Tokenizing an E-mail header

struct rfc822t *tokens=rfc822t_alloc_new(const char *header,
                void (*err_func)(const char *, int, void *),
                void *func_arg);

void rfc822t_free(tokens);

The rfc822t_alloc_new() function (superceeds rfc822t_alloc(), which is now obsolete) accepts an E-mail header, and parses it into individual tokens. This function allocates and returns a pointer to an rfc822t structure, which is later used by rfc822a_alloc() to extract individual addresses from these tokens.

If err_func 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 header pointer, an index to the syntax error in the header string, and the func_arg argument.

The semantics of err_func are subject to change. It is recommended to leave this argument as NULL in the current version of the library.

rfc822t_alloc() returns a pointer to a dynamically-allocated rfc822t structure. A NULL pointer is returned if there's insufficient memory to allocate this structure. The rfc822t_free() function destroys rfc822t structure and frees all dynamically allocated memory.

Extracting E-mail addresses

struct rfc822a *addrs=rfc822a_alloc(struct rfc822t *tokens);

void rfc822a_free(addrs);

The rfc822a_alloc() function returns a dynamically-allocated rfc822a structure, that contains individual addresses that were logically parsed from a rfc822t structure. The rfc822a_alloc() function returns NULL if there was insufficient memory to allocate the rfc822a structure. The rfc822a_free() function destroys the rfc822a function, and frees all associated dynamically-allocated memory. The rfc822t structure passed to rfc822a_alloc() must not be destroyed before rfc822a_free() destroys the rfc822a structure.

The rfc822a structure has the following fields:

struct rfc822a {
        struct rfc822addr *addrs;
        int     naddrs;
} ;

The naddrs field gives the number of rfc822addr structures that are pointed to by addrs, which is an array. Each rfc822addr structure represents either an address found in the original E-mail header, or the contents of some legacy "syntactical sugar". For example, the following is a valid E-mail header:

To: recipient-list: tom@example.com, john@example.com;

Typically, all of this, except for "To:", is tokenized by rfc822t_alloc(), then parsed by rfc822a_alloc(). "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:

struct rfc822addr {
        struct rfc822token *tokens;
        struct rfc822token *name;
} ;

If tokens 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.

name 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. name will be NULL if the recipient name was not provided. For the following address: Tom Jones <tjones@example.com> - the tokens field points to the tokenized form of "tjones@example.com", and name points to the tokenized form of "Tom Jones".

Each rfc822token structure contains the following fields:

struct rfc822token {
        struct rfc822token *next;
        int token;
        const char *ptr;
        int len;
} ;

The next pointer builds a linked list of all tokens in this name or address. The possible values for the token field are:

When a rfc822token structure does not represent a special character, the ptr field points to a text string giving its contents. The contents are NOT null-terminated, the len field contains the number of characters included. The macro rfc822_is_atom(token) indicates whether ptr and len are used for the given token. Currently rfc822_is_atom() returns true if token is a zero byte, '"', or '('.

Note that it's possible that len might be zero. This happens with null addresses used as return addresses for delivery status notifications.

Working with E-mail addresses

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);

These functions are used to work with individual addresses that are parsed by rfc822a_alloc().

rfc822_deladdr() removes a single rfc822addr structure, whose index is given, from the address array in rfc822addr. naddrs is decremented by one.

rfc822tok_print() converts a tokenized list of rfc822token objects into a text string. The callback function, func, is called one character at a time, for every character in the tokenized objects. An arbitrary pointer, func_arg, 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.

rfc822_print() 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 print_func is used to print each individual address, one character at a time. Between the addresses, the print_separator function is called to print the address separator, usually the string ", ". The callback_arg argument is passed along unchanged, as an additional argument to these functions.

The functions rfc822_addrlist() and rfc822_namelist() also print the contents of the entire rfc822a 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.

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 rfc822a structure, given its index. 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.

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 xml:lang="en">

#include <rfc822.h>

#include <rfc2047.h>

cc ... -lrfc822

struct rfc822t *tokens=rfc822t_alloc_new(const char *header,
                void (*err_func)(const char *, int, void *),
                void *func_arg);

void rfc822t_free(tokens);

struct rfc822a *addrs=rfc822a_alloc(struct rfc822t *tokens);

void rfc822a_free(addrs);

struct rfc822a {
        struct rfc822addr *addrs;
        int     naddrs;
} ;

To: recipient-list: tom@example.com, john@example.com;

struct rfc822addr {
        struct rfc822token *tokens;
        struct rfc822token *name;
} ;

struct rfc822token {
        struct rfc822token *next;