msgpack: support datetime extended type

Tarantool supports datetime type since version 2.10.0 [1]. This patch
introduced the support of Tarantool datetime type in msgpack decoders
and encoders.

The Tarantool datetime type is mapped to new tarantool.Datetime type
which inherits pandas.Timestamp [2]. pandas.Timestamp was chosen as a
base class because it could be used to store both nanoseconds and
timezone information. In-build Python datetime.datetime supports
microseconds at most, numpy.datetime64 do not support timezones. There
are two reasons to use custom type instead of plain pandas.Timestamp:
- tzindex may be lost on conversion to pandas.Timestamp
- Tarantool datetime interval type is planned to be stored in custom
  type tarantool.Interval and we'll need a way to support arithmetic
  between datetime and interval.

msgpack encoder supports encoding pandas.Timestamp with
tarantool.Datetime tools, but it always decodes to tarantool.Datetime.
If you plan to work with tarantool datetimes, please stick to the
tarantool.Datetime object rather than pure pandas.Timestamp. You can
create tarantool.Datetime from pandas.Timestamp or by using the same
API as in plain pandas.Timestamp. If you used numpy.datetime64 or
datetime.datetime in your logic, you can use pandas.to_datetime64() and
pandas.to_datetime() converters.

This patch does not yet introduce the support of timezones in datetime.

1. tarantool/tarantool#5941
2. https://pandas.pydata.org/docs/reference/api/pandas.Timestamp.html

Part of #204

Author: DifferentialOrange

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Decimal type support (#203).
 - UUID type support (#202).
+- Datetime type support and tarantool.Datetime type (#204).
 
 ### Changed
 - Bump msgpack requirement to 1.0.4 (PR #223).

requirements.txt

@@ -1 +1,2 @@
 msgpack>=1.0.4
+pandas

tarantool/__init__.py

@@ -32,6 +32,10 @@
     ENCODING_DEFAULT,
 )
 
+from tarantool.msgpack_ext.types import (
+    Datetime,
+)
+
 __version__ = "0.9.0"
 
 
@@ -91,7 +95,7 @@ def connectmesh(addrs=({'host': 'localhost', 'port': 3301},), user=None,
 
 __all__ = ['connect', 'Connection', 'connectmesh', 'MeshConnection', 'Schema',
            'Error', 'DatabaseError', 'NetworkError', 'NetworkWarning',
-           'SchemaError', 'dbapi']
+           'SchemaError', 'dbapi', 'Datetime']
 
 # ConnectionPool is supported only for Python 3.7 or newer.
 if sys.version_info.major >= 3 and sys.version_info.minor >= 7:

tarantool/error.py

@@ -119,6 +119,16 @@ class MsgpackWarning(UserWarning):
     Warning with encoding or decoding of MP_EXT types
     '''
 
+class ExtTypeError(ValueError):
+    '''
+    Error related to tarantool.Datetime type
+    '''
+
+class ExtTypeWarning(UserWarning):
+    '''
+    Warning related to tarantool.Datetime type
+    '''
+
 __all__ = ("Warning", "Error", "InterfaceError", "DatabaseError", "DataError",
            "OperationalError", "IntegrityError", "InternalError",
            "ProgrammingError", "NotSupportedError", "MsgpackError",

tarantool/msgpack_ext/datetime.py

@@ -0,0 +1,9 @@
+from tarantool.msgpack_ext.types import Datetime
+
+EXT_ID = 4
+
+def encode(obj):
+    return Datetime.msgpack_encode(obj)
+
+def decode(data):
+    return Datetime(data)

tarantool/msgpack_ext/packer.py

@@ -1,13 +1,19 @@
 from decimal import Decimal
 from uuid import UUID
 from msgpack import ExtType
+import pandas
+
+import tarantool.msgpack_ext.types as types
 
 import tarantool.msgpack_ext.decimal as ext_decimal
 import tarantool.msgpack_ext.uuid as ext_uuid
+import tarantool.msgpack_ext.datetime as ext_datetime
 
 encoders = [
-    {'type': Decimal, 'ext': ext_decimal},
-    {'type': UUID,    'ext': ext_uuid   },
+    {'type': Decimal,          'ext': ext_decimal },
+    {'type': UUID,             'ext': ext_uuid    },
+    {'type': types.Datetime,   'ext': ext_datetime},
+    {'type': pandas.Timestamp, 'ext': ext_datetime},
 ]
 
 def default(obj):

tarantool/msgpack_ext/types/__init__.py

@@ -0,0 +1,3 @@
+from tarantool.msgpack_ext.types.datetime import Datetime
+
+__all__ = ['Datetime']

tarantool/msgpack_ext/types/datetime.py

@@ -0,0 +1,95 @@
+import pandas
+
+# https://www.tarantool.io/ru/doc/latest/dev_guide/internals/msgpack_extensions/#the-datetime-type
+#
+# The datetime MessagePack representation looks like this:
+# +---------+----------------+==========+-----------------+
+# | MP_EXT  | MP_DATETIME    | seconds  | nsec; tzoffset; |
+# | = d7/d8 | = 4            |          | tzindex;        |
+# +---------+----------------+==========+-----------------+
+# MessagePack data contains:
+#
+# * Seconds (8 bytes) as an unencoded 64-bit signed integer stored in the
+#   little-endian order.
+# * The optional fields (8 bytes), if any of them have a non-zero value.
+#   The fields include nsec (4 bytes), tzoffset (2 bytes), and
+#   tzindex (2 bytes) packed in the little-endian order.
+#
+# seconds is seconds since Epoch, where the epoch is the point where the time
+# starts, and is platform dependent. For Unix, the epoch is January 1,
+# 1970, 00:00:00 (UTC). Tarantool uses a double type, see a structure
+# definition in src/lib/core/datetime.h and reasons in
+# https://github.com/tarantool/tarantool/wiki/Datetime-internals#intervals-in-c
+#
+# nsec is nanoseconds, fractional part of seconds. Tarantool uses int32_t, see
+# a definition in src/lib/core/datetime.h.
+#
+# tzoffset is timezone offset in minutes from UTC. Tarantool uses a int16_t type,
+# see a structure definition in src/lib/core/datetime.h.
+#
+# tzindex is Olson timezone id. Tarantool uses a int16_t type, see a structure
+# definition in src/lib/core/datetime.h. If both tzoffset and tzindex are
+# specified, tzindex has the preference and the tzoffset value is ignored.
+
+SECONDS_SIZE_BYTES  = 8
+NSEC_SIZE_BYTES     = 4
+TZOFFSET_SIZE_BYTES = 2
+TZINDEX_SIZE_BYTES  = 2
+
+BYTEORDER = 'little'
+
+NSEC_IN_SEC = 1000000000
+
+
+def get_bytes_as_int(data, cursor, size):
+    part = data[cursor:cursor + size]
+    return int.from_bytes(part, BYTEORDER, signed=True), cursor + size
+
+def get_int_as_bytes(data, size):
+    return data.to_bytes(size, byteorder=BYTEORDER, signed=True)
+
+def msgpack_decode(data):
+    cursor = 0
+    seconds, cursor = get_bytes_as_int(data, cursor, SECONDS_SIZE_BYTES)
+
+    if len(data) > SECONDS_SIZE_BYTES:
+        nsec, cursor     = get_bytes_as_int(data, cursor, NSEC_SIZE_BYTES)
+        tzoffset, cursor = get_bytes_as_int(data, cursor, TZOFFSET_SIZE_BYTES)
+        tzindex, cursor  = get_bytes_as_int(data, cursor, TZINDEX_SIZE_BYTES)
+    else:
+        nsec = 0
+        tzoffset = 0
+        tzindex = 0
+
+    if (tzoffset != 0) or (tzindex != 0):
+        raise NotImplementedError
+
+    total_nsec = seconds * NSEC_IN_SEC + nsec
+
+    dt = pandas.to_datetime(total_nsec, unit='ns')
+    return dt, tzoffset, tzindex
+
+class Datetime(pandas.Timestamp):
+    def __new__(cls, *args, **kwargs):
+        if len(args) > 0 and isinstance(args[0], bytes):
+            dt, tzoffset, tzindex = msgpack_decode(args[0])
+        else:
+            dt = super().__new__(cls, *args, **kwargs)
+
+        dt.__class__ = cls
+        return dt
+
+    def msgpack_encode(self):
+        seconds = self.value // NSEC_IN_SEC
+        nsec = self.value % NSEC_IN_SEC
+        tzoffset = 0
+        tzindex = 0
+
+        buf = get_int_as_bytes(seconds, SECONDS_SIZE_BYTES)
+
+        if (nsec != 0) or (tzoffset != 0) or (tzindex != 0):
+            buf = buf + get_int_as_bytes(nsec, NSEC_SIZE_BYTES)
+            buf = buf + get_int_as_bytes(tzoffset, TZOFFSET_SIZE_BYTES)
+            buf = buf + get_int_as_bytes(tzindex, TZINDEX_SIZE_BYTES)
+
+        return buf

tarantool/msgpack_ext/unpacker.py

@@ -1,9 +1,11 @@
 import tarantool.msgpack_ext.decimal as ext_decimal
 import tarantool.msgpack_ext.uuid as ext_uuid
+import tarantool.msgpack_ext.datetime as ext_datetime
 
 decoders = {
-    ext_decimal.EXT_ID: ext_decimal.decode,
-    ext_uuid.EXT_ID   : ext_uuid.decode   ,
+    ext_decimal.EXT_ID : ext_decimal.decode ,
+    ext_uuid.EXT_ID    : ext_uuid.decode    ,
+    ext_datetime.EXT_ID: ext_datetime.decode,
 }
 
 def ext_hook(code, data):

test/suites/lib/skip.py

@@ -154,3 +154,14 @@ def skip_or_run_UUID_test(func):
 
     return skip_or_run_test_tarantool(func, '2.4.1',
                                       'does not support UUID type')
+
+def skip_or_run_datetime_test(func):
+    """Decorator to skip or run datetime-related tests depending on
+    the tarantool version.
+
+    Tarantool supports datetime type only since 2.10.0 version.
+    See https://github.com/tarantool/tarantool/issues/5941
+    """
+
+    return skip_or_run_test_pcall_require(func, 'datetime',
+                                      'does not support datetime type')