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 <pwd.h>
  15
  16 static char pathname[PATH_MAX];
  17 static char bad_path[] = "/bad-path/";
  18
  19 static char *cleanup_path(char *path)
  20 {
  21         /* Clean it up */
  22         if (!memcmp(path, "./", 2)) {
  23                 path += 2;
  24                 while (*path == '/')
  25                         path++;
  26         }
  27         return path;
  28 }
  29
  30 char *mkpath(const char *fmt, ...)
  31 {
  32         va_list args;
  33         unsigned len;
  34
  35         va_start(args, fmt);
  36         len = vsnprintf(pathname, PATH_MAX, fmt, args);
  37         va_end(args);
  38         if (len >= PATH_MAX)
  39                 return bad_path;
  40         return cleanup_path(pathname);
  41 }
  42
  43 char *git_path(const char *fmt, ...)
  44 {
  45         const char *git_dir = get_git_dir();
  46         va_list args;
  47         unsigned len;
  48
  49         len = strlen(git_dir);
  50         if (len > PATH_MAX-100)
  51                 return bad_path;
  52         memcpy(pathname, git_dir, len);
  53         if (len && git_dir[len-1] != '/')
  54                 pathname[len++] = '/';
  55         va_start(args, fmt);
  56         len += vsnprintf(pathname + len, PATH_MAX - len, fmt, args);
  57         va_end(args);
  58         if (len >= PATH_MAX)
  59                 return bad_path;
  60         return cleanup_path(pathname);
  61 }
  62
  63
  64 /* git_mkstemp() - create tmp file honoring TMPDIR variable */
  65 int git_mkstemp(char *path, size_t len, const char *template)
  66 {
  67         char *env, *pch = path;
  68
  69         if ((env = getenv("TMPDIR")) == NULL) {
  70                 strcpy(pch, "/tmp/");
  71                 len -= 5;
  72                 pch += 5;
  73         } else {
  74                 size_t n = snprintf(pch, len, "%s/", env);
  75
  76                 len -= n;
  77                 pch += n;
  78         }
  79
  80         safe_strncpy(pch, template, len);
  81
  82         return mkstemp(path);
  83 }
  84
  85
  86 char *safe_strncpy(char *dest, const char *src, size_t n)
  87 {
  88         strncpy(dest, src, n);
  89         dest[n - 1] = '\0';
  90
  91         return dest;
  92 }
  93
  94 int validate_symref(const char *path)
  95 {
  96         struct stat st;
  97         char *buf, buffer[256];
  98         int len, fd;
  99
 100         if (lstat(path, &st) < 0)
 101                 return -1;
 102
 103         /* Make sure it is a "refs/.." symlink */
 104         if (S_ISLNK(st.st_mode)) {
 105                 len = readlink(path, buffer, sizeof(buffer)-1);
 106                 if (len >= 5 && !memcmp("refs/", buffer, 5))
 107                         return 0;
 108                 return -1;
 109         }
 110
 111         /*
 112          * Anything else, just open it and try to see if it is a symbolic ref.
 113          */
 114         fd = open(path, O_RDONLY);
 115         if (fd < 0)
 116                 return -1;
 117         len = read(fd, buffer, sizeof(buffer)-1);
 118         close(fd);
 119
 120         /*
 121          * Is it a symbolic ref?
 122          */
 123         if (len < 4 || memcmp("ref:", buffer, 4))
 124                 return -1;
 125         buf = buffer + 4;
 126         len -= 4;
 127         while (len && isspace(*buf))
 128                 buf++, len--;
 129         if (len >= 5 && !memcmp("refs/", buf, 5))
 130                 return 0;
 131         return -1;
 132 }
 133
 134 static char *current_dir(void)
 135 {
 136         return getcwd(pathname, sizeof(pathname));
 137 }
 138
 139 static int user_chdir(char *path)
 140 {
 141         char *dir = path;
 142
 143         if(*dir == '~') {               /* user-relative path */
 144                 struct passwd *pw;
 145                 char *slash = strchr(dir, '/');
 146
 147                 dir++;
 148                 /* '~/' and '~' (no slash) means users own home-dir */
 149                 if(!*dir || *dir == '/')
 150                         pw = getpwuid(getuid());
 151                 else {
 152                         if (slash) {
 153                                 *slash = '\0';
 154                                 pw = getpwnam(dir);
 155                                 *slash = '/';
 156                         }
 157                         else
 158                                 pw = getpwnam(dir);
 159                 }
 160
 161                 /* make sure we got something back that we can chdir() to */
 162                 if(!pw || chdir(pw->pw_dir) < 0)
 163                         return -1;
 164
 165                 if(!slash || !slash[1]) /* no path following username */
 166                         return 0;
 167
 168                 dir = slash + 1;
 169         }
 170
 171         /* ~foo/path/to/repo is now path/to/repo and we're in foo's homedir */
 172         if(chdir(dir) < 0)
 173                 return -1;
 174
 175         return 0;
 176 }
 177
 178 char *enter_repo(char *path, int strict)
 179 {
 180         if(!path)
 181                 return NULL;
 182
 183         if (strict) {
 184                 if (chdir(path) < 0)
 185                         return NULL;
 186         }
 187         else {
 188                 if (!*path)
 189                         ; /* happy -- no chdir */
 190                 else if (!user_chdir(path))
 191                         ; /* happy -- as given */
 192                 else if (!user_chdir(mkpath("%s.git", path)))
 193                         ; /* happy -- uemacs --> uemacs.git */
 194                 else
 195                         return NULL;
 196                 (void)chdir(".git");
 197         }
 198
 199         if(access("objects", X_OK) == 0 && access("refs", X_OK) == 0 &&
 200            validate_symref("HEAD") == 0) {
 201                 putenv("GIT_DIR=.");
 202                 return current_dir();
 203         }
 204
 205         return NULL;
 206 }