Fix a crash in the FileStream::Context::Read code path where we were invoking a NULL callback.

net/base/file_stream_context_win.cc

Index: net/base/file_stream_context_win.cc
diff --git a/net/base/file_stream_context_win.cc b/net/base/file_stream_context_win.cc
index 5ffbde72388293a339e46430846f4be6df62695c..e6c1b528bc09cf130054ebcd71118283716c24cc 100644
--- a/net/base/file_stream_context_win.cc
+++ b/net/base/file_stream_context_win.cc
@@ -174,6 +174,8 @@ void FileStream::Context::OnIOCompleted(
 }
 
 void FileStream::Context::InvokeUserCallback() {
+  if (callback_.is_null())
+    return;
   // For an asynchonous Read operation don't invoke the user callback until
   // we receive the IO completion notification and the asynchronous Read
   // completion notification.
@@ -203,15 +205,18 @@ void FileStream::Context::ReadAsync(
   DWORD bytes_read = 0;
   BOOL ret = ::ReadFile(file, buf->data(), buf_len, &bytes_read, overlapped);
   origin_thread_loop->PostTask(
-      FROM_HERE, base::Bind(&FileStream::Context::ReadAsyncResult,
-                            base::Unretained(context), ret ? bytes_read : 0,
-                            ret ? 0 : ::GetLastError()));
+      FROM_HERE,
+      base::Bind(&FileStream::Context::ReadAsyncResult,
+                 base::Unretained(context), ret, bytes_read, ::GetLastError()));
 }
 
-void FileStream::Context::ReadAsyncResult(DWORD bytes_read, DWORD os_error) {
-  if (!os_error)
+void FileStream::Context::ReadAsyncResult(BOOL read_file_ret,
+                                          DWORD bytes_read,
+                                          DWORD os_error) {
+  if (read_file_ret) {

[rvargas (doing something else), 2015/02/12 23:53:35]

Note that the original logic was:
       DWORD bytes_read;
  73   if (!ReadFile(file_.GetPlatformFile(), buf->data(), buf_len,	
  74                 &bytes_read, &io_context_.overlapped)) {	
  75     IOResult error = IOResult::FromOSError(GetLastError());	
  76     if (error.os_error == ERROR_HANDLE_EOF)	
  77       return 0;  // Report EOF by returning 0 bytes read.	
  78     if (error.os_error == ERROR_IO_PENDING)	
  79       IOCompletionIsPending(callback, buf);	
  80     else	
  81       LOG(WARNING) << "ReadFile failed: " << error.os_error;	
  82     return static_cast<int>(error.result);	
  83   }	
  85   IOCompletionIsPending(callback, buf);

We can avoid calling InvokeUserCallback twice.

if (read_file_ret) there is no need to look at os_error.

How about:

async_read_completed = true;
if (read_file_ret) {
  result_ = br
  InvokeUserCb
} else {
  if (!io_pending)
    OnIoCompleted(0) // and move the warning to line 163
}

[ananta, 2015/02/13 00:17:00]

Did something similar.

+    DCHECK(!os_error);
     result_ = bytes_read;
-
+  }
   IOResult error = IOResult::FromOSError(os_error);
   if (error.os_error == ERROR_HANDLE_EOF) {
     // Report EOF by returning 0 bytes read.