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<title>rfc822 - RFC 822 parsing library</title>
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<h1>rfc822 - RFC 822 parsing library</h1>
<h2>SYNOPSIS</h2>
<p><code>#include &lt;rfc822.h&gt;</code></p>
<p><code>#include &lt;rfc2047.h&gt;</code></p>
<p><code>cc ... -lrfc822</code></p>
<h2>DESCRIPTION</h2>
<p>The rfc822 library provides functions for parsing E-mail headers in the RFC
822 format. This library also includes some functions to help with encoding
and decoding 8-bit text, as defined by RFC 2047.</p>
<p>The format used by E-mail headers to encode sender and recipient
information is defined by RFC 822. The format allows the actual E-mail
address and the sender/recipient name to be expressed together, for example:
<code>John Smith &lt;jsmith@example.com&gt;</code></p>
<p>The main purposes of the rfc822 library is to:</p>
<p>1) Parse a text string containing a list of RFC 822-formatted address into
its logical components: names and E-mail addresses.</p>
<p>2) Access those individual components.</p>
<p>3) Allow some limited modifications of the parsed structure, and then
convert it back into a text string.</p>
<h3>Tokenizing an E-mail header</h3>
<pre>struct rfc822t *tokens=rfc822t_alloc(const char *header,
void (*err_func)(const char *, int));
void rfc822t_free(tokens);</pre>
<p>The rfc822t_alloc() function accepts an E-mail <i>header</i>, and parses it
into individual tokens. This function allocates and returns a pointer to a
<i>rfc822t</i> structure, which is later used by the <i>rfc822a_alloc</i>
function to extract individual addresses from these tokens.</p>
<p>If <i>err_func</i> argument, if not NULL, is a pointer to a callback
function. The function is called in the event that the E-mail header is
corrupted to the point that it cannot even be parsed. This is a rare
instances -- most forms of corruption are still valid at least on the lexical
level. The only time this error is reported is in the event of mismatched
parenthesis, angle brackets, or quotes. The callback function receives the
<i>header</i> pointer, and an index to the syntax error in the header
string.</p>
<p>The semantics of <i>err_func</i> are subject to change. It is recommended
to leave this argument as NULL in the current version of the library.</p>
<p>rfc822t_alloc() returns a pointer to a dynamically-allocated <i>rfc822t</i>
structure. A NULL pointer is returned if there's insufficient memory to
allocate this structure. The rfc822t_free() function is used to destroy the
<i>rfc822t</i> structure and to free all the dynamically allocated memory.</p>
<p>NOTE: Until rfc822t_free() is called, the contents of <i>header</i> MUST
NOT be destroyed or altered in any way. The contents of <i>header</i> are not
modified by rfc822t_alloc(), however the <i>rfc822t</i> structure contains
pointers to portions of the supplied <i>header</i>.</p>
<h3>Extracting E-mail addresses</h3>
<pre>struct rfc822a *addrs=rfc822a_alloc(struct rfc822t *tokens);
void rfc822a_free(addrs);</pre>
<p>The rfc822a_alloc() function returns a dynamically-allocated <i>rfc822a</i>
structure, that contains individual addresses that were logically extracted
from a <i>rfc822t</i> structure. The rfc822a_alloc() function returns NULL if
there was insufficient memory to allocate the <i>rfc822a</i> structure. The
rfc822a_free() function destroys the <i>rfc822a</i> function, and frees all
associated dynamically-allocated memory. The <i>rfc822t</i> structure passed
to rfc822a_alloc() must not be destroyed before rfc822a_free() destroys the
<i>rfc822a</i> structure.</p>
<p>The <i>rfc822a</i> structure has the following fields:</p>
<pre>struct rfc822a {
struct rfc822addr *addrs;
int naddrs;
} ;</pre>
<p>The <i>naddrs</i> field gives the number of <i>rfc822addr</i> structures
that are pointed to by <i>addrs</i>, which is an array. Each <i>rfc822addr</i>
structure represents either an address found in the original E-mail header,
<i>or the contents of some legacy "syntactical sugar"</i>. For example, the
following is a valid E-mail header:</p>
<pre>To: recipient-list: tom@example.com, john@example.com;</pre>
<p>Typically, all of this, sans the "To:" part, is tokenized by
rfc822t_alloc(), then parsed by rfc822a_alloc(). The "recipient-list:" and
the trailing semicolon is a legacy mailing list specification that is no
longer in widespread use, but still must be accounted for. The resulting
<i>rfc822a</i> structure will have four <i>rfc822addr</i> structures, one for
"recipient-list:", one for each address, and one for the trailing semicolon.
Each <i>rfc822a</i> structure has the following fields:</p>
<pre>struct rfc822addr {
struct rfc822token *tokens;
struct rfc822token *name;
} ;</pre>
<p>If <i>tokens</i> is a null pointer, this structure represents some
non-address portion of the original header, such as "recipient-list:" or a
semicolon. Otherwise it points to a structure that represents the E-mail
address in tokenized form.</p>
<p><i>name</i> either points to the tokenized form of a non-address portion of
the original header, or to a tokenized form of the recipient's name.
<i>name</i> will be NULL if the recipient name was not provided. For the
following address: <code>Tom Jones &lt;tjones@example.com&gt;</code> The
<i>tokens</i> field will point to the tokenized form of "tjones@example.com",
and <i>name</i> points to the tokenized form of "Tom Jones".</p>
<p>Each <i>rfc822token</i> structure contains the following fields:</p>
<pre>struct rfc822token {
struct rfc822token *next;
int token;
const char *ptr;
int len;
} ;</pre>
<p>The <i>next</i> pointer builds a linked list of all tokens in this name or
address. The possible values for the <i>token</i> field are:</p>
<ul>
<li>0x00 - this is a simple atom - a sequence of non-special characters that
is delimited by whitespace or special characters (see below).<br>
<br>
</li>
<li>0x22 - the value of the ascii quote - this is a quoted string.<br>
<br>
</li>
<li>'(' - this is an old style comment. A deprecated form of E-mail
addressing uses, as an example, "john@example.com (John Smith)" instead of
"John Smith &lt;john@example.com&gt;". This old-style notation defined
parenthesized content as arbitrary comments. The <i>rfc822token</i> with
<i>token</i> set to '(' is created for the contents of the entire
comment.<br>
<br>
</li>
<li>'&lt;', '&gt;', '@', and many others - the remaining possible values of
<i>token</i> include all the characters in RFC 822 headers that have
special significance.</li>
</ul>
<p>When a <i>rfc822token</i> structure does not represent a special character,
the <i>ptr</i> field points to a text string giving its contents. The contents
are NOT null-terminated, the <i>len</i> field contains the number of
characters included. The macro rfc822_is_atom(token) indicates whether
<i>ptr</i> and <i>len</i> are used for the given <i>token</i>. Currently
rfc822_is_atom() returns true if <i>token</i> is a zero byte, '"', or '('.</p>
<p>Note that it's possible that <i>len</i> might be zero. This will be the
case for null addresses used as return addresses for delivery status
notifications.</p>
<h3>Working with E-mail addresses</h3>
<pre>void rfc822_deladdr(struct rfc822a *addrs, int index);
void rfc822tok_print(const struct rfc822token *list,
void (*func)(char, void *), void *func_arg);
void rfc822_print(const struct rfc822a *addrs,
void (*print_func)(char, void *),
void (*print_separator)(const char *, void *), void *callback_arg);
void rfc822_addrlist(const struct rfc822a *addrs,
void (*print_func)(char, void *),
void *callback_arg);
void rfc822_namelist(const struct rfc822a *addrs,
void (*print_func)(char, void *),
void *callback_arg);
void rfc822_praddr(const struct rfc822a *addrs,
int index,
void (*print_func)(char, void *),
void *callback_arg);
void rfc822_prname(const struct rfc822a *addrs,
int index,
void (*print_func)(char, void *),
void *callback_arg);
void rfc822_prname_orlist(const struct rfc822a *addrs,
int index,
void (*print_func)(char, void *),
void *callback_arg);
char *rfc822_gettok(const struct rfc822token *list);
char *rfc822_getaddrs(const struct rfc822a *addrs);
char *rfc822_getaddr(const struct rfc822a *addrs, int index);
char *rfc822_getname(const struct rfc822a *addrs, int index);
char *rfc822_getname_orlist(const struct rfc822a *addrs, int index);
char *rfc822_getaddrs_wrap(const struct rfc822a *, int);</pre>
<p>These functions are used to work with individual addresses that are parsed
by rfc822a_alloc().</p>
<p>rfc822_deladdr() removes a single <i>rfc822addr</i> structure, whose
<i>index</i> is given, from the address array in <i>rfc822addr</i>.
<i>naddrs</i> is decremented by one.</p>
<p>rfc822tok_print() converts a tokenized <i>list</i> of <i>rfc822token</i>
objects into a text string. The callback function, <i>func</i>, is called one
character at a time, for every character in the tokenized objects. An
arbitrary pointer, <i>func_arg</i>, is passed unchanged as the additional
argument to the callback function. rfc822tok_print() is not usually the most
convenient and efficient function, but it has its uses.</p>
<p>rfc822_print() takes an entire <i>rfc822a</i> structure, and uses the
callback functions to print the contained addresses, in their original form,
separated by commas. The function pointed to by <i>print_func</i> is used to
print each individual address, one character at a time. Between the
addresses, the <i>print_separator</i> function is called to print the address
separator, usually the string ", ". The <i>callback_arg</i> argument is passed
along unchanged, as an additional argument to these functions.</p>
<p>The functions rfc822_addrlist() and rfc822_namelist() also print the
contents of the entire <i>rfc822a</i> structure, but in a different way.
rfc822_addrlist() prints just the actual E-mail addresses, not the recipient
names or comments. Each E-mail address is followed by a newline character.
rfc822_namelist() prints just the names or comments, followed by newlines.</p>
<p>The functions rfc822_praddr() and rfc822_prname() are just like
rfc822_addrlist() and rfc822_namelist(), except that they print a single name
or address in the <i>rfc822a</i> structure, given its <i>index</i>. The
functions rfc822_gettok(), rfc822_getaddrs(), rfc822_getaddr(), and
rfc822_getname() are equivalent to rfc822tok_print(), rfc822_print(),
rfc822_praddr() and rfc822_prname(), but, instead of using a callback function
pointer, these functions write the output into a dynamically allocated buffer.
That buffer must be destroyed by free(3) after use. These functions will
return a null pointer in the event of a failure to allocate memory for the
buffer.</p>
<p>rfc822_prname_orlist() is similar to rfc822_prname(), except that it will
also print the legacy RFC822 group list syntax (which are also parsed by
rfc822a_alloc()). rfc822_praddr() will print an empty string for an index
that corresponds to a group list name (or terminated semicolon).
rfc822_prname() will also print an empty string. rfc822_prname_orlist() will
instead print either the name of the group list, or a single string ";".
rfc822_getname_orlist() will instead save it into a dynamically allocated
buffer.</p>
<p>The function rfc822_getaddrs_wrap() is similar to rfc822_getaddrs(), except
that the generated text is wrapped on or about the 73rd column, using newline
characters.</p>
<h3>Working with dates</h3>
<pre>time_t timestamp=rfc822_parsedt(const char *datestr)
const char *datestr=rfc822_mkdate(time_t timestamp);
void rfc822_mkdate_buf(time_t timestamp, char *buffer);</pre>
<p>These functions convert between timestamps and dates expressed in the Date:
E-mail header format.</p>
<p>rfc822_parsedt() returns the timestamp corresponding to the given date
string (0 if there was a syntax error).</p>
<p>rfc822_mkdate() returns a date string corresponding to the given timestamp.
rfc822_mkdate_buf() writes the date string into the given buffer instead,
which must be of sufficient size to accommodate it.</p>
<h3>Working with 8-bit MIME-encoded headers</h3>
<pre>int error=rfc2047_decode(const char *text,
int (*callback_func)(const char *, int, const char *, void *),
void *callback_arg);
extern char *str=rfc2047_decode_simple(const char *text);
extern char *str=rfc2047_decode_enhanced(const char *text,
const char *charset);
void rfc2047_print(const struct rfc822a *a,
const char *charset,
void (*print_func)(char, void *),
void (*print_separator)(const char *, void *), void *);
char *buffer=rfc2047_encode_str(const char *string,
const char *charset);
int error=rfc2047_encode_callback(const char *string,
const char *charset,
int (*func)(const char *, size_t, void *),
void *callback_arg);
char *buffer=rfc2047_encode_header(const struct rfc822a *a,
const char *charset);</pre>
<p>These functions provide additional logic to encode or decode 8-bit content
in 7-bit RFC 822 headers, as specified in RFC 2047.</p>
<p>rfc2047_decode() is a basic RFC 2047 decoding function. It receives a
pointer to some 7bit RFC 2047-encoded text, and a callback function. The
callback function is repeatedly called. Each time it's called it receives a
piece of decoded text. The arguments are: a pointer to a text fragment, number
of bytes in the text fragment, followed by a pointer to the character set of
the text fragment. The character set pointer is NULL for portions of the
original text that are not RFC 2047-encoded.</p>
<p>The callback function also receives <i>callback_arg</i>, as its last
argument. If the callback function returns a non-zero value, rfc2047_decode()
terminates, returning that value. Otherwise, rfc2047_decode() returns 0 after
a successful decoding. rfc2047_decode() returns -1 if it was unable to
allocate sufficient memory.</p>
<p>rfc2047_decode_simple() and rfc2047_decode_enhanced() are alternatives to
rfc2047_decode() which forego a callback function, and return the decoded text
in a dynamically-allocated memory buffer. The buffer must be free(3)-ed after
use. rfc2047_decode_simple() discards all character set specifications, and
merely decodes any 8-bit text. rfc2047_decode_enhanced() is a compromise to
discarding all character set information. The local character set being used
is specified as the second argument to rfc2047_decode_enhanced(). Any RFC
2047-encoded text in a different character set will be prefixed by the name of
the character set, in brackets, in the resulting output.</p>
<p>rfc2047_decode_simple() and rfc2047_decode_enhanced() return a null pointer
if they are unable to allocate sufficient memory.</p>
<p>The rfc2047_print() function is equivalent to rfc822_print(), followed by
rfc2047_decode_enhanced() on the result. The callback functions are used in
an identical fashion, except that they receive text that's already
decoded.</p>
<p>The function rfc2047_encode_str() takes a <i>string</i> and <i>charset</i>
being the name of the local character set, then encodes any 8-bit portions of
<i>string</i> using RFC 2047 encoding. rfc2047_encode_str() returns a
dynamically-allocated buffer with the result, which must be free(3)-ed after
use, or NULL if there was insufficient memory to allocate the buffer.</p>
<p>The function rfc2047_encode_callback() is similar to rfc2047_encode_str()
except that the callback function is repeatedly called to received the
encoding string. Each invocation of the callback function receives a pointer
to a portion of the encoded text, the number of characters in this portion,
and <i>callback_arg</i>.</p>
<p>The function rfc2047_encode_header() is basically equivalent to
rfc822_getaddrs(), followed by rfc2047_encode_str();</p>
<h3>Working with subjects</h3>
<pre>char *basesubj=rfc822_coresubj(const char *subj)
char *basesubj=rfc822_coresubj_nouc(const char *subj)</pre>
<p>This function takes the contents of the subject header, and returns the
"core" subject header that's used in the specification of the IMAP THREAD
function. This function is designed to strip all subject line artifacts that
might've been added in the process of forwarding or replying to a message.
Currently, rfc822_coresubj() performs the following transformations:</p>
<ul>
<li>Whitespace - leading and trailing whitespace is removed. Consecutive
whitespace characters are collapsed into a single whitespace character.
All whitespace characters are replaced by a space.<br>
<br>
</li>
<li>Re:, (fwd) [foo] - these artifacts (and several others) are removed from
the subject line.</li>
</ul>
<p>Note that this function does NOT do MIME decoding. In order to implement
IMAP THREAD, it is necessary to call something like rfc2047_decode() before
calling rfc822_coresubj().</p>
<p>This function returns a pointer to a dynamically-allocated buffer, which
must be free(3)-ed after use.</p>
<p>rfc822_coresubj_nouc() is like rfc822_coresubj(), except that the subject
is not converted to uppercase.</p>
<h2>SEE ALSO</h2>
<a href="rfc2045.html">rfc2045(3)</a>, <a
href="reformime.html">reformime(1)</a>, <a
href="reformail.html">reformail(1)</a>.</body>
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