nsIStreamConverter

This article is in need of a technical review.

Provides an interface to implement when you have code that converts data from one type to another.
Inherits from: nsIStreamListener Last changed in Gecko 1.7

Suppose you had code that converted plain text into HTML. You could implement this interface to allow everyone else to use your conversion logic using a standard api.

Stream converter users

There are currently two ways to use a stream converter:

  1. Synchronous: Stream to Stream. You can supply the service with a stream of type X and it will convert it to your desired output type and return a converted (blocking) stream to you.
  2. Asynchronous: nsIStreamListener to nsIStreamListener. You can supply data directly to the converter by calling it's nsIStreamListener.OnDataAvailable() method. It will then convert that data from type X to your desired output type and return converted data to you via the nsIStreamListener you passed in by calling its nsIStreamListener.OnDataAvailable() method.
Stream converter suppliers

Registering a stream converter: Stream converter registration is a two step process. First of all the stream converter implementation must register itself with the component manager using a contractid in the format below. Second, the stream converter must add the contractid to the registry.

Stream converter contractid format (the stream converter root key is defined in this file):

@mozilla.org/streamconv;1?from=FROM_MIME_TYPE&to=TO_MIME_TYPE

Method overview

void asyncConvertData(in string aFromType, in string aToType, in nsIStreamListener aListener, in nsISupports aCtxt);
nsIInputStream convert(in nsIInputStream aFromStream, in string aFromType, in string aToType, in nsISupports aCtxt);

Methods

asyncConvertData()

Asynchronous version: Converts data arriving via the converter's nsIStreamListener.OnDataAvailable() method from one type to another, pushing the converted data out to the caller via aListener::OnDataAvailable().

Use this method when you want to proxy (and convert) nsIStreamListener callbacks asynchronously.

void asyncConvertData(
  in string aFromType,
  in string aToType,
  in nsIStreamListener aListener,
  in nsISupports aCtxt
);
Parameters
aFromType
The MIME type of the original/raw data.
aToType
The MIME type of the converted data.
aListener
The listener who receives the converted data.
aCtxt
Either an opaque context, or a converter specific context (implementation specific).

convert()

Synchronous version: Converts a stream of one type, to a stream of another type.

Use this method when you have a stream you want to convert.

nsIInputStream convert(
  in nsIInputStream aFromStream,
  in string aFromType,
  in string aToType,
  in nsISupports aCtxt
);
Parameters
aFromStream
The stream representing the original/raw data.
aFromType
The MIME type of aFromStream.
aToType
The MIME type of the returned stream.
aCtxt
Either an opaque context, or a converter specific context (implementation specific).
Return value

The converted stream.

Note: The returned stream may not already be converted. An efficient stream converter implementation will converter data on demand rather than buffering the converted data until it is used.

Document Tags and Contributors

Contributors to this page: kscarfone, trevorh, Sheppy
Last updated by: Sheppy,