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/*

 * Copyright (c) 2008 Jakub Jermar

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * - Redistributions of source code must retain the above copyright

 *   notice, this list of conditions and the following disclaimer.

 * - Redistributions in binary form must reproduce the above copyright

 *   notice, this list of conditions and the following disclaimer in the

 *   documentation and/or other materials provided with the distribution.

 * - The name of the author may not be used to endorse or promote products

 *   derived from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

/** @addtogroup libc 

 * @{

 */ 

/**

 * @file

 * @brief

 */

#include <stdlib.h>

/** Token types used for tokenization of path. */

typedef enum {

	TK_INVALID,

	TK_SLASH,

	TK_DOT,

	TK_DOTDOT,

	TK_COMP,

	TK_NUL

} tokval_t;

typedef struct {

	tokval_t kind;

	char *start;

	char *stop;

} token_t;

/** Fake up the TK_SLASH token. */

static token_t slash_token(char *start)

{

	token_t ret;

	ret.kind = TK_SLASH;

	ret.start = start;

	ret.stop = start;

	return ret;

}

/** Given a token, return the next token. */

static token_t next_token(token_t *cur)

{

	token_t ret;

	if (cur->stop[1] == '\0') {

		ret.kind = TK_NUL;

		ret.start = cur->stop + 1;

		ret.stop = ret.start;

		return ret;

	}

	if (cur->stop[1] == '/') {

		ret.kind = TK_SLASH;

		ret.start = cur->stop + 1;

		ret.stop = ret.start;

		return ret;

	}

	if (cur->stop[1] == '.' && (!cur->stop[2] || cur->stop[2] == '/')) {

		ret.kind = TK_DOT;

		ret.start = cur->stop + 1;

		ret.stop = ret.start;

		return ret;

	}

	if (cur->stop[1] == '.' && cur->stop[2] == '.' &&

	    (!cur->stop[3] || cur->stop[3] == '/')) {

		ret.kind = TK_DOTDOT;

		ret.start = cur->stop + 1;

		ret.stop = cur->stop + 2;

		return ret;

	}

	unsigned i;

	for (i = 1; cur->stop[i] && cur->stop[i] != '/'; i++)

		;

	ret.kind = TK_COMP;

	ret.start = &cur->stop[1];

	ret.stop = &cur->stop[i - 1];

	return ret;

}

/** States used by canonify(). */

typedef enum {

	S_INI,

	S_A,

	S_B,

	S_C,

	S_ACCEPT,

	S_RESTART,

	S_REJECT

} state_t;

typedef struct {

	state_t s;

	void (* f)(token_t *, token_t *, token_t *);

} change_state_t;

/*

 * Actions that can be performed when transitioning from one

 * state of canonify() to another.

 */

static void set_first_slash(token_t *t, token_t *tfsl, token_t *tlcomp)

{

	*tfsl = *t;

}

static void save_component(token_t *t, token_t *tfsl, token_t *tlcomp)

{

	*tlcomp = *t;

}

static void terminate_slash(token_t *t, token_t *tfsl, token_t *tlcomp)

{

	if (tfsl->stop[1])	/* avoid writing to a well-formatted path */

		tfsl->stop[1] = '\0';

}

static void remove_trailing_slash(token_t *t, token_t *tfsl, token_t *tlcomp)

{

	t->start[-1] = '\0';

}

/** Eat the extra '/'..

 *

 * @param t		The current TK_SLASH token.

 */

static void shift_slash(token_t *t, token_t *tfsl, token_t *tlcomp)

{

	char *p = t->start;

	char *q = t->stop + 1;

	while ((*p++ = *q++))

		;

}

/** Eat the extra '.'.

 *

 * @param t		The current TK_DOT token.

 */

static void shift_dot(token_t *t, token_t *tfsl, token_t *tlcomp)

{

	char *p = t->start;

	char *q = t->stop + 1;

	while ((*p++ = *q++))

		;

}

/** Collapse the TK_COMP TK_SLASH TK_DOTDOT pattern.

 *

 * @param t		The current TK_DOTDOT token.

 * @param tlcomp	The last TK_COMP token.

 */

static void shift_dotdot(token_t *t, token_t *tfsl, token_t *tlcomp)

{

	char *p = tlcomp->start;

	char *q = t->stop + 1;

	while ((*p++ = *q++))

		;

}

/** Transition function for canonify(). */

static change_state_t trans[4][6] = {

	[S_INI] = {

		[TK_SLASH] = {

			.s = S_A,

			.f = set_first_slash,

		},

		[TK_DOT] = {

			.s = S_REJECT,

			.f = NULL,

		},

		[TK_DOTDOT] = {

			.s = S_REJECT,

			.f = NULL,

		},

		[TK_COMP] = {

			.s = S_REJECT,

			.f = NULL,

		},

		[TK_NUL] = {

			.s = S_REJECT,

			.f = NULL,

		},

		[TK_INVALID] = {

			.s = S_REJECT,

			.f = NULL,

		},

	},

	[S_A] = {

		[TK_SLASH] = {

			.s = S_A,

			.f = set_first_slash,

		},

		[TK_DOT] = {

			.s = S_A,

			.f = NULL,

		},

		[TK_DOTDOT] = {

			.s = S_A,

			.f = NULL,

		},

		[TK_COMP] = {

			.s = S_B,

			.f = save_component,

		},

		[TK_NUL] = {

			.s = S_ACCEPT,

			.f = terminate_slash,

		},

		[TK_INVALID] = {

			.s = S_REJECT,

			.f = NULL,

		},

	},

	[S_B] = {

		[TK_SLASH] = {

			.s = S_C,

			.f = NULL,

		},

		[TK_DOT] = {

			.s = S_REJECT,

			.f = NULL,

		},

		[TK_DOTDOT] = {

			.s = S_REJECT,

			.f = NULL,

		},

		[TK_COMP] = {

			.s = S_REJECT,

			.f = NULL,

		},

		[TK_NUL] = {

			.s = S_ACCEPT,

			.f = NULL,

		},

		[TK_INVALID] = {

			.s = S_REJECT,

			.f = NULL,

		},

	},

	[S_C] = {

		[TK_SLASH] = {

			.s = S_RESTART,

			.f = shift_slash,

		},

		[TK_DOT] = {

			.s = S_RESTART,

			.f = shift_dot,

		},

		[TK_DOTDOT] = {

			.s = S_RESTART,

			.f = shift_dotdot,

		},

		[TK_COMP] = {

			.s = S_B,

			.f = save_component,

		},

		[TK_NUL] = {

			.s = S_ACCEPT,

			.f = remove_trailing_slash,

		},

		[TK_INVALID] = {

			.s = S_REJECT,

			.f = NULL,

		},

	}

};

/** Canonify a file system path.

 *

 * A file system path is canonical, if the following holds:

 * 1) the path is absolute (i.e. a/b/c is not canonical)

 * 2) there is no trailing slash in the path (i.e. /a/b/c is not canonical)

 * 3) there is no extra slash in the path (i.e. /a//b/c is not canonical)

 * 4) there is no '.' component in the path (i.e. /a/./b/c is not canonical)

 * 5) there is no '..' component in the path (i.e. /a/b/../c is not canonical) 

 *

 * This function makes a potentially non-canonical file system path canonical.

 * It works in-place and requires a NULL-terminated input string.

 *

 * @param path		Path to be canonified.

 * @param lenp		Pointer where the length of the final path will be

 *			stored. Can be NULL.

 *

 * @return		Canonified path or NULL on failure.

 */

char *canonify(char *path, size_t *lenp)

{

	state_t state;

	token_t t;

	token_t tfsl;		/* first slash */

	token_t tlcomp;		/* last component */

	if (*path != '/')

		return NULL;

	tfsl = slash_token(path);

restart:

	state = S_INI;

	t = tfsl;

	tlcomp = tfsl;

	while (state != S_ACCEPT && state != S_RESTART && state != S_REJECT) {

		if (trans[state][t.kind].f)

			trans[state][t.kind].f(&t, &tfsl, &tlcomp);

		state = trans[state][t.kind].s;

		t = next_token(&t);

	}

	switch (state) {

	case S_RESTART:

		goto restart;

	case S_REJECT:

		return NULL;

	case S_ACCEPT:

		if (lenp)

			*lenp = (size_t)((tlcomp.stop - tfsl.start) + 1);

		return tfsl.start; 

	default:

		abort();

	}

}

/**

 * @}

 */