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A netstream is an input channel that is read block by block. The * fragment of the channel currently loaded into memory is called the * current window of the netstream. The window can be thought as * look-ahead buffer. * * Picture: * *
* 0 pos_in pos_in + window_length EOF
* +------------------+-------------------+--------------------------+
* ====================
* The current window
*
* * You can use a netstream like an in_obj_channel, and read characters * and strings from the stream. The bytes come first from the look-ahead * buffer, and if there are not enough bytes, they are loaded from the * underlying channel. After every read operation it is tried to enlarge * the window such that it contains at least one block. * * If you want that the window becomes larger, you can call want (to * enlarge the window to a certain size) or want_another_block (to load * just another block from the underlying channel). Note that this affects only * the current window and not the future size of the window. * * Note Buffer_underrun: netstreams can cope with underruns of underlying * channels. An underrun happens when it is not possible to ensure the * minimum window size. However, it is possible that the window size * sinks under the minimum, but the Buffer_underrun is deferred until the * next call of an input method. Furthermore, there is a problem in the skip * method which may only be partially executed, i.e. the method skips some * bytes and then raises Buffer_underrun.
Make an in_obj_stream on top of an in_obj_channel. The block_size * can be specified; it defaults to 4096. * * If len is passed, this parameter limits the length of the channel: * Only the first len bytes are read from the input channel, then an EOF * is simulated even if the input channel is longer.
A sub stream is the part of the whole stream from the current position * to an arbitrary other position that is determined by len and * delimiter. len specifies the maximum length of the sub stream. * delimiter is an arbitrary string that indicates the end of the * sub stream (the delimiter is not part of the sub stream; i.e. the * sub stream ends immediately before the delimiter). * * While reading from the sub stream, not only the current position of * the sub stream moves, but also the current position of the main * stream. This means that it must be avoided to read data from the * main stream while the sub stream is in use. The typical pattern * is: * - Read from the main stream until the beginning of a section is * recognized * - Create a sub stream at this point * - Read from the sub stream until EOF * - Continue reading the main stream. The next character of the main * stream is exactly the character following the EOF of the sub stream