base64.c

linux下面的Base64编码源代码

/* base64.c: MIME BASE64编码与解码器,读标准输入. 赵建军, 2000.1.12.a */
/* 2000.2.19.A: 增文件处理. */
#include "stdio.h"
#include "string.h"
#include "stdlib.h"
#include "ctype.h"
char	*base="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
union
{
 struct
 {
  unsigned long d:6;
  unsigned long c:6;
  unsigned long b:6;
  unsigned long a:6;
 }s;
 unsigned char	c[3];
}u;
int	decode=0;
main(int argc,char **argv)
{
 extern char	*optarg;
 extern int	optind;
 int		c;
 FILE		*fp;
 while ((c=getopt(argc,argv,"u"))!=EOF)
 {
  switch(c)
  {
   case 'u': decode=1; break;
   default: usage(); break;
  }
 }
 if (argc==optind)
 {
  if (isatty(0)) usage();
  if (decode) base64decode(stdin,stdout); else base64encode(stdin,stdout);
 }
 else
 for (;optind<argc;optind++)
 {
  fp=fopen(argv[optind],"r");
  if (fp==0) { fprintf(stderr,"%s: fopen %s error.\n",argv[0],argv[optind]); continue; }
  if (decode) base64decode(fp,stdout); else base64encode(fp,stdout);
  fclose(fp);
 }
 exit(0);
}
usage()
{
 fprintf(stderr,"base64: MIME BASE64 encoder and decoder, by zzz ([e-mail]) at 2000.1.11.m\n");
 fprintf(stderr,"Usage: base64 [-u] [file1] [file2] ...\n");
 exit(1);
}
base64encode(FILE *fp,FILE *fq)
{
 int	ch,n,h=0,flag=0;
 while (1)
 {
  u.c[0]=u.c[1]=u.c[2]=0;
  for (n=0;n<3;n++)
  {
   ch=fgetc(fp);
   if (ch==EOF) break;
   u.c[2-n]=ch;
  }
  if (n==0) break;
  flag=1;
  switch(n)
  {
   case 1: fprintf(fq,"%c%c==",base[u.s.a],base[u.s.b]);break;
   case 2: fprintf(fq,"%c%c%c=",base[u.s.a],base[u.s.b],base[u.s.c]);break;
   case 3: fprintf(fq,"%c%c%c%c",base[u.s.a],base[u.s.b],base[u.s.c],base[u.s.d]);break;
  }
  if (h==15) { h=0; fprintf(fq,"\n"); } else h++;
 }
 if (flag&&h) fprintf(fq,"\n");
}
base64decode(FILE *fp,FILE *fq)
{
 int	c1,c2,c3,c4;
 while (1)
 {
  /* c1 */
  c1=fgetc(fp);
  while (c1!=EOF&&isspace(c1)) c1=fgetc(fp);
  if (c1==EOF) break;
  if (strchr(base,c1)==NULL&&c1!='=')
  {
   fprintf(fq,"Error: %c : not BASE64 code!\n",c1);
   return 1;
  }
  /* c2 */
  c2=fgetc(fp);
  if (c2==EOF)
  {
   fprintf(fq,"Error: unexpected EOF in BASE64 code!\n");
   return 1;
  }
  if (strchr(base,c2)==NULL&&c2!='=')
  {
   fprintf(fq,"Error: %c : not BASE64 code!\n",c2);
   return 1;
  }
  /* c3 */
  c3=fgetc(fp);
  if (c3==EOF)
  {
   fprintf(fq,"Error: unexpected EOF in BASE64 code!\n");
   return 1;
  }
  if (strchr(base,c3)==NULL&&c3!='=')
  {
   fprintf(fq,"Error: %c : not BASE64 code!\n",c3);
   return 1;
  }
  /* c4 */
  c4=fgetc(fp);
  if (c4==EOF)
  {
   fprintf(fq,"Error: unexpected EOF in BASE64 code!\n");
   return 1;
  }
  if (strchr(base,c4)==NULL&&c4!='=')
  {
   fprintf(fq,"Error: %c : not BASE64 code!\n",c4);
   return 1;
  }
  /* check format:[A-Za-z0-9+/][A-Za-z0-9+/][A-Za-z0-9+/=][A-Za-z0-9+/=] */
  if (strchr(base,c1)&&strchr(base,c2)&&(strchr(base,c3)||c3=='=')&&
  	((c3=='='&&c4=='=')||(c3!='='&&(c4=='='||strchr(base,c4)))))
  {
   u.s.a=strchr(base,c1)-base;
   u.s.b=strchr(base,c2)-base;
   if (c3=='=')
   {
    /* one byte output */
    fprintf(fq,"%c",u.c[2]);
   }
   else
   if (c4=='=')
   {
    /* two byte output */
    u.s.c=strchr(base,c3)-base;
    fprintf(fq,"%c%c",u.c[2],u.c[1]);
   }
   else
   {
    /* three byte output */
    u.s.c=strchr(base,c3)-base;
    u.s.d=strchr(base,c4)-base;
    fprintf(fq,"%c%c%c",u.c[2],u.c[1],u.c[0]);
   }
  }
  else
  {
   fprintf(fq,"Error: %c%c%c%c : not BASE64 code!\n",c1,c2,c3,c4);
   return 1;
  }
 }
 return 0;
}