Add m-esr52 at 52.6.0

3 files changed, 856 insertions, 0 deletions

diff --git a/image/encoders/png/moz.build b/image/encoders/png/moz.build
new file mode 100644
index 000000000..e6665e424
--- /dev/null
+++ b/image/encoders/png/moz.build
@@ -0,0 +1,15 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+SOURCES += [
+    'nsPNGEncoder.cpp',
+]
+
+LOCAL_INCLUDES += [
+    '/image',
+]
+
+FINAL_LIBRARY = 'xul'
diff --git a/image/encoders/png/nsPNGEncoder.cpp b/image/encoders/png/nsPNGEncoder.cpp
new file mode 100644
index 000000000..66294146d
--- /dev/null
+++ b/image/encoders/png/nsPNGEncoder.cpp
@@ -0,0 +1,758 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * 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 "ImageLogging.h"
+#include "nsCRT.h"
+#include "nsPNGEncoder.h"
+#include "nsStreamUtils.h"
+#include "nsString.h"
+#include "prprf.h"
+
+using namespace mozilla;
+
+static LazyLogModule sPNGEncoderLog("PNGEncoder");
+
+NS_IMPL_ISUPPORTS(nsPNGEncoder, imgIEncoder, nsIInputStream,
+                  nsIAsyncInputStream)
+
+nsPNGEncoder::nsPNGEncoder() : mPNG(nullptr), mPNGinfo(nullptr),
+                               mIsAnimation(false),
+                               mFinished(false),
+                               mImageBuffer(nullptr), mImageBufferSize(0),
+                               mImageBufferUsed(0), mImageBufferReadPoint(0),
+                               mCallback(nullptr),
+                               mCallbackTarget(nullptr), mNotifyThreshold(0),
+                               mReentrantMonitor(
+                                              "nsPNGEncoder.mReentrantMonitor")
+{ }
+
+nsPNGEncoder::~nsPNGEncoder()
+{
+  if (mImageBuffer) {
+    free(mImageBuffer);
+    mImageBuffer = nullptr;
+  }
+  // don't leak if EndImageEncode wasn't called
+  if (mPNG) {
+    png_destroy_write_struct(&mPNG, &mPNGinfo);
+  }
+}
+
+// nsPNGEncoder::InitFromData
+//
+//    One output option is supported: "transparency=none" means that the
+//    output PNG will not have an alpha channel, even if the input does.
+//
+//    Based partially on gfx/cairo/cairo/src/cairo-png.c
+//    See also media/libpng/libpng-manual.txt
+
+NS_IMETHODIMP
+nsPNGEncoder::InitFromData(const uint8_t* aData,
+                           uint32_t aLength, // (unused, req'd by JS)
+                           uint32_t aWidth,
+                           uint32_t aHeight,
+                           uint32_t aStride,
+                           uint32_t aInputFormat,
+                           const nsAString& aOutputOptions)
+{
+  NS_ENSURE_ARG(aData);
+  nsresult rv;
+
+  rv = StartImageEncode(aWidth, aHeight, aInputFormat, aOutputOptions);
+  if (!NS_SUCCEEDED(rv)) {
+    return rv;
+  }
+
+  rv = AddImageFrame(aData, aLength, aWidth, aHeight, aStride,
+                     aInputFormat, aOutputOptions);
+  if (!NS_SUCCEEDED(rv)) {
+    return rv;
+  }
+
+  rv = EndImageEncode();
+
+  return rv;
+}
+
+
+// nsPNGEncoder::StartImageEncode
+//
+//
+// See ::InitFromData for other info.
+NS_IMETHODIMP
+nsPNGEncoder::StartImageEncode(uint32_t aWidth,
+                               uint32_t aHeight,
+                               uint32_t aInputFormat,
+                               const nsAString& aOutputOptions)
+{
+  bool useTransparency = true, skipFirstFrame = false;
+  uint32_t numFrames = 1;
+  uint32_t numPlays = 0; // For animations, 0 == forever
+
+  // can't initialize more than once
+  if (mImageBuffer != nullptr) {
+    return NS_ERROR_ALREADY_INITIALIZED;
+  }
+
+  // validate input format
+  if (aInputFormat != INPUT_FORMAT_RGB &&
+      aInputFormat != INPUT_FORMAT_RGBA &&
+      aInputFormat != INPUT_FORMAT_HOSTARGB)
+    return NS_ERROR_INVALID_ARG;
+
+  // parse and check any provided output options
+  nsresult rv = ParseOptions(aOutputOptions, &useTransparency, &skipFirstFrame,
+                             &numFrames, &numPlays, nullptr, nullptr,
+                             nullptr, nullptr, nullptr);
+  if (rv != NS_OK) {
+    return rv;
+  }
+
+#ifdef PNG_APNG_SUPPORTED
+  if (numFrames > 1) {
+    mIsAnimation = true;
+  }
+
+#endif
+
+  // initialize
+  mPNG = png_create_write_struct(PNG_LIBPNG_VER_STRING,
+                                 nullptr,
+                                 ErrorCallback,
+                                 WarningCallback);
+  if (!mPNG) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  mPNGinfo = png_create_info_struct(mPNG);
+  if (!mPNGinfo) {
+    png_destroy_write_struct(&mPNG, nullptr);
+    return NS_ERROR_FAILURE;
+  }
+
+  // libpng's error handler jumps back here upon an error.
+  // Note: It's important that all png_* callers do this, or errors
+  // will result in a corrupt time-warped stack.
+  if (setjmp(png_jmpbuf(mPNG))) {
+    png_destroy_write_struct(&mPNG, &mPNGinfo);
+    return NS_ERROR_FAILURE;
+  }
+
+  // Set up to read the data into our image buffer, start out with an 8K
+  // estimated size. Note: we don't have to worry about freeing this data
+  // in this function. It will be freed on object destruction.
+  mImageBufferSize = 8192;
+  mImageBuffer = (uint8_t*)malloc(mImageBufferSize);
+  if (!mImageBuffer) {
+    png_destroy_write_struct(&mPNG, &mPNGinfo);
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  mImageBufferUsed = 0;
+
+  // set our callback for libpng to give us the data
+  png_set_write_fn(mPNG, this, WriteCallback, nullptr);
+
+  // include alpha?
+  int colorType;
+  if ((aInputFormat == INPUT_FORMAT_HOSTARGB ||
+       aInputFormat == INPUT_FORMAT_RGBA)  &&
+       useTransparency)
+    colorType = PNG_COLOR_TYPE_RGB_ALPHA;
+  else
+    colorType = PNG_COLOR_TYPE_RGB;
+
+  png_set_IHDR(mPNG, mPNGinfo, aWidth, aHeight, 8, colorType,
+               PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,
+               PNG_FILTER_TYPE_DEFAULT);
+
+#ifdef PNG_APNG_SUPPORTED
+  if (mIsAnimation) {
+    png_set_first_frame_is_hidden(mPNG, mPNGinfo, skipFirstFrame);
+    png_set_acTL(mPNG, mPNGinfo, numFrames, numPlays);
+  }
+#endif
+
+  // XXX: support PLTE, gAMA, tRNS, bKGD?
+
+  png_write_info(mPNG, mPNGinfo);
+
+  return NS_OK;
+}
+
+// Returns the number of bytes in the image buffer used.
+NS_IMETHODIMP
+nsPNGEncoder::GetImageBufferUsed(uint32_t* aOutputSize)
+{
+  NS_ENSURE_ARG_POINTER(aOutputSize);
+  *aOutputSize = mImageBufferUsed;
+  return NS_OK;
+}
+
+// Returns a pointer to the start of the image buffer
+NS_IMETHODIMP
+nsPNGEncoder::GetImageBuffer(char** aOutputBuffer)
+{
+  NS_ENSURE_ARG_POINTER(aOutputBuffer);
+  *aOutputBuffer = reinterpret_cast<char*>(mImageBuffer);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPNGEncoder::AddImageFrame(const uint8_t* aData,
+                            uint32_t aLength, // (unused, req'd by JS)
+                            uint32_t aWidth,
+                            uint32_t aHeight,
+                            uint32_t aStride,
+                            uint32_t aInputFormat,
+                            const nsAString& aFrameOptions)
+{
+  bool useTransparency= true;
+  uint32_t delay_ms = 500;
+#ifdef PNG_APNG_SUPPORTED
+  uint32_t dispose_op = PNG_DISPOSE_OP_NONE;
+  uint32_t blend_op = PNG_BLEND_OP_SOURCE;
+#else
+  uint32_t dispose_op;
+  uint32_t blend_op;
+#endif
+  uint32_t x_offset = 0, y_offset = 0;
+
+  // must be initialized
+  if (mImageBuffer == nullptr) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  // EndImageEncode was done, or some error occurred earlier
+  if (!mPNG) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  // validate input format
+  if (aInputFormat != INPUT_FORMAT_RGB &&
+      aInputFormat != INPUT_FORMAT_RGBA &&
+      aInputFormat != INPUT_FORMAT_HOSTARGB)
+    return NS_ERROR_INVALID_ARG;
+
+  // libpng's error handler jumps back here upon an error.
+  if (setjmp(png_jmpbuf(mPNG))) {
+    png_destroy_write_struct(&mPNG, &mPNGinfo);
+    return NS_ERROR_FAILURE;
+  }
+
+  // parse and check any provided output options
+  nsresult rv = ParseOptions(aFrameOptions, &useTransparency, nullptr,
+                             nullptr, nullptr, &dispose_op, &blend_op,
+                             &delay_ms, &x_offset, &y_offset);
+  if (rv != NS_OK) {
+    return rv;
+  }
+
+#ifdef PNG_APNG_SUPPORTED
+  if (mIsAnimation) {
+    // XXX the row pointers arg (#3) is unused, can it be removed?
+    png_write_frame_head(mPNG, mPNGinfo, nullptr,
+                         aWidth, aHeight, x_offset, y_offset,
+                         delay_ms, 1000, dispose_op, blend_op);
+  }
+#endif
+
+  // Stride is the padded width of each row, so it better be longer
+  // (I'm afraid people will not understand what stride means, so
+  // check it well)
+  if ((aInputFormat == INPUT_FORMAT_RGB &&
+      aStride < aWidth * 3) ||
+      ((aInputFormat == INPUT_FORMAT_RGBA ||
+      aInputFormat == INPUT_FORMAT_HOSTARGB) &&
+      aStride < aWidth * 4)) {
+    NS_WARNING("Invalid stride for InitFromData/AddImageFrame");
+    return NS_ERROR_INVALID_ARG;
+  }
+
+#ifdef PNG_WRITE_FILTER_SUPPORTED
+  png_set_filter(mPNG, PNG_FILTER_TYPE_BASE, PNG_FILTER_VALUE_NONE);
+#endif
+
+  // write each row: if we add more input formats, we may want to
+  // generalize the conversions
+  if (aInputFormat == INPUT_FORMAT_HOSTARGB) {
+    // PNG requires RGBA with post-multiplied alpha, so we need to
+    // convert
+    UniquePtr<uint8_t[]> row = MakeUnique<uint8_t[]>(aWidth * 4);
+    for (uint32_t y = 0; y < aHeight; y++) {
+      ConvertHostARGBRow(&aData[y * aStride], row.get(), aWidth, useTransparency);
+      png_write_row(mPNG, row.get());
+    }
+  } else if (aInputFormat == INPUT_FORMAT_RGBA && !useTransparency) {
+    // RBGA, but we need to strip the alpha
+    UniquePtr<uint8_t[]> row = MakeUnique<uint8_t[]>(aWidth * 4);
+    for (uint32_t y = 0; y < aHeight; y++) {
+      StripAlpha(&aData[y * aStride], row.get(), aWidth);
+      png_write_row(mPNG, row.get());
+    }
+  } else if (aInputFormat == INPUT_FORMAT_RGB ||
+             aInputFormat == INPUT_FORMAT_RGBA) {
+    // simple RBG(A), no conversion needed
+    for (uint32_t y = 0; y < aHeight; y++) {
+      png_write_row(mPNG, (uint8_t*)&aData[y * aStride]);
+    }
+
+  } else {
+    NS_NOTREACHED("Bad format type");
+    return NS_ERROR_INVALID_ARG;
+  }
+
+#ifdef PNG_APNG_SUPPORTED
+  if (mIsAnimation) {
+    png_write_frame_tail(mPNG, mPNGinfo);
+  }
+#endif
+
+  return NS_OK;
+}
+
+
+NS_IMETHODIMP
+nsPNGEncoder::EndImageEncode()
+{
+  // must be initialized
+  if (mImageBuffer == nullptr) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  // EndImageEncode has already been called, or some error
+  // occurred earlier
+  if (!mPNG) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  // libpng's error handler jumps back here upon an error.
+  if (setjmp(png_jmpbuf(mPNG))) {
+    png_destroy_write_struct(&mPNG, &mPNGinfo);
+    return NS_ERROR_FAILURE;
+  }
+
+  png_write_end(mPNG, mPNGinfo);
+  png_destroy_write_struct(&mPNG, &mPNGinfo);
+
+  mFinished = true;
+  NotifyListener();
+
+  // if output callback can't get enough memory, it will free our buffer
+  if (!mImageBuffer) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  return NS_OK;
+}
+
+
+nsresult
+nsPNGEncoder::ParseOptions(const nsAString& aOptions,
+                           bool* useTransparency,
+                           bool* skipFirstFrame,
+                           uint32_t* numFrames,
+                           uint32_t* numPlays,
+                           uint32_t* frameDispose,
+                           uint32_t* frameBlend,
+                           uint32_t* frameDelay,
+                           uint32_t* offsetX,
+                           uint32_t* offsetY)
+{
+#ifdef PNG_APNG_SUPPORTED
+  // Make a copy of aOptions, because strtok() will modify it.
+  nsAutoCString optionsCopy;
+  optionsCopy.Assign(NS_ConvertUTF16toUTF8(aOptions));
+  char* options = optionsCopy.BeginWriting();
+
+  while (char* token = nsCRT::strtok(options, ";", &options)) {
+    // If there's an '=' character, split the token around it.
+    char* equals = token;
+    char* value = nullptr;
+    while(*equals != '=' && *equals) {
+      ++equals;
+    }
+    if (*equals == '=') {
+      value = equals + 1;
+    }
+
+    if (value) {
+      *equals = '\0'; // temporary null
+    }
+
+    // transparency=[yes|no|none]
+    if (nsCRT::strcmp(token, "transparency") == 0 && useTransparency) {
+      if (!value) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      if (nsCRT::strcmp(value, "none") == 0 ||
+          nsCRT::strcmp(value, "no") == 0) {
+        *useTransparency = false;
+      } else if (nsCRT::strcmp(value, "yes") == 0) {
+        *useTransparency = true;
+      } else {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+    // skipfirstframe=[yes|no]
+    } else if (nsCRT::strcmp(token, "skipfirstframe") == 0 &&
+               skipFirstFrame) {
+      if (!value) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      if (nsCRT::strcmp(value, "no") == 0) {
+        *skipFirstFrame = false;
+      } else if (nsCRT::strcmp(value, "yes") == 0) {
+        *skipFirstFrame = true;
+      } else {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+    // frames=#
+    } else if (nsCRT::strcmp(token, "frames") == 0 && numFrames) {
+      if (!value) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      if (PR_sscanf(value, "%u", numFrames) != 1) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      // frames=0 is nonsense.
+      if (*numFrames == 0) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+    // plays=#
+    } else if (nsCRT::strcmp(token, "plays") == 0 && numPlays) {
+      if (!value) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      // plays=0 to loop forever, otherwise play sequence specified
+      // number of times
+      if (PR_sscanf(value, "%u", numPlays) != 1) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+    // dispose=[none|background|previous]
+    } else if (nsCRT::strcmp(token, "dispose") == 0 && frameDispose) {
+      if (!value) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      if (nsCRT::strcmp(value, "none") == 0) {
+        *frameDispose = PNG_DISPOSE_OP_NONE;
+      } else if (nsCRT::strcmp(value, "background") == 0) {
+        *frameDispose = PNG_DISPOSE_OP_BACKGROUND;
+      } else if (nsCRT::strcmp(value, "previous") == 0) {
+        *frameDispose = PNG_DISPOSE_OP_PREVIOUS;
+      } else {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+    // blend=[source|over]
+    } else if (nsCRT::strcmp(token, "blend") == 0 && frameBlend) {
+      if (!value) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      if (nsCRT::strcmp(value, "source") == 0) {
+        *frameBlend = PNG_BLEND_OP_SOURCE;
+      } else if (nsCRT::strcmp(value, "over") == 0) {
+        *frameBlend = PNG_BLEND_OP_OVER;
+      } else {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+    // delay=# (in ms)
+    } else if (nsCRT::strcmp(token, "delay") == 0 && frameDelay) {
+      if (!value) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      if (PR_sscanf(value, "%u", frameDelay) != 1) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+    // xoffset=#
+    } else if (nsCRT::strcmp(token, "xoffset") == 0 && offsetX) {
+      if (!value) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      if (PR_sscanf(value, "%u", offsetX) != 1) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+    // yoffset=#
+    } else if (nsCRT::strcmp(token, "yoffset") == 0 && offsetY) {
+      if (!value) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      if (PR_sscanf(value, "%u", offsetY) != 1) {
+        return NS_ERROR_INVALID_ARG;
+      }
+
+    // unknown token name
+    } else
+      return NS_ERROR_INVALID_ARG;
+
+    if (value) {
+      *equals = '='; // restore '=' so strtok doesn't get lost
+    }
+  }
+
+#endif
+  return NS_OK;
+}
+
+
+NS_IMETHODIMP
+nsPNGEncoder::Close()
+{
+  if (mImageBuffer != nullptr) {
+    free(mImageBuffer);
+    mImageBuffer = nullptr;
+    mImageBufferSize = 0;
+    mImageBufferUsed = 0;
+    mImageBufferReadPoint = 0;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPNGEncoder::Available(uint64_t* _retval)
+{
+  if (!mImageBuffer) {
+    return NS_BASE_STREAM_CLOSED;
+    }
+
+  *_retval = mImageBufferUsed - mImageBufferReadPoint;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPNGEncoder::Read(char* aBuf, uint32_t aCount, uint32_t* _retval)
+{
+  return ReadSegments(NS_CopySegmentToBuffer, aBuf, aCount, _retval);
+}
+
+NS_IMETHODIMP
+nsPNGEncoder::ReadSegments(nsWriteSegmentFun aWriter,
+                           void* aClosure, uint32_t aCount,
+                           uint32_t* _retval)
+{
+  // Avoid another thread reallocing the buffer underneath us
+  ReentrantMonitorAutoEnter autoEnter(mReentrantMonitor);
+
+  uint32_t maxCount = mImageBufferUsed - mImageBufferReadPoint;
+  if (maxCount == 0) {
+    *_retval = 0;
+    return mFinished ? NS_OK : NS_BASE_STREAM_WOULD_BLOCK;
+  }
+
+  if (aCount > maxCount) {
+    aCount = maxCount;
+  }
+
+  nsresult rv =
+      aWriter(this, aClosure,
+              reinterpret_cast<const char*>(mImageBuffer+mImageBufferReadPoint),
+              0, aCount, _retval);
+  if (NS_SUCCEEDED(rv)) {
+    NS_ASSERTION(*_retval <= aCount, "bad write count");
+    mImageBufferReadPoint += *_retval;
+  }
+
+  // errors returned from the writer end here!
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPNGEncoder::IsNonBlocking(bool* _retval)
+{
+  *_retval = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPNGEncoder::AsyncWait(nsIInputStreamCallback* aCallback,
+                        uint32_t aFlags,
+                        uint32_t aRequestedCount,
+                        nsIEventTarget* aTarget)
+{
+  if (aFlags != 0) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  if (mCallback || mCallbackTarget) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  mCallbackTarget = aTarget;
+  // 0 means "any number of bytes except 0"
+  mNotifyThreshold = aRequestedCount;
+  if (!aRequestedCount) {
+    mNotifyThreshold = 1024; // We don't want to notify incessantly
+  }
+
+  // We set the callback absolutely last, because NotifyListener uses it to
+  // determine if someone needs to be notified.  If we don't set it last,
+  // NotifyListener might try to fire off a notification to a null target
+  // which will generally cause non-threadsafe objects to be used off the main
+  // thread
+  mCallback = aCallback;
+
+  // What we are being asked for may be present already
+  NotifyListener();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPNGEncoder::CloseWithStatus(nsresult aStatus)
+{
+  return Close();
+}
+
+// nsPNGEncoder::ConvertHostARGBRow
+//
+//    Our colors are stored with premultiplied alphas, but PNGs use
+//    post-multiplied alpha. This swaps to PNG-style alpha.
+//
+//    Copied from gfx/cairo/cairo/src/cairo-png.c
+
+void
+nsPNGEncoder::ConvertHostARGBRow(const uint8_t* aSrc, uint8_t* aDest,
+                                 uint32_t aPixelWidth,
+                                 bool aUseTransparency)
+{
+  uint32_t pixelStride = aUseTransparency ? 4 : 3;
+  for (uint32_t x = 0; x < aPixelWidth; x++) {
+    const uint32_t& pixelIn = ((const uint32_t*)(aSrc))[x];
+    uint8_t* pixelOut = &aDest[x * pixelStride];
+
+    uint8_t alpha = (pixelIn & 0xff000000) >> 24;
+    pixelOut[pixelStride - 1] = alpha; // overwritten below if pixelStride == 3
+    if (alpha == 255) {
+      pixelOut[0] = (pixelIn & 0xff0000) >> 16;
+      pixelOut[1] = (pixelIn & 0x00ff00) >>  8;
+      pixelOut[2] = (pixelIn & 0x0000ff)      ;
+    } else if (alpha == 0) {
+      pixelOut[0] = pixelOut[1] = pixelOut[2] = 0;
+    } else {
+      pixelOut[0] = (((pixelIn & 0xff0000) >> 16) * 255 + alpha / 2) / alpha;
+      pixelOut[1] = (((pixelIn & 0x00ff00) >>  8) * 255 + alpha / 2) / alpha;
+      pixelOut[2] = (((pixelIn & 0x0000ff)      ) * 255 + alpha / 2) / alpha;
+    }
+  }
+}
+
+
+// nsPNGEncoder::StripAlpha
+//
+//    Input is RGBA, output is RGB
+
+void
+nsPNGEncoder::StripAlpha(const uint8_t* aSrc, uint8_t* aDest,
+                          uint32_t aPixelWidth)
+{
+  for (uint32_t x = 0; x < aPixelWidth; x++) {
+    const uint8_t* pixelIn = &aSrc[x * 4];
+    uint8_t* pixelOut = &aDest[x * 3];
+    pixelOut[0] = pixelIn[0];
+    pixelOut[1] = pixelIn[1];
+    pixelOut[2] = pixelIn[2];
+  }
+}
+
+
+// nsPNGEncoder::WarningCallback
+
+void
+nsPNGEncoder::WarningCallback(png_structp png_ptr,
+                            png_const_charp warning_msg)
+{
+  MOZ_LOG(sPNGEncoderLog, LogLevel::Warning,
+         ("libpng warning: %s\n", warning_msg));
+}
+
+
+// nsPNGEncoder::ErrorCallback
+
+void
+nsPNGEncoder::ErrorCallback(png_structp png_ptr,
+                            png_const_charp error_msg)
+{
+  MOZ_LOG(sPNGEncoderLog, LogLevel::Error, ("libpng error: %s\n", error_msg));
+  png_longjmp(png_ptr, 1);
+}
+
+// nsPNGEncoder::WriteCallback
+
+void // static
+nsPNGEncoder::WriteCallback(png_structp png, png_bytep data,
+                            png_size_t size)
+{
+  nsPNGEncoder* that = static_cast<nsPNGEncoder*>(png_get_io_ptr(png));
+  if (!that->mImageBuffer) {
+    return;
+  }
+
+  if (that->mImageBufferUsed + size > that->mImageBufferSize) {
+    // When we're reallocing the buffer we need to take the lock to ensure
+    // that nobody is trying to read from the buffer we are destroying
+    ReentrantMonitorAutoEnter autoEnter(that->mReentrantMonitor);
+
+    // expand buffer, just double each time
+    that->mImageBufferSize *= 2;
+    uint8_t* newBuf = (uint8_t*)realloc(that->mImageBuffer,
+                                        that->mImageBufferSize);
+    if (!newBuf) {
+      // can't resize, just zero (this will keep us from writing more)
+      free(that->mImageBuffer);
+      that->mImageBuffer = nullptr;
+      that->mImageBufferSize = 0;
+      that->mImageBufferUsed = 0;
+      return;
+    }
+    that->mImageBuffer = newBuf;
+  }
+  memcpy(&that->mImageBuffer[that->mImageBufferUsed], data, size);
+  that->mImageBufferUsed += size;
+  that->NotifyListener();
+}
+
+void
+nsPNGEncoder::NotifyListener()
+{
+  // We might call this function on multiple threads (any threads that call
+  // AsyncWait and any that do encoding) so we lock to avoid notifying the
+  // listener twice about the same data (which generally leads to a truncated
+  // image).
+  ReentrantMonitorAutoEnter autoEnter(mReentrantMonitor);
+
+  if (mCallback &&
+      (mImageBufferUsed - mImageBufferReadPoint >= mNotifyThreshold ||
+       mFinished)) {
+    nsCOMPtr<nsIInputStreamCallback> callback;
+    if (mCallbackTarget) {
+      callback = NS_NewInputStreamReadyEvent(mCallback, mCallbackTarget);
+    } else {
+      callback = mCallback;
+    }
+
+    NS_ASSERTION(callback, "Shouldn't fail to make the callback");
+    // Null the callback first because OnInputStreamReady could reenter
+    // AsyncWait
+    mCallback = nullptr;
+    mCallbackTarget = nullptr;
+    mNotifyThreshold = 0;
+
+    callback->OnInputStreamReady(this);
+  }
+}
diff --git a/image/encoders/png/nsPNGEncoder.h b/image/encoders/png/nsPNGEncoder.h
new file mode 100644
index 000000000..95e7d5c19
--- /dev/null
+++ b/image/encoders/png/nsPNGEncoder.h
@@ -0,0 +1,83 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * 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/. */
+
+#ifndef nsPNGEncoder_h
+
+#include <png.h>
+
+#include "imgIEncoder.h"
+#include "nsCOMPtr.h"
+
+#include "mozilla/Attributes.h"
+#include "mozilla/ReentrantMonitor.h"
+
+#define NS_PNGENCODER_CID \
+{ /* 38d1592e-b81e-432b-86f8-471878bbfe07 */         \
+     0x38d1592e,                                     \
+     0xb81e,                                         \
+     0x432b,                                         \
+    {0x86, 0xf8, 0x47, 0x18, 0x78, 0xbb, 0xfe, 0x07} \
+}
+
+// Provides PNG encoding functionality. Use InitFromData() to do the
+// encoding. See that function definition for encoding options.
+
+class nsPNGEncoder final : public imgIEncoder
+{
+  typedef mozilla::ReentrantMonitor ReentrantMonitor;
+public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_IMGIENCODER
+  NS_DECL_NSIINPUTSTREAM
+  NS_DECL_NSIASYNCINPUTSTREAM
+
+  nsPNGEncoder();
+
+protected:
+  ~nsPNGEncoder();
+  nsresult ParseOptions(const nsAString& aOptions,
+                        bool* useTransparency,
+                        bool* skipFirstFrame,
+                        uint32_t* numAnimatedFrames,
+                        uint32_t* numIterations,
+                        uint32_t* frameDispose,
+                        uint32_t* frameBlend,
+                        uint32_t* frameDelay,
+                        uint32_t* offsetX,
+                        uint32_t* offsetY);
+  void ConvertHostARGBRow(const uint8_t* aSrc, uint8_t* aDest,
+                          uint32_t aPixelWidth, bool aUseTransparency);
+  void StripAlpha(const uint8_t* aSrc, uint8_t* aDest,
+                  uint32_t aPixelWidth);
+  static void WarningCallback(png_structp png_ptr, png_const_charp warning_msg);
+  static void ErrorCallback(png_structp png_ptr, png_const_charp error_msg);
+  static void WriteCallback(png_structp png, png_bytep data, png_size_t size);
+  void NotifyListener();
+
+  png_struct* mPNG;
+  png_info* mPNGinfo;
+
+  bool mIsAnimation;
+  bool mFinished;
+
+  // image buffer
+  uint8_t* mImageBuffer;
+  uint32_t mImageBufferSize;
+  uint32_t mImageBufferUsed;
+
+  uint32_t mImageBufferReadPoint;
+
+  nsCOMPtr<nsIInputStreamCallback> mCallback;
+  nsCOMPtr<nsIEventTarget> mCallbackTarget;
+  uint32_t mNotifyThreshold;
+
+  // nsPNGEncoder is designed to allow one thread to pump data into it while
+  // another reads from it.  We lock to ensure that the buffer remains
+  // append-only while we read from it (that it is not realloced) and to
+  // ensure that only one thread dispatches a callback for each call to
+  // AsyncWait.
+  ReentrantMonitor mReentrantMonitor;
+};
+#endif // nsPNGEncoder_h