nsIInputStream.idl

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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#include "nsISupports.idl"

interface nsIInputStream;

%{C++
/**
 * The signature of the writer function passed to ReadSegments. This
 * is the "consumer" of data that gets read from the stream's buffer.
 *
 * @param aInStream stream being read
 * @param aClosure opaque parameter passed to ReadSegments
 * @param aFromSegment pointer to memory owned by the input stream.  This is
 *                     where the writer function should start consuming data.
 * @param aToOffset amount of data already consumed by this writer during this
 *                  ReadSegments call.  This is also the sum of the aWriteCount
 *                  returns from this writer over the previous invocations of
 *                  the writer by this ReadSegments call.
 * @param aCount Number of bytes available to be read starting at aFromSegment
 * @param [out] aWriteCount number of bytes read by this writer function call
 *
 * Implementers should return the following:
 *
 * @return NS_OK and (*aWriteCount > 0) if consumed some data
 * @return <any-error> if not interested in consuming any data
 *
 * Errors are never passed to the caller of ReadSegments.
 *
 * NOTE: returning NS_OK and (*aWriteCount = 0) has undefined behavior.
 */
typedef NS_CALLBACK(nsWriteSegmentFun)(nsIInputStream *aInStream,
                                       void *aClosure,
                                       const char *aFromSegment,
                                       PRUint32 aToOffset,
                                       PRUint32 aCount,
                                       PRUint32 *aWriteCount);
%}

native nsWriteSegmentFun(nsWriteSegmentFun);

/**
 * nsIInputStream
 *
 * An interface describing a readable stream of data.  An input stream may be
 * "blocking" or "non-blocking" (see the IsNonBlocking method).  A blocking
 * input stream may suspend the calling thread in order to satisfy a call to
 * Close, Available, Read, or ReadSegments.  A non-blocking input stream, on
 * the other hand, must not block the calling thread of execution.
 *
 * NOTE: blocking input streams are often read on a background thread to avoid
 * locking up the main application thread.  For this reason, it is generally
 * the case that a blocking input stream should be implemented using thread-
 * safe AddRef and Release.
 */
[scriptable, uuid(fa9c7f6c-61b3-11d4-9877-00c04fa0cf4a)]
interface nsIInputStream : nsISupports
{
    /** 
     * Close the stream.  This method causes subsequent calls to Read and
     * ReadSegments to return 0 bytes read to indicate end-of-file.  Any
     * subsequent calls to Available should throw NS_BASE_STREAM_CLOSED.
     */
    void close();

    /**
     * Determine number of bytes available in the stream.  A non-blocking
     * stream that does not yet have any data to read should return 0 bytes
     * from this method (i.e., it must not throw the NS_BASE_STREAM_WOULD_BLOCK
     * exception).
     * 
     * In addition to the number of bytes available in the stream, this method
     * also informs the caller of the current status of the stream.  A stream
     * that is closed will throw an exception when this method is called.  That
     * enables the caller to know the condition of the stream before attempting
     * to read from it.  If a stream is at end-of-file, but not closed, then
     * this method returns 0 bytes available.  (Note: some nsIInputStream
     * implementations automatically close when eof is reached; some do not).
     *
     * @return number of bytes currently available in the stream, or
     *   PR_UINT32_MAX if the size of the stream exceeds PR_UINT32_MAX.
     *
     * @throws NS_BASE_STREAM_CLOSED if the stream is closed normally.
     * @throws <other-error> if the stream is closed due to some error
     *   condition
     */
    unsigned long available();

    /** 
     * Read data from the stream.
     *
     * @param aBuf the buffer into which the data is to be read
     * @param aCount the maximum number of bytes to be read
     *
     * @return number of bytes read (may be less than aCount).
     * @return 0 if reached end-of-file
     *
     * @throws NS_BASE_STREAM_WOULD_BLOCK if reading from the input stream would
     *   block the calling thread (non-blocking mode only)
     * @throws <other-error> on failure
     *
     * NOTE: this method should not throw NS_BASE_STREAM_CLOSED.
     */
    [noscript] unsigned long read(in charPtr aBuf, in unsigned long aCount);

    /**
     * Low-level read method that provides access to the stream's underlying
     * buffer.  The writer function may be called multiple times for segmented
     * buffers.  ReadSegments is expected to keep calling the writer until
     * either there is nothing left to read or the writer returns an error.
     * ReadSegments should not call the writer with zero bytes to consume.
     *
     * @param aWriter the "consumer" of the data to be read
     * @param aClosure opaque parameter passed to writer 
     * @param aCount the maximum number of bytes to be read
     *
     * @return number of bytes read (may be less than aCount)
     * @return 0 if reached end-of-file (or if aWriter refused to consume data)
     *
     * @throws NS_BASE_STREAM_WOULD_BLOCK if reading from the input stream would
     *   block the calling thread (non-blocking mode only)
     * @throws NS_ERROR_NOT_IMPLEMENTED if the stream has no underlying buffer
     * @throws <other-error> on failure
     *
     * NOTE: this function may be unimplemented if a stream has no underlying
     * buffer (e.g., socket input stream).
     *
     * NOTE: this method should not throw NS_BASE_STREAM_CLOSED.
     */
    [noscript] unsigned long readSegments(in nsWriteSegmentFun aWriter,
                                          in voidPtr aClosure,
                                          in unsigned long aCount);

    /**
     * @return true if stream is non-blocking
     *
     * NOTE: reading from a blocking input stream will block the calling thread
     * until at least one byte of data can be extracted from the stream.
     *
     * NOTE: a non-blocking input stream may implement nsIAsyncInputStream to
     * provide consumers with a way to wait for the stream to have more data
     * once its read method is unable to return any data without blocking.
     */
    boolean isNonBlocking();
};