pathfind.c revision 285612 
1/*  -*- Mode: C -*-  */
2
3/* pathfind.c --- find a FILE  MODE along PATH */
4
5/* Author: Gary V Vaughan <gvaughan@oranda.demon.co.uk> */
6
7/* Code: */
8
9static char *
10pathfind( char const * path,
11          char const * fname,
12          char const * mode );
13
14#include "compat.h"
15#ifndef HAVE_PATHFIND
16#if defined(__windows__) && !defined(__CYGWIN__)
17static char *
18pathfind( char const * path,
19          char const * fname,
20          char const * mode )
21{
22    return strdup(fname);
23}
24#else
25
26static char * make_absolute(char const * string, char const * dot_path);
27static char * canonicalize_pathname(char * path);
28static char * extract_colon_unit(char * dir, char const * string, int * p_index);
29
30/**
31 * local implementation of pathfind.
32 * @param[in] path  colon separated list of directories
33 * @param[in] fname the name we are hunting for
34 * @param[in] mode  the required file mode
35 * @returns an allocated string with the full path, or NULL
36 */
37static char *
38pathfind( char const * path,
39          char const * fname,
40          char const * mode )
41{
42    int    p_index   = 0;
43    int    mode_bits = 0;
44    char * res_path  = NULL;
45    char   zPath[ AG_PATH_MAX + 1 ];
46
47    if (strchr( mode, 'r' )) mode_bits |= R_OK;
48    if (strchr( mode, 'w' )) mode_bits |= W_OK;
49    if (strchr( mode, 'x' )) mode_bits |= X_OK;
50
51    /*
52     *  FOR each non-null entry in the colon-separated path, DO ...
53     */
54    for (;;) {
55        DIR  * dirP;
56        char * colon_unit = extract_colon_unit( zPath, path, &p_index );
57
58        if (colon_unit == NULL)
59            break;
60
61        dirP = opendir( colon_unit );
62
63        /*
64         *  IF the directory is inaccessable, THEN next directory
65         */
66        if (dirP == NULL)
67            continue;
68
69        for (;;) {
70            struct dirent *entP = readdir( dirP );
71
72            if (entP == (struct dirent *)NULL)
73                break;
74
75            /*
76             *  IF the file name matches the one we are looking for, ...
77             */
78            if (strcmp(entP->d_name, fname) == 0) {
79                char * abs_name = make_absolute(fname, colon_unit);
80
81                /*
82                 *  Make sure we can access it in the way we want
83                 */
84                if (access(abs_name, mode_bits) >= 0) {
85                    /*
86                     *  We can, so normalize the name and return it below
87                     */
88                    res_path = canonicalize_pathname(abs_name);
89                }
90
91                free(abs_name);
92                break;
93            }
94        }
95
96        closedir( dirP );
97
98        if (res_path != NULL)
99            break;
100    }
101
102    return res_path;
103}
104
105/*
106 * Turn STRING  (a pathname) into an  absolute  pathname, assuming  that
107 * DOT_PATH contains the symbolic location of  `.'.  This always returns
108 * a new string, even if STRING was an absolute pathname to begin with.
109 */
110static char *
111make_absolute( char const * string, char const * dot_path )
112{
113    char * result;
114    int result_len;
115
116    if (!dot_path || *string == '/') {
117        result = strdup( string );
118    } else {
119        if (dot_path && dot_path[0]) {
120            result = malloc( 2 + strlen( dot_path ) + strlen( string ) );
121            strcpy( result, dot_path );
122            result_len = (int)strlen(result);
123            if (result[result_len - 1] != '/') {
124                result[result_len++] = '/';
125                result[result_len] = '\0';
126            }
127        } else {
128            result = malloc( 3 + strlen( string ) );
129            result[0] = '.'; result[1] = '/'; result[2] = '\0';
130            result_len = 2;
131        }
132
133        strcpy( result + result_len, string );
134    }
135
136    return result;
137}
138
139/*
140 * Canonicalize PATH, and return a  new path.  The new path differs from
141 * PATH in that:
142 *
143 *    Multiple `/'s     are collapsed to a single `/'.
144 *    Leading `./'s     are removed.
145 *    Trailing `/.'s    are removed.
146 *    Trailing `/'s     are removed.
147 *    Non-leading `../'s and trailing `..'s are handled by removing
148 *                    portions of the path.
149 */
150static char *
151canonicalize_pathname( char *path )
152{
153    int i, start;
154    char stub_char, *result;
155
156    /* The result cannot be larger than the input PATH. */
157    result = strdup( path );
158
159    stub_char = (*path == '/') ? '/' : '.';
160
161    /* Walk along RESULT looking for things to compact. */
162    i = 0;
163    while (result[i]) {
164        while (result[i] != '\0' && result[i] != '/')
165            i++;
166
167        start = i++;
168
169        /* If we didn't find any  slashes, then there is nothing left to
170         * do.
171         */
172        if (!result[start])
173            break;
174
175        /* Handle multiple `/'s in a row. */
176        while (result[i] == '/')
177            i++;
178
179#if !defined (apollo)
180        if ((start + 1) != i)
181#else
182        if ((start + 1) != i && (start != 0 || i != 2))
183#endif /* apollo */
184        {
185            strcpy( result + start + 1, result + i );
186            i = start + 1;
187        }
188
189        /* Handle backquoted `/'. */
190        if (start > 0 && result[start - 1] == '\\')
191            continue;
192
193        /* Check for trailing `/', and `.' by itself. */
194        if ((start && !result[i])
195            || (result[i] == '.' && !result[i+1])) {
196            result[--i] = '\0';
197            break;
198        }
199
200        /* Check for `../', `./' or trailing `.' by itself. */
201        if (result[i] == '.') {
202            /* Handle `./'. */
203            if (result[i + 1] == '/') {
204                strcpy( result + i, result + i + 1 );
205                i = (start < 0) ? 0 : start;
206                continue;
207            }
208
209            /* Handle `../' or trailing `..' by itself. */
210            if (result[i + 1] == '.' &&
211                (result[i + 2] == '/' || !result[i + 2])) {
212                while (--start > -1 && result[start] != '/')
213                    ;
214                strcpy( result + start + 1, result + i + 2 );
215                i = (start < 0) ? 0 : start;
216                continue;
217            }
218        }
219    }
220
221    if (!*result) {
222        *result = stub_char;
223        result[1] = '\0';
224    }
225
226    return result;
227}
228
229/*
230 * Given a  string containing units of information separated  by colons,
231 * return the next one  pointed to by (P_INDEX), or NULL if there are no
232 * more.  Advance (P_INDEX) to the character after the colon.
233 */
234static char *
235extract_colon_unit(char * pzDir, char const * string, int * p_index)
236{
237    char * pzDest = pzDir;
238    int    ix     = *p_index;
239
240    if (string == NULL)
241        return NULL;
242
243    if ((unsigned)ix >= strlen( string ))
244        return NULL;
245
246    {
247        char const * pzSrc = string + ix;
248
249        while (*pzSrc == ':')  pzSrc++;
250
251        for (;;) {
252            char ch = (*(pzDest++) = *(pzSrc++));
253            switch (ch) {
254            case ':':
255                pzDest[-1] = NUL;
256                /* FALLTHROUGH */
257            case NUL:
258                goto copy_done;
259            }
260
261            if ((unsigned long)(pzDest - pzDir) >= AG_PATH_MAX)
262                break;
263        } copy_done:;
264
265        ix = (int)(pzSrc - string);
266    }
267
268    if (*pzDir == NUL)
269        return NULL;
270
271    *p_index = ix;
272    return pzDir;
273}
274#endif /* __windows__ / __CYGWIN__ */
275#endif /* HAVE_PATHFIND */
276
277/*
278 * Local Variables:
279 * mode: C
280 * c-file-style: "stroustrup"
281 * indent-tabs-mode: nil
282 * End:
283 * end of compat/pathfind.c */
284