Reject invalid zip files

Closes #7

taas_client/cli.py

 import datetime
 import sys
 import time
+import zipfile
 from pathlib import Path
 
 import httpx
@@ -86,6 +87,10 @@ def check_project_file(path: Path, force: bool) -> None:
         else:
             console.print("Continuing submission since --force has been given.\n")
 
+    if not zipfile.is_zipfile(path):
+        console.print(f"[red]{path.name} is not a valid .zip file.[/]")
+        raise typer.Exit(1)
+
 
 @app.command()
 def upload_file(

tests/test_cli.py

@@ -4,6 +4,7 @@ import os
 import io
 import pathlib
 import datetime
+import zipfile
 
 import rich.console
 import rich.panel
@@ -260,7 +261,8 @@ def test_project(
     time_machine.move_to(FROZEN_TIME)
 
     project_path = tmp_path / "project.zip"
-    project_path.touch()
+    with zipfile.ZipFile(project_path, "w"):
+        pass
 
     result = runner.run("--project", str(project_path))
 
@@ -298,9 +300,8 @@ def test_project_size_limit(
 
     file_size_mb = 2 if hard_limit else 1
     project_path = tmp_path / "project.zip"
-    with project_path.open("wb") as f:
-        f.seek(file_size_mb * 1024 * 1024)
-        f.write(b"\x00")
+    with zipfile.ZipFile(project_path, "w") as zf:
+        zf.writestr("data.bin", "\x00" * file_size_mb * 1024 * 1024)
 
     flags = ["--project"]
     if force:
@@ -311,6 +312,17 @@ def test_project_size_limit(
     assert result.stdout == golden_special.out["output"]
 
 
+def test_project_invalid_zip(
+    runner: Runner,
+    tmp_path: pathlib.Path,
+):
+    project_path = tmp_path / "project.zip"
+    project_path.touch()
+    result = runner.run("--project", str(project_path))
+    assert result.exit_code == 1
+    assert result.stdout == "project.zip is not a valid .zip file.\n"
+
+
 def test_version(
     runner: Runner,
     httpx_mock: HTTPXMock,