fix(core): stop get_image_dimensions crashing on bare base64 and unfetchable URLs

get_image_dimensions documents 'URL or base64 encoded string' input,
but the base64 branch unconditionally split on ',' and unpacked two
values, so bare base64 (no data: prefix) raised ValueError, and a URL
whose download failed fell into the same branch and crashed the same
way — instead of reaching the documented 'sensible default dimensions'
fallback that only the unknown-image-format path could reach.

The base64 branch now accepts both data-URL and bare base64 forms and
treats a decode error as 'use defaults'; an unfetchable URL or
undecodable payload leaves img_data unset and skips image-format
detection, falling through to DEFAULT_IMAGE_WIDTH/HEIGHT.

litellm/litellm_core_utils/token_counter.py

@@ -213,12 +213,19 @@ def get_image_dimensions(
                     img_data = body
         except Exception:
             pass
-    if img_data is None:
-        # Not a URL or fetch failed — assume base64
-        _header, encoded = data.split(",", 1)
-        img_data = base64.b64decode(encoded)
+    if img_data is None and not data.startswith(("http://", "https://")):
+        # Not a URL — assume base64. Accept both data-URL form
+        # ('data:<mime>;base64,<payload>') and bare base64; on a decode
+        # error, leave img_data unset so the default dimensions are used.
+        encoded = data.partition(",")[2] if data.startswith("data:") else data
+        try:
+            img_data = base64.b64decode(encoded)
+        except ValueError:
+            verbose_logger.debug("Failed to decode base64 image data; using default dimensions")
 
-    img_type: Final = get_image_type(img_data)
+    # A URL that could not be fetched (or base64 that could not be decoded)
+    # leaves img_data unset — fall through to the default dimensions below.
+    img_type: Final = get_image_type(img_data) if img_data is not None else None
 
     if img_type == "png":
         w, h = struct.unpack(">LL", img_data[16:24])

tests/test_litellm/litellm_core_utils/test_token_counter.py

@@ -526,6 +526,53 @@ def test_img_url_token_counter(img_url, monkeypatch):
     assert height is not None
 
 
+def test_get_image_dimensions_bare_base64():
+    """
+    Bare base64 (no 'data:' URL prefix) is documented input for
+    get_image_dimensions and must not crash on the ','-split of a data URL.
+    """
+    import base64
+    import struct
+
+    from litellm.litellm_core_utils.token_counter import get_image_dimensions
+
+    # Minimal PNG header carrying 100x200 dimensions.
+    png = base64.b64encode(
+        b"\x89PNG\r\n\x1a\n" + b"\x00" * 8 + struct.pack(">LL", 100, 200) + b"\x00" * 16
+    )
+    assert get_image_dimensions(data=png.decode()) == (100, 200)
+
+
+def test_get_image_dimensions_unfetchable_url_returns_defaults(monkeypatch):
+    """A URL that cannot be fetched falls back to the default dimensions instead of raising."""
+
+    def _raise(client, url, **kwargs):
+        raise RuntimeError("connection failed")
+
+    monkeypatch.setattr(
+        "litellm.litellm_core_utils.token_counter.safe_get",
+        _raise,
+    )
+    from litellm.constants import DEFAULT_IMAGE_HEIGHT, DEFAULT_IMAGE_WIDTH
+    from litellm.litellm_core_utils.token_counter import get_image_dimensions
+
+    assert get_image_dimensions(data="https://invalid.invalid/x.png") == (
+        DEFAULT_IMAGE_WIDTH,
+        DEFAULT_IMAGE_HEIGHT,
+    )
+
+
+def test_get_image_dimensions_undecodable_data_returns_defaults():
+    """Data that is neither a fetchable URL nor decodable base64 uses the defaults."""
+    from litellm.constants import DEFAULT_IMAGE_HEIGHT, DEFAULT_IMAGE_WIDTH
+    from litellm.litellm_core_utils.token_counter import get_image_dimensions
+
+    assert get_image_dimensions(data="not-an-image!") == (
+        DEFAULT_IMAGE_WIDTH,
+        DEFAULT_IMAGE_HEIGHT,
+    )
+
+
 def test_token_encode_disallowed_special():
     encode(model="gpt-3.5-turbo", text="Hello, world! <|endoftext|>")
     token_counter(model="gpt-3.5-turbo", text="Hello, world! <|endoftext|>")