extmod/vfs_lfsx: Normalize path name in chdir.

This change scans for '.', '..' and multiple '/' and normalizes the new
path name.  If the resulting path does not exist, an error is raised.
Non-existing interim path elements are ignored if they are removed during
normalization.

Author: robert-hh

extmod/vfs_lfsx.c

@@ -283,8 +283,45 @@ STATIC mp_obj_t MP_VFS_LFSx(chdir)(mp_obj_t self_in, mp_obj_t path_in) {
     }
 
     // If not at root add trailing / to make it easy to build paths
+    // and then normalise the path
     if (vstr_len(&self->cur_dir) != 1) {
         vstr_add_byte(&self->cur_dir, '/');
+
+        #define CWD_LEN (vstr_len(&self->cur_dir))
+        size_t to = 1;
+        size_t from = 1;
+        char *cwd = vstr_str(&self->cur_dir);
+        while (from < CWD_LEN) {
+            for (; cwd[from] == '/' && from < CWD_LEN; ++from) {
+                // Scan for the start
+            }
+            if (from > to) {
+                // Found excessive slash chars, squeeze them out
+                vstr_cut_out_bytes(&self->cur_dir, to, from - to);
+                from = to;
+            }
+            for (; cwd[from] != '/' && from < CWD_LEN; ++from) {
+                // Scan for the next /
+            }
+            if ((from - to) == 1 && cwd[to] == '.') {
+                // './', ignore
+                vstr_cut_out_bytes(&self->cur_dir, to, ++from - to);
+                from = to;
+            } else if ((from - to) == 2 && cwd[to] == '.' && cwd[to + 1] == '.') {
+                // '../', skip back
+                if (to > 1) {
+                    // Only skip back if not at the tip
+                    for (--to; to > 1 && cwd[to - 1] != '/'; --to) {
+                        // Skip back
+                    }
+                }
+                vstr_cut_out_bytes(&self->cur_dir, to, ++from - to);
+                from = to;
+            } else {
+                // Normal element, keep it and just move the offset
+                to = ++from;
+            }
+        }
     }
 
     return mp_const_none;

tests/extmod/vfs_lfs.py

@@ -98,6 +98,8 @@ def test(bdev, vfs_class):
     print(list(vfs.ilistdir()))
 
     # getcwd, chdir
+    vfs.mkdir("/testdir2")
+    vfs.mkdir("/testdir/subdir")
     print(vfs.getcwd())
     vfs.chdir("/testdir")
     print(vfs.getcwd())
@@ -111,7 +113,29 @@ def test(bdev, vfs_class):
     # chdir back to root and remove testdir
     vfs.chdir("/")
     print(vfs.getcwd())
+    vfs.chdir("testdir")
+    print(vfs.getcwd())
+    vfs.chdir("..")
+    print(vfs.getcwd())
+    vfs.chdir("testdir/subdir")
+    print(vfs.getcwd())
+    vfs.chdir("../..")
+    print(vfs.getcwd())
+    vfs.chdir("/./testdir2")
+    print(vfs.getcwd())
+    vfs.chdir("../testdir")
+    print(vfs.getcwd())
+    vfs.chdir("../..")
+    print(vfs.getcwd())
+    vfs.chdir(".//testdir")
+    print(vfs.getcwd())
+    vfs.chdir("subdir/./")
+    print(vfs.getcwd())
+    vfs.chdir("/")
+    print(vfs.getcwd())
+    vfs.rmdir("testdir/subdir")
     vfs.rmdir("testdir")
+    vfs.rmdir("testdir2")
 
 
 bdev = RAMBlockDevice(30)

tests/extmod/vfs_lfs.py.exp

@@ -23,6 +23,16 @@ write 3
 (32768, 0, 0, 0, 0, 0, 0, 0, 0, 0)
 (32768, 0, 0, 0, 0, 0, 0, 0, 0, 0)
 /
+/testdir
+/
+/testdir/subdir
+/
+/testdir2
+/testdir
+/
+/testdir
+/testdir/subdir
+/
 test <class 'VfsLfs2'>
 (1024, 1024, 30, 28, 28, 0, 0, 0, 0, 255)
 (1024, 1024, 30, 28, 28, 0, 0, 0, 0, 255)
@@ -48,3 +58,13 @@ write 3
 (32768, 0, 0, 0, 0, 0, 0, 0, 0, 0)
 (32768, 0, 0, 0, 0, 0, 0, 0, 0, 0)
 /
+/testdir
+/
+/testdir/subdir
+/
+/testdir2
+/testdir
+/
+/testdir
+/testdir/subdir
+/