mdw@git.distorted.org.uk Git - mLib/blob - buf/lbuf.h

   1 /* -*-c-*-
   2  *
   3  * Block-to-line buffering
   4  *
   5  * (c) 1999 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of the mLib utilities library.
  11  *
  12  * mLib is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * mLib is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with mLib; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 #ifndef MLIB_LBUF_H
  29 #define MLIB_LBUF_H
  30
  31 #ifdef __cplusplus
  32   extern "C" {
  33 #endif
  34
  35 /*----- Line buffering ----------------------------------------------------*
  36  *
  37  * The line buffer accepts as input arbitrary-sized lumps of data and
  38  * converts them, by passing them to a client-supplied function, into a
  39  * sequence of lines.  It's particularly useful when performing multiplexed
  40  * network I/O.  It's not normally acceptable to block while waiting for the
  41  * rest of a text line to arrive, for example.  The line buffer stores the
  42  * start of the line until the rest of it arrives later.
  43  *
  44  * A line is a piece of text terminated by either a linefeed or a carriage-
  45  * return/linefeed pair.  (The former is there to cope with Unix; the latter
  46  * copes with Internet-format line ends.)
  47  *
  48  * There's a limit to the size of lines that the buffer can cope with.  It's
  49  * not hard to remove this limit, but it's probably a bad idea in a lot of
  50  * cases, because it'd allow a remote user to gobble arbitrary amounts of
  51  * your memory.  If a line exceeds the limit, it is truncated: the initial
  52  * portion of the line is processed normally, and the remaining portion is
  53  * simply discarded.
  54  *
  55  * Lines extracted from the input data are passed, one at a time, to a
  56  * `handler function', along with a caller-supplied pointer argument to
  57  * provide the handler with some context.  The line read is null-terminated
  58  * and does not include the trailing newline characters.  It is legal for a
  59  * handler function to modify the string it is passed.  However, writing
  60  * beyond the terminating null byte is not allowed.  An end-of-file condition
  61  * is signalled to the handler by passing it a null pointer rather than the
  62  * address of a string.
  63  *
  64  * A complexity arises because of the concept of a `disabled' buffer.
  65  * Disablement is really a higher-level concept, but it turns out to be
  66  * important to implement it here.  It's useful for a line handler function
  67  * to `disable' itself, so that it doesn't get called any more.  For example,
  68  * this might happen if it encouters an error, or when it finishes reading
  69  * everything it wanted to read.  The line buffer needs to be `in the loop'
  70  * so that it stops attempting to flush any further lines stored in its
  71  * buffer towards a handler function which isn't ready to accept them.
  72  * Buffers are initially enabled, although higher- level buffering systems
  73  * might well disable them immediately for their own purposes.
  74  */
  75
  76 /*----- Header files ------------------------------------------------------*/
  77
  78 #include <stddef.h>
  79
  80 #ifndef MLIB_ARENA_H
  81 #  include "arena.h"
  82 #endif
  83
  84 /*----- Data structures ---------------------------------------------------*/
  85
  86 /* --- The buffer structure --- *
  87  *
  88  * The only thing that's safe to fiddle with in here is the @lbuf_enable@
  89  * flag.  Only higher-level buffering systems should be playing with even
  90  * that.
  91  */
  92
  93 struct lbuf;
  94
  95 typedef void lbuf_func(char */*s*/, size_t /*len*/, void */*p*/);
  96
  97 typedef struct lbuf {
  98   lbuf_func *func;                      /* Handler function */
  99   void *p;                              /* Argument for handler */
 100   size_t len;                           /* Length of data in buffer */
 101   size_t sz;                            /* Buffer size */
 102   unsigned delim;                       /* Delimiter to look for */
 103   unsigned f;                           /* Various useful state flags */
 104   arena *a;                             /* Memory allocation arena */
 105   char *buf;                            /* The actual buffer */
 106 } lbuf;
 107
 108 #define LBUF_CR 1u                      /* Read a carriage return */
 109 #define LBUF_ENABLE 2u                  /* Buffer is currently enabled */
 110 #define LBUF_CLOSE 4u                   /* Buffer is now closed */
 111
 112 enum {
 113   LBUF_CRLF = 256,
 114   LBUF_STRICTCRLF = 257
 115 };
 116
 117 /*----- Functions provided ------------------------------------------------*/
 118
 119 /* --- @lbuf_flush@ --- *
 120  *
 121  * Arguments:   @lbuf *b@ = pointer to buffer block
 122  *              @char *p@ = pointer to where to start searching
 123  *              @size_t len@ = length of new material added
 124  *
 125  * Returns:     ---
 126  *
 127  * Use:         Flushes any complete lines in a line buffer.  New material
 128  *              is assumed to have been added starting at @p@.  If @p@ is
 129  *              null, then the scan starts at the beginning of the buffer,
 130  *              and the size of data already in the buffer is used in place
 131  *              of @len@.
 132  *
 133  *              It is assumed that the buffer is initially enabled.  You
 134  *              shouldn't be contributing data to a disabled buffer anyway.
 135  *              However, the buffer handler may at some point disable itself,
 136  *              and @lbuf_flush@ can cope with this eventuality.  Any pending
 137  *              data is left at the start of the buffer and can be flushed
 138  *              out by calling @lbuf_flush(b, 0, 0)@ if the buffer is ever
 139  *              re-enabled.
 140  */
 141
 142 extern void lbuf_flush(lbuf */*b*/, char */*p*/, size_t /*len*/);
 143
 144 /* --- @lbuf_close@ --- *
 145  *
 146  * Arguments:   @lbuf *b@ = pointer to buffer block
 147  *
 148  * Returns:     ---
 149  *
 150  * Use:         Empties the buffer of any data currently lurking in it, and
 151  *              informs the client that this has happened.  It's assumed that
 152  *              the buffer is enabled: you shouldn't be reading close events
 153  *              on disabled buffers.
 154  */
 155
 156 extern void lbuf_close(lbuf */*b*/);
 157
 158 /* --- @lbuf_free@ --- *
 159  *
 160  * Arguments:   @lbuf *b@ = pointer to buffer block
 161  *              @char **p@ = output pointer to free space
 162  *
 163  * Returns:     Free buffer size.
 164  *
 165  * Use:         Returns the free portion of a line buffer.  Data can then be
 166  *              written to this portion, and split out into lines by calling
 167  *              @lbuf_flush@.
 168  */
 169
 170 extern size_t lbuf_free(lbuf */*b*/, char **/*p*/);
 171
 172 /* --- @lbuf_snarf@ --- *
 173  *
 174  * Arguments:   @lbuf *b@ = pointer to buffer block
 175  *              @const void *p@ = pointer to input data buffer
 176  *              @size_t sz@ = size of data in input buffer
 177  *
 178  * Returns:     ---
 179  *
 180  * Use:         Snarfs the data from the input buffer and spits it out as
 181  *              lines.  This interface ignores the complexities of dealing
 182  *              with disablement: you should be using @lbuf_free@ to
 183  *              contribute data if you want to cope with that.
 184  */
 185
 186 extern void lbuf_snarf(lbuf */*b*/, const void */*p*/, size_t /*sz*/);
 187
 188 /* --- @lbuf_setsize@ --- *
 189  *
 190  * Arguments:   @lbuf *b@ = pointer to buffer block
 191  *              @size_t sz@ = requested maximum line size
 192  *
 193  * Returns:     ---
 194  *
 195  * Use:         Allocates a buffer of the requested size reading lines.
 196  */
 197
 198 extern void lbuf_setsize(lbuf */*b*/, size_t /*sz*/);
 199
 200 /* --- @lbuf_init@ --- *
 201  *
 202  * Arguments:   @lbuf *b@ = pointer to buffer block
 203  *              @lbuf_func *func@ = handler function
 204  *              @void *p@ = argument pointer for @func@
 205  *
 206  * Returns:     ---
 207  *
 208  * Use:         Initializes a line buffer block.  Any recognized lines are
 209  *              passed to @func@ for processing.
 210  */
 211
 212 extern void lbuf_init(lbuf */*b*/, lbuf_func */*func*/, void */*p*/);
 213
 214 /* --- @lbuf_destroy@ --- *
 215  *
 216  * Arguments:   @lbuf *b@ = pointer to buffer block
 217  *
 218  * Returns:     ---
 219  *
 220  * Use:         Deallocates a line buffer and frees any resources it owned.
 221  */
 222
 223 extern void lbuf_destroy(lbuf */*b*/);
 224
 225 /*----- That's all, folks -------------------------------------------------*/
 226
 227 #ifdef __cplusplus
 228   }
 229 #endif
 230
 231 #endif