[mLib] / base64.c

/* -*-c-*-
 *
 * Base64 encoding and decoding.
 *
 * (c) 1997 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of the mLib utilities library.
 *
 * mLib is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * mLib is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with mLib; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Header files ------------------------------------------------------*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "base64.h"
#include "dstr.h"

/*----- Important tables --------------------------------------------------*/

static const char encodemap[] = { "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                                  "abcdefghijklmnopqrstuvwxyz"
                                  "0123456789+/" };

static const signed char decodemap[] = {
  -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 0x */
  -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 1x */
  -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,  /* 2x */
  52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,  /* 3x */
  -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,  /* 4x */
  15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,  /* 5x */
  -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36 ,37, 38, 39, 40,  /* 6x */
  41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1   /* 7x */
};

/*----- Main code ---------------------------------------------------------*/

/* --- @base64_encode@ --- *
 *
 * Arguments:   @base64_ctx *ctx@ = pointer to a context block
 *              @const void *p@ = pointer to a source buffer
 *              @size_t sz@ = size of the source buffer
 *              @dstr *d@ = pointer to destination string
 *
 * Returns:     ---
 *
 * Use:         Encodes a binary string in base64.  To flush out the final
 *              few characters (if necessary), pass a null source pointer.
 */

void base64_encode(base64_ctx *ctx,
                   const void *p, size_t sz,
                   dstr *d)
{
  if (p) {
    unsigned long acc = ctx->acc;
    unsigned qsz = ctx->qsz;
    const unsigned char *src = p;

    while (sz) {
      acc = (acc << 8) | *src++;
      qsz++;
      sz--;
      if (qsz == 3) {
        DPUTC(d, encodemap[(acc >> 18) & 0x3f]);
        DPUTC(d, encodemap[(acc >> 12) & 0x3f]);
        DPUTC(d, encodemap[(acc >>  6) & 0x3f]);
        DPUTC(d, encodemap[(acc >>  0) & 0x3f]);
        ctx->lnlen += 4;
        if (ctx->maxline && ctx->lnlen >= ctx->maxline) {
          dstr_puts(d, ctx->indent);
          ctx->lnlen = 0;
        }
        qsz = 0;
        acc = 0;
      }
    }

    ctx->acc = acc;
    ctx->qsz = qsz;
  } else {
    unsigned long acc = ctx->acc;
    unsigned qsz = ctx->qsz;

    switch (qsz) {
      case 0:
        break;
      case 1:
        acc <<= 16;
        DPUTC(d, encodemap[(acc >> 18) & 0x3f]);
        DPUTC(d, encodemap[(acc >> 12) & 0x3f]);
        DPUTC(d, '=');
        DPUTC(d, '=');
        ctx->lnlen += 4;
        break;
      case 2:
        acc <<= 8;
        DPUTC(d, encodemap[(acc >> 18) & 0x3f]);
        DPUTC(d, encodemap[(acc >> 12) & 0x3f]);
        DPUTC(d, encodemap[(acc >>  6) & 0x3f]);
        DPUTC(d, '=');
        ctx->lnlen += 4;
        break;
    }
    ctx->qsz = 0;
    ctx->acc = 0;
  }
}

/* --- @base64_decode@ --- *
 *
 * Arguments:   @base64_ctx *ctx@ = pointer to a context block
 *              @const void *p@ = pointer to a source buffer
 *              @size_t sz@ = size of the source buffer
 *              @dstr *d@ = pointer to destination string
 *
 * Returns:     ---
 *
 * Use:         Decodes a binary string in base64.  To flush out the final
 *              few characters (if necessary), pass a null source pointer.
 */

void base64_decode(base64_ctx *ctx,
                   const void *p, size_t sz,
                   dstr *d)
{
  if (p) {
    unsigned long acc = ctx->acc;
    unsigned qsz = ctx->qsz;
    const char *src = p;
    int ch;

    while (sz) {

      /* --- Get the next character and convert it --- */

      ch = *src++;
      if (ch >= 128 || ch < 0)
        ch = -1;
      else
        ch = decodemap[ch];
      sz--;
      if (ch == -1)
        continue;

      /* --- Bung it in the accumulator --- */

      acc = (acc << 6) | ch;
      qsz++;

      /* --- Maybe write out a completed triplet --- */

      if (qsz == 4) {
        DPUTC(d, (acc >> 16) & 0xff);
        DPUTC(d, (acc >>  8) & 0xff);
        DPUTC(d, (acc >>  0) & 0xff);
        acc = 0;
        qsz = 0;
      }
    }

    ctx->acc = acc;
    ctx->qsz = qsz;
  } else {

    /* --- Notes about the tail-end bits --- *
     *
     * Ending Base64 decoding is messy.  The reference I'm using to define
     * the encoding, RFC1521 section 5.2, is a little hazy on exactly what to
     * do at the end.  It explains that I'm meant to ignore spurious `='
     * characters, and points out that I'm not guaranteed to see anything
     * interesting at the end.  I'll play safe here, and ignore all `='
     * characters, relying on my client to work out when to stop feeding me
     * data.  I'll use the queue size to work out how many tail-end bytes
     * I ought to write.
     */

    unsigned long acc = ctx->acc;
    unsigned qsz = ctx->qsz;

    /* --- Now fiddle with everything else --- *
     *
     * There's a bodge here for invalid encodings which have only one hextet
     * in the final group.  I'm not sure this is really worth having, but it
     * might save some unexpected behaviour.  (Not that you won't still get
     * unexpected behaviour if the stream is completely empty, of course.)
     */

    if (qsz) {
      acc <<= 6 * (4 - qsz);
      qsz *= 6;
      if (qsz < 8)
        qsz = 8;
      while (qsz >= 8) {
        DPUTC(d, (acc >> 16) & 0xff);
        acc <<= 8;
        qsz -= 8;
      }
    }

    /* --- That seems to be good enough --- */

    ctx->qsz = 0;
    ctx->acc = 0;
  }
}

/* --- @base64_init@ --- *
 *
 * Arguments:   @base64_ctx *ctx@ = pointer to context block to initialize
 *
 * Returns:     ---
 *
 * Use:         Initializes a base64 context properly.
 */

void base64_init(base64_ctx *ctx)
{
  ctx->acc = 0;
  ctx->qsz = 0;
  ctx->lnlen = 0;
  ctx->indent = "\n";
  ctx->maxline = 72;
}

/*----- Test driver code --------------------------------------------------*/

#ifdef TEST_RIG

int main(int argc, char *argv[])
{
  unsigned char buf[BUFSIZ];
  dstr d = DSTR_INIT;
  base64_ctx ctx;
  void (*proc)(base64_ctx *, const void *, size_t, dstr *);
  size_t sz;

  base64_init(&ctx);

  if (argc > 1 && strcmp(argv[1], "-d") == 0)
    proc = base64_decode;
  else {
    proc = base64_encode;
    putchar('\t');
    ctx.indent = "\n\t";
    ctx.maxline = 64;
  }

  do {
    sz = fread(buf, 1, sizeof(buf), stdin);
    if (sz) {
      proc(&ctx, buf, sz, &d);
      dstr_write(&d, stdout);
      dstr_destroy(&d);
    }
  } while (sz == sizeof(buf));

  proc(&ctx, 0, 0, &d);
  dstr_write(&d, stdout);

  if (proc == base64_encode)
    putchar('\n');

  return (0);
}

#endif

/*----- That's all, folks -------------------------------------------------*/