path.c

   1 /*
   2  * Utilities for paths and pathnames
   3  */
   4 #include "cache.h"
   5 #include "strbuf.h"
   6 #include "string-list.h"
   7
   8 static int get_st_mode_bits(const char *path, int *mode)
   9 {
  10         struct stat st;
  11         if (lstat(path, &st) < 0)
  12                 return -1;
  13         *mode = st.st_mode;
  14         return 0;
  15 }
  16
  17 static char bad_path[] = "/bad-path/";
  18
  19 static char *get_pathname(void)
  20 {
  21         static char pathname_array[4][PATH_MAX];
  22         static int index;
  23         return pathname_array[3 & ++index];
  24 }
  25
  26 static char *cleanup_path(char *path)
  27 {
  28         /* Clean it up */
  29         if (!memcmp(path, "./", 2)) {
  30                 path += 2;
  31                 while (*path == '/')
  32                         path++;
  33         }
  34         return path;
  35 }
  36
  37 char *mksnpath(char *buf, size_t n, const char *fmt, ...)
  38 {
  39         va_list args;
  40         unsigned len;
  41
  42         va_start(args, fmt);
  43         len = vsnprintf(buf, n, fmt, args);
  44         va_end(args);
  45         if (len >= n) {
  46                 strlcpy(buf, bad_path, n);
  47                 return buf;
  48         }
  49         return cleanup_path(buf);
  50 }
  51
  52 static char *vsnpath(char *buf, size_t n, const char *fmt, va_list args)
  53 {
  54         const char *git_dir = get_git_dir();
  55         size_t len;
  56
  57         len = strlen(git_dir);
  58         if (n < len + 1)
  59                 goto bad;
  60         memcpy(buf, git_dir, len);
  61         if (len && !is_dir_sep(git_dir[len-1]))
  62                 buf[len++] = '/';
  63         len += vsnprintf(buf + len, n - len, fmt, args);
  64         if (len >= n)
  65                 goto bad;
  66         return cleanup_path(buf);
  67 bad:
  68         strlcpy(buf, bad_path, n);
  69         return buf;
  70 }
  71
  72 char *git_snpath(char *buf, size_t n, const char *fmt, ...)
  73 {
  74         char *ret;
  75         va_list args;
  76         va_start(args, fmt);
  77         ret = vsnpath(buf, n, fmt, args);
  78         va_end(args);
  79         return ret;
  80 }
  81
  82 char *git_pathdup(const char *fmt, ...)
  83 {
  84         char path[PATH_MAX], *ret;
  85         va_list args;
  86         va_start(args, fmt);
  87         ret = vsnpath(path, sizeof(path), fmt, args);
  88         va_end(args);
  89         return xstrdup(ret);
  90 }
  91
  92 char *mkpathdup(const char *fmt, ...)
  93 {
  94         char *path;
  95         struct strbuf sb = STRBUF_INIT;
  96         va_list args;
  97
  98         va_start(args, fmt);
  99         strbuf_vaddf(&sb, fmt, args);
 100         va_end(args);
 101         path = xstrdup(cleanup_path(sb.buf));
 102
 103         strbuf_release(&sb);
 104         return path;
 105 }
 106
 107 char *mkpath(const char *fmt, ...)
 108 {
 109         va_list args;
 110         unsigned len;
 111         char *pathname = get_pathname();
 112
 113         va_start(args, fmt);
 114         len = vsnprintf(pathname, PATH_MAX, fmt, args);
 115         va_end(args);
 116         if (len >= PATH_MAX)
 117                 return bad_path;
 118         return cleanup_path(pathname);
 119 }
 120
 121 char *git_path(const char *fmt, ...)
 122 {
 123         char *pathname = get_pathname();
 124         va_list args;
 125         char *ret;
 126
 127         va_start(args, fmt);
 128         ret = vsnpath(pathname, PATH_MAX, fmt, args);
 129         va_end(args);
 130         return ret;
 131 }
 132
 133 char *git_path_submodule(const char *path, const char *fmt, ...)
 134 {
 135         char *pathname = get_pathname();
 136         struct strbuf buf = STRBUF_INIT;
 137         const char *git_dir;
 138         va_list args;
 139         unsigned len;
 140
 141         len = strlen(path);
 142         if (len > PATH_MAX-100)
 143                 return bad_path;
 144
 145         strbuf_addstr(&buf, path);
 146         if (len && path[len-1] != '/')
 147                 strbuf_addch(&buf, '/');
 148         strbuf_addstr(&buf, ".git");
 149
 150         git_dir = read_gitfile(buf.buf);
 151         if (git_dir) {
 152                 strbuf_reset(&buf);
 153                 strbuf_addstr(&buf, git_dir);
 154         }
 155         strbuf_addch(&buf, '/');
 156
 157         if (buf.len >= PATH_MAX)
 158                 return bad_path;
 159         memcpy(pathname, buf.buf, buf.len + 1);
 160
 161         strbuf_release(&buf);
 162         len = strlen(pathname);
 163
 164         va_start(args, fmt);
 165         len += vsnprintf(pathname + len, PATH_MAX - len, fmt, args);
 166         va_end(args);
 167         if (len >= PATH_MAX)
 168                 return bad_path;
 169         return cleanup_path(pathname);
 170 }
 171
 172 int validate_headref(const char *path)
 173 {
 174         struct stat st;
 175         char *buf, buffer[256];
 176         unsigned char sha1[20];
 177         int fd;
 178         ssize_t len;
 179
 180         if (lstat(path, &st) < 0)
 181                 return -1;
 182
 183         /* Make sure it is a "refs/.." symlink */
 184         if (S_ISLNK(st.st_mode)) {
 185                 len = readlink(path, buffer, sizeof(buffer)-1);
 186                 if (len >= 5 && !memcmp("refs/", buffer, 5))
 187                         return 0;
 188                 return -1;
 189         }
 190
 191         /*
 192          * Anything else, just open it and try to see if it is a symbolic ref.
 193          */
 194         fd = open(path, O_RDONLY);
 195         if (fd < 0)
 196                 return -1;
 197         len = read_in_full(fd, buffer, sizeof(buffer)-1);
 198         close(fd);
 199
 200         /*
 201          * Is it a symbolic ref?
 202          */
 203         if (len < 4)
 204                 return -1;
 205         if (!memcmp("ref:", buffer, 4)) {
 206                 buf = buffer + 4;
 207                 len -= 4;
 208                 while (len && isspace(*buf))
 209                         buf++, len--;
 210                 if (len >= 5 && !memcmp("refs/", buf, 5))
 211                         return 0;
 212         }
 213
 214         /*
 215          * Is this a detached HEAD?
 216          */
 217         if (!get_sha1_hex(buffer, sha1))
 218                 return 0;
 219
 220         return -1;
 221 }
 222
 223 static struct passwd *getpw_str(const char *username, size_t len)
 224 {
 225         struct passwd *pw;
 226         char *username_z = xmemdupz(username, len);
 227         pw = getpwnam(username_z);
 228         free(username_z);
 229         return pw;
 230 }
 231
 232 /*
 233  * Return a string with ~ and ~user expanded via getpw*.  If buf != NULL,
 234  * then it is a newly allocated string. Returns NULL on getpw failure or
 235  * if path is NULL.
 236  */
 237 char *expand_user_path(const char *path)
 238 {
 239         struct strbuf user_path = STRBUF_INIT;
 240         const char *to_copy = path;
 241
 242         if (path == NULL)
 243                 goto return_null;
 244         if (path[0] == '~') {
 245                 const char *first_slash = strchrnul(path, '/');
 246                 const char *username = path + 1;
 247                 size_t username_len = first_slash - username;
 248                 if (username_len == 0) {
 249                         const char *home = getenv("HOME");
 250                         if (!home)
 251                                 goto return_null;
 252                         strbuf_addstr(&user_path, home);
 253                 } else {
 254                         struct passwd *pw = getpw_str(username, username_len);
 255                         if (!pw)
 256                                 goto return_null;
 257                         strbuf_addstr(&user_path, pw->pw_dir);
 258                 }
 259                 to_copy = first_slash;
 260         }
 261         strbuf_addstr(&user_path, to_copy);
 262         return strbuf_detach(&user_path, NULL);
 263 return_null:
 264         strbuf_release(&user_path);
 265         return NULL;
 266 }
 267
 268 /*
 269  * First, one directory to try is determined by the following algorithm.
 270  *
 271  * (0) If "strict" is given, the path is used as given and no DWIM is
 272  *     done. Otherwise:
 273  * (1) "~/path" to mean path under the running user's home directory;
 274  * (2) "~user/path" to mean path under named user's home directory;
 275  * (3) "relative/path" to mean cwd relative directory; or
 276  * (4) "/absolute/path" to mean absolute directory.
 277  *
 278  * Unless "strict" is given, we check "%s/.git", "%s", "%s.git/.git", "%s.git"
 279  * in this order. We select the first one that is a valid git repository, and
 280  * chdir() to it. If none match, or we fail to chdir, we return NULL.
 281  *
 282  * If all goes well, we return the directory we used to chdir() (but
 283  * before ~user is expanded), avoiding getcwd() resolving symbolic
 284  * links.  User relative paths are also returned as they are given,
 285  * except DWIM suffixing.
 286  */
 287 const char *enter_repo(const char *path, int strict)
 288 {
 289         static char used_path[PATH_MAX];
 290         static char validated_path[PATH_MAX];
 291
 292         if (!path)
 293                 return NULL;
 294
 295         if (!strict) {
 296                 static const char *suffix[] = {
 297                         "/.git", "", ".git/.git", ".git", NULL,
 298                 };
 299                 const char *gitfile;
 300                 int len = strlen(path);
 301                 int i;
 302                 while ((1 < len) && (path[len-1] == '/'))
 303                         len--;
 304
 305                 if (PATH_MAX <= len)
 306                         return NULL;
 307                 strncpy(used_path, path, len); used_path[len] = 0 ;
 308                 strcpy(validated_path, used_path);
 309
 310                 if (used_path[0] == '~') {
 311                         char *newpath = expand_user_path(used_path);
 312                         if (!newpath || (PATH_MAX - 10 < strlen(newpath))) {
 313                                 free(newpath);
 314                                 return NULL;
 315                         }
 316                         /*
 317                          * Copy back into the static buffer. A pity
 318                          * since newpath was not bounded, but other
 319                          * branches of the if are limited by PATH_MAX
 320                          * anyway.
 321                          */
 322                         strcpy(used_path, newpath); free(newpath);
 323                 }
 324                 else if (PATH_MAX - 10 < len)
 325                         return NULL;
 326                 len = strlen(used_path);
 327                 for (i = 0; suffix[i]; i++) {
 328                         struct stat st;
 329                         strcpy(used_path + len, suffix[i]);
 330                         if (!stat(used_path, &st) &&
 331                             (S_ISREG(st.st_mode) ||
 332                             (S_ISDIR(st.st_mode) && is_git_directory(used_path)))) {
 333                                 strcat(validated_path, suffix[i]);
 334                                 break;
 335                         }
 336                 }
 337                 if (!suffix[i])
 338                         return NULL;
 339                 gitfile = read_gitfile(used_path) ;
 340                 if (gitfile)
 341                         strcpy(used_path, gitfile);
 342                 if (chdir(used_path))
 343                         return NULL;
 344                 path = validated_path;
 345         }
 346         else if (chdir(path))
 347                 return NULL;
 348
 349         if (access("objects", X_OK) == 0 && access("refs", X_OK) == 0 &&
 350             validate_headref("HEAD") == 0) {
 351                 set_git_dir(".");
 352                 check_repository_format();
 353                 return path;
 354         }
 355
 356         return NULL;
 357 }
 358
 359 static int calc_shared_perm(int mode)
 360 {
 361         int tweak;
 362
 363         if (shared_repository < 0)
 364                 tweak = -shared_repository;
 365         else
 366                 tweak = shared_repository;
 367
 368         if (!(mode & S_IWUSR))
 369                 tweak &= ~0222;
 370         if (mode & S_IXUSR)
 371                 /* Copy read bits to execute bits */
 372                 tweak |= (tweak & 0444) >> 2;
 373         if (shared_repository < 0)
 374                 mode = (mode & ~0777) | tweak;
 375         else
 376                 mode |= tweak;
 377
 378         return mode;
 379 }
 380
 381
 382 int adjust_shared_perm(const char *path)
 383 {
 384         int old_mode, new_mode;
 385
 386         if (!shared_repository)
 387                 return 0;
 388         if (get_st_mode_bits(path, &old_mode) < 0)
 389                 return -1;
 390
 391         new_mode = calc_shared_perm(old_mode);
 392         if (S_ISDIR(old_mode)) {
 393                 /* Copy read bits to execute bits */
 394                 new_mode |= (new_mode & 0444) >> 2;
 395                 new_mode |= FORCE_DIR_SET_GID;
 396         }
 397
 398         if (((old_mode ^ new_mode) & ~S_IFMT) &&
 399                         chmod(path, (new_mode & ~S_IFMT)) < 0)
 400                 return -2;
 401         return 0;
 402 }
 403
 404 static int have_same_root(const char *path1, const char *path2)
 405 {
 406         int is_abs1, is_abs2;
 407
 408         is_abs1 = is_absolute_path(path1);
 409         is_abs2 = is_absolute_path(path2);
 410         return (is_abs1 && is_abs2 && tolower(path1[0]) == tolower(path2[0])) ||
 411                (!is_abs1 && !is_abs2);
 412 }
 413
 414 /*
 415  * Give path as relative to prefix.
 416  *
 417  * The strbuf may or may not be used, so do not assume it contains the
 418  * returned path.
 419  */
 420 const char *relative_path(const char *in, const char *prefix,
 421                           struct strbuf *sb)
 422 {
 423         int in_len = in ? strlen(in) : 0;
 424         int prefix_len = prefix ? strlen(prefix) : 0;
 425         int in_off = 0;
 426         int prefix_off = 0;
 427         int i = 0, j = 0;
 428
 429         if (!in_len)
 430                 return "./";
 431         else if (!prefix_len)
 432                 return in;
 433
 434         if (have_same_root(in, prefix)) {
 435                 /* bypass dos_drive, for "c:" is identical to "C:" */
 436                 if (has_dos_drive_prefix(in)) {
 437                         i = 2;
 438                         j = 2;
 439                 }
 440         } else {
 441                 return in;
 442         }
 443
 444         while (i < prefix_len && j < in_len && prefix[i] == in[j]) {
 445                 if (is_dir_sep(prefix[i])) {
 446                         while (is_dir_sep(prefix[i]))
 447                                 i++;
 448                         while (is_dir_sep(in[j]))
 449                                 j++;
 450                         prefix_off = i;
 451                         in_off = j;
 452                 } else {
 453                         i++;
 454                         j++;
 455                 }
 456         }
 457
 458         if (
 459             /* "prefix" seems like prefix of "in" */
 460             i >= prefix_len &&
 461             /*
 462              * but "/foo" is not a prefix of "/foobar"
 463              * (i.e. prefix not end with '/')
 464              */
 465             prefix_off < prefix_len) {
 466                 if (j >= in_len) {
 467                         /* in="/a/b", prefix="/a/b" */
 468                         in_off = in_len;
 469                 } else if (is_dir_sep(in[j])) {
 470                         /* in="/a/b/c", prefix="/a/b" */
 471                         while (is_dir_sep(in[j]))
 472                                 j++;
 473                         in_off = j;
 474                 } else {
 475                         /* in="/a/bbb/c", prefix="/a/b" */
 476                         i = prefix_off;
 477                 }
 478         } else if (
 479                    /* "in" is short than "prefix" */
 480                    j >= in_len &&
 481                    /* "in" not end with '/' */
 482                    in_off < in_len) {
 483                 if (is_dir_sep(prefix[i])) {
 484                         /* in="/a/b", prefix="/a/b/c/" */
 485                         while (is_dir_sep(prefix[i]))
 486                                 i++;
 487                         in_off = in_len;
 488                 }
 489         }
 490         in += in_off;
 491         in_len -= in_off;
 492
 493         if (i >= prefix_len) {
 494                 if (!in_len)
 495                         return "./";
 496                 else
 497                         return in;
 498         }
 499
 500         strbuf_reset(sb);
 501         strbuf_grow(sb, in_len);
 502
 503         while (i < prefix_len) {
 504                 if (is_dir_sep(prefix[i])) {
 505                         strbuf_addstr(sb, "../");
 506                         while (is_dir_sep(prefix[i]))
 507                                 i++;
 508                         continue;
 509                 }
 510                 i++;
 511         }
 512         if (!is_dir_sep(prefix[prefix_len - 1]))
 513                 strbuf_addstr(sb, "../");
 514
 515         strbuf_addstr(sb, in);
 516
 517         return sb->buf;
 518 }
 519
 520 /*
 521  * A simpler implementation of relative_path
 522  *
 523  * Get relative path by removing "prefix" from "in". This function
 524  * first appears in v1.5.6-1-g044bbbc, and makes git_dir shorter
 525  * to increase performance when traversing the path to work_tree.
 526  */
 527 const char *remove_leading_path(const char *in, const char *prefix)
 528 {
 529         static char buf[PATH_MAX + 1];
 530         int i = 0, j = 0;
 531
 532         if (!prefix || !prefix[0])
 533                 return in;
 534         while (prefix[i]) {
 535                 if (is_dir_sep(prefix[i])) {
 536                         if (!is_dir_sep(in[j]))
 537                                 return in;
 538                         while (is_dir_sep(prefix[i]))
 539                                 i++;
 540                         while (is_dir_sep(in[j]))
 541                                 j++;
 542                         continue;
 543                 } else if (in[j] != prefix[i]) {
 544                         return in;
 545                 }
 546                 i++;
 547                 j++;
 548         }
 549         if (
 550             /* "/foo" is a prefix of "/foo" */
 551             in[j] &&
 552             /* "/foo" is not a prefix of "/foobar" */
 553             !is_dir_sep(prefix[i-1]) && !is_dir_sep(in[j])
 554            )
 555                 return in;
 556         while (is_dir_sep(in[j]))
 557                 j++;
 558         if (!in[j])
 559                 strcpy(buf, ".");
 560         else
 561                 strcpy(buf, in + j);
 562         return buf;
 563 }
 564
 565 /*
 566  * It is okay if dst == src, but they should not overlap otherwise.
 567  *
 568  * Performs the following normalizations on src, storing the result in dst:
 569  * - Ensures that components are separated by '/' (Windows only)
 570  * - Squashes sequences of '/'.
 571  * - Removes "." components.
 572  * - Removes ".." components, and the components the precede them.
 573  * Returns failure (non-zero) if a ".." component appears as first path
 574  * component anytime during the normalization. Otherwise, returns success (0).
 575  *
 576  * Note that this function is purely textual.  It does not follow symlinks,
 577  * verify the existence of the path, or make any system calls.
 578  *
 579  * prefix_len != NULL is for a specific case of prefix_pathspec():
 580  * assume that src == dst and src[0..prefix_len-1] is already
 581  * normalized, any time "../" eats up to the prefix_len part,
 582  * prefix_len is reduced. In the end prefix_len is the remaining
 583  * prefix that has not been overridden by user pathspec.
 584  */
 585 int normalize_path_copy_len(char *dst, const char *src, int *prefix_len)
 586 {
 587         char *dst0;
 588
 589         if (has_dos_drive_prefix(src)) {
 590                 *dst++ = *src++;
 591                 *dst++ = *src++;
 592         }
 593         dst0 = dst;
 594
 595         if (is_dir_sep(*src)) {
 596                 *dst++ = '/';
 597                 while (is_dir_sep(*src))
 598                         src++;
 599         }
 600
 601         for (;;) {
 602                 char c = *src;
 603
 604                 /*
 605                  * A path component that begins with . could be
 606                  * special:
 607                  * (1) "." and ends   -- ignore and terminate.
 608                  * (2) "./"           -- ignore them, eat slash and continue.
 609                  * (3) ".." and ends  -- strip one and terminate.
 610                  * (4) "../"          -- strip one, eat slash and continue.
 611                  */
 612                 if (c == '.') {
 613                         if (!src[1]) {
 614                                 /* (1) */
 615                                 src++;
 616                         } else if (is_dir_sep(src[1])) {
 617                                 /* (2) */
 618                                 src += 2;
 619                                 while (is_dir_sep(*src))
 620                                         src++;
 621                                 continue;
 622                         } else if (src[1] == '.') {
 623                                 if (!src[2]) {
 624                                         /* (3) */
 625                                         src += 2;
 626                                         goto up_one;
 627                                 } else if (is_dir_sep(src[2])) {
 628                                         /* (4) */
 629                                         src += 3;
 630                                         while (is_dir_sep(*src))
 631                                                 src++;
 632                                         goto up_one;
 633                                 }
 634                         }
 635                 }
 636
 637                 /* copy up to the next '/', and eat all '/' */
 638                 while ((c = *src++) != '\0' && !is_dir_sep(c))
 639                         *dst++ = c;
 640                 if (is_dir_sep(c)) {
 641                         *dst++ = '/';
 642                         while (is_dir_sep(c))
 643                                 c = *src++;
 644                         src--;
 645                 } else if (!c)
 646                         break;
 647                 continue;
 648
 649         up_one:
 650                 /*
 651                  * dst0..dst is prefix portion, and dst[-1] is '/';
 652                  * go up one level.
 653                  */
 654                 dst--;  /* go to trailing '/' */
 655                 if (dst <= dst0)
 656                         return -1;
 657                 /* Windows: dst[-1] cannot be backslash anymore */
 658                 while (dst0 < dst && dst[-1] != '/')
 659                         dst--;
 660                 if (prefix_len && *prefix_len > dst - dst0)
 661                         *prefix_len = dst - dst0;
 662         }
 663         *dst = '\0';
 664         return 0;
 665 }
 666
 667 int normalize_path_copy(char *dst, const char *src)
 668 {
 669         return normalize_path_copy_len(dst, src, NULL);
 670 }
 671
 672 /*
 673  * path = Canonical absolute path
 674  * prefixes = string_list containing normalized, absolute paths without
 675  * trailing slashes (except for the root directory, which is denoted by "/").
 676  *
 677  * Determines, for each path in prefixes, whether the "prefix"
 678  * is an ancestor directory of path.  Returns the length of the longest
 679  * ancestor directory, excluding any trailing slashes, or -1 if no prefix
 680  * is an ancestor.  (Note that this means 0 is returned if prefixes is
 681  * ["/"].) "/foo" is not considered an ancestor of "/foobar".  Directories
 682  * are not considered to be their own ancestors.  path must be in a
 683  * canonical form: empty components, or "." or ".." components are not
 684  * allowed.
 685  */
 686 int longest_ancestor_length(const char *path, struct string_list *prefixes)
 687 {
 688         int i, max_len = -1;
 689
 690         if (!strcmp(path, "/"))
 691                 return -1;
 692
 693         for (i = 0; i < prefixes->nr; i++) {
 694                 const char *ceil = prefixes->items[i].string;
 695                 int len = strlen(ceil);
 696
 697                 if (len == 1 && ceil[0] == '/')
 698                         len = 0; /* root matches anything, with length 0 */
 699                 else if (!strncmp(path, ceil, len) && path[len] == '/')
 700                         ; /* match of length len */
 701                 else
 702                         continue; /* no match */
 703
 704                 if (len > max_len)
 705                         max_len = len;
 706         }
 707
 708         return max_len;
 709 }
 710
 711 /* strip arbitrary amount of directory separators at end of path */
 712 static inline int chomp_trailing_dir_sep(const char *path, int len)
 713 {
 714         while (len && is_dir_sep(path[len - 1]))
 715                 len--;
 716         return len;
 717 }
 718
 719 /*
 720  * If path ends with suffix (complete path components), returns the
 721  * part before suffix (sans trailing directory separators).
 722  * Otherwise returns NULL.
 723  */
 724 char *strip_path_suffix(const char *path, const char *suffix)
 725 {
 726         int path_len = strlen(path), suffix_len = strlen(suffix);
 727
 728         while (suffix_len) {
 729                 if (!path_len)
 730                         return NULL;
 731
 732                 if (is_dir_sep(path[path_len - 1])) {
 733                         if (!is_dir_sep(suffix[suffix_len - 1]))
 734                                 return NULL;
 735                         path_len = chomp_trailing_dir_sep(path, path_len);
 736                         suffix_len = chomp_trailing_dir_sep(suffix, suffix_len);
 737                 }
 738                 else if (path[--path_len] != suffix[--suffix_len])
 739                         return NULL;
 740         }
 741
 742         if (path_len && !is_dir_sep(path[path_len - 1]))
 743                 return NULL;
 744         return xstrndup(path, chomp_trailing_dir_sep(path, path_len));
 745 }
 746
 747 int daemon_avoid_alias(const char *p)
 748 {
 749         int sl, ndot;
 750
 751         /*
 752          * This resurrects the belts and suspenders paranoia check by HPA
 753          * done in <435560F7.4080006@zytor.com> thread, now enter_repo()
 754          * does not do getcwd() based path canonicalization.
 755          *
 756          * sl becomes true immediately after seeing '/' and continues to
 757          * be true as long as dots continue after that without intervening
 758          * non-dot character.
 759          */
 760         if (!p || (*p != '/' && *p != '~'))
 761                 return -1;
 762         sl = 1; ndot = 0;
 763         p++;
 764
 765         while (1) {
 766                 char ch = *p++;
 767                 if (sl) {
 768                         if (ch == '.')
 769                                 ndot++;
 770                         else if (ch == '/') {
 771                                 if (ndot < 3)
 772                                         /* reject //, /./ and /../ */
 773                                         return -1;
 774                                 ndot = 0;
 775                         }
 776                         else if (ch == 0) {
 777                                 if (0 < ndot && ndot < 3)
 778                                         /* reject /.$ and /..$ */
 779                                         return -1;
 780                                 return 0;
 781                         }
 782                         else
 783                                 sl = ndot = 0;
 784                 }
 785                 else if (ch == 0)
 786                         return 0;
 787                 else if (ch == '/') {
 788                         sl = 1;
 789                         ndot = 0;
 790                 }
 791         }
 792 }
 793
 794 static int only_spaces_and_periods(const char *path, size_t len, size_t skip)
 795 {
 796         if (len < skip)
 797                 return 0;
 798         len -= skip;
 799         path += skip;
 800         while (len-- > 0) {
 801                 char c = *(path++);
 802                 if (c != ' ' && c != '.')
 803                         return 0;
 804         }
 805         return 1;
 806 }
 807
 808 int is_ntfs_dotgit(const char *name)
 809 {
 810         int len;
 811
 812         for (len = 0; ; len++)
 813                 if (!name[len] || name[len] == '\\' || is_dir_sep(name[len])) {
 814                         if (only_spaces_and_periods(name, len, 4) &&
 815                                         !strncasecmp(name, ".git", 4))
 816                                 return 1;
 817                         if (only_spaces_and_periods(name, len, 5) &&
 818                                         !strncasecmp(name, "git~1", 5))
 819                                 return 1;
 820                         if (name[len] != '\\')
 821                                 return 0;
 822                         name += len + 1;
 823                         len = -1;
 824                 }
 825 }
 826
 827 char *xdg_config_home(const char *filename)
 828 {
 829         const char *home, *config_home;
 830
 831         assert(filename);
 832         config_home = getenv("XDG_CONFIG_HOME");
 833         if (config_home && *config_home)
 834                 return mkpathdup("%s/git/%s", config_home, filename);
 835
 836         home = getenv("HOME");
 837         if (home)
 838                 return mkpathdup("%s/.config/git/%s", home, filename);
 839         return NULL;
 840 }