xpcom/io/nsIInputStream.idl

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #include "nsISupports.idl"
   7
   8 interface nsIInputStream;
   9
  10 %{C++
  11 /**
  12  * The signature of the writer function passed to ReadSegments. This
  13  * is the "consumer" of data that gets read from the stream's buffer.
  14  *
  15  * @param aInStream stream being read
  16  * @param aClosure opaque parameter passed to ReadSegments
  17  * @param aFromSegment pointer to memory owned by the input stream.  This is
  18  *                     where the writer function should start consuming data.
  19  * @param aToOffset amount of data already consumed by this writer during this
  20  *                  ReadSegments call.  This is also the sum of the aWriteCount
  21  *                  returns from this writer over the previous invocations of
  22  *                  the writer by this ReadSegments call.
  23  * @param aCount Number of bytes available to be read starting at aFromSegment
  24  * @param [out] aWriteCount number of bytes read by this writer function call
  25  *
  26  * Implementers should return the following:
  27  *
  28  * @return NS_OK and (*aWriteCount > 0) if consumed some data
  29  * @return <any-error> if not interested in consuming any data
  30  *
  31  * Errors are never passed to the caller of ReadSegments.
  32  *
  33  * NOTE: returning NS_OK and (*aWriteCount = 0) has undefined behavior.
  34  */
  35 typedef nsresult (*nsWriteSegmentFun)(nsIInputStream *aInStream,
  36                                       void *aClosure,
  37                                       const char *aFromSegment,
  38                                       uint32_t aToOffset,
  39                                       uint32_t aCount,
  40                                       uint32_t *aWriteCount);
  41 %}
  42
  43 native nsWriteSegmentFun(nsWriteSegmentFun);
  44
  45 /**
  46  * nsIInputStream
  47  *
  48  * An interface describing a readable stream of data.  An input stream may be
  49  * "blocking" or "non-blocking" (see the IsNonBlocking method).  A blocking
  50  * input stream may suspend the calling thread in order to satisfy a call to
  51  * Close, Available, Read, or ReadSegments.  A non-blocking input stream, on
  52  * the other hand, must not block the calling thread of execution.
  53  *
  54  * NOTE: blocking input streams are often read on a background thread to avoid
  55  * locking up the main application thread.  For this reason, it is generally
  56  * the case that a blocking input stream should be implemented using thread-
  57  * safe AddRef and Release.
  58  */
  59 [scriptable, builtinclass, uuid(53cdbc97-c2d7-4e30-b2c3-45b2ee79db18)]
  60 interface nsIInputStream : nsISupports
  61 {
  62     /**
  63      * Close the stream.  This method causes subsequent calls to Read and
  64      * ReadSegments to return 0 bytes read to indicate end-of-file.  Any
  65      * subsequent calls to Available or StreamStatus should throw
  66      * NS_BASE_STREAM_CLOSED.
  67      *
  68      * Succeeds (without side effects) if already closed.
  69      */
  70     void close();
  71
  72     /**
  73      * Determine number of bytes available in the stream.  A non-blocking
  74      * stream that does not yet have any data to read should return 0 bytes
  75      * from this method (i.e., it must not throw the NS_BASE_STREAM_WOULD_BLOCK
  76      * exception).
  77      *
  78      * In addition to the number of bytes available in the stream, this method
  79      * also informs the caller of the current status of the stream.  A stream
  80      * that is closed will throw an exception when this method is called.  That
  81      * enables the caller to know the condition of the stream before attempting
  82      * to read from it.  If a stream is at end-of-file, but not closed, then
  83      * this method returns 0 bytes available.  (Note: some nsIInputStream
  84      * implementations automatically close when eof is reached; some do not).
  85      *
  86      * NOTE: Streams implementing nsIAsyncInputStream must automatically close
  87      * when eof is reached, as otherwise it is impossible to distinguish between
  88      * a stream waiting for more data and a stream at EOF using Available().
  89      *
  90      * @return number of bytes currently available in the stream.
  91      *
  92      * @throws NS_BASE_STREAM_CLOSED if the stream is closed normally.
  93      * @throws <other-error> if the stream is closed due to some error
  94      *   condition
  95      */
  96     unsigned long long available();
  97
  98     /**
  99      * Check the current status of the stream.  A stream that is closed will
 100      * throw an exception when this method is called.  That enables the caller
 101      * to know the condition of the stream before attempting to read from it.
 102      *
 103      * This method will not throw NS_BASE_STREAM_WOULD_BLOCK, even if the stream
 104      * is an non-blocking stream with no data. A non-blocking stream that does
 105      * not yet have any data to read should return NS_OK.
 106      *
 107      * NOTE: Unlike available, his method should not block the calling thread
 108      * (e.g. to query the state of a file descriptor), even when called on a
 109      * blocking stream.
 110      *
 111      * @throws NS_BASE_STREAM_CLOSED if the stream closed normally
 112      * @throws <other-error> if the stream closed with a different status
 113      */
 114     void streamStatus();
 115
 116     /**
 117      * Read data from the stream.
 118      *
 119      * @param aBuf the buffer into which the data is to be read
 120      * @param aCount the maximum number of bytes to be read
 121      *
 122      * @return number of bytes read (may be less than aCount).
 123      * @return 0 if reached end-of-file
 124      *
 125      * @throws NS_BASE_STREAM_WOULD_BLOCK if reading from the input stream would
 126      *   block the calling thread (non-blocking mode only)
 127      * @throws <other-error> on failure
 128      *
 129      * NOTE: this method should not throw NS_BASE_STREAM_CLOSED.
 130      */
 131     [noscript] unsigned long read(in charPtr aBuf, in unsigned long aCount);
 132
 133     /**
 134      * Low-level read method that provides access to the stream's underlying
 135      * buffer.  The writer function may be called multiple times for segmented
 136      * buffers.  ReadSegments is expected to keep calling the writer until
 137      * either there is nothing left to read or the writer returns an error.
 138      * ReadSegments should not call the writer with zero bytes to consume.
 139      *
 140      * @param aWriter the "consumer" of the data to be read
 141      * @param aClosure opaque parameter passed to writer
 142      * @param aCount the maximum number of bytes to be read
 143      *
 144      * @return number of bytes read (may be less than aCount)
 145      * @return 0 if reached end-of-file (or if aWriter refused to consume data)
 146      *
 147      * @throws NS_BASE_STREAM_WOULD_BLOCK if reading from the input stream would
 148      *   block the calling thread (non-blocking mode only)
 149      * @throws NS_ERROR_NOT_IMPLEMENTED if the stream has no underlying buffer
 150      * @throws <other-error> on failure
 151      *
 152      * NOTE: this function may be unimplemented if a stream has no underlying
 153      * buffer (e.g., socket input stream).
 154      *
 155      * NOTE: this method should not throw NS_BASE_STREAM_CLOSED.
 156      */
 157     [noscript] unsigned long readSegments(in nsWriteSegmentFun aWriter,
 158                                           in voidPtr aClosure,
 159                                           in unsigned long aCount);
 160
 161     /**
 162      * @return true if stream is non-blocking
 163      *
 164      * NOTE: reading from a blocking input stream will block the calling thread
 165      * until at least one byte of data can be extracted from the stream.
 166      *
 167      * NOTE: a non-blocking input stream may implement nsIAsyncInputStream to
 168      * provide consumers with a way to wait for the stream to have more data
 169      * once its read method is unable to return any data without blocking.
 170      */
 171     boolean isNonBlocking();
 172 };