Correct boundaries check for int; raise OverflowError for such cases

Since there is no error in a value representation and PyLong_AsLong(-Long)
raises exactly that exception if the value exceed the destination range, it
should be OverflowError instead of ValueError. Also make error message be
similar to one from the original OverflowError raised by PyLong_AsLong.

asyncpg/protocol/codecs/int.pyx

@@ -19,10 +19,17 @@ cdef bool_decode(ConnectionSettings settings, FastReadBuffer buf):
 
 
 cdef int2_encode(ConnectionSettings settings, WriteBuffer buf, obj):
-    cdef long val = cpython.PyLong_AsLong(obj)
-    if val < -32768 or val > 32767:
-        raise ValueError(
-            'integer too large to be encoded as INT2: {!r}'.format(val))
+    cdef int overflow = 0
+    cdef long val
+
+    try:
+        val = cpython.PyLong_AsLong(obj)
+    except OverflowError:
+        overflow = 1
+
+    if overflow or val < -32768 or val > 32767:
+        raise OverflowError(
+            'int too big to be encoded as INT2: {!r}'.format(obj))
 
     buf.write_int32(2)
     buf.write_int16(<int16_t>val)
@@ -33,20 +40,45 @@ cdef int2_decode(ConnectionSettings settings, FastReadBuffer buf):
 
 
 cdef int4_encode(ConnectionSettings settings, WriteBuffer buf, obj):
-    cdef int32_t val = <int32_t>cpython.PyLong_AsLong(obj)
+    cdef int overflow = 0
+    cdef long val
+
+    try:
+        val = cpython.PyLong_AsLong(obj)
+    except OverflowError:
+        overflow = 1
+
+    # "long" and "long long" have the same size for x86_64, need an extra check
+    if overflow or (sizeof(val) > 4 and (val < -2147483648 or
+                                         val > 2147483647)):
+        raise OverflowError(
+            'int too big to be encoded as INT4: {!r}'.format(obj))
 
     buf.write_int32(4)
-    buf.write_int32(val)
+    buf.write_int32(<int32_t>val)
 
 
 cdef int4_decode(ConnectionSettings settings, FastReadBuffer buf):
     return cpython.PyLong_FromLong(hton.unpack_int32(buf.read(4)))
 
 
 cdef int8_encode(ConnectionSettings settings, WriteBuffer buf, obj):
-    cdef int64_t val = cpython.PyLong_AsLongLong(obj)
+    cdef int overflow = 0
+    cdef long long val
+
+    try:
+        val = cpython.PyLong_AsLongLong(obj)
+    except OverflowError:
+        overflow = 1
+
+    # Just in case for systems with "long long" bigger than 8 bytes
+    if overflow or (sizeof(val) > 8 and (val < -9223372036854775808 or
+                                         val > 9223372036854775807)):
+        raise OverflowError(
+            'int too big to be encoded as INT8: {!r}'.format(obj))
+
     buf.write_int32(8)
-    buf.write_int64(val)
+    buf.write_int64(<int64_t>val)
 
 
 cdef int8_decode(ConnectionSettings settings, FastReadBuffer buf):

tests/test_codecs.py

@@ -472,7 +472,11 @@ async def test_invalid_input(self):
                 '2',
                 'aa',
             ]),
-            ('smallint', ValueError, 'integer too large', [
+            ('smallint', OverflowError, 'int too big to be encoded as INT2', [
+                2**256,  # check for the same exception for any big numbers
+                decimal.Decimal("2000000000000000000000000000000"),
+                0xffff,
+                0xffffffff,
                 32768,
                 -32769
             ]),
@@ -484,10 +488,24 @@ async def test_invalid_input(self):
                 '2',
                 'aa',
             ]),
+            ('int', OverflowError, 'int too big to be encoded as INT4', [
+                2**256,  # check for the same exception for any big numbers
+                decimal.Decimal("2000000000000000000000000000000"),
+                0xffffffff,
+                2**31,
+                -2**31 - 1,
+            ]),
             ('int8', TypeError, 'an integer is required', [
                 '2',
                 'aa',
             ]),
+            ('bigint', OverflowError, 'int too big to be encoded as INT8', [
+                2**256,  # check for the same exception for any big numbers
+                decimal.Decimal("2000000000000000000000000000000"),
+                0xffffffffffffffff,
+                2**63,
+                -2**63 - 1,
+            ]),
             ('text', TypeError, 'expected str, got bytes', [
                 b'foo'
             ]),