Make the getBytes/peekBytes methods of Stream/DecodeStream/ChunkedStream able to return Uint8ClampedArrays

The built-in image decoders are already returning data as `Uint8ClampedArray`, and subsequently the JPEG/JBIG2/JPX streams are as well. However, for general streams we obviously don't want to force the use of `Uint8ClampedArray` unless an "Image" is actually being decoded.
Hence this patch, which adds a parameter that allows the caller of the `getBytes`/`peekBytes` methods to force a `Uint8ClampedArray` (rather than a `Uint8Array`) to be returned.

src/core/chunked_stream.js

@@ -181,16 +181,17 @@ var ChunkedStream = (function ChunkedStreamClosure() {
       return (b0 << 24) + (b1 << 16) + (b2 << 8) + b3;
     },
 
-    // returns subarray of original buffer
+    // Returns subarray of original buffer, should only be read.
-    // should only be read
+    getBytes(length, forceClamped = false) {
-    getBytes: function ChunkedStream_getBytes(length) {
       var bytes = this.bytes;
       var pos = this.pos;
       var strEnd = this.end;
 
       if (!length) {
         this.ensureRange(pos, strEnd);
-        return bytes.subarray(pos, strEnd);
+        let subarray = bytes.subarray(pos, strEnd);
+        // `this.bytes` is always a `Uint8Array` here.
+        return (forceClamped ? new Uint8ClampedArray(subarray) : subarray);
       }
 
       var end = pos + length;
@@ -200,7 +201,9 @@ var ChunkedStream = (function ChunkedStreamClosure() {
       this.ensureRange(pos, end);
 
       this.pos = end;
-      return bytes.subarray(pos, end);
+      let subarray = bytes.subarray(pos, end);
+      // `this.bytes` is always a `Uint8Array` here.
+      return (forceClamped ? new Uint8ClampedArray(subarray) : subarray);
     },
 
     peekByte: function ChunkedStream_peekByte() {
@@ -209,8 +212,8 @@ var ChunkedStream = (function ChunkedStreamClosure() {
       return peekedByte;
     },
 
-    peekBytes: function ChunkedStream_peekBytes(length) {
+    peekBytes(length, forceClamped = false) {
-      var bytes = this.getBytes(length);
+      var bytes = this.getBytes(length, forceClamped);
       this.pos -= bytes.length;
       return bytes;
     },

src/core/stream.js

@@ -56,30 +56,33 @@ var Stream = (function StreamClosure() {
       var b3 = this.getByte();
       return (b0 << 24) + (b1 << 16) + (b2 << 8) + b3;
     },
-    // returns subarray of original buffer
+    // Returns subarray of original buffer, should only be read.
-    // should only be read
+    getBytes(length, forceClamped = false) {
-    getBytes: function Stream_getBytes(length) {
       var bytes = this.bytes;
       var pos = this.pos;
       var strEnd = this.end;
 
       if (!length) {
-        return bytes.subarray(pos, strEnd);
+        let subarray = bytes.subarray(pos, strEnd);
+        // `this.bytes` is always a `Uint8Array` here.
+        return (forceClamped ? new Uint8ClampedArray(subarray) : subarray);
       }
       var end = pos + length;
       if (end > strEnd) {
         end = strEnd;
       }
       this.pos = end;
-      return bytes.subarray(pos, end);
+      let subarray = bytes.subarray(pos, end);
+      // `this.bytes` is always a `Uint8Array` here.
+      return (forceClamped ? new Uint8ClampedArray(subarray) : subarray);
     },
     peekByte: function Stream_peekByte() {
       var peekedByte = this.getByte();
       this.pos--;
       return peekedByte;
     },
-    peekBytes: function Stream_peekBytes(length) {
+    peekBytes(length, forceClamped = false) {
-      var bytes = this.getBytes(length);
+      var bytes = this.getBytes(length, forceClamped);
       this.pos -= bytes.length;
       return bytes;
     },
@@ -181,7 +184,7 @@ var DecodeStream = (function DecodeStreamClosure() {
       var b3 = this.getByte();
       return (b0 << 24) + (b1 << 16) + (b2 << 8) + b3;
     },
-    getBytes: function DecodeStream_getBytes(length) {
+    getBytes(length, forceClamped = false) {
       var end, pos = this.pos;
 
       if (length) {
@@ -203,15 +206,18 @@ var DecodeStream = (function DecodeStreamClosure() {
       }
 
       this.pos = end;
-      return this.buffer.subarray(pos, end);
+      let subarray = this.buffer.subarray(pos, end);
+      // `this.buffer` is either a `Uint8Array` or `Uint8ClampedArray` here.
+      return (forceClamped && !(subarray instanceof Uint8ClampedArray) ?
+              new Uint8ClampedArray(subarray) : subarray);
     },
     peekByte: function DecodeStream_peekByte() {
       var peekedByte = this.getByte();
       this.pos--;
       return peekedByte;
     },
-    peekBytes: function DecodeStream_peekBytes(length) {
+    peekBytes(length, forceClamped = false) {
-      var bytes = this.getBytes(length);
+      var bytes = this.getBytes(length, forceClamped);
       this.pos -= bytes.length;
       return bytes;
     },

test/unit/stream_spec.js

@@ -59,6 +59,11 @@ describe('stream', function() {
       expect(result).toMatchTypedArray(
         new Uint8Array([100, 3, 101, 2, 102, 1])
       );
+
+      predictor.reset();
+      let clampedResult = predictor.getBytes(6, /* forceClamped = */ true);
+      expect(clampedResult).toEqual(
+        new Uint8ClampedArray([100, 3, 101, 2, 102, 1]));
     });
   });
 });