@ -5,6 +5,7 @@ import PropTypes from 'prop-types';
 
 import React, {Component} from 'react';
 import {FormattedMessage} from 'react-intl';
+import exif2css from 'exif2css';
 
 import FormError from 'components/form_error.jsx';
 import loadingGif from 'images/load.gif';
@@ -41,26 +42,89 @@ export default class SettingPicture extends Component {
         }
     }
 
+    componentWillUnmount() {
+        if (this.previewBlob) {
+            URL.revokeObjectURL(this.previewBlob);
+        }
+    }
+
     setPicture = (file) => {
         if (file) {
-            var reader = new FileReader();
+            this.previewBlob = URL.createObjectURL(file);
 
+            var reader = new FileReader();
             reader.onload = (e) => {
+                const orientation = this.getExifOrientation(e.target.result);
+                const orientationStyles = this.getOrientationStyles(orientation);
+
                 this.setState({
-                    image: e.target.result
+                    image: this.previewBlob,
+                    orientationStyles
                 });
             };
-            reader.readAsDataURL(file);
+            reader.readAsArrayBuffer(file);
         }
     }
 
+    // based on https://stackoverflow.com/questions/7584794/accessing-jpeg-exif-rotation-data-in-javascript-on-the-client-side/32490603#32490603
+    getExifOrientation(data) {
+        var view = new DataView(data);
+
+        if (view.getUint16(0, false) !== 0xFFD8) {
+            return -2;
+        }
+
+        var length = view.byteLength;
+        var offset = 2;
+
+        while (offset < length) {
+            var marker = view.getUint16(offset, false);
+            offset += 2;
+
+            if (marker === 0xFFE1) {
+                if (view.getUint32(offset += 2, false) !== 0x45786966) {
+                    return -1;
+                }
+
+                var little = view.getUint16(offset += 6, false) === 0x4949;
+                offset += view.getUint32(offset + 4, little);
+                var tags = view.getUint16(offset, little);
+                offset += 2;
+
+                for (var i = 0; i < tags; i++) {
+                    if (view.getUint16(offset + (i * 12), little) === 0x0112) {
+                        return view.getUint16(offset + (i * 12) + 8, little);
+                    }
+                }
+            } else if ((marker & 0xFF00) === 0xFF00) {
+                offset += view.getUint16(offset, false);
+            } else {
+                break;
+            }
+        }
+        return -1;
+    }
+
+    getOrientationStyles(orientation) {
+        const {
+            transform,
+            'transform-origin': transformOrigin
+        } = exif2css(orientation);
+        return {transform, transformOrigin};
+    }
+
     render() {
         let img;
         if (this.props.file) {
+            const imageStyles = {
+                backgroundImage: 'url(' + this.state.image + ')',
+                ...this.state.orientationStyles
+            };
+
             img = (
                 <div
                     className='profile-img-preview'
-                    style={{backgroundImage: 'url(' + this.state.image + ')'}}
+                    style={imageStyles}
                 />
             );
         } else {