SYN-208/SYN-228: Add runtime checks on startup to enforce that JPEG/PNG...

SYN-208/SYN-228: Add runtime checks on startup to enforce that JPEG/PNG support is included when installing pillow.

synapse/media/v1/__init__.py

+# -*- coding: utf-8 -*-
+import PIL.Image
+
+# check for JPEG support.
+try:
+    PIL.Image._getdecoder("rgb", "jpeg", None)
+except IOError as e:
+    if str(e).startswith("decoder jpeg not available"):
+        raise Exception(
+            "FATAL: jpeg codec not supported. Install pillow correctly! "
+            " 'sudo apt-get install libjpeg-dev' then 'pip install -I pillow'"
+        )
+except Exception:
+    # any other exception is fine
+    pass
+
+
+# check for PNG support.
+try:
+    PIL.Image._getdecoder("rgb", "zip", None)
+except IOError as e:
+    if str(e).startswith("decoder zip not available"):
+        raise Exception(
+            "FATAL: zip codec not supported. Install pillow correctly! "
+            " 'sudo apt-get install libjpeg-dev' then 'pip install -I pillow'"
+        )
+except Exception:
+    # any other exception is fine
+    pass
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