Handle case for missing HiPS tiles

Signed-off-by: Adeel Ahmad <adeelahmad14@hotmail.com>

hips/tiles/fetch.py

@@ -81,7 +81,11 @@ def fetch_tiles(tile_metas: List[HipsTileMeta], hips_survey: HipsSurveyPropertie
 
     tiles = []
     for idx, response in enumerate(response_all):
-        tiles.append(HipsTile(tile_metas[idx], response['raw_data']))
+        try:
+            response['raw_data']
+            tiles.append(HipsTile(tile_metas[idx], response['raw_data']))
+        except KeyError:
+            tiles.append(HipsTile(tile_metas[idx], b'', is_missing=True))
 
     return tiles
 
@@ -92,9 +96,11 @@ def fetch_tile_urllib(url: str, timeout: float) -> dict:
         with urllib.request.urlopen(url, timeout=timeout) as conn:
             return {'raw_data': conn.read(), 'url': url}
     except urllib.error.HTTPError as error:
+        # If the tile is missing, enable the `is_missing` flag in HipsTile.
         if error.code == 404:
-            error.msg = f'Tile not found at:\n{url}'
-        raise
+            return {'is_missing': True}
+        #     error.msg = f'Tile not found at:\n{url}'
+        # raise
     except urllib.error.URLError as error:
         if isinstance(error.reason, socket.timeout):
             raise TimeoutError(f'The server timed out while fetching the tile at:\n{url}')

hips/tiles/tile.py

@@ -154,6 +154,8 @@ class HipsTile:
         Metadata of HiPS tile
     raw_data : `bytes`
         Raw data (copy of bytes from file)
+    is_missing : `bool`
+        To check whether the tile is missing or not
 
     Examples
     --------
@@ -175,9 +177,10 @@ class HipsTile:
     int16
     """
 
-    def __init__(self, meta: HipsTileMeta, raw_data: bytes) -> None:
+    def __init__(self, meta: HipsTileMeta, raw_data: bytes, is_missing: bool = False) -> None:
         self.meta = meta
         self.raw_data = raw_data
+        self.is_missing = is_missing
         self._data = None
 
     def __eq__(self, other: "HipsTile") -> bool:
@@ -259,8 +262,10 @@ def data(self) -> np.ndarray:
 
         See the `to_numpy` function.
         """
-        if self._data is None:
+        if self._data is None and not self.is_missing:
             self._data = self.to_numpy(self.raw_data, self.meta.file_format)
+        elif self.is_missing:
+            self._data = np.zeros((compute_image_shape(self.meta.width, self.meta.width, self.meta.file_format)))
 
         return self._data
 
@@ -295,6 +300,7 @@ def to_numpy(raw_data: bytes, fmt: str) -> np.ndarray:
         elif fmt in {"jpg", "png"}:
             with Image.open(bio) as image:
                 data = np.array(image)
+
             # Flip tile to be consistent with FITS orientation
             data = np.flipud(data)
         else:
@@ -316,6 +322,7 @@ def read(cls, meta: HipsTileMeta, filename: str = None) -> "HipsTile":
         filename : str
             Filename
         """
+        # TODO: Handle case for files that don't exist.
         raw_data = Path(filename).read_bytes()
         return cls(meta, raw_data)
 
@@ -330,6 +337,7 @@ def fetch(cls, meta: HipsTileMeta, url: str) -> "HipsTile":
         url : str
             URL containing HiPS tile
         """
+        # TODO: Add timeout and error handling.
         with urllib.request.urlopen(url) as response:
             raw_data = response.read()