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Merge pull request #40 from status-im/remove/payload
Update status-whisper-usage-spec.md
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Oskar Thorén
GitHub
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@ -10,11 +10,6 @@
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- [Terminology](#terminology)
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- [Basic Assumption](#basic-assumption)
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- [Protocol Overview](#protocol-overview)
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- [Payload](#payload)
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- [Content types](#content-types)
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- [Message types](#message-types)
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- [Clock vs Timestamp and message ordering](#clock-vs-timestamp-and-message-ordering)
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- [Replies](#replies)
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- [Whisper adapter](#whisper-adapter)
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- [Whisper node configuration](#whisper-node-configuration)
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- [Keys management](#keys-management)
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@ -91,65 +86,6 @@ Offline messaging describes how the protocol handles delivering messages when on
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The protocol does not specify additional things like peers discovery, running Whisper nodes, underlying p2p protocols etc.
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# Payload
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Payload is an array of bytes exchanged between peers. In the case of this protocol, the payload is encoded using [transit format](https://github.com/cognitect/transit-format). It is a text-based format so even encoded version is easily readable by humans.
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Payload contains the following fields:
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1. text `string`
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2. content type `enum { text/plain }` (more in [Content types](#content-types))
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3. message type `enum { public-group-user-message, user-message, group-user-message }` (more in [Message types](#message-types))
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4. clock `int64`
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5. timestamp `int64`
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6. content `struct { chat-id string, text string }`
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Example of a valid encoded payload:
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```
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["~#c4",["abc123","text/plain","~:public-group-user-message",154593077368201,1545930773682,["^ ","~:chat-id","testing-adamb","~:text","abc123"]]]
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```
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As you can see, the message is an array and each index value has its meaning:
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* 0: `c4` is a decoder handler identification for the current payload format. Identifications allow to register handlers for many different types of payload
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* 1: array which items correspond to the described payload fields above
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For more details regarding serialization and deserialization please consult [transit format](https://github.com/cognitect/transit-format) specification.
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## Content types
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Content types are required for a proper interpretation of incoming messaages. Not each message is a plain text but may carry a different information.
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The following content types MUST be supported:
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* `text/plain` identifies a message which content is a plain text
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* `sticker` TODO
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* `status` TODO
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* `command` TODO
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* `command-request` TODO
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* `emoji` TODO
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TODO: select which are required and which are client-specific.
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## Message types
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Message types are required to decide how a particular message is encrypted (more in [Whisper > Message encryption](#message-encryption)) and what metadata needs to be attacjed (more in [Whisper > Topic](#topic)) when passing a message to the transport layer.
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The following messages types MUST be supported:
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* `public-group-user-message` is a message to the public group
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* `user-message` is a private message
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* `group-user-message` is a message to the private group.
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## Clock vs Timestamp and message ordering
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`timestamp` MUST be Unix time calculated when the message is created. Because the peers in the Whisper network should have synchronized time, `timestamp` values should be fairly accurate among all Whisper network participants.
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`clock` SHOULD be calculated using the algorithm of [Lamport timestamps](https://en.wikipedia.org/wiki/Lamport_timestamps). When there are messages available in a chat, `clock`'s value is calculated based on the last received message in a particular chat: `last-message-clock-value + 1`. If there are no messages, `clock` is initialized with `timestamp`'s value.
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`clock` value is used for the message ordering. Due to the used algorithm and distributed nature of the system, we achieve casual ordering which might produce counterintuitive results in some edge cases. For example, when one joins a public chat and sends a message before receiving the exist messages, their message `clock` value might be lower and the message will end up in the past when the historical messages are fetched.
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## Replies
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TBD
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# Whisper adapter
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Whisper in version 6 has been chosen as an messages exchange protocol because it was designed as an off-chain communication layer for the Ethereum nodes. It supports e2e encryption and uses epidemic spread to route data to all members of the network. It also provides [darkness to some extent](https://github.com/ethereum/go-ethereum/wiki/Achieving-Darkness).
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