Bug 1754004 - Part 5: Only implement nsISeekableStream on nsBufferedStreams if it's implemented by the underlying stream, r=asuth,necko-reviewers,dragana

Previously, nsBufferedStreams would always implement nsISeekableStream, whether
or not the underlying stream did, and would only fail when trying to seek. This
makes it much more difficult to compensate and correctly transform streams when
they need to be seekable.

Differential Revision: https://phabricator.services.mozilla.com/D141042

netwerk/base/nsBufferedStreams.cpp

@@ -50,7 +50,14 @@ using mozilla::Some;
 
 nsBufferedStream::~nsBufferedStream() { Close(); }
 
-NS_IMPL_ISUPPORTS(nsBufferedStream, nsITellableStream, nsISeekableStream)
+NS_IMPL_ADDREF(nsBufferedStream)
+NS_IMPL_RELEASE(nsBufferedStream)
+
+NS_INTERFACE_MAP_BEGIN(nsBufferedStream)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+  NS_INTERFACE_MAP_ENTRY(nsITellableStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsISeekableStream, mSeekable)
+NS_INTERFACE_MAP_END
 
 nsresult nsBufferedStream::Init(nsISupports* aStream, uint32_t bufferSize) {
   NS_ASSERTION(aStream, "need to supply a stream");
@@ -59,6 +66,8 @@ nsresult nsBufferedStream::Init(nsISupports* aStream, uint32_t bufferSize) {
   mBufferSize = bufferSize;
   mBufferStartOffset = 0;
   mCursor = 0;
+  nsCOMPtr<nsISeekableStream> seekable = do_QueryInterface(mStream);
+  mSeekable = seekable;
   mBuffer = new (mozilla::fallible) char[bufferSize];
   if (mBuffer == nullptr) {
     return NS_ERROR_OUT_OF_MEMORY;

netwerk/base/nsBufferedStreams.h

@@ -58,6 +58,7 @@ class nsBufferedStream : public nsISeekableStream {
 
   bool mBufferDisabled{false};
   bool mEOF{false};  // True if mStream is at EOF
+  bool mSeekable{true};
   uint8_t mGetBufferCount{0};
 };