libbb/base64.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Utility routines.
   4  *
   5  * Copyright 2003, Glenn McGrath
   6  * Copyright 2010, Denys Vlasenko
   7  *
   8  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   9  */
  10 #include "libbb.h"
  11
  12 //kbuild:lib-y += base64.o
  13
  14 void FAST_FUNC read_base64(FILE *src_stream, FILE *dst_stream, int flags)
  15 {
  16 /* Note that EOF _can_ be passed as exit_char too */
  17 #define exit_char    ((int)(signed char)flags)
  18 #define uu_style_end (flags & BASE64_FLAG_UUEND)
  19
  20         int term_count = 0;
  21
  22         while (1) {
  23                 unsigned char translated[4];
  24                 int count = 0;
  25
  26                 /* Process one group of 4 chars */
  27                 while (count < 4) {
  28                         char *table_ptr;
  29                         int ch;
  30
  31                         /* Get next _valid_ character.
  32                          * bb_uuenc_tbl_base64[] contains this string:
  33                          *  0         1         2         3         4         5         6
  34                          *  012345678901234567890123456789012345678901234567890123456789012345
  35                          * "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=\n"
  36                          */
  37                         do {
  38                                 ch = fgetc(src_stream);
  39                                 if (ch == exit_char && count == 0)
  40                                         return;
  41                                 if (ch == EOF)
  42                                         bb_error_msg_and_die("truncated base64 input");
  43                                 table_ptr = strchr(bb_uuenc_tbl_base64, ch);
  44 //TODO: add BASE64_FLAG_foo to die on bad char?
  45 //Note that then we may need to still allow '\r' (for mail processing)
  46                         } while (!table_ptr);
  47
  48                         /* Convert encoded character to decimal */
  49                         ch = table_ptr - bb_uuenc_tbl_base64;
  50
  51                         if (ch == 65 /* '\n' */) {
  52                                 /* Terminating "====" line? */
  53                                 if (uu_style_end && term_count == 4)
  54                                         return; /* yes */
  55                                 continue;
  56                         }
  57                         /* ch is 64 if char was '=', otherwise 0..63 */
  58                         translated[count] = ch & 63; /* 64 -> 0 */
  59                         if (ch == 64) {
  60                                 term_count++;
  61                                 break;
  62                         }
  63                         term_count = 0;
  64                         count++;
  65                 }
  66
  67                 /* Merge 6 bit chars to 8 bit.
  68                  * count can be < 4 when we decode the tail:
  69                  * "eQ==" -> "y", not "y NUL NUL"
  70                  */
  71                 if (count > 1)
  72                         fputc(translated[0] << 2 | translated[1] >> 4, dst_stream);
  73                 if (count > 2)
  74                         fputc(translated[1] << 4 | translated[2] >> 2, dst_stream);
  75                 if (count > 3)
  76                         fputc(translated[2] << 6 | translated[3], dst_stream);
  77         } /* while (1) */
  78 }