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/* Time-stamp: <2005-10-25 21:04:57 poser>
*
* Copyright (C) 2003 William J. Poser (billposer@alum.mit.edu)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
* or go to the web page: http://www.gnu.org/licenses/gpl.txt.
*/
/*
* This function reads as little as possible in order to check the magic number.
* With two exceptions, it is safe to assume that on return from this function
* the file pointer points to the first byte of the Unicode data.
*
* The first exception is when it returns NOMAGICNUMBER. In order to return
* this value, it is necessary to read the first four bytes of the input,
* which in this case are actual data, not part of the magic number.
* The second exception is when it returns FT_UTF16_BS. To decide that
* the input is of this type rather than FT_UTF32_BS, it is necessary to
* read four bytes, of which only the first two belong to the magic
* number. The third and fourth bytes represent the first character.
*
* In either of these cases, if you wish to read the input from the first
* character, it will be necessary to seek backward. Since it is not possible
* to seek on pipes, this may be a problem. As a way around this problem,
* in these two cases the external variable UDataBegin is set to the
* address of static storage containing the two or four bytes of character
* data that have already been read.
*/
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include "uniftypes.h"
#define HDRLEN 4
#define MSGLEN 128
unsigned char *UDataBegin; /* This variable is intentionally NOT static */
static char msg[MSGLEN];
static unsigned char utf16_magic[] = {0xFE,0xFE};
static unsigned char utf16bs_magic[] = {0xFF,0xFE};
static unsigned char scsu_magic[] = {0x0E,0xFE,0xFF};
static unsigned char utf8_magic[] = {0xEF,0xBB,0xBF};
static unsigned char utf32_magic[] = {0x00,0x00,0xFE,0xFF};
static unsigned char utfebcdic_magic[] = {0xDD,0x73,0x73,0x73};
static unsigned char utf32bs_magic[] = {0xFF,0xFE,0x00,0x00};
/* Return a Unicode file's type based on the magic number */
int Read_UMagic_Number(int infd)
{
static unsigned char hdr[HDRLEN];
ssize_t nread;
nread=read(infd,hdr,2);
if(nread < 2){
snprintf(msg,MSGLEN-1,"Could not read 2 bytes to check magic number.\n");
perror(msg);
}
if(memcmp(hdr,utf16_magic,2) == 0) return FT_UTF_16;
if(memcmp(hdr,utf16bs_magic,2) == 0){
nread=read(infd,&hdr[2],2);
if(nread < 2){
snprintf(msg,MSGLEN-1,"Could not read 4 bytes to check magic number.\n");
perror(msg);
}
if(memcmp(hdr,utf32bs_magic,4) == 0) return FT_UTF_32BS;
else{
UDataBegin = &hdr[2];
return FT_UTF_16BS;
}
}
nread=read(infd,&hdr[2],1);
if(nread < 1){
snprintf(msg,MSGLEN-1,"Could not read 3 bytes to check magic number.\n");
perror(msg);
}
if(memcmp(hdr,scsu_magic,3) == 0) return FT_SCSU;
if(memcmp(hdr,utf8_magic,3) == 0) return FT_UTF_8;
nread=read(infd,&hdr[3],1);
if(nread < 1){
snprintf(msg,MSGLEN-1,"Could not read 4 bytes to check magic number.\n");
perror(msg);
}
if(memcmp(hdr,utf32_magic,4) == 0) return FT_UTF_32;
if(memcmp(hdr,utfebcdic_magic,4) == 0) return FT_UTF_EBCDIC;
UDataBegin = hdr;
return NOMAGICNUMBER;
}
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