<refentry id="gmime-streams">
  <refmeta>
    <refentrytitle>Streams</refentrytitle>
    <refmiscinfo>GMime Library</refmiscinfo>
  </refmeta>

  <refnamediv>
    <refname>Streams</refname>
    <refpurpose>How to use Streams</refpurpose>
  </refnamediv>
  <refsect1 id="stream-overview">
    <title>Overview of Streams</title>
    <para>Streams are the fundamental method for reading and writing
    data used by GMime. You'll probably notice that the basic API is 
    similar to that of the low-level Unix I/O layer (read(), write(), 
    lseek(), etc) with some additional niceties such as a printf-like 
    function.</para>

    <para>The three (3) basic stream types are: GMimeStreamFile,
    GMimeStreamFs and GMimeStreamMem. You can manipulate all three
    streams using the GMimeStream interfaces. In addition, some of
    these streams have extended interfaces to allow more fine grained
    manipulation.</para>

    <para>GMimeStreamFile and GMimeStreamFs are very similar in that
    they are both meant for reading and writing data to the file
    system (in the form of files). Since GMimeStreamFile is an
    abstracted layer above the standard libc FILE type, one of the
    added benefits is buffered I/O. GMimeStreamFs, on the other hand,
    is an abstracted layer above Unix file descriptors. While a
    GMimeStreamFs can be used on top of a UNIX socket or pipe, you
    must be careful because sockets and pipes are not seekable
    (see GMimeStreamPipe for a solution to this).</para>

    <para>Unlike the previous 2 stream types, GMimeStreamMem does not
    interact with the file system at all (except maybe the swap
    partition/file indirectly). Memory streams are handy when you want
    reads and writes to be nearly instantaneous and/or if you don't
    want to create a temporary file on disk.</para>

    <para>The five (5) advanced stream types are GMimeStreamMmap,
    GMimeStreamNull, GMimeStreamPipe, GMimeStreamBuffer and
    GMimeStreamFilter.</para>

    <para>Our most simple stream, GMimeStreamNull, is the stream
    equivalent of /dev/null on Unix systems. The main difference is
    that GMimeStreamNull records the number of bytes written to it -
    you may find this useful if you need to know the number of bytes a
    GMimeObject (for example) will require.</para>

    <para>GMimeStreamMmap is a memory-mapped stream. This isn't
    guaranteed to work on all systems since not all systems support
    the POSIX mmap system call, but for those that do - this might
    present a faster stream than GMimeStreamFs and/or
    GMimeStreamFile. You'll have to do some experimentation to know
    for sure.</para>

    <para>GMimeStreamPipe is just like GMimeStreamFs except that it
    doesn't support seeking, thus being perfect for use with sockets
    and pipes.</para>

    <para>The GMimeStreamBuffer can be used on top of any other type
    of stream and has 3 modes: block reads, block writes, and cached
    reads. Block reads are especially useful if you will be making a
    lot of small reads from a stream that accesses the file
    system. Block writes are useful for very much the same reason. The
    final mode, cached reads, can become memory intensive but can be
    very helpful when inheriting from a stream that does not support
    seeking (Note: this mode is the least tested so be careful using
    it).</para>

    <para>Our final stream type, GMimeStreamFilter, can also be used
    on top of another stream. This stream, as you may have guessed,
    filters reads and writes to its inherited stream. For example, one
    could write a compression filter and apply it to a
    GMimeStreamFilter and any further reads or writes would be
    (un)compressed.</para>
  </refsect1>
</refentry>
