raise parsing error when trying to open file with the wrong file id

fspy_blender/fspy.py

@@ -37,6 +37,8 @@ def __init__(self, project_path):
     project_file = open(project_path, "rb")
 
     file_id = unpack('<I', project_file.read(4))[0]
+    if 2037412710 != file_id:
+        raise ParsingError("Trying to import a file that is not an fSpy project")
     self.project_version = unpack('<I', project_file.read(4))[0]
     if self.project_version != 1:
         raise ParsingError("Unsupported fSpy project file version " + str(self.project_version))

test/test.py

@@ -17,6 +17,13 @@ def test_wrong_project_version(self):
         with self.assertRaises(fspy.ParsingError):
             project = fspy.Project(self.project_path('invalid_project_version.fspy'))
 
+    def test_invalid_file_type(self):
+        """
+        Opening files that are not fSpy project files should fail
+        """
+        with self.assertRaises(fspy.ParsingError):
+            project = fspy.Project(self.project_path('json_export.json'))
+
     # Helper to get the path of a test project
     def project_path(self, project_name):
         return os.path.join('test_data', project_name)

test_data/json_export.json

@@ -0,0 +1,86 @@
+{
+  "principalPoint": {
+    "x": 0,
+    "y": 0
+  },
+  "viewTransform": {
+    "rows": [
+      [
+        -0.8432786760114586,
+        0.0008594611278942136,
+        -0.5374758933300462,
+        0.3346571584818884
+      ],
+      [
+        -0.0005363911022935677,
+        0.9999968777735306,
+        0.002440640853491923,
+        -0.9315262352851599
+      ],
+      [
+        0.537476312844526,
+        0.0023464376744316683,
+        -0.8432755820971535,
+        -4.120414307919244
+      ],
+      [
+        0,
+        0,
+        0,
+        1
+      ]
+    ]
+  },
+  "cameraTransform": {
+    "rows": [
+      [
+        -0.8432786760114587,
+        -0.000536391102293568,
+        0.5374763128445262,
+        2.4963346727504696
+      ],
+      [
+        0.0008594611278942138,
+        0.9999968777735309,
+        0.0023464376744316688,
+        0.9409039973967737
+      ],
+      [
+        -0.5374758933300462,
+        0.002440640853491923,
+        -0.8432755820971537,
+        -3.292501097791757
+      ],
+      [
+        0,
+        0,
+        0,
+        1
+      ]
+    ]
+  },
+  "horizontalFieldOfView": 1.5479845321227295,
+  "verticalFieldOfView": 1.1518580723726943,
+  "vanishingPoints": [
+    {
+      "x": 1.6051650133994935,
+      "y": 0.001021010320067342
+    },
+    {
+      "x": -0.652074716204382,
+      "y": 0.0029610261811691915
+    },
+    {
+      "x": -0.3747357368992343,
+      "y": -436.0110710388304
+    }
+  ],
+  "vanishingPointAxes": [
+    "xNegative",
+    "zPositive",
+    "yPositive"
+  ],
+  "relativeFocalLength": 1.0230759978297743,
+  "imageWidth": 1439,
+  "imageHeight": 956
+}