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diff --git a/docs/tutorial/gmime-tut.sgml b/docs/tutorial/gmime-tut.sgml new file mode 100644 index 0000000..57b3c61 --- /dev/null +++ b/docs/tutorial/gmime-tut.sgml @@ -0,0 +1,681 @@ +<!doctype book PUBLIC "-//OASIS//DTD DocBook V3.1//EN" [ +<!notation PNG system "PNG"> +<!entity % local.notation.class "| PNG"> +]> +<book id="gmime-tut"> + + <bookinfo> + <title>GMime 2.6 tutorial</title> + <date>Oct 28, 2010</date> + <authorgroup> + <author> + <firstname>Jeffrey</firstname> + <surname>Stedfast</surname> + <affiliation> + <address> + <email>fejj@gnome.org</email> + </address> + </affiliation> + </author> + </authorgroup> + <abstract> + <para>This tutorial is meant to demonstrate how to use the GMime + C API.</para> + </abstract> + </bookinfo> + + <toc></toc> + + <!-- ***************************************************************** --> + <chapter id="ch-availability"> + <title>Tutorial Availability</title> + + <para>A copy of this tutorial is distributed with each source-code +release of GMime in both SGML and HTML formats. For binary +distributions, please check with your vendor.</para> + + <para>An online version of this tutorial is also available at <ulink +url="http://spruce.sourceforge.net/gmime/tutorial/">http://spruce.sourceforge.net/gmime/tutorial/</ulink>. + </para> + + </chapter> + + <!-- ***************************************************************** --> + <chapter id="ch-introduction"> + <title>Introduction</title> + + <para>GMime is a library for parsing and creating messages using the +Multipurpose Internet Mail Extension (MIME) format. It is licensed +under the <ulink +url="http://http://www.gnu.org/licenses/licenses.html#LGPL">GNU Lesser General +Public License (LGPL)</ulink> so you are free to develop your Free +Software applications using GMime without having to spend anything for +licenses or royalties.</para> + + <para>The primary author and maintainer of GMime is:</para> + + <itemizedlist> + <listitem> + <simpara>Jeffrey Stedfast <ulink url="mailto:fejj@gnome.org">fejj@gnome.org</ulink></simpara> + </listitem> + </itemizedlist> + + <para>GMime is essentially an object-oriented application programmers +interface (API). Although written completely in C, it is implemented +using the idea of classes and callback functions (pointers to +functions).</para> + + <para>GMime is built upon another library called GLib which also +serves as the foundation for such libraries as the GIMP ToolKit +(Gtk+). GLib is mostly a portability layer but also contains +additional functionality such as hash tables, linked lists, etc. For +more information on GLib, you should see the API reference at <ulink +url="http://library.gnome.org/devel/glib/stable/">http://library.gnome.org/devel/glib/stable/</ulink>.</para> + + </chapter> + + <!-- ***************************************************************** --> + <chapter id="ch-getting-started"> + <title>Getting Started</title> + + <para>The first thing you need to do, of course, is download the +GMime source and install it. You can always get the latest version +from <ulink url="http://download.gnome.org/pub/GNOME/sources/gmime/">http://download.gnome.org/pub/GNOME/sources/gmime/</ulink>. GMime +uses GNU autoconf for configuration. Once untar'd, type +<literal>./configure --help</literal> to see a list of options.</para> + + <para>More information about building GMime is available in either the +source distribution under <filename>docs/reference/</filename> or via +the online reference at <ulink +url="http://library.gnome.org/devel/gmime/stable/gmime-building.html">http://library.gnome.org/devel/gmime/stable/gmime-building.html</ulink>.</para> + + </chapter> + + <!-- ***************************************************************** --> + <chapter id="ch-basics"> + <title>Getting Down to the Basics</title> + + <!-- ----------------------------------------------------------------- --> + <sect1 id="sec-compiling"> + <title>Compiling</title> + + <para>The first thing you need to learn how to do is compile + your program with the proper compiler flags so that your program + will include the correct GMime headers and linker flags.</para> + + <para>To compile and link a simple program, you'll want to do + the following:</para> + + <para> + <literallayout> + <literal>gcc -g -Wall -o simple simple.c `pkg-config --cflags --libs gmime-2.4`</literal> + </literallayout> + </para> + </sect1> + + <!-- ----------------------------------------------------------------- --> + <sect1 id="sec-stream-basics"> + <title>GMimeStream Basics</title> + + <para>Before we get too deep into using GMime, it is important + to understand how to use the underlying I/O classes since GMime + is so very heavily dependant upon them.</para> + + <para>If you've looked at the API at all already, you will have + probably noticed that the stream functions work very much like + those of the standard low-level UNIX I/O functions (those that + use file descriptors) but with a few extras taken from the + higher-level Standard C I/O API.</para> + + <para>Let's take a moment to regres back to our early days of + programming where we learned how to write "Hello World!" on the + console:</para> + + <programlisting role="C"> +#include <stdio.h> + +int main (int argc, char **argv) +{ + fprintf (stdout, "Hello World!\n"); + fflush (stdout); + + return 0; +} + </programlisting> + + <para>Everyone should recognize what that program does. The + above program, rewritten to use GMime's stream classes would + look something like this:</para> + + <programlisting role="C"> +#include <stdio.h> +#include <gmime/gmime.h> + +int main (int argc, char **argv) +{ + GMimeStream *stream; + + /* initialize GMime */ + g_mime_init (0); + + /* create a stream around stdout */ + stream = g_mime_stream_file_new (stdout); + + /* 'printf' */ + g_mime_stream_printf (stream, "Hello World!\n"); + + /* flush stdout */ + g_mime_stream_flush (stream); + + /* free/close the stream */ + g_object_unref (stream); + + return 0; +} + </programlisting> + + <para>Hopefully, the only thing that may be new to you in either + of the above examples is the flushing of the stream after + writing to it. Most likely, in both examples, it is an unneeded + call, however it is there for completeness and you should + probably get into the habbit of flushing a stream after you've + finished writing to it. Like fflush(), g_mime_stream_flush() + will flush any write-buffers that the previous write-calls may + have left.</para> + + <para>The first function called in the second example is + <literal>g_mime_init</literal> with a value of + <literal>0</literal>. If you haven't guessed, + <literal>g_mime_init</literal> initializes the GMime library. It + takes a single bit-mask argument specifying which options to + enable. Currently there is only one optional bit-flag, + <literal>GMIME_INIT_FLAG_UTF8</literal> which is the default + anyway, so a value of <literal>0</literal> is used here. The + UTF-8 flag only exists for historical reasons.</para> + + <para>The only other line that should need explaining might be:</para> + + <programlisting role="C"> + stream = g_mime_stream_file_new (stdout); + </programlisting> + + <para>This line creates a new object of type GMimeStreamFile which + takes a <literal>FILE*</literal> argument. Once the + GMimeStreamFile is created, it takes ownership of the + <literal>FILE*</literal> so be careful if you want to be able to + ever use that <literal>FILE*</literal> handle again later in + your program or if you do not wish for it to be closed when the + GMimeStreamFile is closed later.</para> + + <para>One way of working around this is to do something like the + following example:</para> + + <programlisting role="C"> +#include <stdio.h> +#include <unistd.h> +#include <gmime/gmime.h> + +int main (int argc, char **argv) +{ + GMimeStream *stream; + + /* initialize GMime */ + g_mime_init (0); + + /* create a stream around stdout */ + stream = g_mime_stream_fs_new (dup (fileno (stdout))); + + /* 'printf' */ + g_mime_stream_printf (stream, "Hello World!\n"); + + /* flush stdout */ + g_mime_stream_flush (stream); + + /* free/close the stream */ + g_object_unref (stream); + + return 0; +} + </programlisting> + + <para>Here we have made a duplicate copy of stdout to give to + <literal>g_mime_stream_fs_new()</literal>. GMimeStreamFs is the + second type of stream meant for basic I/O, but instead of using + a <literal>FILE*</literal> handle, it instead uses an integer + file descriptor. The <literal>fileno()</literal> function + returns the integer file descriptor for a given + <literal>FILE*</literal> handle. The <literal>dup()</literal> + function makes a duplicate of the file descriptor passed to + it. More information can be read about these 2 functions by + using <literal>man</literal> on your local UNIX system or by + reading the Reference Manual for your libc.</para> + + <para>There are also some functions to tell GMimeStreamFile, + GMimeStreamFs and GMimeStreamMem that they are not the owners of + the backend storage and so when they are destroyed, they should + not close the file or free the memory buffer + (respectively). These functions are:</para> + + <programlisting role="C"> +void g_mime_stream_file_set_owner (GMimeStreamFile *stream, gboolean owner); +void g_mime_stream_fs_set_owner (GMimeStreamFs *stream, gboolean owner); +void g_mime_stream_mem_set_owner (GMimeStreamMem *stream, gboolean owner); + </programlisting> + + <para>Next, let's examine some of the other stream + functions.</para> + + <programlisting role="C"> + g_mime_stream_eos (stream); + </programlisting> + + <para>This function is useful for finding out if the + End-Of-Stream has been reached. This is similar in functionality + to Standard C's <literal>feof()</literal> function.</para> + + <programlisting role="C"> + g_mime_stream_reset (stream); + </programlisting> + + <para>This function will reset the state of a stream. Usually + this only means 'rewinding' to the beginning of the file. For + more complex streams, such as GMimeStreamFilter, however, this + will also reset the state of all of the filters that have been + attached to it (more on this later).</para> + + <programlisting role="C"> + g_mime_stream_length (stream); + </programlisting> + + <para>This function will return the length of the stream if + known, or -1 otherwise. For the most part, this function should + be avoided unless you absolutely need to know the stream length + and there is no other way to get it. The reason to avoid using + it is that it may be inaccurate if any filters are to be applied + as well as possibly being slow depending on the underlying + storage device.</para> + + <programlisting role="C"> + g_mime_stream_substream (stream, start, end); + </programlisting> + + <para>This function will return a substream of the original + stream, where the beginning of the new substream is the start + offset and the end is the end offset. These start and end + offsets MUST be within the bounds of the original + stream. Substreams can be useful if you want to only allow + reading and writing to a subsection of the original + stream.</para> + + <programlisting role="C"> + g_mime_stream_read (stream, buf, n); + </programlisting> + + <para>Like POSIX <literal>read()</literal>, this function will + try to read <literal>n</literal> bytes from the stream + into <literal>buf</literal>, but be warned that it is not + guaranteed to read the full requested buffer size if that much + data is not currently available.</para> + + <programlisting role="C"> + g_mime_stream_write (stream, buf, n); + </programlisting> + + <para>Like POSIX <literal>write()</literal> and standard + C's <literal>fwrite()</literal>, this function will write a + buffer of the specified length to the underlying + stream. However, unlike the POSIX <literal>write()</literal> + function, it will only fail if an irrecoverable error has + occurred and so it is not necessary to loop write attempts until + the entire buffer is written.</para> + + <programlisting role="C"> + g_mime_stream_seek (stream, offset, GMIME_STREAM_SEEK_SET); + g_mime_stream_seek (stream, offset, GMIME_STREAM_SEEK_CUR); + g_mime_stream_seek (stream, offset, GMIME_STREAM_SEEK_END); + </programlisting> + + <para>This function works exactly like the + POSIX <literal>lseek()</literal> or standard + C's <literal>fseek()</literal> functions.</para> + + </sect1> + + <!-- ----------------------------------------------------------------- --> + <sect1 id="sec-stream-classes"> + <title>Stream Class Overview</title> + + <para>There are a number of stream classes included with GMime, + but we are only going to go over the more widely useful stream + classes. You should be able to figure out the others on your + own.</para> + + <para>We've already seen GMimeStreamFile and GMimeStreamFs in + action in the prevous chapter, so let's skip them and start with + GMimeStreamMem.</para> + + <para>GMimeStremMem is a stream abstraction that reads and + writes to a memory buffer. Like any other stream, the basic + stream functions (read, write, seek, substream, eos, etc) apply + here as well. Internally, GMimeStreamMem uses the GLib + GByteArray structure for storage so you may want to read up on + that.</para> + + <para>There are several ways to instantiate a GMimeStreamMem + object. You will probably use + <literal>g_mime_stream_mem_new()</literal> most of the + time. There may be times, however, when you will already have a + memory buffer that you'd like to use as a stream. There are + several ways to create a GMimeStreamMem object to use this + buffer (or a copy of it).</para> + + <para>The first is + <literal>g_mime_stream_mem_new_with_byte_array()</literal>. This + assumes that you are already using a GByteArray and want to use + it as a stream. As explained in the previous chapter about + GMimeStreamFile and ownership, the same applies here. When the + GMimeStreamMem is destroyed, so is the GByteArray structure and + the memory buffer it contained. To get around this, create a new + GMimeStreamMem object using + <literal>g_mime_stream_mem_new()</literal> and then use + <literal>g_mime_stream_mem_set_byte_array()</literal> to set the + GByteArray as the memory buffer. This will make it so that + GMimeStreamMem does not own the GByteArray, so when the + GMimeStremMem object is destroyed, the GByteArray will + remain.</para> + + <para>Also at your disposal for creating GMimeStreamMem objects + with an initial buffer is + <literal>g_mime_stream_mem_new_with_buffer()</literal>. This + function, however, will duplicate the buffer passed to it so if + you have memory quotas you are trying to keep, you may wish to + find a way to use one of the above methods.</para> + + <para>That pretty much sums up how to use GMimeStreamMem. The + next most widely used stream class is probably + GMimeStreamBuffer. This stream class actually wraps another + stream object adding additional functionality such as read and + write buffering and a few additional read methods.</para> + + <para>As you may or may not know, buffering reads and writes is + a great way to improve I/O performance in applications. The time + it takes to do a lot of small reads and writes accumulates + fast.</para> + + <para>When using a GMimeStreamBuffer in + <literal>GMIME_STREAM_BUFFER_BLOCK_READ</literal> mode, a block + of 4K (4096 bytes) will be read into an intermediate + buffer. Each time your application performs a read on this + GMimeStreamBuffer stream, a chunk of that intermediate buffer + will be copied to your read buffer until all 4K have been read, + at which point GMimeStreamBuffer will pre-scan the next 4K and so + on.</para> + + <para>Similarly, using mode + <literal>GMIME_STREAM_BUFFER_BLOCK_WRITE</literal> will copy + each of your application write-buffers into an intermediate 4K + buffer. When that 4K buffer fills up, it will be flushed to the + underlying stream. You may also use + <literal>g_mime_stream_flush()</literal> to force the + intermediate buffer to be written to the underlying + stream.</para> + + <para>Note that the intermediate buffer size is 4096 bytes. You + should be aware that if you will mostly be reading and writing + blocks of larger than 4K, it is probably best to avoid using + GMimeStreamBuffer as it will not likely gain you any performance + and may decrease performance instead.</para> + + <para>GMimeStreamBuffer also adds 2 convenience functions for + reading. While they will both work with any stream class, they + are obviously much faster if used with a GMimeStreamBuffer in + mode <literal>GMIME_STREAM_BUFFER_BLOCK_READ</literal>. These + functions are:</para> + + <programlisting role="C"> +ssize_t g_mime_stream_buffer_gets (GMimeStream *stream, char *buf, size_t max); + +void g_mime_stream_buffer_readln (GMimeStream *stream, GByteArray *buffer); + </programlisting> + + <para>The first function is similar to Standard C's + <literal>fgets()</literal> function (although the arguments are + in a slightly different order). It reads up to the first + <literal>max - 1</literal> bytes, stopping after a + <literal>\n</literal> character, if found. <literal>buf</literal> + will always be nul-terminated.</para> + + <para>The second function, + <literal>g_mime_stream_buffer_readln()</literal>, has no + Standard C equivalent that I am aware of, but you should get the + idea of what it does based on the function name (I hope). It + reads exactly one (1) line (including the <literal>\n</literal> + character) and appends it to the end of + <literal>buffer</literal>.</para> + + <para>The last stream class you really need to know (and the + last one I have the patience to explain) is + GMimeStreamFilter. This is a special stream class which you can + attach GMimeFilters to so that reading/writing to this stream + will automagically convert the stream from one form to + another. GMime uses this stream internally for converting base64 + encoded attachments into their raw form and vice versa.</para> + + <note> + <para>As previously mentioned in the last chapter concerning + <literal>g_mime_stream_reset()</literal>, resetting a + GMimeStreamFilter stream will also reset all of the filters + applied.</para> + </note> + + <para>A great example usage of GMimeStreamFilter can be found in + the <filename>src/uuencode.c</filename> source file found in the + source distribution. Here's a clip of that source file + illustrating how to use stream filters:</para> + + <programlisting role="C"> + GMimeStream *istream, *ostream, *fstream; + GMimeFilter *filter; + int fd; + + ... + + if (g_mime_stream_printf (ostream, "begin %.3o %s\n", st.st_mode & 0777, name) == -1) { + fprintf (stderr, "%s: %s\n", progname, strerror (errno)); + g_object_unref (ostream); + exit (1); + } + + istream = g_mime_stream_fs_new (fd); + + fstream = g_mime_stream_filter_new (ostream); + + filter = g_mime_filter_basic_new (GMIME_CONTENT_ENCODING_UUENCODE, TRUE); + g_mime_stream_filter_add ((GMimeStreamFilter *) fstream, filter); + g_object_unref (filter); + + if (g_mime_stream_write_to_stream (istream, fstream) == -1) { + fprintf (stderr, "%s: %s\n", progname, strerror (errno)); + g_object_unref (fstream); + g_object_unref (istream); + g_object_unref (ostream); + exit (1); + } + + g_mime_stream_flush (fstream); + g_object_unref (fstream); + g_object_unref (istream); + + if (g_mime_stream_write_string (ostream, "end\n") == -1) { + fprintf (stderr, "%s: %s\n", progname, strerror (errno)); + g_object_unref (ostream); + exit (1); + } + + g_object_unref (ostream); + </programlisting> + + <para>The above snippet of code will read the contents of the input + stream (<literal>istream</literal>) and write it to our output + stream (<literal>ostream</literal>), but only after it has + passed through our filter-stream + (<literal>fstream</literal>). The filter attached to + <literal>fstream</literal> is one of the basic MIME filters that + encodes data in the traditional UUCP format. You have probably + run a program to do this many times in the past using the UNIX + command <literal>uuencode</literal>. Never thought writing a + replacement for <literal>uuencode</literal> could be so easy, + did you? Well, it is. And not only is it <emphasis>that + easy</emphasis>, but it also runs faster than the + <literal>uuencode</literal> shipped with GNU Sharutils (at least + up to and including the 4.2.1 release).</para> + + </sect1> + + <!-- ----------------------------------------------------------------- --> + <sect1 id="sec-filter-classes"> + <title>Filter Class Overview</title> + + <para>GMime comes pre-bundled with a number of stream filters + for your convenience and more may be added in the future. For + now, let's breeze through a summary of some of the more important + ones:</para> + + <para>GMimeFilterBasic is used quite a lot internally in GMime + for encoding and decoding the content of MIME parts. This class + contains a mode for encoding and decoding each of Base64, + Quoted-Printable, and Uuencode.</para> + + <para>If you are interested in converting between charsets for + your users, you will likely want to become familiar with + GMimeFilterCharset which provides a convenient way to convert + text streams of one charset into another charset.</para> + + <para>GMimeFilterCRLF will likely become very useful to you if + you are implementing any internet standards or DOS/UNIX + compatability. This filter is meant for converting line endings + from the traditional UNIX sequence (LF) to the internet standard + (and DOS) sequence, CRLF, and vice versa. Also included in this + filter is a way to escape and unescape lines beginning with '.' + in the method used by the SMTP and POP protocols.</para> + + <para>GMimeFilterFrom is one you will likely need to use if ever + you need to write to an mbox-formatted mail spool. At present, + it has 2 modes: <literal>GMIME_FILTER_FROM_MODE_ESCAPE</literal> + and <literal>GMIME_FILTER_FROM_MODE_ARMOR</literal>. If you are + writing to an mbox-formatted spool, you will always want to use + the <literal>ESCAPE</literal> mode which will escape lines + beginning with "From " by prepending a '>' character, resulting + in ">From ". The other mode might come in handy if you are + implementing a multipart/signed method where you are + quoted-printable encoding a text stream and need to special-case + From-lines in order to protect against UNIX systems which will + alter the message when writing it to an mbox file such as the + previously mentioned filter mode. The result is something like + "=46rom " which prevents the need to prepend a '>' character + when the message arrives at a UNIX machine.</para> + + <para>Also included are: GMimeFilterBest (which will likely not + concern you), GMimeFilterEnriched (which will convert + text/enriched and/or text/rtf to text/html), and GMimeFilterHTML + which will convert text/plain into text/html with options to + wrap strings that appear to be hyperlinks with appropriate <a + href=...> tags; GMimeFilterStrip (again, likely this won't + concern you), and finally GMimeFilterYenc which will encode or + decode the YEncode encoding.</para> + + <para>For an example on how to use filters, please see the end + of the previous chapter where it talks about GMimeStreamFilter + and provides a snippet from + <filename>src/uuencode.c</filename></para> + + <note> + <para>Note: Since it may be non-obvious, filters are applied + to a stream in the same order that they are added to the + GMimeFilterStream. This means that if you add a base64 encode + filter and then add a CRLF filter, the stream will first be + base64 encoded and then the end-of-line formatting will be + canonicalised to CRLF.</para> + </note> + + </sect1> + + </chapter> + + <!-- ***************************************************************** --> + <chapter id="ch-mime"> + <title>MIME, MIME, and more MIME</title> + + <!-- ----------------------------------------------------------------- --> + <sect1 id="sec-mime-part"> + <title>GMimePart</title> + + <para>Since most people seem to want to know how to "save an + attachment", let's start there.</para> + + <para>Given a GMimePart object, the first step to saving an + attachment is probably going to be figuring out what the + filename is. To do that, you'll likely want to do something + like:</para> + + <programlisting role="C"> +static void +save_attachment (GMimePart *part) +{ + GMimeDataWrapper *content; + const char *filename; + GMimeStream *stream; + int fd; + + filename = g_mime_part_get_filename (part); + ... + </programlisting> + + <para>The <literal>g_mime_part_get_filename()</literal> function + will first check for a <literal>filename</literal> parameter in + the Content-Disposition header. If that parameter exists, + it will return the value as the filename. However, if that does + not exist, it will fall back to checking for the + <literal>name</literal> parameter sometimes found in the + Content-Type header and return that value if it exists + (Microsoft Outlook, for example, will set the name parameter, + but will not set the filename parameter). If neither of these + param values are found, it will simply return + <literal>NULL</literal>.</para> + + <para>Now that you've got a filename for the MIME part (well, + assuming that it isn't NULL - in which case you'll have to + prompt the user or make up your own filename or something), the + next step is to open an output stream and write the MIME part's + content to disk:</para> + + <programlisting role="C"> + ... + if ((fd = open (filename, O_CREAT | O_WRONLY, 0666)) == -1) + return; + + stream = g_mime_stream_fs_new (fd); + + content = g_mime_part_get_content_object (part); + g_mime_data_wrapper_write_to_stream (content, stream); + g_mime_stream_flush (stream); + g_object_unref (stream); +} + </programlisting> + + <para>In order to get the content of a MIME part (eg. the body + of a part, not including the headers), you'll want to use + <literal>g_mime_part_get_content_object()</literal>. To write + the content object to a stream, you can use + <literal>g_mime_data_wrapper_write_to_stream()</literal>. On + fail, this function will return <literal>-1</literal>, otherwise + it will return some positive value which will usually equate to + the number of bytes written (but not always, due to filter + transformations); generally it's a good idea to not rely on the + returned value for anything other than error-checking.</para> + + </sect1> + + </chapter> + +</book> |