path.c

   1 /*
   2  * I'm tired of doing "vsnprintf()" etc just to open a
   3  * file, so here's a "return static buffer with printf"
   4  * interface for paths.
   5  *
   6  * It's obviously not thread-safe. Sue me. But it's quite
   7  * useful for doing things like
   8  *
   9  *   f = open(mkpath("%s/%s.git", base, name), O_RDONLY);
  10  *
  11  * which is what it's designed for.
  12  */
  13 #include "cache.h"
  14 #include "strbuf.h"
  15
  16 static char bad_path[] = "/bad-path/";
  17
  18 static char *get_pathname(void)
  19 {
  20         static char pathname_array[4][PATH_MAX];
  21         static int index;
  22         return pathname_array[3 & ++index];
  23 }
  24
  25 static char *cleanup_path(char *path)
  26 {
  27         /* Clean it up */
  28         if (!memcmp(path, "./", 2)) {
  29                 path += 2;
  30                 while (*path == '/')
  31                         path++;
  32         }
  33         return path;
  34 }
  35
  36 char *mksnpath(char *buf, size_t n, const char *fmt, ...)
  37 {
  38         va_list args;
  39         unsigned len;
  40
  41         va_start(args, fmt);
  42         len = vsnprintf(buf, n, fmt, args);
  43         va_end(args);
  44         if (len >= n) {
  45                 strlcpy(buf, bad_path, n);
  46                 return buf;
  47         }
  48         return cleanup_path(buf);
  49 }
  50
  51 static char *git_vsnpath(char *buf, size_t n, const char *fmt, va_list args)
  52 {
  53         const char *git_dir = get_git_dir();
  54         size_t len;
  55
  56         len = strlen(git_dir);
  57         if (n < len + 1)
  58                 goto bad;
  59         memcpy(buf, git_dir, len);
  60         if (len && !is_dir_sep(git_dir[len-1]))
  61                 buf[len++] = '/';
  62         len += vsnprintf(buf + len, n - len, fmt, args);
  63         if (len >= n)
  64                 goto bad;
  65         return cleanup_path(buf);
  66 bad:
  67         strlcpy(buf, bad_path, n);
  68         return buf;
  69 }
  70
  71 char *git_snpath(char *buf, size_t n, const char *fmt, ...)
  72 {
  73         va_list args;
  74         va_start(args, fmt);
  75         (void)git_vsnpath(buf, n, fmt, args);
  76         va_end(args);
  77         return buf;
  78 }
  79
  80 char *git_pathdup(const char *fmt, ...)
  81 {
  82         char path[PATH_MAX];
  83         va_list args;
  84         va_start(args, fmt);
  85         (void)git_vsnpath(path, sizeof(path), fmt, args);
  86         va_end(args);
  87         return xstrdup(path);
  88 }
  89
  90 char *mkpath(const char *fmt, ...)
  91 {
  92         va_list args;
  93         unsigned len;
  94         char *pathname = get_pathname();
  95
  96         va_start(args, fmt);
  97         len = vsnprintf(pathname, PATH_MAX, fmt, args);
  98         va_end(args);
  99         if (len >= PATH_MAX)
 100                 return bad_path;
 101         return cleanup_path(pathname);
 102 }
 103
 104 char *git_path(const char *fmt, ...)
 105 {
 106         const char *git_dir = get_git_dir();
 107         char *pathname = get_pathname();
 108         va_list args;
 109         unsigned len;
 110
 111         len = strlen(git_dir);
 112         if (len > PATH_MAX-100)
 113                 return bad_path;
 114         memcpy(pathname, git_dir, len);
 115         if (len && git_dir[len-1] != '/')
 116                 pathname[len++] = '/';
 117         va_start(args, fmt);
 118         len += vsnprintf(pathname + len, PATH_MAX - len, fmt, args);
 119         va_end(args);
 120         if (len >= PATH_MAX)
 121                 return bad_path;
 122         return cleanup_path(pathname);
 123 }
 124
 125 char *git_path_submodule(const char *path, const char *fmt, ...)
 126 {
 127         char *pathname = get_pathname();
 128         struct strbuf buf = STRBUF_INIT;
 129         const char *git_dir;
 130         va_list args;
 131         unsigned len;
 132
 133         len = strlen(path);
 134         if (len > PATH_MAX-100)
 135                 return bad_path;
 136
 137         strbuf_addstr(&buf, path);
 138         if (len && path[len-1] != '/')
 139                 strbuf_addch(&buf, '/');
 140         strbuf_addstr(&buf, ".git");
 141
 142         git_dir = read_gitfile_gently(buf.buf);
 143         if (git_dir) {
 144                 strbuf_reset(&buf);
 145                 strbuf_addstr(&buf, git_dir);
 146         }
 147         strbuf_addch(&buf, '/');
 148
 149         if (buf.len >= PATH_MAX)
 150                 return bad_path;
 151         memcpy(pathname, buf.buf, buf.len + 1);
 152
 153         strbuf_release(&buf);
 154         len = strlen(pathname);
 155
 156         va_start(args, fmt);
 157         len += vsnprintf(pathname + len, PATH_MAX - len, fmt, args);
 158         va_end(args);
 159         if (len >= PATH_MAX)
 160                 return bad_path;
 161         return cleanup_path(pathname);
 162 }
 163
 164 /* git_mkstemp() - create tmp file honoring TMPDIR variable */
 165 int git_mkstemp(char *path, size_t len, const char *template)
 166 {
 167         const char *tmp;
 168         size_t n;
 169
 170         tmp = getenv("TMPDIR");
 171         if (!tmp)
 172                 tmp = "/tmp";
 173         n = snprintf(path, len, "%s/%s", tmp, template);
 174         if (len <= n) {
 175                 errno = ENAMETOOLONG;
 176                 return -1;
 177         }
 178         return mkstemp(path);
 179 }
 180
 181 /* git_mkstemps() - create tmp file with suffix honoring TMPDIR variable. */
 182 int git_mkstemps(char *path, size_t len, const char *template, int suffix_len)
 183 {
 184         const char *tmp;
 185         size_t n;
 186
 187         tmp = getenv("TMPDIR");
 188         if (!tmp)
 189                 tmp = "/tmp";
 190         n = snprintf(path, len, "%s/%s", tmp, template);
 191         if (len <= n) {
 192                 errno = ENAMETOOLONG;
 193                 return -1;
 194         }
 195         return mkstemps(path, suffix_len);
 196 }
 197
 198 /* Adapted from libiberty's mkstemp.c. */
 199
 200 #undef TMP_MAX
 201 #define TMP_MAX 16384
 202
 203 int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
 204 {
 205         static const char letters[] =
 206                 "abcdefghijklmnopqrstuvwxyz"
 207                 "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 208                 "0123456789";
 209         static const int num_letters = 62;
 210         uint64_t value;
 211         struct timeval tv;
 212         char *template;
 213         size_t len;
 214         int fd, count;
 215
 216         len = strlen(pattern);
 217
 218         if (len < 6 + suffix_len) {
 219                 errno = EINVAL;
 220                 return -1;
 221         }
 222
 223         if (strncmp(&pattern[len - 6 - suffix_len], "XXXXXX", 6)) {
 224                 errno = EINVAL;
 225                 return -1;
 226         }
 227
 228         /*
 229          * Replace pattern's XXXXXX characters with randomness.
 230          * Try TMP_MAX different filenames.
 231          */
 232         gettimeofday(&tv, NULL);
 233         value = ((size_t)(tv.tv_usec << 16)) ^ tv.tv_sec ^ getpid();
 234         template = &pattern[len - 6 - suffix_len];
 235         for (count = 0; count < TMP_MAX; ++count) {
 236                 uint64_t v = value;
 237                 /* Fill in the random bits. */
 238                 template[0] = letters[v % num_letters]; v /= num_letters;
 239                 template[1] = letters[v % num_letters]; v /= num_letters;
 240                 template[2] = letters[v % num_letters]; v /= num_letters;
 241                 template[3] = letters[v % num_letters]; v /= num_letters;
 242                 template[4] = letters[v % num_letters]; v /= num_letters;
 243                 template[5] = letters[v % num_letters]; v /= num_letters;
 244
 245                 fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, mode);
 246                 if (fd > 0)
 247                         return fd;
 248                 /*
 249                  * Fatal error (EPERM, ENOSPC etc).
 250                  * It doesn't make sense to loop.
 251                  */
 252                 if (errno != EEXIST)
 253                         break;
 254                 /*
 255                  * This is a random value.  It is only necessary that
 256                  * the next TMP_MAX values generated by adding 7777 to
 257                  * VALUE are different with (module 2^32).
 258                  */
 259                 value += 7777;
 260         }
 261         /* We return the null string if we can't find a unique file name.  */
 262         pattern[0] = '\0';
 263         return -1;
 264 }
 265
 266 int git_mkstemp_mode(char *pattern, int mode)
 267 {
 268         /* mkstemp is just mkstemps with no suffix */
 269         return git_mkstemps_mode(pattern, 0, mode);
 270 }
 271
 272 int gitmkstemps(char *pattern, int suffix_len)
 273 {
 274         return git_mkstemps_mode(pattern, suffix_len, 0600);
 275 }
 276
 277 int validate_headref(const char *path)
 278 {
 279         struct stat st;
 280         char *buf, buffer[256];
 281         unsigned char sha1[20];
 282         int fd;
 283         ssize_t len;
 284
 285         if (lstat(path, &st) < 0)
 286                 return -1;
 287
 288         /* Make sure it is a "refs/.." symlink */
 289         if (S_ISLNK(st.st_mode)) {
 290                 len = readlink(path, buffer, sizeof(buffer)-1);
 291                 if (len >= 5 && !memcmp("refs/", buffer, 5))
 292                         return 0;
 293                 return -1;
 294         }
 295
 296         /*
 297          * Anything else, just open it and try to see if it is a symbolic ref.
 298          */
 299         fd = open(path, O_RDONLY);
 300         if (fd < 0)
 301                 return -1;
 302         len = read_in_full(fd, buffer, sizeof(buffer)-1);
 303         close(fd);
 304
 305         /*
 306          * Is it a symbolic ref?
 307          */
 308         if (len < 4)
 309                 return -1;
 310         if (!memcmp("ref:", buffer, 4)) {
 311                 buf = buffer + 4;
 312                 len -= 4;
 313                 while (len && isspace(*buf))
 314                         buf++, len--;
 315                 if (len >= 5 && !memcmp("refs/", buf, 5))
 316                         return 0;
 317         }
 318
 319         /*
 320          * Is this a detached HEAD?
 321          */
 322         if (!get_sha1_hex(buffer, sha1))
 323                 return 0;
 324
 325         return -1;
 326 }
 327
 328 static struct passwd *getpw_str(const char *username, size_t len)
 329 {
 330         struct passwd *pw;
 331         char *username_z = xmalloc(len + 1);
 332         memcpy(username_z, username, len);
 333         username_z[len] = '\0';
 334         pw = getpwnam(username_z);
 335         free(username_z);
 336         return pw;
 337 }
 338
 339 /*
 340  * Return a string with ~ and ~user expanded via getpw*.  If buf != NULL,
 341  * then it is a newly allocated string. Returns NULL on getpw failure or
 342  * if path is NULL.
 343  */
 344 char *expand_user_path(const char *path)
 345 {
 346         struct strbuf user_path = STRBUF_INIT;
 347         const char *first_slash = strchrnul(path, '/');
 348         const char *to_copy = path;
 349
 350         if (path == NULL)
 351                 goto return_null;
 352         if (path[0] == '~') {
 353                 const char *username = path + 1;
 354                 size_t username_len = first_slash - username;
 355                 if (username_len == 0) {
 356                         const char *home = getenv("HOME");
 357                         strbuf_add(&user_path, home, strlen(home));
 358                 } else {
 359                         struct passwd *pw = getpw_str(username, username_len);
 360                         if (!pw)
 361                                 goto return_null;
 362                         strbuf_add(&user_path, pw->pw_dir, strlen(pw->pw_dir));
 363                 }
 364                 to_copy = first_slash;
 365         }
 366         strbuf_add(&user_path, to_copy, strlen(to_copy));
 367         return strbuf_detach(&user_path, NULL);
 368 return_null:
 369         strbuf_release(&user_path);
 370         return NULL;
 371 }
 372
 373 /*
 374  * First, one directory to try is determined by the following algorithm.
 375  *
 376  * (0) If "strict" is given, the path is used as given and no DWIM is
 377  *     done. Otherwise:
 378  * (1) "~/path" to mean path under the running user's home directory;
 379  * (2) "~user/path" to mean path under named user's home directory;
 380  * (3) "relative/path" to mean cwd relative directory; or
 381  * (4) "/absolute/path" to mean absolute directory.
 382  *
 383  * Unless "strict" is given, we try access() for existence of "%s.git/.git",
 384  * "%s/.git", "%s.git", "%s" in this order.  The first one that exists is
 385  * what we try.
 386  *
 387  * Second, we try chdir() to that.  Upon failure, we return NULL.
 388  *
 389  * Then, we try if the current directory is a valid git repository.
 390  * Upon failure, we return NULL.
 391  *
 392  * If all goes well, we return the directory we used to chdir() (but
 393  * before ~user is expanded), avoiding getcwd() resolving symbolic
 394  * links.  User relative paths are also returned as they are given,
 395  * except DWIM suffixing.
 396  */
 397 char *enter_repo(char *path, int strict)
 398 {
 399         static char used_path[PATH_MAX];
 400         static char validated_path[PATH_MAX];
 401
 402         if (!path)
 403                 return NULL;
 404
 405         if (!strict) {
 406                 static const char *suffix[] = {
 407                         ".git/.git", "/.git", ".git", "", NULL,
 408                 };
 409                 int len = strlen(path);
 410                 int i;
 411                 while ((1 < len) && (path[len-1] == '/')) {
 412                         path[len-1] = 0;
 413                         len--;
 414                 }
 415                 if (PATH_MAX <= len)
 416                         return NULL;
 417                 if (path[0] == '~') {
 418                         char *newpath = expand_user_path(path);
 419                         if (!newpath || (PATH_MAX - 10 < strlen(newpath))) {
 420                                 free(newpath);
 421                                 return NULL;
 422                         }
 423                         /*
 424                          * Copy back into the static buffer. A pity
 425                          * since newpath was not bounded, but other
 426                          * branches of the if are limited by PATH_MAX
 427                          * anyway.
 428                          */
 429                         strcpy(used_path, newpath); free(newpath);
 430                         strcpy(validated_path, path);
 431                         path = used_path;
 432                 }
 433                 else if (PATH_MAX - 10 < len)
 434                         return NULL;
 435                 else {
 436                         path = strcpy(used_path, path);
 437                         strcpy(validated_path, path);
 438                 }
 439                 len = strlen(path);
 440                 for (i = 0; suffix[i]; i++) {
 441                         strcpy(path + len, suffix[i]);
 442                         if (!access(path, F_OK)) {
 443                                 strcat(validated_path, suffix[i]);
 444                                 break;
 445                         }
 446                 }
 447                 if (!suffix[i] || chdir(path))
 448                         return NULL;
 449                 path = validated_path;
 450         }
 451         else if (chdir(path))
 452                 return NULL;
 453
 454         if (access("objects", X_OK) == 0 && access("refs", X_OK) == 0 &&
 455             validate_headref("HEAD") == 0) {
 456                 set_git_dir(".");
 457                 check_repository_format();
 458                 return path;
 459         }
 460
 461         return NULL;
 462 }
 463
 464 int set_shared_perm(const char *path, int mode)
 465 {
 466         struct stat st;
 467         int tweak, shared, orig_mode;
 468
 469         if (!shared_repository) {
 470                 if (mode)
 471                         return chmod(path, mode & ~S_IFMT);
 472                 return 0;
 473         }
 474         if (!mode) {
 475                 if (lstat(path, &st) < 0)
 476                         return -1;
 477                 mode = st.st_mode;
 478                 orig_mode = mode;
 479         } else
 480                 orig_mode = 0;
 481         if (shared_repository < 0)
 482                 shared = -shared_repository;
 483         else
 484                 shared = shared_repository;
 485         tweak = shared;
 486
 487         if (!(mode & S_IWUSR))
 488                 tweak &= ~0222;
 489         if (mode & S_IXUSR)
 490                 /* Copy read bits to execute bits */
 491                 tweak |= (tweak & 0444) >> 2;
 492         if (shared_repository < 0)
 493                 mode = (mode & ~0777) | tweak;
 494         else
 495                 mode |= tweak;
 496
 497         if (S_ISDIR(mode)) {
 498                 /* Copy read bits to execute bits */
 499                 mode |= (shared & 0444) >> 2;
 500                 mode |= FORCE_DIR_SET_GID;
 501         }
 502
 503         if (((shared_repository < 0
 504               ? (orig_mode & (FORCE_DIR_SET_GID | 0777))
 505               : (orig_mode & mode)) != mode) &&
 506             chmod(path, (mode & ~S_IFMT)) < 0)
 507                 return -2;
 508         return 0;
 509 }
 510
 511 const char *make_relative_path(const char *abs, const char *base)
 512 {
 513         static char buf[PATH_MAX + 1];
 514         int i = 0, j = 0;
 515
 516         if (!base || !base[0])
 517                 return abs;
 518         while (base[i]) {
 519                 if (is_dir_sep(base[i])) {
 520                         if (!is_dir_sep(abs[j]))
 521                                 return abs;
 522                         while (is_dir_sep(base[i]))
 523                                 i++;
 524                         while (is_dir_sep(abs[j]))
 525                                 j++;
 526                         continue;
 527                 } else if (abs[j] != base[i]) {
 528                         return abs;
 529                 }
 530                 i++;
 531                 j++;
 532         }
 533         if (
 534             /* "/foo" is a prefix of "/foo" */
 535             abs[j] &&
 536             /* "/foo" is not a prefix of "/foobar" */
 537             !is_dir_sep(base[i-1]) && !is_dir_sep(abs[j])
 538            )
 539                 return abs;
 540         while (is_dir_sep(abs[j]))
 541                 j++;
 542         if (!abs[j])
 543                 strcpy(buf, ".");
 544         else
 545                 strcpy(buf, abs + j);
 546         return buf;
 547 }
 548
 549 /*
 550  * It is okay if dst == src, but they should not overlap otherwise.
 551  *
 552  * Performs the following normalizations on src, storing the result in dst:
 553  * - Ensures that components are separated by '/' (Windows only)
 554  * - Squashes sequences of '/'.
 555  * - Removes "." components.
 556  * - Removes ".." components, and the components the precede them.
 557  * Returns failure (non-zero) if a ".." component appears as first path
 558  * component anytime during the normalization. Otherwise, returns success (0).
 559  *
 560  * Note that this function is purely textual.  It does not follow symlinks,
 561  * verify the existence of the path, or make any system calls.
 562  */
 563 int normalize_path_copy(char *dst, const char *src)
 564 {
 565         char *dst0;
 566
 567         if (has_dos_drive_prefix(src)) {
 568                 *dst++ = *src++;
 569                 *dst++ = *src++;
 570         }
 571         dst0 = dst;
 572
 573         if (is_dir_sep(*src)) {
 574                 *dst++ = '/';
 575                 while (is_dir_sep(*src))
 576                         src++;
 577         }
 578
 579         for (;;) {
 580                 char c = *src;
 581
 582                 /*
 583                  * A path component that begins with . could be
 584                  * special:
 585                  * (1) "." and ends   -- ignore and terminate.
 586                  * (2) "./"           -- ignore them, eat slash and continue.
 587                  * (3) ".." and ends  -- strip one and terminate.
 588                  * (4) "../"          -- strip one, eat slash and continue.
 589                  */
 590                 if (c == '.') {
 591                         if (!src[1]) {
 592                                 /* (1) */
 593                                 src++;
 594                         } else if (is_dir_sep(src[1])) {
 595                                 /* (2) */
 596                                 src += 2;
 597                                 while (is_dir_sep(*src))
 598                                         src++;
 599                                 continue;
 600                         } else if (src[1] == '.') {
 601                                 if (!src[2]) {
 602                                         /* (3) */
 603                                         src += 2;
 604                                         goto up_one;
 605                                 } else if (is_dir_sep(src[2])) {
 606                                         /* (4) */
 607                                         src += 3;
 608                                         while (is_dir_sep(*src))
 609                                                 src++;
 610                                         goto up_one;
 611                                 }
 612                         }
 613                 }
 614
 615                 /* copy up to the next '/', and eat all '/' */
 616                 while ((c = *src++) != '\0' && !is_dir_sep(c))
 617                         *dst++ = c;
 618                 if (is_dir_sep(c)) {
 619                         *dst++ = '/';
 620                         while (is_dir_sep(c))
 621                                 c = *src++;
 622                         src--;
 623                 } else if (!c)
 624                         break;
 625                 continue;
 626
 627         up_one:
 628                 /*
 629                  * dst0..dst is prefix portion, and dst[-1] is '/';
 630                  * go up one level.
 631                  */
 632                 dst--;  /* go to trailing '/' */
 633                 if (dst <= dst0)
 634                         return -1;
 635                 /* Windows: dst[-1] cannot be backslash anymore */
 636                 while (dst0 < dst && dst[-1] != '/')
 637                         dst--;
 638         }
 639         *dst = '\0';
 640         return 0;
 641 }
 642
 643 /*
 644  * path = Canonical absolute path
 645  * prefix_list = Colon-separated list of absolute paths
 646  *
 647  * Determines, for each path in prefix_list, whether the "prefix" really
 648  * is an ancestor directory of path.  Returns the length of the longest
 649  * ancestor directory, excluding any trailing slashes, or -1 if no prefix
 650  * is an ancestor.  (Note that this means 0 is returned if prefix_list is
 651  * "/".) "/foo" is not considered an ancestor of "/foobar".  Directories
 652  * are not considered to be their own ancestors.  path must be in a
 653  * canonical form: empty components, or "." or ".." components are not
 654  * allowed.  prefix_list may be null, which is like "".
 655  */
 656 int longest_ancestor_length(const char *path, const char *prefix_list)
 657 {
 658         char buf[PATH_MAX+1];
 659         const char *ceil, *colon;
 660         int len, max_len = -1;
 661
 662         if (prefix_list == NULL || !strcmp(path, "/"))
 663                 return -1;
 664
 665         for (colon = ceil = prefix_list; *colon; ceil = colon+1) {
 666                 for (colon = ceil; *colon && *colon != PATH_SEP; colon++);
 667                 len = colon - ceil;
 668                 if (len == 0 || len > PATH_MAX || !is_absolute_path(ceil))
 669                         continue;
 670                 strlcpy(buf, ceil, len+1);
 671                 if (normalize_path_copy(buf, buf) < 0)
 672                         continue;
 673                 len = strlen(buf);
 674                 if (len > 0 && buf[len-1] == '/')
 675                         buf[--len] = '\0';
 676
 677                 if (!strncmp(path, buf, len) &&
 678                     path[len] == '/' &&
 679                     len > max_len) {
 680                         max_len = len;
 681                 }
 682         }
 683
 684         return max_len;
 685 }
 686
 687 /* strip arbitrary amount of directory separators at end of path */
 688 static inline int chomp_trailing_dir_sep(const char *path, int len)
 689 {
 690         while (len && is_dir_sep(path[len - 1]))
 691                 len--;
 692         return len;
 693 }
 694
 695 /*
 696  * If path ends with suffix (complete path components), returns the
 697  * part before suffix (sans trailing directory separators).
 698  * Otherwise returns NULL.
 699  */
 700 char *strip_path_suffix(const char *path, const char *suffix)
 701 {
 702         int path_len = strlen(path), suffix_len = strlen(suffix);
 703
 704         while (suffix_len) {
 705                 if (!path_len)
 706                         return NULL;
 707
 708                 if (is_dir_sep(path[path_len - 1])) {
 709                         if (!is_dir_sep(suffix[suffix_len - 1]))
 710                                 return NULL;
 711                         path_len = chomp_trailing_dir_sep(path, path_len);
 712                         suffix_len = chomp_trailing_dir_sep(suffix, suffix_len);
 713                 }
 714                 else if (path[--path_len] != suffix[--suffix_len])
 715                         return NULL;
 716         }
 717
 718         if (path_len && !is_dir_sep(path[path_len - 1]))
 719                 return NULL;
 720         return xstrndup(path, chomp_trailing_dir_sep(path, path_len));
 721 }
 722
 723 int daemon_avoid_alias(const char *p)
 724 {
 725         int sl, ndot;
 726
 727         /*
 728          * This resurrects the belts and suspenders paranoia check by HPA
 729          * done in <435560F7.4080006@zytor.com> thread, now enter_repo()
 730          * does not do getcwd() based path canonicalization.
 731          *
 732          * sl becomes true immediately after seeing '/' and continues to
 733          * be true as long as dots continue after that without intervening
 734          * non-dot character.
 735          */
 736         if (!p || (*p != '/' && *p != '~'))
 737                 return -1;
 738         sl = 1; ndot = 0;
 739         p++;
 740
 741         while (1) {
 742                 char ch = *p++;
 743                 if (sl) {
 744                         if (ch == '.')
 745                                 ndot++;
 746                         else if (ch == '/') {
 747                                 if (ndot < 3)
 748                                         /* reject //, /./ and /../ */
 749                                         return -1;
 750                                 ndot = 0;
 751                         }
 752                         else if (ch == 0) {
 753                                 if (0 < ndot && ndot < 3)
 754                                         /* reject /.$ and /..$ */
 755                                         return -1;
 756                                 return 0;
 757                         }
 758                         else
 759                                 sl = ndot = 0;
 760                 }
 761                 else if (ch == 0)
 762                         return 0;
 763                 else if (ch == '/') {
 764                         sl = 1;
 765                         ndot = 0;
 766                 }
 767         }
 768 }
 769
 770 int offset_1st_component(const char *path)
 771 {
 772         if (has_dos_drive_prefix(path))
 773                 return 2 + is_dir_sep(path[2]);
 774         return is_dir_sep(path[0]);
 775 }