324 lines
15 KiB
HTML
324 lines
15 KiB
HTML
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
|
||
|
|
"http://www.w3.org/TR/REC-html40/loose.dtd">
|
||
|
|
<html>
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html">
|
||
|
|
<title>rfc2045 - RFC 2045 (MIME) parsing library</title>
|
||
|
|
<!-- $Id$ -->
|
||
|
|
<!-- Copyright 2000 Double Precision, Inc. See COPYING for -->
|
||
|
|
<!-- distribution information. -->
|
||
|
|
<!-- SECTION 3X -->
|
||
|
|
</head>
|
||
|
|
|
||
|
|
<body text="#000000" bgcolor="#FFFFFF" link="#0000EE" vlink="#551A8B"
|
||
|
|
alink="#FF0000">
|
||
|
|
<h1>rfc2045 - RFC 2045 (MIME) parsing library</h1>
|
||
|
|
|
||
|
|
<h2>SYNOPSIS</h2>
|
||
|
|
|
||
|
|
<p><code>#include <rfc2045.h></code></p>
|
||
|
|
|
||
|
|
<p><code>cc ... -lrfc2045 -lrfc822</code></p>
|
||
|
|
|
||
|
|
<h2>DESCRIPTION</h2>
|
||
|
|
|
||
|
|
<p>The rfc2045 library is used to parse and work with MIME-formatted messages.
|
||
|
|
The rfc2045 library is used to:</p>
|
||
|
|
|
||
|
|
<p>1) Parse the structure of a MIME formatted message</p>
|
||
|
|
|
||
|
|
<p>2) Examine the contents of each MIME section</p>
|
||
|
|
|
||
|
|
<p>3) Optionally rewrite and reformat the message.</p>
|
||
|
|
|
||
|
|
<h2>Creating an rfc2045 structure</h2>
|
||
|
|
<pre>#include <rfc2045.h>
|
||
|
|
|
||
|
|
struct rfc2045 *ptr=rfc2045_alloc();
|
||
|
|
void rfc2045_parse(struct rfc2045 *ptr, const char *txt, size_t cnt);
|
||
|
|
|
||
|
|
struct rfc2045 *ptr=rfc2045_fromfd(int fd);
|
||
|
|
struct rfc2045 *ptr=rfc2045_fromfp(FILE *fp);
|
||
|
|
|
||
|
|
void rfc2045_free(struct rfc2045 *ptr);
|
||
|
|
|
||
|
|
void rfc2045_error(const char *errmsg)
|
||
|
|
{
|
||
|
|
perror(errmsg);
|
||
|
|
exit(0);
|
||
|
|
}</pre>
|
||
|
|
|
||
|
|
<p>The <i>rfc2045</i> structure is created from an existing message. The
|
||
|
|
function rfc2045_alloc() allocates the structure, then rfc2045_parse() is
|
||
|
|
called to initialize the structure based on the contents of the message.
|
||
|
|
<i>txt</i> points to the contents of the message, and <i>cnt</i> contains the
|
||
|
|
number of bytes in the message.</p>
|
||
|
|
|
||
|
|
<p>Large messages can be parsed by calling rfc2045_parse() multiple number of
|
||
|
|
times, each time passing a portion of the overall message. There is no need to
|
||
|
|
call a separate function after the entire message has been parsed -- the
|
||
|
|
<i>rfc2045</i> structure is created dynamically, on the fly.</p>
|
||
|
|
|
||
|
|
<p>rfc2045_alloc() returns NULL if there was insufficient memory to allocate
|
||
|
|
the structure. The rfc2045_parse() also allocates memory, internally, however
|
||
|
|
no error indication is return in the event of a memory allocation failure.
|
||
|
|
Instead, the function rfc2045_error() is called, with <i>errmsg</i> set to
|
||
|
|
"Out of memory". rfc2045_error() is also called by <i>rfc2045_alloc()</i> also
|
||
|
|
calls rfc2045_error(), prior to returning a NULL pointer.</p>
|
||
|
|
|
||
|
|
<p>The rfc2045_error() function is not included in the rfc2045 library, it
|
||
|
|
must be defined by the application to report the error in some appropriate
|
||
|
|
way. All functions below will use rfc2045_error() to report an error condition
|
||
|
|
(currently only insufficient memory is reported), in addition to returning any
|
||
|
|
kind of an error indicator. Some functions do not return an error indicator,
|
||
|
|
so rfc2045_error() is the only reliable way to detect a failure.</p>
|
||
|
|
|
||
|
|
<p>The rfc2045_fromfd() function initializes an <i>rfc2045</i> structure from
|
||
|
|
a file descriptor. It is equivalent to calling rfc2045_alloc(), then reading
|
||
|
|
the contents of the given file descriptor, and calling rfc2045_parse(). The
|
||
|
|
rfc2045_fromfp() function initializes an <i>rfc2045</i> structure from a
|
||
|
|
FILE.</p>
|
||
|
|
|
||
|
|
<p>After the <i>rfc2045</i> structure is initialized, the functions described
|
||
|
|
below may be used to access and work with the contents of the structure. When
|
||
|
|
the <i>rfc2045</i> structure is no longer needed, the function rfc2045_free()
|
||
|
|
deallocates and destroys the structure.</p>
|
||
|
|
|
||
|
|
<h2>Structure of a MIME message</h2>
|
||
|
|
<pre>struct rfc2045 {
|
||
|
|
|
||
|
|
struct rfc2045 *parent;
|
||
|
|
|
||
|
|
struct rfc2045 *firstpart;
|
||
|
|
struct rfc2045 *next;
|
||
|
|
int isdummy;
|
||
|
|
int rfcviolation;
|
||
|
|
} ;</pre>
|
||
|
|
|
||
|
|
<p>The <i>rfc2045</i> has many fields, only some are publicly documented. A
|
||
|
|
MIME message is represented by a recursive tree of linked <i>rfc2045</i>
|
||
|
|
structures. Each instance of the <i>rfc2045</i> structure represents a single
|
||
|
|
MIME section of a MIME message.</p>
|
||
|
|
|
||
|
|
<p>The top-level structure representing the entire message is created by the
|
||
|
|
rfc2045_alloc() function. The remaining structures are created dynamically by
|
||
|
|
rfc2045_parse(). Any <i>rfc2045</i> structure, except ones whose
|
||
|
|
<i>isdummy</i> flag is set, may be used as an argument to any function
|
||
|
|
described in the following chapters.</p>
|
||
|
|
|
||
|
|
<p>The <i>rfcviolation</i> field in the top-level <i>rfc2045</i> is set to
|
||
|
|
indicate any errors encountered while parsing the MIME message.
|
||
|
|
<i>rfcviolation</i> is a bitmask of the following flags:</p>
|
||
|
|
<ul>
|
||
|
|
<li><code>RFC2045_ERR8BITHEADER</code> - illegal 8-bit characters in MIME
|
||
|
|
headers.<br>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
<li><code>RFC2045_ERR8BITCONTENT</code> - illegal 8-bit contents of a MIME
|
||
|
|
section that has a 7bit transfer encoding.<br>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
<li><code>RFC2045_ERR2COMPLEX</code> - the message has too many MIME
|
||
|
|
sections, this is a potential denial-of-service attack.</li>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<p>In each <i>rfc2045</i> structure representing a multipart MIME section (or
|
||
|
|
one containing message/rfc822 content), the <i>firstpart</i> pointer points to
|
||
|
|
the first MIME section in the multipart MIME section (or the included
|
||
|
|
"message/rfc822" MIME section). If there are more than one MIME sections in a
|
||
|
|
multipart MIME section <i>firstpart->next</i> gets you the second MIME
|
||
|
|
section, <i>firstpart->next->next</i> gets you the third MIME section, and so
|
||
|
|
on. <i>parent</i> points to the parent MIME section, which is NULL for the
|
||
|
|
top-level MIME section.</p>
|
||
|
|
|
||
|
|
<p>Not all MIME sections are created equal. In a multipart MIME section,
|
||
|
|
there is an initial, unused, "filler" section before the first MIME delimiter
|
||
|
|
(see RFC 2045 for more information). This filler section typically contains a
|
||
|
|
terse message saying that this is a MIME-formatted message, or something
|
||
|
|
similar of that kind. This is not considered to be a "real" MIME section, and
|
||
|
|
all MIME-aware software must ignore those. These filler sections are
|
||
|
|
designated by setting the "isdummy" flag to non-zero. All <i>rfc2045</i>
|
||
|
|
structures that have "isdummy" set must be completely ignored, and skipped
|
||
|
|
over, when traversing the <i>rfc2045</i> tree.</p>
|
||
|
|
|
||
|
|
<h2>Basic MIME information</h2>
|
||
|
|
<pre>const char *content_type, *content_transfer_encoding,
|
||
|
|
*content_character_set;
|
||
|
|
|
||
|
|
void rfc2045_mimeinfo(const struct rfc2045 *ptr,
|
||
|
|
&content_type, &content_transfer_encoding,
|
||
|
|
&content_character_set);
|
||
|
|
|
||
|
|
off_t start_pos, end_pos, start_body, nlines, nbodylines;
|
||
|
|
|
||
|
|
void rfc2045_mimepos(const struct rfc2045 *ptr,
|
||
|
|
&start_pos, &end_pos, &start_body, &nlines,
|
||
|
|
&nbodylines);</pre>
|
||
|
|
|
||
|
|
<p>The rfc2045_mimeinfo() function returns the content type, encoding method,
|
||
|
|
and the character set of a given MIME section. Where a MIME section does not
|
||
|
|
specify any property, rfc2045_mimeinfo() automatically supplies a default
|
||
|
|
value. The character set is only meaningful for MIME sections containing a
|
||
|
|
text content type, however it is still defaulted for other sections. It is
|
||
|
|
not permissible to supply a NULL pointer for any argument to
|
||
|
|
rfc2045_mimeinfo().</p>
|
||
|
|
|
||
|
|
<p>The rfc2045_mimepos() function is used to locate the position of the given
|
||
|
|
MIME section in the original message. It is not permissible to supply a NULL
|
||
|
|
pointer for any argument to rfc2045_mimepos(). All arguments must be
|
||
|
|
used.</p>
|
||
|
|
|
||
|
|
<p><i>start_pos</i> and <i>end_pos</i> point to the starting and the ending
|
||
|
|
offset, from the beginning of the message, of this MIME section. <i>nlines</i>
|
||
|
|
is initialized to the number of lines of text in this MIME section. The
|
||
|
|
starting offset points to the start of MIME headers in this section.
|
||
|
|
<i>start_body</i> is initialized to point to the starting offset of the actual
|
||
|
|
contents of this MIME section, and <i>nbodylines</i> is set to the number of
|
||
|
|
lines of actual content in this MIME section.</p>
|
||
|
|
<pre>const char *id=rfc2045_content_id(
|
||
|
|
const struct rfc2045 *ptr);
|
||
|
|
|
||
|
|
const char *desc=rfc2045_content_description(
|
||
|
|
const struct rfc2045 *ptr);
|
||
|
|
|
||
|
|
const char *lang=rfc2045_content_language(
|
||
|
|
const struct rfc2045 *ptr);
|
||
|
|
|
||
|
|
const char *md5=rfc2045_content_md5(
|
||
|
|
const struct rfc2045 *ptr);</pre>
|
||
|
|
|
||
|
|
<p>These functions return the contents of the corresponding MIME headers. If
|
||
|
|
these headers do not exist, these functions return an empty string, "", NOT a
|
||
|
|
null pointer.</p>
|
||
|
|
<pre>char *id=rfc2045_related_start(const struct rfc2045 *ptr);</pre>
|
||
|
|
|
||
|
|
<p>This function returns the <i>start</i> parameter of the Content-Type:
|
||
|
|
header, which is used by multipart/related content. This function returns a
|
||
|
|
dynamically-allocated buffer, which must be free(3)-ed after use (a null
|
||
|
|
pointer is returned if there was insufficient memory for the buffer, and
|
||
|
|
rfc2045_error() is called).</p>
|
||
|
|
<pre>const char *disposition, *name, *filename;
|
||
|
|
|
||
|
|
void rfc2045_dispositioninfo(const struct rfc2045 *ptr,
|
||
|
|
&disposition, &name, &filename);</pre>
|
||
|
|
|
||
|
|
<p>rfc2045_dispositioninfo() returns the disposition specifications of a MIME
|
||
|
|
section. For MIME sections that do not specify the type of disposition
|
||
|
|
(inline or attachment), the name or the filename of the attachment, the
|
||
|
|
corresponding pointer is initialized to NULL.</p>
|
||
|
|
<pre>char *url=rfc2045_content_base(struct rfc2045 *ptr);
|
||
|
|
|
||
|
|
char *url=rfc2045_append_url(const char *base, const char *url);</pre>
|
||
|
|
|
||
|
|
<p>These functions are used to work with multipart/related MIME messages. The
|
||
|
|
rfc2045_content_base() returns the contents of either the Content-Base: or the
|
||
|
|
Content-Location: header. If both are present, they are logically combined.
|
||
|
|
The rfc2045_append_url() function combines two URLs, <i>base</i> and
|
||
|
|
<i>url</i>, and returns the absolute URL that results from the
|
||
|
|
combination.</p>
|
||
|
|
|
||
|
|
<p>Both functions return a pointer to a dynamically-allocated buffer that must
|
||
|
|
be free(3)-ed after it is no longer needed. Both functions return NULL if
|
||
|
|
there was no sufficient memory to allocate the buffer. rfc2045_content_base()
|
||
|
|
returns an empty string in the event that there are no Content-Base: or
|
||
|
|
Content-Location: headers. Either argument to rfc2045_append_url() may be a
|
||
|
|
NULL, or an empty string.</p>
|
||
|
|
|
||
|
|
<h2>Decoding a MIME section</h2>
|
||
|
|
<pre>void rfc2045_cdecode_start(struct rfc2045 *ptr,
|
||
|
|
int (*callback_func)(const char *, size_t, void *),
|
||
|
|
void *callback_arg);
|
||
|
|
|
||
|
|
int rfc2045_cdecode(struct rfc2045 *ptr, const char *stuff,
|
||
|
|
size_t nstuff);
|
||
|
|
|
||
|
|
int rfc2045_cdecode_end(struct rfc2045 *ptr);</pre>
|
||
|
|
|
||
|
|
<p>These functions are used to return the raw contents of the given MIME
|
||
|
|
section, transparently decoding quoted-printable or base64-encoded content.
|
||
|
|
Because the rfc2045 library does not require the message to be read from a
|
||
|
|
file (it can be stored in a memory buffer), the application is responsible for
|
||
|
|
reading the contents of the message and calling rfc2045_cdecode().</p>
|
||
|
|
|
||
|
|
<p>The rfc2045_cdecode_start() function is used to begin the process of
|
||
|
|
decoding the given MIME section. After calling rfc2045_cdecode_start(), the
|
||
|
|
application must the repeatedly call rfc2045_cdecode() with the contents of
|
||
|
|
the MIME message between the offsets given by the <i>start_body</i> and
|
||
|
|
<i>end_pos</i> return values from rfc2045_mimepos() function. The
|
||
|
|
rfc2045_cdecode() function can be called repeatedly, if necessary, for
|
||
|
|
successive portions of the MIME section. After the last MIME section, the
|
||
|
|
rfc2045_cdecode_end() function is called to finish decoding the MIME
|
||
|
|
section.</p>
|
||
|
|
|
||
|
|
<p>rfc2045_cdecode() and rfc2045_cdecode_end() repeatedly call the
|
||
|
|
callback_func() function, with the decoded contents of the MIME section. The
|
||
|
|
first argument to callback_func() is a pointer to a portion of the decoded
|
||
|
|
content, the second argument is the number of bytes in this portion. The
|
||
|
|
third argument is <i>callback_arg</i>.</p>
|
||
|
|
|
||
|
|
<p>callback_func() is required to return zero, to continue decoding. If
|
||
|
|
callback_func() returns non-zero, the decoding immediately stops and
|
||
|
|
rfc2045_cdecode() or rfc2045_cdecode_end() will terminate with callback_func's
|
||
|
|
return code.</p>
|
||
|
|
|
||
|
|
<h2>Rewriting MIME messages</h2>
|
||
|
|
|
||
|
|
<p>The rfc2045 library contains functions that can be used to rewrite a MIME
|
||
|
|
message in order to convert 8-bit data to 7-bit encoding method, or to convert
|
||
|
|
7-bit encoded data to full 8-bit data, if possible.</p>
|
||
|
|
<pre>struct rfc2045 *ptr=rfc2045_alloc_ac();
|
||
|
|
int necessary=rfc2045_ac_check(struct rfc2045 *ptr, int mode);
|
||
|
|
|
||
|
|
int error=rfc2045_rewrite(struct rfc2045 *ptr,
|
||
|
|
int fdin,
|
||
|
|
int fdout,
|
||
|
|
const char *appname);
|
||
|
|
|
||
|
|
int rfc2045_rewrite_func(struct rfc2045 *p, int fdin,
|
||
|
|
int (*funcout)(const char *, int, void *), void *funcout_arg,
|
||
|
|
const char *appname);</pre>
|
||
|
|
|
||
|
|
<p>When rewriting will be used, the rfc2045_alloc_ac() function must be used
|
||
|
|
to create the initial <i>rfc2045</i> structure. This function allocates some
|
||
|
|
additional structures that are used in rewriting. The rfc2045_parse() function
|
||
|
|
is used to parse the message, as usual. The rfc2045_free() function will also
|
||
|
|
be used normally to destroy the <i>rfc2045</i> structure, when all is said and
|
||
|
|
done.</p>
|
||
|
|
|
||
|
|
<p>The rfc2045_ac_check() function must be called to determine whether
|
||
|
|
rewriting is necessary. <i>mode</i> must be set to one of the following
|
||
|
|
values:</p>
|
||
|
|
<ul>
|
||
|
|
<li><code>RFC2045_RW_7BIT</code> - we want to generate 7-bit content. If the
|
||
|
|
original message contains any 8-bit content it will be converted to 7-bit
|
||
|
|
content using quoted-printable encoding.</li>
|
||
|
|
<li><code>RFC2045_RW_8BIT</code> - we want to generate 8-bit content. If the
|
||
|
|
original message contains any 7-bit quoted-printable content it should be
|
||
|
|
rewritten as 8-bit content.</li>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<p>The rfc2045_ac_check() function returns non-zero if there's any content in
|
||
|
|
the MIME message that should be converted, OR if there are any missing MIME
|
||
|
|
headers. rfc2045_ac_check() returns zero if there's no need to rewrite the
|
||
|
|
message. However it might still be worthwhile to rewrite the message anyway.
|
||
|
|
There are some instances where it is desirable to provide defaults for some
|
||
|
|
missing MIME headers, but they are too trivial to require the message to be
|
||
|
|
rewritten. One such case would be a missing Content-Transfer-Encoding: header
|
||
|
|
for a multipart section.</p>
|
||
|
|
|
||
|
|
<p>Either the rfc2045_rewrite() or the rfc2045_rewrite_func() function is used
|
||
|
|
to rewrite the message. The only difference is that rfc2045_rewrite() writes
|
||
|
|
the new message to a given file descriptor, <i>fdout</i>, while
|
||
|
|
rfc2045_rewrite_func() repeatedly calls the <i>funcout</i> function. Both
|
||
|
|
function read the original message from <i>fdin</i>. <i>funcout</i> receives
|
||
|
|
to a portion of the MIME message, the number of bytes in the specified
|
||
|
|
portion, and <i>funcout_arg</i>. When either function rewrites a MIME section,
|
||
|
|
an informational header gets appended, noting that the message was converted
|
||
|
|
by <i>appname</i>.</p>
|
||
|
|
|
||
|
|
<h2>SEE ALSO</h2>
|
||
|
|
<a href="rfc822.html">rfc822(3)</a>, <a
|
||
|
|
href="reformime.html">reformime(1)</a>, <a
|
||
|
|
href="reformail.html">reformail(1)</a>.</body>
|
||
|
|
</html>
|