如何解码 protobuf Firestore 事件负载

Question

我有一个 Cloud Run 函数，它会在

google.cloud.firestore.document.v1.written

Firestore 事件上触发，如下所述：

from cloudevents.http import CloudEvent
import functions_framework
from google.events.cloud import firestore
from google.protobuf.json_format import MessageToDict

@functions_framework.cloud_event
def hello_firestore(cloud_event: CloudEvent) -> None:
    """Triggers by a change to a Firestore document.
    Args:
        cloud_event: cloud event with information on the firestore event trigger
    """
    firestore_payload = firestore.DocumentEventData()
    firestore_payload._pb.ParseFromString(cloud_event.data)

    # Convert protobuf to dictionary
    old_value_dict = MessageToDict(firestore_payload.old_value._pb) if firestore_payload.old_value else {}
    new_value_dict = MessageToDict(firestore_payload.value._pb) if firestore_payload.value else {}
    print(new_value_dict)
    print(old_value_dict)

但是，输出似乎是这种格式：

{
    "name": "projects/my-gcp-project/databases/mydb/documents/mycollection/e2767cc0-2e04-452d-9b7b-fc170e2128ec",
    "fields": {
        "created_at": {"stringValue": "2024-10-31T11:09:34.760557Z"},
        "session_id": {"stringValue": "e2767cc0-2e04-452d-9b7b-fc170e2128ec"},
        "user_profile": {
            "mapValue": {
                "fields": {
                    "age": {"integerValue": "36"},
                    "name": {"stringValue": "Andrew"},
                    "middle_name": {"nullValue": None}
                }
            }
        },
    ....
    "createTime": "2024-10-31T11:09:34.802575Z",
    "updateTime": "2024-10-31T12:13:36.154031Z",
}

如何以编程方式解码消息，以便将所有内容转换为 Python 本机类型，格式如下：

{
  "created_at": "2024-10-31T11:09:34.760557Z",
  "session_id": "e2767cc0-2e04-452d-9b7b-fc170e2128ec",
  "user_profile": {
      "age": 36, 
      "name": "Andrew", 
      "middle_name": None,
  }
}

Answer 1

令人惊讶的是，Google 的库中似乎没有（！？）进行此转换的功能。

正如 @frank-van-puffelen 所建议的，该功能虽然乏味但很简单：

requirements.txt

：

google-cloud-firestore==2.19.0
google-events==0.13.0

main.py

：

from proto.marshal.collections.maps import MapComposite

from google.events.cloud.firestore import (
    Document,
    DocumentEventData,
    ArrayValue,
    MapValue,
    Value,
)


def DocumentToDict(d: Document) -> dict:
    return {
        "name": d.name,
        "fields": MapCompositeToDict(d.fields),
        "create_time": d.create_time,
        "update_time": d.update_time,
    }


def ArrayValueToList(a: ArrayValue) -> list:
    result: list = []
    for value in a.values:
        result.append(ValueToDict(value))

    return result

def MapCompositeToDict(m: MapComposite) -> dict:
    result: dict = {}
    for key, value in m.items():
        key: str
        value: Value
        result[key] = ValueToDict(value)

    return result

def ValueToDict(v: Value) -> dict:
    λs = {
        "null_value": lambda v: None,
        "boolean_value": lambda v: v.boolean_value,
        "integer_value": lambda v: v.integer_value,
        "double_value": lambda v: v.double_value,
        "timestamp_value": lambda v: v.timestamp_value,
        "string_value": lambda v: v.string_value,
        "bytes_value": lambda v: v.bytes_value,
        "reference_value": lambda v: v.reference_value,
        "geo_point_value": lambda v: v.geo_point_value,
        "array_value": lambda v: ArrayValueToList(v.array_value),
        "map_value": lambda v: MapCompositeToDict(v.map_value.fields),
    }

    type = v._pb.WhichOneof("value_type")
    λ = λs[type]
    if λ is None:
        raise ValueError(f"Unknown type: {type}")
    
    return λ(v)


data = """
{
  "name": "projects/my-gcp-project/databases/mydb/documents/mycollection/e2767cc0-2e04-452d-9b7b-fc170e2128ec",
  "fields": {
      "created_at": {"stringValue": "2024-10-31T11:09:34.760557Z"},
      "session_id": {"stringValue": "e2767cc0-2e04-452d-9b7b-fc170e2128ec"},
      "user_profile": {
          "mapValue": {
              "fields": {
                  "age": {"integerValue": "36"},
                  "name": {"stringValue": "Andrew"},
                  "middle_name": {"nullValue": 0}
              }
          }
      }
    }, 
  "createTime": "2024-10-31T11:09:34.802575Z",
  "updateTime": "2024-10-31T12:13:36.154031Z"
}
"""
value: Document = Document.from_json(data)

d: dict = DocumentToDict(value)
print(d["fields"])

产量：

{
  'created_at': '2024-10-31T11:09:34.760557Z',
  'session_id': 'e2767cc0-2e04-452d-9b7b-fc170e2128ec',
  'user_profile': {
    'age': 36,
    'middle_name': None,
    'name': 'Andrew'
  }
}