Add a method to read a stream without advancing it.

src/core/SkStream.cpp

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkStream.h"
@@ skipping 349 matching lines @@
     if (size > dataSize - fOffset) {
         size = dataSize - fOffset;
     }
     if (buffer) {
         memcpy(buffer, fData->bytes() + fOffset, size);
     }
     fOffset += size;
     return size;
 }
 
+bool SkMemoryStream::peek(void* buffer, size_t size) const {
+    SkASSERT(buffer != NULL);
+    const size_t position = fOffset;
+    if (size > fData->size() - position) {
+        // The stream is not large enough to satisfy this request.
+        return false;
+    }
+    SkMemoryStream* nonConstThis = const_cast<SkMemoryStream*>(this);
+#ifdef SK_DEBUG

[bungeman-skia, 2015/04/02 18:24:09]

Should this be SkDEBUGCODE(...) instead? Then it would fit on the one line, like

SkDEBUGCODE(const size_t bytesRead =) nonConstThis->read(buffer, size); 

[scroggo, 2015/04/02 19:49:43]

Yes. Much better.

+    const size_t bytesRead =
+#endif
+    nonConstThis->read(buffer, size);
+    SkASSERT(bytesRead == size);
+    nonConstThis->fOffset = position;
+    return true;
+}
+
 bool SkMemoryStream::isAtEnd() const {
     return fOffset == fData->size();
 }
 
 bool SkMemoryStream::rewind() {
     fOffset = 0;
     return true;
 }
 
 SkMemoryStream* SkMemoryStream::duplicate() const {
@@ skipping 528 matching lines @@
     SkDynamicMemoryWStream tempStream;
     const size_t bufferSize = 4096;
     char buffer[bufferSize];
     do {
         size_t bytesRead = stream->read(buffer, bufferSize);
         tempStream.write(buffer, bytesRead);
     } while (!stream->isAtEnd());
     return tempStream.detachAsStream();  // returns a SkBlockMemoryStream,
                                          // cheaper than copying to SkData
 }