'\" t
.\"<!-- Copyright 2001-2007 Double Precision, Inc.  See COPYING for -->
.\"<!-- distribution information. -->
.\"     Title: rfc822
.\"    Author: Sam Varshavchik
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 05/21/2021
.\"    Manual: Double Precision, Inc.
.\"    Source: Courier Mail Server
.\"  Language: English
.\"
.TH "RFC822" "3" "05/21/2021" "Courier Mail Server" "Double Precision, Inc\&."
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.nh
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.\" * MAIN CONTENT STARTS HERE *
.\" -----------------------------------------------------------------
.SH "NAME"
rfc822 \- RFC 822 parsing library
.SH "SYNOPSIS"
.sp
.nf
#include <rfc822\&.h>

#include <rfc2047\&.h>

cc \&.\&.\&. \-lrfc822
.fi
.SH "DESCRIPTION"
.PP
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\&.
.PP
The format used by E\-mail headers to encode sender and recipient information is defined by
\m[blue]\fBRFC 822\fR\m[]\&\s-2\u[1]\d\s+2
(and its successor,
\m[blue]\fBRFC 2822\fR\m[]\&\s-2\u[2]\d\s+2)\&. The format allows the actual E\-mail address and the sender/recipient name to be expressed together, for example:
John Smith <jsmith@example\&.com>
.PP
The main purposes of the rfc822 library is to:
.PP
1) Parse a text string containing a list of RFC 822\-formatted address into its logical components: names and E\-mail addresses\&.
.PP
2) Access those individual components\&.
.PP
3) Allow some limited modifications of the parsed structure, and then convert it back into a text string\&.
.SS "Tokenizing an E\-mail header"
.sp
.if n \{\
.RS 4
.\}
.nf
struct rfc822t *tokens=rfc822t_alloc_new(const char *header,
                void (*err_func)(const char *, int, void *),
                void *func_arg);

void rfc822t_free(tokens);
.fi
.if n \{\
.RE
.\}
.PP
The
\fBrfc822t_alloc_new\fR() function (superceeds
\fBrfc822t_alloc\fR(), which is now obsolete) accepts an E\-mail
\fIheader\fR, and parses it into individual tokens\&. This function allocates and returns a pointer to an
rfc822t
structure, which is later used by
\fBrfc822a_alloc\fR() to extract individual addresses from these tokens\&.
.PP
If
\fIerr_func\fR
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 instance \-\- 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
\fIheader\fR
pointer, an index to the syntax error in the header string, and the
\fIfunc_arg\fR
argument\&.
.PP
The semantics of
\fIerr_func\fR
are subject to change\&. It is recommended to leave this argument as NULL in the current version of the library\&.
.PP
\fBrfc822t_alloc\fR() returns a pointer to a dynamically\-allocated
rfc822t
structure\&. A NULL pointer is returned if there\*(Aqs insufficient memory to allocate this structure\&. The
\fBrfc822t_free\fR() function destroys
rfc822t
structure and frees all dynamically allocated memory\&.
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBNote\fR
.ps -1
.br
.PP
Until
\fBrfc822t_free\fR() is called, the contents of
\fIheader\fR
MUST NOT be destroyed or altered in any way\&. The contents of
\fIheader\fR
are not modified by
\fBrfc822t_alloc\fR(), however the
rfc822t
structure contains pointers to portions of the supplied
\fIheader\fR, and they must remain valid\&.
.sp .5v
.RE
.SS "Extracting E\-mail addresses"
.sp
.if n \{\
.RS 4
.\}
.nf
struct rfc822a *addrs=rfc822a_alloc(struct rfc822t *tokens);

void rfc822a_free(addrs);
.fi
.if n \{\
.RE
.\}
.PP
The
\fBrfc822a_alloc\fR() function returns a dynamically\-allocated
rfc822a
structure, that contains individual addresses that were logically parsed from a
rfc822t
structure\&. The
\fBrfc822a_alloc\fR() function returns NULL if there was insufficient memory to allocate the
rfc822a
structure\&. The
\fBrfc822a_free\fR() function destroys the
rfc822a
function, and frees all associated dynamically\-allocated memory\&. The
rfc822t
structure passed to
\fBrfc822a_alloc\fR() must not be destroyed before
\fBrfc822a_free\fR() destroys the
rfc822a
structure\&.
.PP
The
rfc822a
structure has the following fields:
.sp
.if n \{\
.RS 4
.\}
.nf
struct rfc822a {
        struct rfc822addr *addrs;
        int     naddrs;
} ;
.fi
.if n \{\
.RE
.\}
.PP
The
\fInaddrs\fR
field gives the number of
rfc822addr
structures that are pointed to by
\fIaddrs\fR, which is an array\&. Each
rfc822addr
structure represents either an address found in the original E\-mail header,
\fIor the contents of some legacy "syntactical sugar"\fR\&. For example, the following is a valid E\-mail header:
.sp
.if n \{\
.RS 4
.\}
.nf
To: recipient\-list: tom@example\&.com, john@example\&.com;
.fi
.if n \{\
.RE
.\}
.PP
Typically, all of this, except for "To:", is tokenized by
\fBrfc822t_alloc\fR(), then parsed by
\fBrfc822a_alloc\fR()\&. "recipient\-list:" and the trailing semicolon is a legacy mailing list specification that is no longer in widespread use, but must still must be accounted for\&. The resulting
rfc822a
structure will have four
rfc822addr
structures: one for "recipient\-list:"; one for each address; and one for the trailing semicolon\&. Each
rfc822a
structure has the following fields:
.sp
.if n \{\
.RS 4
.\}
.nf
struct rfc822addr {
        struct rfc822token *tokens;
        struct rfc822token *name;
} ;
.fi
.if n \{\
.RE
.\}
.PP
If
\fItokens\fR
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\&.
.PP
\fIname\fR
either points to the tokenized form of a non\-address portion of the original header, or to a tokenized form of the recipient\*(Aqs name\&.
\fIname\fR
will be NULL if the recipient name was not provided\&. For the following address:
Tom Jones <tjones@example\&.com>
\- the
\fItokens\fR
field points to the tokenized form of "tjones@example\&.com", and
\fIname\fR
points to the tokenized form of "Tom Jones"\&.
.PP
Each
rfc822token
structure contains the following fields:
.sp
.if n \{\
.RS 4
.\}
.nf
struct rfc822token {
        struct rfc822token *next;
        int token;
        const char *ptr;
        int len;
} ;
.fi
.if n \{\
.RE
.\}
.PP
The
\fInext\fR
pointer builds a linked list of all tokens in this name or address\&. The possible values for the
\fItoken\fR
field are:
.PP
0x00
.RS 4
This is a simple atom \- a sequence of non\-special characters that is delimited by whitespace or special characters (see below)\&.
.RE
.PP
0x22
.RS 4
The value of the ascii quote \- this is a quoted string\&.
.RE
.PP
Open parenthesis: \*(Aq(\*(Aq
.RS 4
This is an old style comment\&. A deprecated form of E\-mail addressing uses \- for example \- "john@example\&.com (John Smith)" instead of "John Smith <john@example\&.com>"\&. This old\-style notation defined parenthesized content as arbitrary comments\&. The
rfc822token
with
\fItoken\fR
set to \*(Aq(\*(Aq is created for the contents of the entire comment\&.
.RE
.PP
Symbols: \*(Aq<\*(Aq, \*(Aq>\*(Aq, \*(Aq@\*(Aq, and many others
.RS 4
The remaining possible values of
\fItoken\fR
include all the characters in RFC 822 headers that have special significance\&.
.RE
.PP
When a
rfc822token
structure does not represent a special character, the
\fIptr\fR
field points to a text string giving its contents\&. The contents are NOT null\-terminated, the
\fIlen\fR
field contains the number of characters included\&. The macro rfc822_is_atom(token) indicates whether
\fIptr\fR
and
\fIlen\fR
are used for the given
\fItoken\fR\&. Currently
\fBrfc822_is_atom\fR() returns true if
\fItoken\fR
is a zero byte, \*(Aq"\*(Aq, or \*(Aq(\*(Aq\&.
.PP
Note that it\*(Aqs possible that
\fIlen\fR
might be zero\&. This happens with null addresses used as return addresses for delivery status notifications\&.
.SS "Working with E\-mail addresses"
.sp
.if n \{\
.RS 4
.\}
.nf
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);
.fi
.if n \{\
.RE
.\}
.PP
These functions are used to work with individual addresses that are parsed by
\fBrfc822a_alloc\fR()\&.
.PP
\fBrfc822_deladdr\fR() removes a single
rfc822addr
structure, whose
\fIindex\fR
is given, from the address array in
rfc822addr\&.
\fInaddrs\fR
is decremented by one\&.
.PP
\fBrfc822tok_print\fR() converts a tokenized
\fIlist\fR
of
rfc822token
objects into a text string\&. The callback function,
\fIfunc\fR, is called one character at a time, for every character in the tokenized objects\&. An arbitrary pointer,
\fIfunc_arg\fR, is passed unchanged as the additional argument to the callback function\&.
\fBrfc822tok_print\fR() is not usually the most convenient and efficient function, but it has its uses\&.
.PP
\fBrfc822_print\fR() takes an entire
rfc822a
structure, and uses the callback functions to print the contained addresses, in their original form, separated by commas\&. The function pointed to by
\fIprint_func\fR
is used to print each individual address, one character at a time\&. Between the addresses, the
\fIprint_separator\fR
function is called to print the address separator, usually the string ", "\&. The
\fIcallback_arg\fR
argument is passed along unchanged, as an additional argument to these functions\&.
.PP
The functions
\fBrfc822_addrlist\fR() and
\fBrfc822_namelist\fR() also print the contents of the entire
rfc822a
structure, but in a different way\&.
\fBrfc822_addrlist\fR() prints just the actual E\-mail addresses, not the recipient names or comments\&. Each E\-mail address is followed by a newline character\&.
\fBrfc822_namelist\fR() prints just the names or comments, followed by newlines\&.
.PP
The functions
\fBrfc822_praddr\fR() and
\fBrfc822_prname\fR() are just like
\fBrfc822_addrlist\fR() and
\fBrfc822_namelist\fR(), except that they print a single name or address in the
rfc822a
structure, given its
\fIindex\fR\&. The functions
\fBrfc822_gettok\fR(),
\fBrfc822_getaddrs\fR(),
\fBrfc822_getaddr\fR(), and
\fBrfc822_getname\fR() are equivalent to
\fBrfc822tok_print\fR(),
\fBrfc822_print\fR(),
\fBrfc822_praddr\fR() and
\fBrfc822_prname\fR(), but, instead of using a callback function pointer, these functions write the output into a dynamically allocated buffer\&. That buffer must be destroyed by
\fBfree\fR(3) after use\&. These functions will return a null pointer in the event of a failure to allocate memory for the buffer\&.
.PP
\fBrfc822_prname_orlist\fR() is similar to
\fBrfc822_prname\fR(), except that it will also print the legacy RFC822 group list syntax (which are also parsed by
\fBrfc822a_alloc\fR())\&.
\fBrfc822_praddr\fR() will print an empty string for an index that corresponds to a group list name (or terminated semicolon)\&.
\fBrfc822_prname\fR() will also print an empty string\&.
\fBrfc822_prname_orlist\fR() will instead print either the name of the group list, or a single string ";"\&.
\fBrfc822_getname_orlist\fR() will instead save it into a dynamically allocated buffer\&.
.PP
The function
\fBrfc822_getaddrs_wrap\fR() is similar to
\fBrfc822_getaddrs\fR(), except that the generated text is wrapped on or about the 73rd column, using newline characters\&.
.SS "Working with dates"
.sp
.if n \{\
.RS 4
.\}
.nf
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);
.fi
.if n \{\
.RE
.\}
.PP
These functions convert between timestamps and dates expressed in the
Date:
E\-mail header format\&.
.PP
\fBrfc822_parsedt\fR() returns the timestamp corresponding to the given date string (0 if there was a syntax error)\&.
.PP
\fBrfc822_mkdate\fR() returns a date string corresponding to the given timestamp\&.
\fBrfc822_mkdate_buf\fR() writes the date string into the given buffer instead, which must be big enough to accommodate it\&.
.SS "Working with 8\-bit MIME\-encoded headers"
.sp
.if n \{\
.RS 4
.\}
.nf
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);
.fi
.if n \{\
.RE
.\}
.PP
These functions provide additional logic to encode or decode 8\-bit content in 7\-bit RFC 822 headers, as specified in RFC 2047\&.
.PP
\fBrfc2047_decode\fR() 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\*(Aqs 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\&.
.PP
The callback function also receives
\fIcallback_arg\fR, as its last argument\&. If the callback function returns a non\-zero value,
\fBrfc2047_decode\fR() terminates, returning that value\&. Otherwise,
\fBrfc2047_decode\fR() returns 0 after a successful decoding\&.
\fBrfc2047_decode\fR() returns \-1 if it was unable to allocate sufficient memory\&.
.PP
\fBrfc2047_decode_simple\fR() and
\fBrfc2047_decode_enhanced\fR() are alternatives to
\fBrfc2047_decode\fR() which forego a callback function, and return the decoded text in a dynamically\-allocated memory buffer\&. The buffer must be
\fBfree\fR(3)\-ed after use\&.
\fBrfc2047_decode_simple\fR() discards all character set specifications, and merely decodes any 8\-bit text\&.
\fBrfc2047_decode_enhanced\fR() is a compromise to discarding all character set information\&. The local character set being used is specified as the second argument to
\fBrfc2047_decode_enhanced\fR()\&. 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\&.
.PP
\fBrfc2047_decode_simple\fR() and
\fBrfc2047_decode_enhanced\fR() return a null pointer if they are unable to allocate sufficient memory\&.
.PP
The
\fBrfc2047_print\fR() function is equivalent to
\fBrfc822_print\fR(), followed by
\fBrfc2047_decode_enhanced\fR() on the result\&. The callback functions are used in an identical fashion, except that they receive text that\*(Aqs already decoded\&.
.PP
The function
\fBrfc2047_encode_str\fR() takes a
\fIstring\fR
and
\fIcharset\fR
being the name of the local character set, then encodes any 8\-bit portions of
\fIstring\fR
using RFC 2047 encoding\&.
\fBrfc2047_encode_str\fR() returns a dynamically\-allocated buffer with the result, which must be
\fBfree\fR(3)\-ed after use, or NULL if there was insufficient memory to allocate the buffer\&.
.PP
The function
\fBrfc2047_encode_callback\fR() is similar to
\fBrfc2047_encode_str\fR() 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
\fIcallback_arg\fR\&.
.PP
The function
\fBrfc2047_encode_header\fR() is basically equivalent to
\fBrfc822_getaddrs\fR(), followed by
\fBrfc2047_encode_str\fR();
.SS "Working with subjects"
.sp
.if n \{\
.RS 4
.\}
.nf
char *basesubj=rfc822_coresubj(const char *subj);

char *basesubj=rfc822_coresubj_nouc(const char *subj);
.fi
.if n \{\
.RE
.\}
.PP
This function takes the contents of the subject header, and returns the "core" subject header that\*(Aqs used in the specification of the IMAP THREAD function\&. This function is designed to strip all subject line artifacts that might\*(Aqve been added in the process of forwarding or replying to a message\&. Currently,
\fBrfc822_coresubj\fR() performs the following transformations:
.PP
Whitespace
.RS 4
Leading and trailing whitespace is removed\&. Consecutive whitespace characters are collapsed into a single whitespace character\&. All whitespace characters are replaced by a space\&.
.RE
.PP
Re:, (fwd) [foo]
.RS 4
These artifacts (and several others) are removed from the subject line\&.
.RE
.PP
Note that this function does NOT do MIME decoding\&. In order to implement IMAP THREAD, it is necessary to call something like
\fBrfc2047_decode\fR() before calling
\fBrfc822_coresubj\fR()\&.
.PP
This function returns a pointer to a dynamically\-allocated buffer, which must be
\fBfree\fR(3)\-ed after use\&.
.PP
\fBrfc822_coresubj_nouc\fR() is like
\fBrfc822_coresubj\fR(), except that the subject is not converted to uppercase\&.
.SH "SEE ALSO"
.PP
\m[blue]\fB\fBrfc2045\fR(3)\fR\m[]\&\s-2\u[3]\d\s+2,
\m[blue]\fB\fBreformail\fR(1)\fR\m[]\&\s-2\u[4]\d\s+2,
\m[blue]\fB\fBreformime\fR(1)\fR\m[]\&\s-2\u[5]\d\s+2\&.
.SH "AUTHOR"
.PP
\fBSam Varshavchik\fR
.RS 4
Author
.RE
.SH "NOTES"
.IP " 1." 4
RFC 822
.RS 4
\%http://www.rfc-editor.org/rfc/rfc822.txt
.RE
.IP " 2." 4
RFC 2822
.RS 4
\%http://www.rfc-editor.org/rfc/rfc2822.txt
.RE
.IP " 3." 4
\fBrfc2045\fR(3)
.RS 4
\%http://www.courier-mta.org/rfc2045.html
.RE
.IP " 4." 4
\fBreformail\fR(1)
.RS 4
\%http://www.courier-mta.org/reformail.html
.RE
.IP " 5." 4
\fBreformime\fR(1)
.RS 4
\%http://www.courier-mta.org/reformime.html
.RE
