Request an asynchronous read of count bytes from the stream into a new glib.Bytes When the operation is finished callback will be called. You can then call InputStream.readBytesFinish to get the result of the operation.
During an async request no other sync and async calls are allowed on stream, and will result in G_IO_ERROR_PENDING errors.
A value of count larger than G_MAXSSIZE will cause a G_IO_ERROR_INVALID_ARGUMENT error.
On success, the new glib.Bytes will be passed to the callback. It is not an error if this is smaller than the requested size, as it can happen e.g. near the end of a file, but generally we try to read as many bytes as requested. Zero is returned on end of file (or if count is zero), but never otherwise.
Any outstanding I/O request with higher priority (lower numerical value) will be executed before an outstanding request with lower priority. Default priority is G_PRIORITY_DEFAULT.
the number of bytes that will be read from the stream
the [I/O priority][io-priority] of the request
optional gio.Cancellable object, NULL to ignore.
callback to call when the request is satisfied
the data to pass to callback function