Commit 68184463 authored by Ray Kraesig's avatar Ray Kraesig
Browse files

Bug 1815987 - Rewrite data-read loop in OnDataAvailable r=yjuglaret 

The read-loop in OnDataAvailable is needlessly baroque and uses a very
strange dialect of Hungarian notation. Factor out the zero-element case
for simplicity (of explication, if nothing else), and add justificatory
comments as appropriate.

Differential Revision: https://phabricator.services.mozilla.com/D171001
parent 65ff8912

widget/windows/nsDataObj.cpp

+35 −11
Original line number Diff line number Diff line
@@ -125,26 +125,50 @@ nsDataObj::CStream::OnDataAvailable( 
    uint64_t aOffset,  // offset within the stream

    uint32_t aCount)   // bytes available on this call

{

  // If we've been asked to read zero bytes, call `Read` once, just to ensure

  // any side-effects take place, and return immediately.

  if (aCount == 0) {

    char buffer[1] = {0};

    uint32_t bytesReadByCall = 0;

    nsresult rv = aInputStream->Read(buffer, 0, &bytesReadByCall);

    MOZ_ASSERT(bytesReadByCall == 0);

    return rv;

  }



  // Extend the write buffer for the incoming data.

  uint8_t* buffer = mChannelData.AppendElements(aCount, fallible);

  size_t oldLength = mChannelData.Length();

  char* buffer =

      reinterpret_cast<char*>(mChannelData.AppendElements(aCount, fallible));

  if (!buffer) {

    return NS_ERROR_OUT_OF_MEMORY;

  }

  NS_ASSERTION((mChannelData.Length() == (aOffset + aCount)),

  MOZ_ASSERT(mChannelData.Length() == (aOffset + aCount),

             "stream length mismatch w/write buffer");



  // Read() may not return aCount on a single call, so loop until we've

  // accumulated all the data OnDataAvailable has promised.

  nsresult rv;

  uint32_t odaBytesReadTotal = 0;

  do {

  uint32_t bytesRead = 0;

  while (bytesRead < aCount) {

    uint32_t bytesReadByCall = 0;

    rv = aInputStream->Read((char*)(buffer + odaBytesReadTotal), aCount,

    nsresult rv = aInputStream->Read(buffer + bytesRead, aCount - bytesRead,

                                     &bytesReadByCall);

    odaBytesReadTotal += bytesReadByCall;

  } while (aCount < odaBytesReadTotal && NS_SUCCEEDED(rv));

    bytesRead += bytesReadByCall;



    if (bytesReadByCall == 0) {

      // A `bytesReadByCall` of zero indicates EOF without failure... but we

      // were promised `aCount` elements and haven't gotten them. Return a

      // generic failure.

      rv = NS_ERROR_FAILURE;

    }



    if (NS_FAILED(rv)) {

      // Drop any trailing uninitialized elements before erroring out.

      mChannelData.RemoveElementsAt(oldLength + bytesRead, aCount - bytesRead);

      return rv;

    }

  }

  return NS_OK;

}



NS_IMETHODIMP nsDataObj::CStream::OnStartRequest(nsIRequest* aRequest) {

  mChannelResult = NS_OK;