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26 <h2><span class="refentrytitle">GMime Streams</span></h2>
27 <p>GMime Streams — How to use GMime Streams</p>
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31 <div class="refsect1">
32 <a name="stream-overview"></a><h2>Overview of Streams</h2>
33 <p>Streams are the fundamental method for reading and writing
34 data used by GMime. You'll probably notice that the basic API is
35 similar to that of the low-level Unix I/O layer (read(), write(),
36 lseek(), etc) with some additional nicities such as a printf-like
38 <p>The three (3) basic stream types are: GMimeStreamFile,
39 GMimeStreamFs and GMimeStreamMem. You can manipulate all three
40 streams using the GMimeStream interfaces. In addition, some of
41 these streams have extended interfaces to allow more fine grained
43 <p>GMimeStreamFile and GMimeStreamFs are very similar in that
44 they are both meant for reading and writing data to the file
45 system (in the form of files). Since GMimeStreamFile is an
46 abstracted layer above the standard libc FILE type, one of the
47 added benefits is buffered I/O. GMimeStreamFs, on the other hand,
48 is an abstracted layer above Unix file descriptors. While a
49 GMimeStreamFs can be used on top of a UNIX socket or pipe, you
50 must be careful because sockets and pipes are not seekable.</p>
51 <p>Unlike the previous 2 stream types, GMimeStreamMem does not
52 interact with the file system at all (except maybe the swap
53 partition/file indirectly). Memory streams are handy when you want
54 reads and writes to be nearly instantaneous and/or if you don't
55 want to create a temporary file on disk.</p>
56 <p>The four (4) advanced stream types are GMimeStreamMmap,
57 GMimeStreamNull, GMimeStreamBuffer and GMimeStreamFilter.</p>
58 <p>Our most simple stream, GMimeStreamNull, is the stream
59 equivalent of /dev/null on Unix systems. The main difference is
60 that GMimeStreamNull records the number of bytes written to it -
61 you may find this useful if you need to know the number of bytes a
62 GMimeObject (for example) will require.</p>
63 <p>GMimeStreamMmap is a memory-mapped stream. This isn't
64 guarenteed to work on all systems since not all systems support
65 the POSIX mmap system call, but for those that do - this might
66 present a faster stream than GMimeStreamFs and/or
67 GMimeStreamFile. You'll have to do some experimentation to know
69 <p>The GMimeStreamBuffer can be used on top of any other type
70 of stream and has 3 modes: block reads, block writes, and cached
71 reads. Block reads are especially useful if you will be making a
72 lot of small reads from a stream that accesses the file
73 system. Block writes are useful for very much the same reason. The
74 final mode, cached reads, can become memory intensive but can be
75 very helpful when inheriting from a stream that does not support
76 seeking (Note: this mode is the least tested so be careful using
78 <p>Our final stream type, GMimeStreamFilter, can also be used
79 on top of another stream. This stream, as you may have guessed,
80 filters reads and writes to its inherited stream. For example, one
81 could write a compression filter and apply it to a
82 GMimeStreamFilter and any further reads or writes would be
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