rfc822/rfc822.3

   1 .\"  <!-- $Id: rfc822.sgml,v 1.5 2007/04/22 15:05:16 mrsam Exp $ -->
   2 .\"  <!-- Copyright 2001-2007 Double Precision, Inc.  See COPYING for -->
   3 .\"  <!-- distribution information. -->
   4 .\"     Title: rfc822
   5 .\"    Author:
   6 .\" Generator: DocBook XSL Stylesheets v1.72.0 <http://docbook.sf.net/>
   7 .\"      Date: 04/22/2007
   8 .\"    Manual: Double Precision, Inc.
   9 .\"    Source: Double Precision, Inc.
  10 .\"
  11 .TH "RFC822" "3" "04/22/2007" "Double Precision, Inc." "Double Precision, Inc."
  12 .\" disable hyphenation
  13 .nh
  14 .\" disable justification (adjust text to left margin only)
  15 .ad l
  16 .SH "NAME"
  17 rfc822 \- RFC 822 parsing library
  18 .SH "SYNOPSIS"
  19 .sp
  20 .RS 4
  21 .nf
  22 #include <rfc822.h>
  23
  24 #include <rfc2047.h>
  25
  26 cc ... \-lrfc822
  27 .fi
  28 .RE
  29 .SH "DESCRIPTION"
  30 .PP
  31 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.
  32 .PP
  33 The format used by E\-mail headers to encode sender and recipient information is defined by
  34 \fIRFC 822\fR\&[1]
  35 (and its successor,
  36 \fIRFC 2822\fR\&[2]). The format allows the actual E\-mail address and the sender/recipient name to be expressed together, for example:
  37 John Smith <jsmith@example.com>
  38 .PP
  39 The main purposes of the rfc822 library is to:
  40 .PP
  41 1) Parse a text string containing a list of RFC 822\-formatted address into its logical components: names and E\-mail addresses.
  42 .PP
  43 2) Access those individual components.
  44 .PP
  45 3) Allow some limited modifications of the parsed structure, and then convert it back into a text string.
  46 .SS "Tokenizing an E\-mail header"
  47 .sp
  48 .RS 4
  49 .nf
  50 struct rfc822t *tokens=rfc822t_alloc_new(const char *header,
  51                 void (*err_func)(const char *, int, void *),
  52                 void *func_arg);
  53
  54 void rfc822t_free(tokens);
  55 .fi
  56 .RE
  57 .PP
  58 The
  59 \fBrfc822t_alloc_new\fR() function (superceeds
  60 \fBrfc822t_alloc\fR(), which is now obsolete) accepts an E\-mail
  61 \fIheader\fR, and parses it into individual tokens. This function allocates and returns a pointer to an
  62 rfc822t
  63 structure, which is later used by
  64 \fBrfc822a_alloc\fR() to extract individual addresses from these tokens.
  65 .PP
  66 If
  67 \fIerr_func\fR
  68 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
  69 \fIheader\fR
  70 pointer, an index to the syntax error in the header string, and the
  71 \fIfunc_arg\fR
  72 argument.
  73 .PP
  74 The semantics of
  75 \fIerr_func\fR
  76 are subject to change. It is recommended to leave this argument as NULL in the current version of the library.
  77 .PP
  78
  79 \fBrfc822t_alloc\fR() returns a pointer to a dynamically\-allocated
  80 rfc822t
  81 structure. A NULL pointer is returned if there's insufficient memory to allocate this structure. The
  82 \fBrfc822t_free\fR() function destroys
  83 rfc822t
  84 structure and frees all dynamically allocated memory.
  85 .sp
  86 .it 1 an-trap
  87 .nr an-no-space-flag 1
  88 .nr an-break-flag 1
  89 .br
  90 \fBNote\fR
  91 .PP
  92 Until
  93 \fBrfc822t_free\fR() is called, the contents of
  94 \fIheader\fR
  95 MUST NOT be destroyed or altered in any way. The contents of
  96 \fIheader\fR
  97 are not modified by
  98 \fBrfc822t_alloc\fR(), however the
  99 rfc822t
 100 structure contains pointers to portions of the supplied
 101 \fIheader\fR, and they must remain valid.
 102 .SS "Extracting E\-mail addresses"
 103 .sp
 104 .RS 4
 105 .nf
 106 struct rfc822a *addrs=rfc822a_alloc(struct rfc822t *tokens);
 107
 108 void rfc822a_free(addrs);
 109 .fi
 110 .RE
 111 .PP
 112 The
 113 \fBrfc822a_alloc\fR() function returns a dynamically\-allocated
 114 rfc822a
 115 structure, that contains individual addresses that were logically parsed from a
 116 rfc822t
 117 structure. The
 118 \fBrfc822a_alloc\fR() function returns NULL if there was insufficient memory to allocate the
 119 rfc822a
 120 structure. The
 121 \fBrfc822a_free\fR() function destroys the
 122 rfc822a
 123 function, and frees all associated dynamically\-allocated memory. The
 124 rfc822t
 125 structure passed to
 126 \fBrfc822a_alloc\fR() must not be destroyed before
 127 \fBrfc822a_free\fR() destroys the
 128 rfc822a
 129 structure.
 130 .PP
 131 The
 132 rfc822a
 133 structure has the following fields:
 134 .sp
 135 .RS 4
 136 .nf
 137 struct rfc822a {
 138         struct rfc822addr *addrs;
 139         int     naddrs;
 140 } ;
 141 .fi
 142 .RE
 143 .PP
 144 The
 145 naddrs
 146 field gives the number of
 147 rfc822addr
 148 structures that are pointed to by
 149 addrs, which is an array. Each
 150 rfc822addr
 151 structure represents either an address found in the original E\-mail header,
 152 \fIor the contents of some legacy "syntactical sugar"\fR. For example, the following is a valid E\-mail header:
 153 .sp
 154 .RS 4
 155 .nf
 156 To: recipient\-list: tom@example.com, john@example.com;
 157 .fi
 158 .RE
 159 .PP
 160 Typically, all of this, except for "To:", is tokenized by
 161 \fBrfc822t_alloc\fR(), then parsed by
 162 \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
 163 rfc822a
 164 structure will have four
 165 rfc822addr
 166 structures: one for "recipient\-list:"; one for each address; and one for the trailing semicolon. Each
 167 rfc822a
 168 structure has the following fields:
 169 .sp
 170 .RS 4
 171 .nf
 172 struct rfc822addr {
 173         struct rfc822token *tokens;
 174         struct rfc822token *name;
 175 } ;
 176 .fi
 177 .RE
 178 .PP
 179 If
 180 tokens
 181 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.
 182 .PP
 183
 184 name
 185 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.
 186 name
 187 will be NULL if the recipient name was not provided. For the following address:
 188 Tom Jones <tjones@example.com>
 189 \- the
 190 tokens
 191 field points to the tokenized form of "tjones@example.com", and
 192 name
 193 points to the tokenized form of "Tom Jones".
 194 .PP
 195 Each
 196 rfc822token
 197 structure contains the following fields:
 198 .sp
 199 .RS 4
 200 .nf
 201 struct rfc822token {
 202         struct rfc822token *next;
 203         int token;
 204         const char *ptr;
 205         int len;
 206 } ;
 207 .fi
 208 .RE
 209 .PP
 210 The
 211 next
 212 pointer builds a linked list of all tokens in this name or address. The possible values for the
 213 token
 214 field are:
 215 .PP
 216 0x00
 217 .RS 4
 218 This is a simple atom \- a sequence of non\-special characters that is delimited by whitespace or special characters (see below).
 219 .RE
 220 .PP
 221 0x22
 222 .RS 4
 223 The value of the ascii quote \- this is a quoted string.
 224 .RE
 225 .PP
 226 Open parenthesis: '('
 227 .RS 4
 228 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
 229 rfc822token
 230 with
 231 token
 232 set to '(' is created for the contents of the entire comment.
 233 .RE
 234 .PP
 235 Symbols: '<', '>', '@', and many others
 236 .RS 4
 237 The remaining possible values of
 238 token
 239 include all the characters in RFC 822 headers that have special significance.
 240 .RE
 241 .PP
 242 When a
 243 rfc822token
 244 structure does not represent a special character, the
 245 ptr
 246 field points to a text string giving its contents. The contents are NOT null\-terminated, the
 247 len
 248 field contains the number of characters included. The macro rfc822_is_atom(token) indicates whether
 249 ptr
 250 and
 251 len
 252 are used for the given
 253 token. Currently
 254 \fBrfc822_is_atom\fR() returns true if
 255 token
 256 is a zero byte, '"', or '('.
 257 .PP
 258 Note that it's possible that
 259 len
 260 might be zero. This happens with null addresses used as return addresses for delivery status notifications.
 261 .SS "Working with E\-mail addresses"
 262 .sp
 263 .RS 4
 264 .nf
 265 void rfc822_deladdr(struct rfc822a *addrs, int index);
 266
 267 void rfc822tok_print(const struct rfc822token *list,
 268         void (*func)(char, void *), void *func_arg);
 269
 270 void rfc822_print(const struct rfc822a *addrs,
 271         void (*print_func)(char, void *),
 272         void (*print_separator)(const char *, void *), void *callback_arg);
 273
 274 void rfc822_addrlist(const struct rfc822a *addrs,
 275                 void (*print_func)(char, void *),
 276                 void *callback_arg);
 277
 278 void rfc822_namelist(const struct rfc822a *addrs,
 279                 void (*print_func)(char, void *),
 280                 void *callback_arg);
 281
 282 void rfc822_praddr(const struct rfc822a *addrs,
 283                 int index,
 284                 void (*print_func)(char, void *),
 285                 void *callback_arg);
 286
 287 void rfc822_prname(const struct rfc822a *addrs,
 288                 int index,
 289                 void (*print_func)(char, void *),
 290                 void *callback_arg);
 291
 292 void rfc822_prname_orlist(const struct rfc822a *addrs,
 293                 int index,
 294                 void (*print_func)(char, void *),
 295                 void *callback_arg);
 296
 297 char *rfc822_gettok(const struct rfc822token *list);
 298 char *rfc822_getaddrs(const struct rfc822a *addrs);
 299 char *rfc822_getaddr(const struct rfc822a *addrs, int index);
 300 char *rfc822_getname(const struct rfc822a *addrs, int index);
 301 char *rfc822_getname_orlist(const struct rfc822a *addrs, int index);
 302
 303 char *rfc822_getaddrs_wrap(const struct rfc822a *, int);
 304 .fi
 305 .RE
 306 .PP
 307 These functions are used to work with individual addresses that are parsed by
 308 \fBrfc822a_alloc\fR().
 309 .PP
 310
 311 \fBrfc822_deladdr\fR() removes a single
 312 rfc822addr
 313 structure, whose
 314 \fIindex\fR
 315 is given, from the address array in
 316 rfc822addr.
 317 naddrs
 318 is decremented by one.
 319 .PP
 320
 321 \fBrfc822tok_print\fR() converts a tokenized
 322 \fIlist\fR
 323 of
 324 rfc822token
 325 objects into a text string. The callback function,
 326 \fIfunc\fR, is called one character at a time, for every character in the tokenized objects. An arbitrary pointer,
 327 \fIfunc_arg\fR, is passed unchanged as the additional argument to the callback function.
 328 \fBrfc822tok_print\fR() is not usually the most convenient and efficient function, but it has its uses.
 329 .PP
 330
 331 \fBrfc822_print\fR() takes an entire
 332 rfc822a
 333 structure, and uses the callback functions to print the contained addresses, in their original form, separated by commas. The function pointed to by
 334 \fIprint_func\fR
 335 is used to print each individual address, one character at a time. Between the addresses, the
 336 \fIprint_separator\fR
 337 function is called to print the address separator, usually the string ", ". The
 338 \fIcallback_arg\fR
 339 argument is passed along unchanged, as an additional argument to these functions.
 340 .PP
 341 The functions
 342 \fBrfc822_addrlist\fR() and
 343 \fBrfc822_namelist\fR() also print the contents of the entire
 344 rfc822a
 345 structure, but in a different way.
 346 \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.
 347 \fBrfc822_namelist\fR() prints just the names or comments, followed by newlines.
 348 .PP
 349 The functions
 350 \fBrfc822_praddr\fR() and
 351 \fBrfc822_prname\fR() are just like
 352 \fBrfc822_addrlist\fR() and
 353 \fBrfc822_namelist\fR(), except that they print a single name or address in the
 354 rfc822a
 355 structure, given its
 356 \fIindex\fR. The functions
 357 \fBrfc822_gettok\fR(),
 358 \fBrfc822_getaddrs\fR(),
 359 \fBrfc822_getaddr\fR(), and
 360 \fBrfc822_getname\fR() are equivalent to
 361 \fBrfc822tok_print\fR(),
 362 \fBrfc822_print\fR(),
 363 \fBrfc822_praddr\fR() and
 364 \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
 365 \fBfree\fR(3) after use. These functions will return a null pointer in the event of a failure to allocate memory for the buffer.
 366 .PP
 367
 368 \fBrfc822_prname_orlist\fR() is similar to
 369 \fBrfc822_prname\fR(), except that it will also print the legacy RFC822 group list syntax (which are also parsed by
 370 \fBrfc822a_alloc\fR()).
 371 \fBrfc822_praddr\fR() will print an empty string for an index that corresponds to a group list name (or terminated semicolon).
 372 \fBrfc822_prname\fR() will also print an empty string.
 373 \fBrfc822_prname_orlist\fR() will instead print either the name of the group list, or a single string ";".
 374 \fBrfc822_getname_orlist\fR() will instead save it into a dynamically allocated buffer.
 375 .PP
 376 The function
 377 \fBrfc822_getaddrs_wrap\fR() is similar to
 378 \fBrfc822_getaddrs\fR(), except that the generated text is wrapped on or about the 73rd column, using newline characters.
 379 .SS "Working with dates"
 380 .sp
 381 .RS 4
 382 .nf
 383 time_t timestamp=rfc822_parsedt(const char *datestr)
 384 const char *datestr=rfc822_mkdate(time_t timestamp);
 385 void rfc822_mkdate_buf(time_t timestamp, char *buffer);
 386 .fi
 387 .RE
 388 .PP
 389 These functions convert between timestamps and dates expressed in the
 390 Date:
 391 E\-mail header format.
 392 .PP
 393
 394 \fBrfc822_parsedt\fR() returns the timestamp corresponding to the given date string (0 if there was a syntax error).
 395 .PP
 396
 397 \fBrfc822_mkdate\fR() returns a date string corresponding to the given timestamp.
 398 \fBrfc822_mkdate_buf\fR() writes the date string into the given buffer instead, which must be big enough to accommodate it.
 399 .SS "Working with 8\-bit MIME\-encoded headers"
 400 .sp
 401 .RS 4
 402 .nf
 403 int error=rfc2047_decode(const char *text,
 404                 int (*callback_func)(const char *, int, const char *, void *),
 405                 void *callback_arg);
 406
 407 extern char *str=rfc2047_decode_simple(const char *text);
 408
 409 extern char *str=rfc2047_decode_enhanced(const char *text,
 410                 const char *charset);
 411
 412 void rfc2047_print(const struct rfc822a *a,
 413         const char *charset,
 414         void (*print_func)(char, void *),
 415         void (*print_separator)(const char *, void *), void *);
 416
 417
 418 char *buffer=rfc2047_encode_str(const char *string,
 419                 const char *charset);
 420
 421 int error=rfc2047_encode_callback(const char *string,
 422         const char *charset,
 423         int (*func)(const char *, size_t, void *),
 424         void *callback_arg);
 425
 426 char *buffer=rfc2047_encode_header(const struct rfc822a *a,
 427         const char *charset);
 428 .fi
 429 .RE
 430 .PP
 431 These functions provide additional logic to encode or decode 8\-bit content in 7\-bit RFC 822 headers, as specified in RFC 2047.
 432 .PP
 433
 434 \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'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.
 435 .PP
 436 The callback function also receives
 437 \fIcallback_arg\fR, as its last argument. If the callback function returns a non\-zero value,
 438 \fBrfc2047_decode\fR() terminates, returning that value. Otherwise,
 439 \fBrfc2047_decode\fR() returns 0 after a successful decoding.
 440 \fBrfc2047_decode\fR() returns \-1 if it was unable to allocate sufficient memory.
 441 .PP
 442
 443 \fBrfc2047_decode_simple\fR() and
 444 \fBrfc2047_decode_enhanced\fR() are alternatives to
 445 \fBrfc2047_decode\fR() which forego a callback function, and return the decoded text in a dynamically\-allocated memory buffer. The buffer must be
 446 \fBfree\fR(3)\-ed after use.
 447 \fBrfc2047_decode_simple\fR() discards all character set specifications, and merely decodes any 8\-bit text.
 448 \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
 449 \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.
 450 .PP
 451
 452 \fBrfc2047_decode_simple\fR() and
 453 \fBrfc2047_decode_enhanced\fR() return a null pointer if they are unable to allocate sufficient memory.
 454 .PP
 455 The
 456 \fBrfc2047_print\fR() function is equivalent to
 457 \fBrfc822_print\fR(), followed by
 458 \fBrfc2047_decode_enhanced\fR() on the result. The callback functions are used in an identical fashion, except that they receive text that's already decoded.
 459 .PP
 460 The function
 461 \fBrfc2047_encode_str\fR() takes a
 462 \fIstring\fR
 463 and
 464 \fIcharset\fR
 465 being the name of the local character set, then encodes any 8\-bit portions of
 466 \fIstring\fR
 467 using RFC 2047 encoding.
 468 \fBrfc2047_encode_str\fR() returns a dynamically\-allocated buffer with the result, which must be
 469 \fBfree\fR(3)\-ed after use, or NULL if there was insufficient memory to allocate the buffer.
 470 .PP
 471 The function
 472 \fBrfc2047_encode_callback\fR() is similar to
 473 \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
 474 \fIcallback_arg\fR.
 475 .PP
 476 The function
 477 \fBrfc2047_encode_header\fR() is basically equivalent to
 478 \fBrfc822_getaddrs\fR(), followed by
 479 \fBrfc2047_encode_str\fR();
 480 .SS "Working with subjects"
 481 .sp
 482 .RS 4
 483 .nf
 484 char *basesubj=rfc822_coresubj(const char *subj);
 485
 486 char *basesubj=rfc822_coresubj_nouc(const char *subj);
 487 .fi
 488 .RE
 489 .PP
 490 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,
 491 \fBrfc822_coresubj\fR() performs the following transformations:
 492 .PP
 493 Whitespace
 494 .RS 4
 495 Leading and trailing whitespace is removed. Consecutive whitespace characters are collapsed into a single whitespace character. All whitespace characters are replaced by a space.
 496 .RE
 497 .PP
 498 Re:, (fwd) [foo]
 499 .RS 4
 500 These artifacts (and several others) are removed from the subject line.
 501 .RE
 502 .PP
 503 Note that this function does NOT do MIME decoding. In order to implement IMAP THREAD, it is necessary to call something like
 504 \fBrfc2047_decode\fR() before calling
 505 \fBrfc822_coresubj\fR().
 506 .PP
 507 This function returns a pointer to a dynamically\-allocated buffer, which must be
 508 \fBfree\fR(3)\-ed after use.
 509 .PP
 510
 511 \fBrfc822_coresubj_nouc\fR() is like
 512 \fBrfc822_coresubj\fR(), except that the subject is not converted to uppercase.
 513 .SH "SEE ALSO"
 514 .PP
 515
 516 \fI\fBrfc2045\fR(3)\fR\&[3],
 517 \fI\fBreformail\fR(1)\fR\&[4],
 518 \fI\fBreformime\fR(1)\fR\&[5].
 519 .SH "REFERENCES"
 520 .IP " 1." 4
 521 RFC 822
 522 .RS 4
 523 \%http://www.rfc\-editor.org/rfc/rfc822.txt
 524 .RE
 525 .IP " 2." 4
 526 RFC 2822
 527 .RS 4
 528 \%http://www.rfc\-editor.org/rfc/rfc2822.txt
 529 .RE
 530 .IP " 3." 4
 531 \fBrfc2045\fR(3)
 532 .RS 4
 533 \%rfc2045.html
 534 .RE
 535 .IP " 4." 4
 536 \fBreformail\fR(1)
 537 .RS 4
 538 \%reformail.html
 539 .RE
 540 .IP " 5." 4
 541 \fBreformime\fR(1)
 542 .RS 4
 543 \%reformime.html
 544 .RE