Add from_buffer() method to BloomFilter c extension.

Also fixes a bug where the bloomfilter buffer was not zeroed-out
properly during initialization.

Fixes #2056

playhouse/_sqlite_ext.pyx

@@ -1099,7 +1099,7 @@ seeds[:] = [0, 1337, 37, 0xabcd, 0xdead, 0xface, 97, 0xed11, 0xcad9, 0x827b]
 cdef bf_t *bf_create(size_t size):
     cdef bf_t *bf = <bf_t *>calloc(1, sizeof(bf_t))
     bf.size = size
-    bf.bits = malloc(size)
+    bf.bits = calloc(1, size)
     return bf
 
 @cython.cdivision(True)
@@ -1152,6 +1152,9 @@ cdef class BloomFilter(object):
         if self.bf:
             bf_free(self.bf)
 
+    def __len__(self):
+        return self.bf.size
+
     def add(self, *keys):
         cdef bytes bkey
 
@@ -1171,6 +1174,19 @@ cdef class BloomFilter(object):
         # embedded NULL bytes.
         return buf
 
+    @classmethod
+    def from_buffer(cls, data):
+        cdef:
+            char *buf
+            Py_ssize_t buflen
+            BloomFilter bloom
+
+        PyBytes_AsStringAndSize(data, &buf, &buflen)
+
+        bloom = BloomFilter(buflen)
+        memcpy(bloom.bf.bits, <void *>buf, buflen)
+        return bloom
+
     @classmethod
     def calculate_size(cls, double n, double p):
         cdef double m = ceil((n * log(p)) / log(1.0 / (pow(2.0, log(2.0)))))

tests/cysqlite.py

@@ -376,9 +376,11 @@ def test_bloomfilter(self):
 
 
 class TestBloomFilter(BaseTestCase):
+    n = 1024
+
     def setUp(self):
         super(TestBloomFilter, self).setUp()
-        self.bf = BloomFilter(1024)
+        self.bf = BloomFilter(self.n)
 
     def test_bloomfilter(self):
         keys = ('charlie', 'huey', 'mickey', 'zaizee', 'nuggie', 'foo', 'bar',
@@ -392,6 +394,33 @@ def test_bloomfilter(self):
             self.assertFalse(key + '-y' in self.bf)
             self.assertFalse(key + ' ' in self.bf)
 
+    def test_bloomfilter_buffer(self):
+        self.assertEqual(len(self.bf), self.n)
+
+        # Buffer is all zeroes when uninitialized.
+        buf = self.bf.to_buffer()
+        self.assertEqual(len(buf), self.n)
+        self.assertEqual(buf, b'\x00' * self.n)
+
+        keys = ('alpha', 'beta', 'gamma', 'delta', 'epsilon', 'zeta')
+        self.bf.add(*keys)
+
+        for key in keys:
+            self.assertTrue(key in self.bf)
+            self.assertFalse(key + '-x' in self.bf)
+
+        # Convert to buffer and then populate a 2nd bloom-filter.
+        buf = self.bf.to_buffer()
+        new_bf = BloomFilter.from_buffer(buf)
+        for key in keys:
+            self.assertTrue(key in new_bf)
+            self.assertFalse(key + '-x' in new_bf)
+
+        # Ensure that the two underlying bloom-filter buffers are equal.
+        self.assertEqual(len(new_bf), self.n)
+        new_buf = new_bf.to_buffer()
+        self.assertEqual(buf, new_buf)
+
 
 class DataTypes(TableFunction):
     columns = ('key', 'value')