retrieve the maximum size for this extension based on the
information available from input_meta. Implementations should attempt
to provide as accurate information as possible as the returned value
will be used to control the amount of possible data in the payload.
Implementations must return the maximum as the allocated size for
writing the extension will be at least the size of the returned value.
Return the amount of data read or <0 on failure.
retrieve the maximum size for this extension based on the information available from input_meta. Implementations should attempt to provide as accurate information as possible as the returned value will be used to control the amount of possible data in the payload. Implementations must return the maximum as the allocated size for writing the extension will be at least the size of the returned value. Return the amount of data read or <0 on failure.