diff -r 000000000000 -r 6474c204b198 xpcom/io/nsSegmentedBuffer.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/io/nsSegmentedBuffer.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,167 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsSegmentedBuffer.h"
+#include "nsMemory.h"
+
+nsresult
+nsSegmentedBuffer::Init(uint32_t segmentSize, uint32_t maxSize)
+{
+    if (mSegmentArrayCount != 0)
+        return NS_ERROR_FAILURE;        // initialized more than once
+    mSegmentSize = segmentSize;
+    mMaxSize = maxSize;
+#if 0 // testing...
+    mSegmentArrayCount = 2;
+#else
+    mSegmentArrayCount = NS_SEGMENTARRAY_INITIAL_COUNT;
+#endif
+    return NS_OK;
+}
+
+char*
+nsSegmentedBuffer::AppendNewSegment()
+{
+    if (GetSize() >= mMaxSize)
+        return nullptr;
+
+    if (mSegmentArray == nullptr) {
+        uint32_t bytes = mSegmentArrayCount * sizeof(char*);
+        mSegmentArray = (char**)nsMemory::Alloc(bytes);
+        if (mSegmentArray == nullptr)
+            return nullptr;
+        memset(mSegmentArray, 0, bytes);
+    }
+    
+    if (IsFull()) {
+        uint32_t newArraySize = mSegmentArrayCount * 2;
+        uint32_t bytes = newArraySize * sizeof(char*);
+        char** newSegArray = (char**)nsMemory::Realloc(mSegmentArray, bytes);
+        if (newSegArray == nullptr)
+            return nullptr;
+        mSegmentArray = newSegArray;
+        // copy wrapped content to new extension
+        if (mFirstSegmentIndex > mLastSegmentIndex) {
+            // deal with wrap around case
+            memcpy(&mSegmentArray[mSegmentArrayCount],
+                   mSegmentArray,
+                   mLastSegmentIndex * sizeof(char*));
+            memset(mSegmentArray, 0, mLastSegmentIndex * sizeof(char*));
+            mLastSegmentIndex += mSegmentArrayCount;
+            memset(&mSegmentArray[mLastSegmentIndex], 0,
+                   (newArraySize - mLastSegmentIndex) * sizeof(char*));
+        }
+        else {
+            memset(&mSegmentArray[mLastSegmentIndex], 0,
+                   (newArraySize - mLastSegmentIndex) * sizeof(char*));
+        }
+        mSegmentArrayCount = newArraySize;
+    }
+
+    char* seg = (char*)moz_malloc(mSegmentSize);
+    if (seg == nullptr) {
+        return nullptr;
+    }
+    mSegmentArray[mLastSegmentIndex] = seg;
+    mLastSegmentIndex = ModSegArraySize(mLastSegmentIndex + 1);
+    return seg;
+}
+
+bool
+nsSegmentedBuffer::DeleteFirstSegment()
+{
+    NS_ASSERTION(mSegmentArray[mFirstSegmentIndex] != nullptr, "deleting bad segment");
+    moz_free(mSegmentArray[mFirstSegmentIndex]);
+    mSegmentArray[mFirstSegmentIndex] = nullptr;
+    int32_t last = ModSegArraySize(mLastSegmentIndex - 1);
+    if (mFirstSegmentIndex == last) {
+        mLastSegmentIndex = last;
+        return true;
+    }
+    else {
+        mFirstSegmentIndex = ModSegArraySize(mFirstSegmentIndex + 1);
+        return false;
+    }
+}
+
+bool
+nsSegmentedBuffer::DeleteLastSegment()
+{
+    int32_t last = ModSegArraySize(mLastSegmentIndex - 1);
+    NS_ASSERTION(mSegmentArray[last] != nullptr, "deleting bad segment");
+    moz_free(mSegmentArray[last]);
+    mSegmentArray[last] = nullptr;
+    mLastSegmentIndex = last;
+    return (bool)(mLastSegmentIndex == mFirstSegmentIndex);
+}
+
+bool
+nsSegmentedBuffer::ReallocLastSegment(size_t newSize)
+{
+    int32_t last = ModSegArraySize(mLastSegmentIndex - 1);
+    NS_ASSERTION(mSegmentArray[last] != nullptr, "realloc'ing bad segment");
+    char *newSegment =
+        (char*)moz_realloc(mSegmentArray[last], newSize);
+    if (newSegment) {
+        mSegmentArray[last] = newSegment;
+        return true;
+    } else {
+        return false;
+    }
+}
+
+void
+nsSegmentedBuffer::Empty()
+{
+    if (mSegmentArray) {
+        for (uint32_t i = 0; i < mSegmentArrayCount; i++) {
+            if (mSegmentArray[i])
+                moz_free(mSegmentArray[i]);
+        }
+        nsMemory::Free(mSegmentArray);
+        mSegmentArray = nullptr;
+    }
+    mSegmentArrayCount = NS_SEGMENTARRAY_INITIAL_COUNT;
+    mFirstSegmentIndex = mLastSegmentIndex = 0;
+}
+
+#if 0
+void
+TestSegmentedBuffer()
+{
+    nsSegmentedBuffer* buf = new nsSegmentedBuffer();
+    NS_ASSERTION(buf, "out of memory");
+    buf->Init(4, 16);
+    char* seg;
+    bool empty;
+    seg = buf->AppendNewSegment();
+    NS_ASSERTION(seg, "AppendNewSegment failed");
+    seg = buf->AppendNewSegment();
+    NS_ASSERTION(seg, "AppendNewSegment failed");
+    seg = buf->AppendNewSegment();
+    NS_ASSERTION(seg, "AppendNewSegment failed");
+    empty = buf->DeleteFirstSegment();
+    NS_ASSERTION(!empty, "DeleteFirstSegment failed");
+    empty = buf->DeleteFirstSegment();
+    NS_ASSERTION(!empty, "DeleteFirstSegment failed");
+    seg = buf->AppendNewSegment();
+    NS_ASSERTION(seg, "AppendNewSegment failed");
+    seg = buf->AppendNewSegment();
+    NS_ASSERTION(seg, "AppendNewSegment failed");
+    seg = buf->AppendNewSegment();
+    NS_ASSERTION(seg, "AppendNewSegment failed");
+    empty = buf->DeleteFirstSegment();
+    NS_ASSERTION(!empty, "DeleteFirstSegment failed");
+    empty = buf->DeleteFirstSegment();
+    NS_ASSERTION(!empty, "DeleteFirstSegment failed");
+    empty = buf->DeleteFirstSegment();
+    NS_ASSERTION(!empty, "DeleteFirstSegment failed");
+    empty = buf->DeleteFirstSegment();
+    NS_ASSERTION(empty, "DeleteFirstSegment failed");
+    delete buf;
+}
+#endif
+
+////////////////////////////////////////////////////////////////////////////////