pgpfiletype.c

来自「著名的加密软件的应用于电子邮件中」· C语言 代码 · 共 210 行

/*
 * pgpFileType.c -- Figure out the type of a file.
 *
 * Copyright (C) 1993-1997 Pretty Good Privacy, Inc. All rights reserved.
 *
 * Written by Colin Plumb.
 *
 * $Id: pgpFileType.c,v 1.1.2.1 1997/06/07 09:51:41 mhw Exp $
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <string.h>	 /* For strcmp */
#include "pgpFileType.h"
#include "pgpPktByte.h"

#define FILETYPELEN	 8	/* # of characters needed */

struct FileTypeInternal {
	unsigned char const pattern[FILETYPELEN]; /* First char is length */
	struct PgpFileType type;
};

/* A character that does not appear in any pattern */
#define ANY	 (unsigned char)255

static struct FileTypeInternal patterns[] =
{
			{ { 2, 26, 11 },	{ "PAK",	".pak", 0 } },
			{ { 2, 31, 139 },	{ "gzip",	".gz", 0 } },
			{ { 2, 31, 157 },	{ "compressed",".Z", 0 } },
			{ { 2, 234, 96 },	{ "Arj",	".arj", 0 } },
					/* ^Z H P % */
			{ { 4,	26, 72, 80,	37 },	{ "Hyper",	".hyp", 0 } },
					/* G I F 8 */
			{ { 4,	71, 73, 70,	56 },	{ "GIF",	".gif", 0 } },
					/* HPAK */
			{ { 4,	72, 80, 65,	75 },	{ "Hpack",	".hpk", 0 } },
					/* P K ^C ^D */
			{ { 4,	80, 75, 3, 4 }, { "Zip",	".zip", 0 } },
					/* Z O O */
			{ { 4,	90, 79, 79, 32 }, { "Zoo",	".zoo", 0 } },
					/* ? ? - l h a 0 -  -lha1- -lha2- and -lha3- */
			{ { 7, ANY, ANY, 45, 108, 104, 48, 45 }, { "LHArc",		".lzh", 0 } },
			{ { 7, ANY, ANY, 45, 108, 104, 49, 45 }, { "LHArc",		".lzh", 0 } },
			{ { 7, ANY, ANY, 45, 108, 104, 50, 45 }, { "LHArc", ".lzh", 0 } },
			{ { 7, ANY, ANY, 45, 108, 104, 51, 45 }, { "LHArc", ".lzh", 0 } },
				 /* ? ? - l h a ? - */
			{ { 7, ANY, ANY, 45, 108, 104, ANY, 45 }, { "LHArc", ".lha", 0 } }
	};

static struct PgpFileType PGPFile = {"PGP", ".pgp", 0};
					/* \250 3 P G P */
static unsigned char const PGPPattern[] = { 5, 168, 3, 80, 71, 80 };

static int
fileTypeMatch (byte const *bytes, byte const *prefix, unsigned len)
	{
			unsigned l = *bytes++;
			unsigned i;

			if (l > len)
				 return 0;
			for (i = 0; i < l; i++)
				 if (bytes[i] != prefix[i] && bytes[i] != ANY)
				 	return 0;
			return 1;	/* Success */
	}

/* Figure out if the file is a recognized type */
struct PgpFileType const *
pgpFileType (byte const *prefix, unsigned len)
	{
			unsigned i;

			for (i = 0; i < sizeof(patterns)/sizeof(*patterns); i++) {
				 if (fileTypeMatch(patterns[i].pattern, prefix, len))
				 	return &patterns[i].type;
			}

			if (pgpFileTypePGP (prefix, len))
				 return &PGPFile;

			return (struct PgpFileType *)0;
}

/*
 * Figure out if a file is a binary PGP file.
 * Returns 1 if it is a PGP file, 0 if it is not.
 */
int
pgpFileTypePGP (byte const *prefix, unsigned len)
	{
			if (!len)
				 return 0;

			/* _All_ PGP messages start with a character 10xxxxxx */
			if (!IS_OLD_PKTBYTE (*prefix))
				 return 0;

			/* Check for a new-style PGP file, using the PGP file header */
			if (fileTypeMatch (PGPPattern, prefix, len))
				 return 1;
				
			/*
			* Check for old-style PGP file, checking the middle bits for
			* known packet types. This needs to match lib/pipe/file/pgpHeader.c
			*/
			switch (OLD_PKTBYTE_TYPE (*prefix)) {
			case PKTBYTE_ESK:
			case PKTBYTE_SIG:
			case PKTBYTE_CONVESK:
			case PKTBYTE_SECKEY:
			case PKTBYTE_PUBKEY:
			case PKTBYTE_SECSUBKEY:
			case PKTBYTE_PUBSUBKEY:
			case PKTBYTE_COMPRESSED:
			case PKTBYTE_CONVENTIONAL:
			case PKTBYTE_LITERAL:
				 /* These are the known packet types */
				 return 1;
			default:
				 /* Its not known -- perhaps something else? */
				 return 0;
			}

			/* NOTREACHED */
			return 0;
	}

/*
 * Figure out if a file is human-readable or not.
 * Returns 0 if text, 1 if binary.
 *
 * A file is considered binary if it contains any illegal control characters
 * or "too many" characters with the 8th bit set. If you're using Latin-1,
 * you might have some such characters, but a binary file probably averages
 * about half odd characters. This test assumes a file is binary if the
 * number of bytes with the high bit set exceeds a quarter of the buffer.
 * EXCEPTION: If working in Russian, Cyrillic is usually placed in the high
 * half, so ignore this test in that case.
 *
 * The legal control characters are:
 * 0 NU null (nul)	ILLEGAL
 * 1 SH start of heading (soh)	ILLEGAL
 * 2 SX start of text (stx)			ILLEGAL
 * 3 EX end of text (etx)	ILLEGAL
 * 4 ET end of transmission (eot)	ILLEGAL
 * 5 EQ enquiry (enq)	ILLEGAL
 * 5 EQ enquiry (enq)	ILLEGAL
 * 6 AK acknowledge (ack)	ILLEGAL
 * 7 BL bell (bel)	legal		'\a'
 * 8 BS backspace (bs)	legal		'\b'
 * 9 HT character tabulation (ht)	legal		'\t'
 * 10 LF line feed (lf)	legal		'\n'
 * 11 VT line tabulation (vt)	legal		'\v'
 * 12 FF form feed (ff)	legal		'\f'
 * 13 CR carriage return (cr)	legal		'\r'
 * 14 SO shift out (so)	ILLEGAL
 * 15 SI shift in (si)	ILLEGAL
 * 16 DL datalink escape (dle)	ILLEGAL
 * 17 D1 device control one (dc1)	ILLEGAL
 * 18 D2 device control two (dc2)	ILLEGAL
 * 19 D3 device control three (dc3)	ILLEGAL
 * 20 D4 device control four (dc4)	ILLEGAL
 * 21 NK negative acknowledge (nak)	ILLEGAL
 * 22 SY syncronous idle (syn)	ILLEGAL
 * 23 EB end of transmission block (etb) ILLEGAL
 * 24 CN cancel (can) ILLEGAL
 * 25 EM end of medium (em) ILLEGAL
 * 26 SB substitute (sub) legal (CP/M & MS-DOS EOF)
 * 27 EC escape (esc) ILLEGAL
 * 28 FS file separator (is4)	ILLEGAL
 * 29 GS group separator (is3)	ILLEGAL
 * 30 RS record separator (is2)	ILLEGAL
 * 31 US unit separator (is1)	ILLEGAL
 *
 * TODO: Worry about EBCDIC
 * TODO: Use the charset rather than the language to decide.
 * TODO: Worry about shift-JIS and other heavy top-8-bit uses.
 */
int
pgpFileTypeBinary(char const *lang, byte const *buf, unsigned len)
	{
			unsigned highlimit;
			char c;

			if (!len)
				 return 1;		/* empty file or error, not a text file */
			if (pgpFileType(buf, len))
				 return 1;

			/* Limit on number of 8th-bit-set characters allowed */
			highlimit = len/4;
			if (lang && strcmp(lang, "ru") == 0)
					highlimit = len;

			do {
					c = *buf++;
					if (c < ' ' && (c < '\a' || c > '\r') && c != 26)
						return 1;	/* Illegal control char */
					if ((c & 0x80) && highlimit-- == 0)
						return 1;	/* Too many 8th bits set */
			} while (--len);

			return 0;
}