fix: Improve safety of logging images with implicit formats

src/dvclive/error.py

@@ -17,6 +17,12 @@ def __init__(self):
         super().__init__("`dvcyaml` path must have filename 'dvc.yaml'")
 
 
+class InvalidImageNameError(DvcLiveError):
+    def __init__(self, name):
+        self.name = name
+        super().__init__(f"Cannot log image with name '{name}'")
+
+
 class InvalidPlotTypeError(DvcLiveError):
     def __init__(self, name):
         from .plots import SKLEARN_PLOTS

src/dvclive/live.py

@@ -31,6 +31,7 @@
 from .error import (
     InvalidDataTypeError,
     InvalidDvcyamlError,
+    InvalidImageNameError,
     InvalidParameterTypeError,
     InvalidPlotTypeError,
     InvalidReportModeError,
@@ -389,11 +390,20 @@ def log_image(
         if not Image.could_log(val):
             raise InvalidDataTypeError(name, type(val))
 
+        # If we're given a path, try loading the image first. This might error out.
         if isinstance(val, (str, PurePath)):
             from PIL import Image as ImagePIL
 
+            suffix = Path(val).suffix
+            if not Path(name).suffix and suffix in Image.suffixes:
+                name = f"{name}{suffix}"
+
             val = ImagePIL.open(val)
 
+        # See if the image name is valid
+        if Path(name).suffix not in Image.suffixes:
+            raise InvalidImageNameError(name)
+
         if name in self._images:
             image = self._images[name]
         else:

tests/plots/test_image.py

@@ -4,6 +4,7 @@
 from PIL import Image
 
 from dvclive import Live
+from dvclive.error import InvalidImageNameError
 from dvclive.plots import Image as LiveImage
 
 
@@ -24,10 +25,37 @@ def test_pil(tmp_dir):
     assert (tmp_dir / live.plots_dir / LiveImage.subfolder / "image.png").exists()
 
 
+def test_pil_omitting_extension_doesnt_save_without_valid_format(tmp_dir):
+    live = Live()
+    img = Image.new("RGB", (10, 10), (250, 250, 250))
+    with pytest.raises(
+        InvalidImageNameError, match="Cannot log image with name 'whoops'"
+    ):
+        live.log_image("whoops", img)
+
+
+def test_pil_omitting_extension_sets_the_format_if_path_given(tmp_dir):
+    live = Live()
+    img = Image.new("RGB", (10, 10), (250, 250, 250))
+
+    # Save it first, we'll reload it and pass it's path to log_image again
+    live.log_image("saved_with_format.png", img)
+
+    # Now try saving without explicit format and check if the format is set correctly.
+    live.log_image(
+        "whoops",
+        (tmp_dir / live.plots_dir / LiveImage.subfolder / "saved_with_format.png"),
+    )
+
+    assert (tmp_dir / live.plots_dir / LiveImage.subfolder / "whoops.png").exists()
+
+
 def test_invalid_extension(tmp_dir):
     live = Live()
     img = Image.new("RGB", (10, 10), (250, 250, 250))
-    with pytest.raises(ValueError, match="unknown file extension"):
+    with pytest.raises(
+        InvalidImageNameError, match="Cannot log image with name 'image.foo'"
+    ):
         live.log_image("image.foo", img)