WarpedVRT does its thing in __init__ rather than start

rasterio/_warp.pyx

@@ -627,19 +627,16 @@ cdef class WarpedVRTReaderBase(DatasetReaderBase):
         if init_dest_nodata is True and 'init_dest' not in warp_extras:
             self.warp_extras['init_dest'] = 'NO_DATA'
 
-    def start(self):
-        """Called to start reading a dataset."""
         cdef GDALDriverH driver = NULL
         cdef GDALDatasetH hds = NULL
         cdef GDALDatasetH hds_warped = NULL
         cdef const char *cypath = NULL
         cdef char *dst_crs_wkt = NULL
         cdef OGRSpatialReferenceH osr = NULL
-        cdef char **warp_extras = NULL
+        cdef char **c_warp_extras = NULL
         cdef GDALWarpOptions *psWOptions = NULL
-
-        cdef float tolerance = self.tolerance
-        cdef int resampling = self.resampling
+        cdef float c_tolerance = tolerance
+        cdef GDALResampleAlg c_resampling = resampling
 
         # Convert destination CRS to a C WKT string.
         try:
@@ -650,13 +647,6 @@ cdef class WarpedVRTReaderBase(DatasetReaderBase):
 
         log.debug("Exported CRS to WKT.")
 
-        #try:
-        #    with nogil:
-        #        hds = GDALOpen(cypath, <GDALAccess>0)
-        #    hds = exc_wrap_pointer(hds)
-        #except CPLE_OpenFailedError as err:
-        #    raise RasterioIOError(err.errmsg)
-
         hds = (<DatasetReaderBase?>self.src_dataset).handle()
         hds = exc_wrap_pointer(hds)
 
@@ -665,24 +655,24 @@ cdef class WarpedVRTReaderBase(DatasetReaderBase):
         for key, val in self.warp_extras.items():
             key = key.upper().encode('utf-8')
             val = str(val).upper().encode('utf-8')
-            warp_extras = CSLSetNameValue(
-                warp_extras, <const char *>key, <const char *>val)
+            c_warp_extras = CSLSetNameValue(
+                c_warp_extras, <const char *>key, <const char *>val)
 
         psWOptions = create_warp_options(
-            <GDALResampleAlg>self.resampling, self.src_nodata,
-            self.dst_nodata, GDALGetRasterCount(hds), <const char **>warp_extras)
+            <GDALResampleAlg>c_resampling, self.src_nodata,
+            self.dst_nodata, GDALGetRasterCount(hds), <const char **>c_warp_extras)
 
         try:
             with nogil:
                 hds_warped = GDALAutoCreateWarpedVRT(
-                    hds, NULL, dst_crs_wkt, <GDALResampleAlg>resampling,
-                    tolerance, psWOptions)
+                    hds, NULL, dst_crs_wkt, c_resampling,
+                    c_tolerance, psWOptions)
             self._hds = exc_wrap_pointer(hds_warped)
         except CPLE_OpenFailedError as err:
             raise RasterioIOError(err.errmsg)
         finally:
             CPLFree(dst_crs_wkt)
-            CSLDestroy(warp_extras)
+            CSLDestroy(c_warp_extras)
             GDALDestroyWarpOptions(psWOptions)
 
 
@@ -702,10 +692,13 @@ cdef class WarpedVRTReaderBase(DatasetReaderBase):
 
         self._closed = False
 
+    def start(self):
+        """Starts the VRT's life cycle."""
+
         log.debug("Dataset %r is started.", self)
 
     def stop(self):
-        """Ends the dataset's life cycle"""
+        """Ends the VRT's life cycle"""
         if self._hds != NULL:
             GDALFlushCache(self._hds)
             GDALClose(self._hds)

rasterio/vrt.py

@@ -19,7 +19,7 @@ class WarpedVRT(WarpedVRTReaderBase, WindowMethodsMixin,
     ----------
 
     src_dataset : dataset
-        The dataset object that is virtually warped.
+        The dataset object to be virtually warped.
     dst_crs : CRS or str
         The warp operation's destination coordinate reference system.
     resampling : int
@@ -28,12 +28,14 @@ class WarpedVRT(WarpedVRTReaderBase, WindowMethodsMixin,
     tolerance : float
         The maximum error tolerance in input pixels when approximating
         the warp transformation. The default is 0.125.
-    src_nodata : float, int, or None
-        The nodata value for the source dataset.
-    dst_nodata : float, int, or None
+    src_nodata : float
+        A nodata value for the source data. It may be a value other
+        than the nodata value of src_dataset.
+    dst_nodata : float, int
         The nodata value for the virtually warped dataset.
     warp_extras : dict
-        GDAL extra warp options.
+        GDAL extra warp options. See
+        http://www.gdal.org/structGDALWarpOptions.html.
 
     Example
     -------
@@ -53,4 +55,10 @@ def __enter__(self):
         return self
 
     def __exit__(self, *args, **kwargs):
+        self.close()
+
+    def __del__(self):
+        self.close()
+
+    def close(self):
         self.stop()

tests/test_warpedvrt.py

@@ -0,0 +1,78 @@
+import boto3
+from packaging.version import parse
+import pytest
+
+import rasterio
+from rasterio.enums import Resampling
+from rasterio.vrt import WarpedVRT
+from rasterio.windows import Window
+
+
+# Custom markers.
+mingdalversion = pytest.mark.skipif(
+    parse(rasterio.__gdal_version__) < parse('2.1.0dev'),
+    reason="S3 raster access requires GDAL 2.1")
+
+credentials = pytest.mark.skipif(
+    not(boto3.Session()._session.get_credentials()),
+    reason="S3 raster access requires credentials")
+
+
+def test_warped_vrt(path_rgb_byte_tif):
+    """A VirtualVRT has the expected VRT properties."""
+    with rasterio.open(path_rgb_byte_tif) as src:
+        vrt = WarpedVRT(src, dst_crs='EPSG:3857')
+        assert vrt.dst_crs == 'EPSG:3857'
+        assert vrt.src_nodata is None
+        assert vrt.dst_nodata is None
+        assert vrt.tolerance == 0.125
+        assert vrt.resampling == Resampling.nearest
+        assert vrt.warp_extras == {'init_dest': 'NO_DATA'}
+
+
+def test_warped_vrt_source(path_rgb_byte_tif):
+    """A VirtualVRT has the expected source dataset."""
+    with rasterio.open(path_rgb_byte_tif) as src:
+        vrt = WarpedVRT(src, dst_crs='EPSG:3857')
+        assert vrt.src_dataset == src
+
+
+def test_wrap_file(path_rgb_byte_tif):
+    """A VirtualVRT has the expected dataset properties."""
+    with rasterio.open(path_rgb_byte_tif) as src:
+        vrt = WarpedVRT(src, dst_crs='EPSG:3857')
+        assert vrt.crs == 'EPSG:3857'
+        assert tuple(round(x, 1) for x in vrt.bounds) == (
+            -8789636.7, 2700460.0, -8524406.4, 2943560.2)
+        assert vrt.name.startswith('WarpedVRT(')
+        assert vrt.name.endswith('tests/data/RGB.byte.tif)')
+        assert vrt.indexes == (1, 2, 3)
+        assert vrt.nodatavals == (0, 0, 0)
+        assert vrt.dtypes == ('uint8', 'uint8', 'uint8')
+        assert vrt.read().shape == (3, 736, 803)
+
+
+def test_warp_extras(path_rgb_byte_tif):
+    """INIT_DEST warp extra is passed through."""
+    with rasterio.open(path_rgb_byte_tif) as src:
+        with WarpedVRT(src, dst_crs='EPSG:3857', init_dest=255) as vrt:
+            rgb = vrt.read()
+            assert (rgb[:, 0, 0] == 255).all()
+
+
+@mingdalversion
+@credentials
+@pytest.mark.network
+def test_wrap_s3():
+    """A warp wrapper's dataset has the expected properties"""
+    L8TIF = "s3://landsat-pds/L8/139/045/LC81390452014295LGN00/LC81390452014295LGN00_B1.TIF"
+    with rasterio.open(L8TIF) as src:
+        with WarpedVRT(src, dst_crs='EPSG:3857') as vrt:
+            assert vrt.crs == 'EPSG:3857'
+            assert tuple(round(x, 1) for x in vrt.bounds) == (
+                9556764.6, 2345109.3, 9804595.9, 2598509.1)
+            assert vrt.name == 'WarpedVRT(s3://landsat-pds/L8/139/045/LC81390452014295LGN00/LC81390452014295LGN00_B1.TIF)'
+            assert vrt.indexes == (1,)
+            assert vrt.nodatavals == (None,)
+            assert vrt.dtypes == ('uint16',)
+            assert vrt.shape == (7827, 7655)