Google Cloud Workflows中解码Firestore事件的Protobuf负载

问题背景 #

我使用YAML定义Google Cloud Workflow，通过EventArc监听Firestore文档保存事件，触发器运行正常，但无法解码收到的Protobuf消息，也找不到相关文档。以下是收到的示例消息和当前Workflow YAML代码，请求指导如何解码给定消息中的Protobuf。

示例消息 #

{
  "data": "CrUECpYECjoKFhIUZX5maXJlY21zLWRlbW8tMjcxNTASIAoIcHJvZHVjdHMaFDByTzUzNnFxR3dzRzdVSEtTUnNjGgwKBmltYWdlcxICSgAaEwoKanNvbl9maWVsZBIFMgCYAQEaRgoKbWFpbl9pbWFnZRI4igEyaW1hZ2VzL3A3c3RwX3Bob3RvLTE1MzE3NDYwMjA3OTgtZTY5NTNjNmU4ZTA0LmF2aWaYAQEaEgoJYXZhaWxhYmxlEgUIAJgBARoUCgtkZXNjcmlwdGlvbhIFWACYAQEaGwoOdXBwZXJjYXNlX25hbWUSCYoBA0NDQ5gBARohChFhdmFpbGFibGVfbG9jYWxlcxIMSgoKCIoBAmVzmAEBGhYKEHJlbGF0ZWRfcHJvZHVjdHMSAkoAGgoKBHRhZ3MSAkoAGg8KBnB1YmxpYxIFCACYAQEaFAoLYW1hem9uX2xpbmsSBVgAmAEBGg4KBXByaWNlEgVYAJgBARoRCgRuYW1lEgmKAQNjY2OYAQEaNwoJcHVibGlzaGVyEioyJRoNCgRuYW1lEgVYAJgBARoUCgtleHRlcm5hbF9pZBIFWACYAQGYAQEaFQoIY3VycmVuY3kSCYoBA0RPTJgBARoRCghjYXRlZ29yeRIFWACYAQEaEwoFYnJhbmQSCooBBHZydnKYAQEaHQoIYWRkZWRfb24SEVIMCOufsrAGEIDqgIcDmAEBKgwI65+ysAYQmNqamwMyDAjrn7KwBhCY2pqbAw==",
  "database": "(default)",
  "datacontenttype": "application/protobuf",
  "dataschema": "https://github.com/googleapis/google-cloudevents/blob/main/proto/google/events/cloud/datastore/v1/data.proto",
  "entity": "products/0rO536qqGwsG7UHKSRsc",
  "id": "8da5a03c-3779-4d46-be20-546841cbaa8c",
  "location": "europe-west1",
  "namespace": "(default)",
  "project": "firecms-demo-27150",
  "source": "//firestore.googleapis.com/projects/firecms-demo-27150/databases/(default)",
  "specversion": "1.0",
  "subject": "documents/products/0rO536qqGwsG7UHKSRsc",
  "time": "2024-04-02T23:08:27.862367Z",
  "type": "google.cloud.datastore.entity.v1.created"
}

当前Workflow YAML代码 #

main:
  params: [event]
  steps:
      - extract_data:
          assign:
            - data: # How do I decode a protobuf from the given message??
          
      - create_document:
            call: googleapis.firestore.v1.projects.databases.documents.patch
            args:
                name: ${name}
                body:
                    fields:
                        test_new_field:
                            stringValue: abc

解决方案 #

Google Cloud Workflow内置了googleapis.events.decode函数，专门用于解码Google Cloud Events的Protobuf数据。你只需要在步骤中调用该函数，传入base64编码的event.data和对应的Protobuf消息类型即可。

修改后的完整YAML代码 #

main:
  params: [event]
  steps:
    - extract_data:
        assign:
          # 解码Protobuf数据，指定对应的消息类型
          - decoded_data: ${googleapis.events.decode(event.data, "google.events.cloud.datastore.v1.EntityEventData")}
          # 提取Firestore实体的字段内容
          - entity_fields: ${decoded_data.value.fields}
          # 从event的subject字段获取文档的完整路径
          - document_name: ${event.subject}
    - create_document:
        call: googleapis.firestore.v1.projects.databases.documents.patch
        args:
          name: ${document_name}
          body:
            fields:
              test_new_field:
                stringValue: abc

关键说明 #

• googleapis.events.decode函数接收两个参数：
  1. 第一个参数是事件中的data字段（base64编码的Protobuf内容）
  2. 第二个参数是Protobuf消息类型的全称，这里对应Firestore实体事件的类型是google.events.cloud.datastore.v1.EntityEventData
• 解码后，decoded_data.value就是触发事件的Firestore实体对象，其fields属性包含了该文档的所有字段数据
• 文档的完整路径可以直接从事件的subject字段获取，无需额外拼接

内容的提问来源于stack exchange，提问作者gatti