xpcom/io/nsIInputStream.idl

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   4  *
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   8  * http://www.mozilla.org/MPL/
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  10  * Software distributed under the License is distributed on an "AS IS" basis,
  11  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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  14  *
  15  * The Original Code is mozilla.org code.
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  17  * The Initial Developer of the Original Code is
  18  * Netscape Communications Corporation.
  19  * Portions created by the Initial Developer are Copyright (C) 1998
  20  * the Initial Developer. All Rights Reserved.
  21  *
  22  * Contributor(s):
  23  *   Warren Harris <warren@netscape.com>
  24  *   Darin Fisher <darin@netscape.com>
  25  *
  26  * Alternatively, the contents of this file may be used under the terms of
  27  * either of the GNU General Public License Version 2 or later (the "GPL"),
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  38  * ***** END LICENSE BLOCK ***** */
  39
  40 #include "nsISupports.idl"
  41
  42 interface nsIInputStream;
  43
  44 %{C++
  45 /**
  46  * The signature of the writer function passed to ReadSegments. This
  47  * is the "consumer" of data that gets read from the stream's buffer.
  48  *
  49  * @param aInStream stream being read
  50  * @param aClosure opaque parameter passed to ReadSegments
  51  * @param aFromSegment pointer to memory owned by the input stream.  This is
  52  *                     where the writer function should start consuming data.
  53  * @param aToOffset amount of data already consumed by this writer during this
  54  *                  ReadSegments call.  This is also the sum of the aWriteCount
  55  *                  returns from this writer over the previous invocations of
  56  *                  the writer by this ReadSegments call.
  57  * @param aCount Number of bytes available to be read starting at aFromSegment
  58  * @param [out] aWriteCount number of bytes read by this writer function call
  59  *
  60  * Implementers should return the following:
  61  *
  62  * @return NS_OK and (*aWriteCount > 0) if consumed some data
  63  * @return <any-error> if not interested in consuming any data
  64  *
  65  * Errors are never passed to the caller of ReadSegments.
  66  *
  67  * NOTE: returning NS_OK and (*aWriteCount = 0) has undefined behavior.
  68  */
  69 typedef NS_CALLBACK(nsWriteSegmentFun)(nsIInputStream *aInStream,
  70                                        void *aClosure,
  71                                        const char *aFromSegment,
  72                                        PRUint32 aToOffset,
  73                                        PRUint32 aCount,
  74                                        PRUint32 *aWriteCount);
  75 %}
  76
  77 native nsWriteSegmentFun(nsWriteSegmentFun);
  78
  79 /**
  80  * nsIInputStream
  81  *
  82  * An interface describing a readable stream of data.  An input stream may be
  83  * "blocking" or "non-blocking" (see the IsNonBlocking method).  A blocking
  84  * input stream may suspend the calling thread in order to satisfy a call to
  85  * Close, Available, Read, or ReadSegments.  A non-blocking input stream, on
  86  * the other hand, must not block the calling thread of execution.
  87  *
  88  * NOTE: blocking input streams are often read on a background thread to avoid
  89  * locking up the main application thread.  For this reason, it is generally
  90  * the case that a blocking input stream should be implemented using thread-
  91  * safe AddRef and Release.
  92  */
  93 [scriptable, uuid(fa9c7f6c-61b3-11d4-9877-00c04fa0cf4a)]
  94 interface nsIInputStream : nsISupports
  95 {
  96     /**
  97      * Close the stream.  This method causes subsequent calls to Read and
  98      * ReadSegments to return 0 bytes read to indicate end-of-file.  Any
  99      * subsequent calls to Available should throw NS_BASE_STREAM_CLOSED.
 100      */
 101     void close();
 102
 103     /**
 104      * Determine number of bytes available in the stream.  A non-blocking
 105      * stream that does not yet have any data to read should return 0 bytes
 106      * from this method (i.e., it must not throw the NS_BASE_STREAM_WOULD_BLOCK
 107      * exception).
 108      *
 109      * In addition to the number of bytes available in the stream, this method
 110      * also informs the caller of the current status of the stream.  A stream
 111      * that is closed will throw an exception when this method is called.  That
 112      * enables the caller to know the condition of the stream before attempting
 113      * to read from it.  If a stream is at end-of-file, but not closed, then
 114      * this method returns 0 bytes available.  (Note: some nsIInputStream
 115      * implementations automatically close when eof is reached; some do not).
 116      *
 117      * @return number of bytes currently available in the stream, or
 118      *   PR_UINT32_MAX if the size of the stream exceeds PR_UINT32_MAX.
 119      *
 120      * @throws NS_BASE_STREAM_CLOSED if the stream is closed normally.
 121      * @throws <other-error> if the stream is closed due to some error
 122      *   condition
 123      */
 124     unsigned long available();
 125
 126     /**
 127      * Read data from the stream.
 128      *
 129      * @param aBuf the buffer into which the data is to be read
 130      * @param aCount the maximum number of bytes to be read
 131      *
 132      * @return number of bytes read (may be less than aCount).
 133      * @return 0 if reached end-of-file
 134      *
 135      * @throws NS_BASE_STREAM_WOULD_BLOCK if reading from the input stream would
 136      *   block the calling thread (non-blocking mode only)
 137      * @throws <other-error> on failure
 138      *
 139      * NOTE: this method should not throw NS_BASE_STREAM_CLOSED.
 140      */
 141     [noscript] unsigned long read(in charPtr aBuf, in unsigned long aCount);
 142
 143     /**
 144      * Low-level read method that provides access to the stream's underlying
 145      * buffer.  The writer function may be called multiple times for segmented
 146      * buffers.  ReadSegments is expected to keep calling the writer until
 147      * either there is nothing left to read or the writer returns an error.
 148      * ReadSegments should not call the writer with zero bytes to consume.
 149      *
 150      * @param aWriter the "consumer" of the data to be read
 151      * @param aClosure opaque parameter passed to writer
 152      * @param aCount the maximum number of bytes to be read
 153      *
 154      * @return number of bytes read (may be less than aCount)
 155      * @return 0 if reached end-of-file (or if aWriter refused to consume data)
 156      *
 157      * @throws NS_BASE_STREAM_WOULD_BLOCK if reading from the input stream would
 158      *   block the calling thread (non-blocking mode only)
 159      * @throws NS_ERROR_NOT_IMPLEMENTED if the stream has no underlying buffer
 160      * @throws <other-error> on failure
 161      *
 162      * NOTE: this function may be unimplemented if a stream has no underlying
 163      * buffer (e.g., socket input stream).
 164      *
 165      * NOTE: this method should not throw NS_BASE_STREAM_CLOSED.
 166      */
 167     [noscript] unsigned long readSegments(in nsWriteSegmentFun aWriter,
 168                                           in voidPtr aClosure,
 169                                           in unsigned long aCount);
 170
 171     /**
 172      * @return true if stream is non-blocking
 173      *
 174      * NOTE: reading from a blocking input stream will block the calling thread
 175      * until at least one byte of data can be extracted from the stream.
 176      *
 177      * NOTE: a non-blocking input stream may implement nsIAsyncInputStream to
 178      * provide consumers with a way to wait for the stream to have more data
 179      * once its read method is unable to return any data without blocking.
 180      */
 181     boolean isNonBlocking();
 182 };