PubsubMessage

A message that is published by publishers and consumed by subscribers. The message must contain either a non-empty data field or at least one attribute. Note that client libraries represent this object differently depending on the language. See the corresponding client library documentation for more information. See quotas and limits for more information about message limits.

JSON representation 
{
  "data": string,
  "attributes": {
    string: string,
    ...
  },
  "messageId": string,
  "publishTime": string,
  "orderingKey": string
}
Fields
data

string (bytes format)

Optional. The message data field. If this field is empty, the message must contain at least one attribute.

A base64-encoded string.
attributes

map (key: string, value: string)

Optional. Attributes for this message. If this field is empty, the message must contain non-empty data. This can be used to filter messages on the subscription.

An object containing a list of "key": value pairs. Example: { "name": "wrench", "mass": "1.3kg", "count": "3" }.
messageId

string

ID of this message, assigned by the server when the message is published. Guaranteed to be unique within the topic. This value may be read by a subscriber that receives a PubsubMessage via a subscriptions.pull call or a push delivery. It must not be populated by the publisher in a topics.publish call.
publishTime

string (Timestamp format)

The time at which the message was published, populated by the server when it receives the topics.publish call. It must not be populated by the publisher in a topics.publish call.

A timestamp in RFC3339 UTC "Zulu" format, with nanosecond resolution and up to nine fractional digits. Examples: "2014-10-02T15:01:23Z" and "2014-10-02T15:01:23.045123456Z".
orderingKey

string

Optional. If non-empty, identifies related messages for which publish order should be respected. If a Subscription has enableMessageOrdering set to true, messages published with the same non-empty orderingKey value will be delivered to subscribers in the order in which they are received by the Pub/Sub system. All PubsubMessages published in a given PublishRequest must specify the same orderingKey value. For more information, see ordering messages.