nsIAsyncInputStream

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Inherits from: nsIInputStream Last changed in Gecko 1.7

If an input stream is non-blocking, it may return NS_BASE_STREAM_WOULD_BLOCK when read. The caller must then wait for the stream to have some data to read. If the stream implements nsIAsyncInputStream, then the caller can use this interface to request an asynchronous notification when the stream becomes readable or closed (via the AsyncWait() method).

While this interface is almost exclusively used with non-blocking streams, it is not necessary that nsIInputStream.isNonBlocking() return true. Nor is it necessary that a non-blocking nsIInputStream implementation also implement nsIAsyncInputStream.

Method overview

void asyncWait(in nsIInputStreamCallback aCallback, in unsigned long aFlags, in unsigned long aRequestedCount, in nsIEventTarget aEventTarget);
void closeWithStatus(in nsresult aStatus);

Constants

Constant Value Description
WAIT_CLOSURE_ONLY (1<<0) If passed to asyncWait(), this flag overrides the default behavior, causing the OnInputStreamReady notification to be suppressed until the stream becomes closed (either as a result of closeWithStatus()/close being called on the stream or possibly due to some error in the underlying stream).

Methods

asyncWait()

Asynchronously wait for the stream to be readable or closed. The notification is one-shot, meaning that each asyncWait call will result in exactly one notification callback. After the OnInputStreamReady event is dispatched, the stream releases its reference to the nsIInputStreamCallback object. It is safe to call asyncWait again from the notification handler.

This method may be called at any time (even if read has not been called). In other words, this method may be called when the stream already has data to read. It may also be called when the stream is closed. If the stream is already readable or closed when asyncWait is called, then the nsIInputStreamCallback.onInputStreamReady() event will be dispatched immediately. Otherwise, the event will be dispatched when the stream becomes readable or closed.

void asyncWait(
  in nsIInputStreamCallback aCallback,
  in unsigned long aFlags,
  in unsigned long aRequestedCount,
  in nsIEventTarget aEventTarget
);
Parameters
aCallback
This object is notified when the stream becomes ready. This parameter may be null to clear an existing callback.
aFlags
This parameter specifies optional flags passed in to configure the behavior of this method. Pass zero to specify no flags.
aRequestedCount
Wait until at least this many bytes can be read. This is only a suggestion to the underlying stream; it may be ignored. The caller may pass zero to indicate no preference.
aEventTarget
Specify null to receive notification on ANY thread (possibly even recursively on the calling thread, that is synchronously), or specify that the notification be delivered to a specific event target.

closeWithStatus()

This method closes the stream and sets its internal status. If the stream is already closed, then this method is ignored. Once the stream is closed, the stream's status cannot be changed. Any successful status code passed to this method is treated as NS_BASE_STREAM_CLOSED, which has an effect equivalent to nsIInputStream.close().

Note: This method exists in part to support pipes, which have both an input end and an output end. If the input end of a pipe is closed, then writes to the output end of the pipe will fail. The error code returned when an attempt is made to write to a "broken" pipe corresponds to the status code passed in when the input end of the pipe was closed, which greatly simplifies working with pipes in some cases.

void closeWithStatus(
  in nsresult aStatus
);
Parameters
aStatus
The error that will be reported if this stream is accessed after it has been closed.

Document Tags and Contributors

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