1. Introduction
2. Requests
   i. FORWARD
   ii. NOTIFY
   iii. REGISTER
   iv. SUBSCRIBE
   v. UNSUBSCRIBE
3. Responses
   i. FAILED
   ii. SUCCESS
4. Signals
   i. CALLBACK
   ii. GOODBYE

Requests

FORWARD

Required Entries

Name	Description
source	The name of the application sending the forwarded notification

Optional Entries

Notes

• Must not include app-id: or event-id parameters;
• The server will use the client's IP address to help identify the source of the forwarded message.

Example

SNP/3.1 FORWARD
source: My App
title: Daily Notice
text: The fire alarm will be tested at 11am today
icon: stock:system-info
END

SUBSCRIBE

Required Entries

Name	Description
forward-to	The URL to send subsequent forwarded notifications to.
reply-port	The port to send subsequent forwarded notifications to.
uid	A unique identifier for the subscription.

Optional Entries

Name	Description
filter	One or more application identifiers separated by semicolons.
filter-type	Either inclusive or exclusive.

Notes

• The client can request all notifications, or only certain notifications, however the server ultimately decides which notifications it will forward;
• The server may require authentication - if so, the authentication details must be included in the request header in the normal way. See the Security section for further information;
• Subscription servers should handle both types of forwarding, however they are not obligated to do so. When sending a SUBSCRIBE request, the client must check the returned status to ensure the server accepted the request;
• The uid should be a string of alphanumeric characters (a GUID is a good example);
• Supplying both reply-port and forward-to is invalid and will return an error;
• See this guide for more detail - and a worked example - on subscriptions.

UNSUBSCRIBE

Required Entries

Name	Description
uid	The unique identifier used in the initial subscription.

Optional Entries

None.

Notes

• The request must be issued from the same IP address that was used for the initial subscription.
• Once a client is unsubscribed, it may resubscribe using either the same or a different password.

Example

SNP/3.1 UNSUBSCRIBE
uid: my_lame_uid
END

Responses

FAILED

A FAILED response indicates the request could not be processed by the server for some reason.

Standard Content

Name	Requirement	Description
error-number	Mandatory	The Snarl status code of the error as a positive integer
error-name	Mandatory	The Snarl status code as a string
reason	Mandatory	Further context or supporting information explaining the error. Must be included, but may be blank

Optional Content

Servers may include additional information in the form of x- header entries. Servers must not return data- entries however.

Notes

None.

Example

SNP/3.1 FAILED
error-number: 202
error-name: NotRegistered
reason:
END

SUCCESS

Standard Content

None.

Optional Content

A success response may contain additional information, however this will be relevant to the request the response pertains to.

Servers may include additional information in the form of x- header entries. Servers should not return data- entries however.

Notes

Examples

Example returning some data:

SNP/3.1 SUCCESS
data-example: some data here
data-value: 23
END

Example returning no extra data:

SNP/3.1 SUCCESS
END

Signals

CALLBACK

A callback signal is sent either to a listening TCP port on the client machine that created the notification, or to a URL as an HTTP POST request.

Due to the asynchronous nature that notifications may appear, and when a user may react to a notification (if at all), callback messages can arrive at any time and in any sequence. The receiving client can determine which callback message refers to which notification using the uid parameter, any data- values included in the notification, or a combination of the two.

Standard Content

None.

SNP/3.1 CALLBACK
callback-number: 303
callback-type: NotificationExpired
uid: 
x-callback-timestamp: Mon, 23 Apr 2018 13:43:55 GMT
END

Optional Content

Name	Value
uid	The uid supplied when the notification was created (if one was provided)
data-*	Any data parameters supplied when the notification was created

Notes

• The server may also include additional metadata in terms of x- headers.

Example

The following callback message indicates that a notification was closed by the end user. The notification was created with a uid of my_lame_uid and included some additional data- parameters:

SNP/3.1 CALLBACK
uid: my_lame_uid
data-guardian: Len
data-wossname: cheese
data-place: On The Bus
END

GOODBYE

A GOODBYE message is sent by a subscription server when it is closing. This can be used to notify subscribers that they should no longer expect to received forwarded notifications from the server. The subscriber is free to attempt to reconnect (as the server may simply be restarting), but should wait a short period of time (at least 30 seconds) before doing so.

Standard Content

Name	Value
uid	The UID specified by the subscriber when it originally subscribed.

Optional Content

Name	Value
x-reason	Human readable text indicating why the server is stopping
x-retry-after	Number of seconds clients should wait before retrying a connection to the server

Notes

None.

Example

SNP/3.1 GOODBYE
uid: some_uid
END