Add RealVNC's JPEG encoding

Add support for RealVNC's JPEG encoding.

Add tests for JPEGDecoder. Fix the corner case of caching Huffman or quantization tables.

3 files changed, 146 insertions, 0 deletions

diff --git a/core/decoders/jpeg.js b/core/decoders/jpeg.js
new file mode 100644
index 0000000..e1f2bdf
--- /dev/null
+++ b/core/decoders/jpeg.js
@@ -0,0 +1,141 @@
+/*
+ * noVNC: HTML5 VNC client
+ * Copyright (C) 2019 The noVNC Authors
+ * Licensed under MPL 2.0 (see LICENSE.txt)
+ *
+ * See README.md for usage and integration instructions.
+ *
+ */
+
+export default class JPEGDecoder {
+    constructor() {
+        // RealVNC will reuse the quantization tables
+        // and Huffman tables, so we need to cache them.
+        this._quantTables = [];
+        this._huffmanTables = [];
+        this._cachedQuantTables = [];
+        this._cachedHuffmanTables = [];
+
+        this._jpegLength = 0;
+        this._segments = [];
+    }
+
+    decodeRect(x, y, width, height, sock, display, depth) {
+        // A rect of JPEG encodings is simply a JPEG file
+        if (!this._parseJPEG(sock.rQslice(0))) {
+            return false;
+        }
+        const data = sock.rQshiftBytes(this._jpegLength);
+        if (this._quantTables.length != 0 && this._huffmanTables.length != 0) {
+            // If there are quantization tables and Huffman tables in the JPEG
+            // image, we can directly render it.
+            display.imageRect(x, y, width, height, "image/jpeg", data);
+            return true;
+        } else {
+            // Otherwise we need to insert cached tables.
+            const sofIndex = this._segments.findIndex(
+                x => x[1] == 0xC0 || x[1] == 0xC2
+            );
+            if (sofIndex == -1) {
+                throw new Error("Illegal JPEG image without SOF");
+            }
+            let segments = this._segments.slice(0, sofIndex);
+            segments = segments.concat(this._quantTables.length ?
+                this._quantTables :
+                this._cachedQuantTables);
+            segments.push(this._segments[sofIndex]);
+            segments = segments.concat(this._huffmanTables.length ?
+                this._huffmanTables :
+                this._cachedHuffmanTables,
+                                       this._segments.slice(sofIndex + 1));
+            let length = 0;
+            for (let i = 0; i < segments.length; i++) {
+                length += segments[i].length;
+            }
+            const data = new Uint8Array(length);
+            length = 0;
+            for (let i = 0; i < segments.length; i++) {
+                data.set(segments[i], length);
+                length += segments[i].length;
+            }
+            display.imageRect(x, y, width, height, "image/jpeg", data);
+            return true;
+        }
+    }
+
+    _parseJPEG(buffer) {
+        if (this._quantTables.length != 0) {
+            this._cachedQuantTables = this._quantTables;
+        }
+        if (this._huffmanTables.length != 0) {
+            this._cachedHuffmanTables = this._huffmanTables;
+        }
+        this._quantTables = [];
+        this._huffmanTables = [];
+        this._segments = [];
+        let i = 0;
+        let bufferLength = buffer.length;
+        while (true) {
+            let j = i;
+            if (j + 2 > bufferLength) {
+                return false;
+            }
+            if (buffer[j] != 0xFF) {
+                throw new Error("Illegal JPEG marker received (byte: " +
+                                   buffer[j] + ")");
+            }
+            const type = buffer[j+1];
+            j += 2;
+            if (type == 0xD9) {
+                this._jpegLength = j;
+                this._segments.push(buffer.slice(i, j));
+                return true;
+            } else if (type == 0xDA) {
+                // start of scan
+                let hasFoundEndOfScan = false;
+                for (let k = j + 3; k + 1 < bufferLength; k++) {
+                    if (buffer[k] == 0xFF && buffer[k+1] != 0x00 &&
+                        !(buffer[k+1] >= 0xD0 && buffer[k+1] <= 0xD7)) {
+                        j = k;
+                        hasFoundEndOfScan = true;
+                        break;
+                    }
+                }
+                if (!hasFoundEndOfScan) {
+                    return false;
+                }
+                this._segments.push(buffer.slice(i, j));
+                i = j;
+                continue;
+            } else if (type >= 0xD0 && type < 0xD9 || type == 0x01) {
+                // No length after marker
+                this._segments.push(buffer.slice(i, j));
+                i = j;
+                continue;
+            }
+            if (j + 2 > bufferLength) {
+                return false;
+            }
+            const length = (buffer[j] << 8) + buffer[j+1] - 2;
+            if (length < 0) {
+                throw new Error("Illegal JPEG length received (length: " +
+                                   length + ")");
+            }
+            j += 2;
+            if (j + length > bufferLength) {
+                return false;
+            }
+            j += length;
+            const segment = buffer.slice(i, j);
+            if (type == 0xC4) {
+                // Huffman tables
+                this._huffmanTables.push(segment);
+            } else if (type == 0xDB) {
+                // Quantization tables
+                this._quantTables.push(segment);
+            }
+            this._segments.push(segment);
+            i = j;
+        }
+    }
+}
diff --git a/core/encodings.js b/core/encodings.js
index 51c0992..f16d033 100644
--- a/core/encodings.js
+++ b/core/encodings.js
@@ -13,6 +13,7 @@ export const encodings = {
     encodingHextile: 5,
     encodingTight: 7,
     encodingTightPNG: -260,
+    encodingJPEG: 21,
 
     pseudoEncodingQualityLevel9: -23,
     pseudoEncodingQualityLevel0: -32,
@@ -39,6 +40,7 @@ export function encodingName(num) {
         case encodings.encodingHextile:  return "Hextile";
         case encodings.encodingTight:    return "Tight";
         case encodings.encodingTightPNG: return "TightPNG";
+        case encodings.encodingJPEG:     return "JPEG";
         default:                         return "[unknown encoding " + num + "]";
     }
 }
diff --git a/core/rfb.js b/core/rfb.js
index bc52f4a..1583103 100644
--- a/core/rfb.js
+++ b/core/rfb.js
@@ -33,6 +33,7 @@ import HextileDecoder from "./decoders/hextile.js";
 import TightDecoder from "./decoders/tight.js";
 import TightPNGDecoder from "./decoders/tightpng.js";
 import ZRLEDecoder from "./decoders/zrle.js";
+import JPEGDecoder from "./decoders/jpeg.js";
 
 // How many seconds to wait for a disconnect to finish
 const DISCONNECT_TIMEOUT = 3;
@@ -220,6 +221,7 @@ export default class RFB extends EventTargetMixin {
         this._decoders[encodings.encodingTight] = new TightDecoder();
         this._decoders[encodings.encodingTightPNG] = new TightPNGDecoder();
         this._decoders[encodings.encodingZRLE] = new ZRLEDecoder();
+        this._decoders[encodings.encodingJPEG] = new JPEGDecoder();
 
         // NB: nothing that needs explicit teardown should be done
         // before this point, since this can throw an exception
@@ -1775,6 +1777,7 @@ export default class RFB extends EventTargetMixin {
             encs.push(encodings.encodingTight);
             encs.push(encodings.encodingTightPNG);
             encs.push(encodings.encodingZRLE);
+            encs.push(encodings.encodingJPEG);
             encs.push(encodings.encodingHextile);
             encs.push(encodings.encodingRRE);
         }