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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>

#include <vfs/canonify.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;

    *tlcomp = *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();

    }

}

/**

 * @}

 */