Merge pull request #5025 from nnethercote/share-zero-length-buffers

Improve how DecodeStream handles empty buffers.

src/core/stream.js

@@ -116,11 +116,17 @@ var StringStream = (function StringStreamClosure() {
 
 // super class for the decoding streams
 var DecodeStream = (function DecodeStreamClosure() {
+  // Lots of DecodeStreams are created whose buffers are never used.  For these
+  // we share a single empty buffer. This is (a) space-efficient and (b) avoids
+  // having special cases that would be required if we used |null| for an empty
+  // buffer.
+  var emptyBuffer = new Uint8Array(0);
+
   function DecodeStream(maybeMinBufferLength) {
     this.pos = 0;
     this.bufferLength = 0;
     this.eof = false;
-    this.buffer = null;
+    this.buffer = emptyBuffer;
     this.minBufferLength = 512;
     if (maybeMinBufferLength) {
       // Compute the first power of two that is as big as maybeMinBufferLength.
@@ -139,23 +145,15 @@ var DecodeStream = (function DecodeStreamClosure() {
     },
     ensureBuffer: function DecodeStream_ensureBuffer(requested) {
       var buffer = this.buffer;
-      var current;
-      if (buffer) {
-        current = buffer.byteLength;
-        if (requested <= current) {
-          return buffer;
-        }
-      } else {
-        current = 0;
+      if (requested <= buffer.byteLength) {
+        return buffer;
       }
       var size = this.minBufferLength;
       while (size < requested) {
         size *= 2;
       }
       var buffer2 = new Uint8Array(size);
-      if (buffer) {
-        buffer2.set(buffer);
-      }
+      buffer2.set(buffer);
       return (this.buffer = buffer2);
     },
     getByte: function DecodeStream_getByte() {
@@ -199,12 +197,6 @@ var DecodeStream = (function DecodeStreamClosure() {
           this.readBlock();
         }
         end = this.bufferLength;
-
-        // checking if bufferLength is still 0 then
-        // the buffer has to be initialized
-        if (!end) {
-          this.buffer = new Uint8Array(0);
-        }
       }
 
       this.pos = end;