Raise a CRSError instead of ValueError + handling for '[]' and ''.

rasterio/crs.py

@@ -10,8 +10,11 @@
 #   {'proj': 'longlat', 'ellps': 'WGS84', 'datum': 'WGS84', 'no_defs': True}
 #
 
+
 import json
+
 from rasterio._base import is_geographic_crs, is_projected_crs, is_same_crs
+from rasterio.errors import CRSError
 from rasterio.five import string_types
 
 
@@ -57,8 +60,9 @@ def from_string(prjs):
             val = json.loads(prjs, strict=False)
         except ValueError:
             raise ValueError('crs appears to be JSON but is not valid')
+
         if not val:
-            raise ValueError("crs is empty JSON")
+            raise CRSError("crs is empty JSON")
         else:
             return val
 
@@ -86,7 +90,12 @@ def from_string(prjs):
         lambda kv: len(kv) == 2 and (kv[0], parse(kv[1])) or (kv[0], True),
         (p.split('=') for p in parts))
 
-    return dict((k, v) for k, v in items if k in all_proj_keys)
+    out = dict((k, v) for k, v in items if k in all_proj_keys)
+
+    if not out:
+        raise CRSError("crs is empty or invalid: {}".format(prjs))
+
+    return out
 
 
 def from_epsg(code):

tests/test_crs.py

@@ -8,6 +8,7 @@ import rasterio
 from rasterio import crs
 from rasterio.crs import (
     is_geographic_crs, is_projected_crs, is_same_crs, is_valid_crs)
+from rasterio.errors import CRSError
 
 
 logging.basicConfig(stream=sys.stderr, level=logging.DEBUG)
@@ -149,5 +150,9 @@ def test_is_valid():
 
 
 def test_empty_json():
-    with pytest.raises(ValueError):
+    with pytest.raises(CRSError):
         crs.from_string('{}')
+    with pytest.raises(CRSError):
+        crs.from_string('[]')
+    with pytest.raises(CRSError):
+        crs.from_string('')