tools/mpremote: For mip install, use hash to skip files that exist.

When using `mip install`, if a file that needs to be downloaded already
exists locally, then the hash of that local file will be computed and if it
matches the known hash of the remote file it will not be downloaded.

Hashes in mip are guaranteed unique, so this change should never leave
stale files on the filesystem.

This behaviour follows that of the `mip` package in `micropython-lib`.

Signed-off-by: Damien George <damien@micropython.org>

tools/mpremote/mpremote/mip.py

@@ -34,6 +34,15 @@ def _ensure_path_exists(transport, path):
         prefix += "/"
 
 
+# Check if the specified path exists and matches the hash.
+def _check_exists(transport, path, short_hash):
+    try:
+        remote_hash = transport.fs_hashfile(path, "sha256")
+    except FileNotFoundError:
+        return False
+    return remote_hash.hex()[: len(short_hash)] == short_hash
+
+
 def _rewrite_url(url, branch=None):
     if not branch:
         branch = "HEAD"
@@ -115,8 +124,11 @@ def _install_json(transport, package_json_url, index, target, version, mpy):
         raise CommandError(f"Invalid url for package: {package_json_url}")
     for target_path, short_hash in package_json.get("hashes", ()):
         fs_target_path = target + "/" + target_path
-        file_url = f"{index}/file/{short_hash[:2]}/{short_hash}"
-        _download_file(transport, file_url, fs_target_path)
+        if _check_exists(transport, fs_target_path, short_hash):
+            print("Exists:", fs_target_path)
+        else:
+            file_url = f"{index}/file/{short_hash[:2]}/{short_hash}"
+            _download_file(transport, file_url, fs_target_path)
     for target_path, url in package_json.get("urls", ()):
         fs_target_path = target + "/" + target_path
         if base_url and not url.startswith(allowed_mip_url_prefixes):