1 files changed, 171 insertions, 0 deletions
diff --git a/libc-bottom-half/sources/chdir.c b/libc-bottom-half/sources/chdir.c
new file mode 100644
index 0000000..37c95a4
--- /dev/null
+++ b/libc-bottom-half/sources/chdir.c
@@ -0,0 +1,171 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <wasi/libc-find-relpath.h>
+#include <wasi/libc.h>
+
+#ifdef _REENTRANT
+void __wasilibc_cwd_lock(void);
+void __wasilibc_cwd_unlock(void);
+#else
+#define __wasilibc_cwd_lock() (void)0
+#define __wasilibc_cwd_unlock() (void)0
+#endif
+extern char *__wasilibc_cwd;
+static int __wasilibc_cwd_mallocd = 0;
+
+int chdir(const char *path)
+{
+    static char *relative_buf = NULL;
+    static size_t relative_buf_len = 0;
+
+    // Find a preopen'd directory as well as a relative path we're anchored
+    // from which we're changing directories to.
+    const char *abs;
+    int parent_fd = __wasilibc_find_relpath_alloc(path, &abs, &relative_buf, &relative_buf_len, 1);
+    if (parent_fd == -1)
+        return -1;
+
+    // Make sure that this directory we're accessing is indeed a directory.
+    struct stat dirinfo;
+    int ret = fstatat(parent_fd, relative_buf, &dirinfo, 0);
+    if (ret == -1)
+        return -1;
+    if (!S_ISDIR(dirinfo.st_mode)) {
+        errno = ENOTDIR;
+        return -1;
+    }
+
+    // Create a string that looks like:
+    //
+    //    __wasilibc_cwd = "/" + abs + "/" + relative_buf
+    //
+    // If `relative_buf` is equal to "." or `abs` is equal to the empty string,
+    // however, we skip that part and the middle slash.
+    size_t abs_len = strlen(abs);
+    int copy_relative = strcmp(relative_buf, ".") != 0;
+    int mid = copy_relative && abs[0] != 0;
+    char *new_cwd = malloc(1 + abs_len + mid + (copy_relative ? strlen(relative_buf) : 0) + 1);
+    if (new_cwd == NULL) {
+        errno = ENOMEM;
+        return -1;
+    }
+    new_cwd[0] = '/';
+    strcpy(new_cwd + 1, abs);
+    if (mid)
+        new_cwd[1 + abs_len] = '/';
+    if (copy_relative)
+        strcpy(new_cwd + 1 + abs_len + mid, relative_buf);
+
+    // And set our new malloc'd buffer into the global cwd, freeing the
+    // previous one if necessary.
+    __wasilibc_cwd_lock();
+    char *prev_cwd = __wasilibc_cwd;
+    __wasilibc_cwd = new_cwd;
+    __wasilibc_cwd_unlock();
+    if (__wasilibc_cwd_mallocd)
+        free(prev_cwd);
+    __wasilibc_cwd_mallocd = 1;
+    return 0;
+}
+
+static const char *make_absolute(const char *path) {
+    static char *make_absolute_buf = NULL;
+    static size_t make_absolute_len = 0;
+
+    // If this path is absolute, then we return it as-is.
+    if (path[0] == '/') {
+        return path;
+    }
+
+#ifndef _REENTRANT
+    // If the path is empty, or points to the current directory, then return
+    // the current directory.
+    if (path[0] == 0 || !strcmp(path, ".") || !strcmp(path, "./")) {
+        return __wasilibc_cwd;
+    }
+#endif
+
+    // If the path starts with `./` then we won't be appending that to the cwd.
+    if (path[0] == '.' && path[1] == '/')
+        path += 2;
+
+    // Otherwise we'll take the current directory, add a `/`, and then add the
+    // input `path`. Note that this doesn't do any normalization (like removing
+    // `/./`).
+    __wasilibc_cwd_lock();
+    size_t cwd_len = strlen(__wasilibc_cwd);
+    size_t path_len = path ? strlen(path) : 0;
+    __wasilibc_cwd_unlock();
+    int need_slash = __wasilibc_cwd[cwd_len - 1] == '/' ? 0 : 1;
+    size_t alloc_len = cwd_len + path_len + 1 + need_slash;
+    if (alloc_len > make_absolute_len) {
+        char *tmp = realloc(make_absolute_buf, alloc_len);
+        if (tmp == NULL) {
+            __wasilibc_cwd_unlock();
+            return NULL;
+        }
+        make_absolute_buf = tmp;
+        make_absolute_len = alloc_len;
+    }
+    strcpy(make_absolute_buf, __wasilibc_cwd);
+    __wasilibc_cwd_unlock();
+
+#ifdef _REENTRANT
+    if (path[0] == 0 || !strcmp(path, ".") || !strcmp(path, "./")) {
+        return make_absolute_buf;
+    }
+#endif
+
+    if (need_slash)
+        strcpy(make_absolute_buf + cwd_len, "/");
+    strcpy(make_absolute_buf + cwd_len + need_slash, path);
+    return make_absolute_buf;
+}
+
+// Helper function defined only in this object file and weakly referenced from
+// `preopens.c` and `posix.c` This function isn't necessary unless `chdir` is
+// pulled in because all paths are otherwise absolute or relative to the root.
+int __wasilibc_find_relpath_alloc(
+    const char *path,
+    const char **abs_prefix,
+    char **relative_buf,
+    size_t *relative_buf_len,
+    int can_realloc
+) {
+    // First, make our path absolute taking the cwd into account.
+    const char *abspath = make_absolute(path);
+    if (abspath == NULL) {
+        errno = ENOMEM;
+        return -1;
+    }
+
+    // Next use our absolute path and split it. Find the preopened `fd` parent
+    // directory and set `abs_prefix`. Next up we'll be trying to fit `rel`
+    // into `relative_buf`.
+    const char *rel;
+    int fd = __wasilibc_find_abspath(abspath, abs_prefix, &rel);
+    if (fd == -1)
+        return -1;
+
+    size_t rel_len = strlen(rel);
+    if (*relative_buf_len < rel_len + 1) {
+        if (!can_realloc) {
+            errno = ERANGE;
+            return -1;
+        }
+        char *tmp = realloc(*relative_buf, rel_len + 1);
+        if (tmp == NULL) {
+            errno = ENOMEM;
+            return -1;
+        }
+        *relative_buf = tmp;
+        *relative_buf_len = rel_len + 1;
+    }
+    strcpy(*relative_buf, rel);
+    return fd;
+}