HTTP Connection Server Reference

This parameter specifies the recipient of a message.

The value must be a registration token, notification key, or topic.

This parameter specifies a list of devices (registration tokens, or IDs) receiving a multicast message. It must contain at least 1 and at most 1000 registration tokens.

Use this parameter only for multicast messaging, not for single recipients. Multicast messages (sending to more than 1 registration tokens) are allowed using HTTP JSON format only.

This parameter is deprecated. Instead, use to to specify message recipients. For more information on how to send messages to multiple devices using to, see Device Group Messaging.

This parameter identifies a group of messages (e.g., with collapse_key: "Updates Available") that can be collapsed, so that only the last message gets sent when delivery can be resumed. This is intended to avoid sending too many of the same messages when the device comes back online or becomes active.

Note that there is no guarantee of the order in which messages get sent.

Note: A maximum of 4 different collapse keys is allowed at any given time. This means a GCM connection server can simultaneously store 4 different send-to-sync messages per client app. If you exceed this number, there is no guarantee which 4 collapse keys the GCM connection server will keep.

Sets the priority of the message. Valid values are "normal" and "high." On iOS, these correspond to APNs priority 5 and 10.

By default, notification messages are sent with high priority, and data messages are sent with normal priority. Normal priority optimizes the client app's battery consumption, and should be used unless immediate delivery is required. For messages with normal priority, the app may receive the message with unspecified delay.

When a message is sent with high priority, it is sent immediately, and the app can wake a sleeping device and open a network connection to your server.

For more information, see Setting the priority of a message.

This parameter is deprecated. After Nov 15th 2016, it will be accepted by GCM, but ignored.

When this parameter is set to true, it indicates that the message should not be sent until the device becomes active.

The default value is false.

This parameter specifies how long (in seconds) the message should be kept in GCM storage if the device is offline. The maximum time to live supported is 4 weeks, and the default value is 4 weeks. For more information, see Setting the lifespan of a message.

This parameter, when set to true, allows developers to test a request without actually sending a message.

The default value is false.

This parameter specifies the custom key-value pairs of the message's payload.

For example, with data:{"score":"3x1"}:

On Android, this would result in an intent extra named score with the string value 3x1.

On iOS, if the message is sent via APNS, it represents the custom data fields. If it is sent via GCM connection server, it would be represented as key value dictionary in AppDelegate application:didReceiveRemoteNotification:.

The key should not be a reserved word ("from" or any word starting with "google" or "gcm"). Do not use any of the words defined in this table (such as collapse_key).

Values in string types are recommended. You have to convert values in objects or other non-string data types (e.g., integers or booleans) to string.

Indicates a sound to play when the device receives the notification. Supports default, or the filename of a sound resource bundled in the app.

Android sound files must reside in /res/raw/, while iOS sound files can be in the main bundle of the client app or in the Library/Sounds folder of the app’s data container. See the iOS Developer Library for more information.

The action associated with a user click on the notification.

On Android, if this is set, an activity with a matching intent filter is launched when user clicks the notification.

If set on iOS, corresponds to category in APNS payload.

Indicates the key to the body string for localization.

On iOS, this corresponds to "loc-key" in APNS payload.

On Android, use the key in the app's string resources when populating this value.

Indicates the string value to replace format specifiers in body string for localization.

On iOS, this corresponds to "loc-args" in APNS payload.

On Android, these are the format arguments for the string resource. For more information, see Formatting strings.

Indicates the key to the title string for localization.

On iOS, this corresponds to "title-loc-key" in APNS payload.

On Android, use the key in the app's string resources when populating this value.

Indicates the string value to replace format specifiers in title string for localization.

On iOS, this corresponds to "title-loc-args" in APNS payload.

On Android, these are the format arguments for the string resource. For more information, see Formatting strings.

This parameter specifies the client apps (registration IDs) receiving the message.

Multicast messaging (sending to more than one registration ID) is allowed using HTTP JSON format only.

This parameter specifies the key-value pairs of the message's payload. There is no limit on the number of key-value parameters, but there is a total message size limit of 4kb.

For instance, in Android, "data.score"."3x1" would result in an intent extra named score with the string value 3x1.

The key should not be a reserved word ("from" or any word starting with "google" or "gcm"). Do not use any of the words defined in this table (such as collapse_key).

• message_id: String specifying a unique ID for each successfully processed message.
• registration_id: Optional string specifying the canonical registration token for the client app that the message was processed and sent to. Sender should use this value as the registration token for future requests. Otherwise, the messages might be rejected.
• error: String specifying the error that occurred when processing the message for the recipient. The possible values can be found in table 9.

• If the client app unregisters with GCM.
• If the client app is automatically unregistered, which can happen if the user uninstalls the application. For example, on iOS, if the APNS Feedback Service reported the APNS token as invalid.
• If the registration token expires (for example, Google might decide to refresh registration tokens, or the APNS token has expired for iOS devices).
• If the client app is updated but the new version is not configured to receive messages.

• Authorization header missing or with invalid syntax in HTTP request.
• Invalid project number sent as key.
• Key valid but with GCM service disabled.
• Request originated from a server not whitelisted in the Server Key IPs.

The server couldn't process the request in time. Retry the same request, but you must:

• Honor the Retry-After header if it is included in the response from the GCM Connection Server.
• Implement exponential back-off in your retry mechanism. (e.g. if you waited one second before the first retry, wait at least two second before the next one, then 4 seconds and so on). If you're sending multiple messages, delay each one independently by an additional random amount to avoid issuing a new request for all messages at the same time.

Senders that cause problems risk being blacklisted.