rfc/content/docs/rfcs/36

slug	title	name	status	tags	editor	contributors
36	36/WAKU2-BINDINGS-API	Waku v2 C Bindings API	draft	waku-core	Richard Ramos <richard@status.im>	Franck Royer <franck@status.im>

Introduction

Native applications that wish to integrate Waku may not be able to use nwaku and its JSON RPC API due to constraints on packaging, performance or executables.

An alternative is to link existing Waku implementation as a static or dynamic library in their application.

This specification describes the C API that SHOULD be implemented by native Waku library and that SHOULD be used to consume them.

Design requirements

The API should be generic enough, so:

• it can be implemented by both nwaku and go-waku C-Bindings,
• it can be consumed from a variety of languages such as C#, Kotlin, Swift, Rust, C++, etc.

The selected format to pass data to and from the API is JSON.

It has been selected due to its widespread usage and easiness of use. Other alternatives MAY replace it in the future (C structure, protobuf) if it brings limitations that need to be lifted.

The API

General

JsonResponse type

All the API functions return a JsonResponse unless specified otherwise. JsonResponse is a char * whose format depends on whether the function was executed successfully or not.

On failure:

{
    error: string;
}

For example:

{
  "error": "the error message"
}

On success:

{
    result: any
}

The type of the result object depends on the function it was returned by.

JsonMessage type

A Waku Message in JSON Format:

{
    payload: string;
    contentTopic: string;
    version: number;
    timestamp: number;
}

Fields:

• payload: base64 encoded payload, waku_utils_base64_encode can be used for this.
• contentTopic: The content topic to be set on the message.
• version: The Waku Message version number.
• timestamp: Unix timestamp in nanoseconds.

DecodedPayload type

A payload once decoded, used when a received Waku Message is encrypted:

interface DecodedPayload {
    pubkey?: string;
    signature?: string;
    data: string;
    padding: string;
  }

Fields:

• pubkey: Public key that signed the message (optional), hex encoded with 0x prefix,
• signature: Message signature (optional), hex encoded with 0x prefix,
• data: Decrypted message payload base64 encoded,
• padding: Padding base64 encoded.

Events

Asynchronous events require a callback to be registered. An example of an asynchronous event that might be emitted is receiving a message. When an event is emitted, this callback will be triggered receiving a JSON string of type JsonSignal.

JsonSignal type

{
    type: string;
    event: any;
}

Fields:

• type: Type of signal being emitted. Currently, only message is available.
• event: Format depends on the type of signal.

For example:

{
  "type": "message",
  "event": {
    "subscriptionId": 1,
    "pubsubTopic": "/waku/2/default-waku/proto",
    "messageId": "0x6496491e40dbe0b6c3a2198c2426b16301688a2daebc4f57ad7706115eac3ad1",
    "wakuMessage": {
      "payload": "TODO",
      "contentTopic": "/my-app/1/notification/proto",
      "version": 1,
      "timestamp": 1647826358000000000
    }
  }
}

type	event Type
message	JsonMessageEvent

JsonMessageEvent type

Type of event field for a message event:

{
    pubsubTopic: string;
    messageId: string;
    wakuMessage: JsonMessage;
}

• pubsubTopic: The pubsub topic on which the message was received.
• messageId: The message id.
• wakuMessage: The message in JsonMessage format.

extern void waku_set_event_callback(void* cb)

Register callback to act as event handler and receive application signals, which are used to react to asynchronous events in Waku.

Parameters

1. void* cb: callback that will be executed when an async event is emitted. The function signature for the callback should be void myCallback(char* jsonSignal)

Node management

JsonConfig type

Type holding a node configuration:

interface JsonSignal {
    host?: string;
    port?: number;
    advertiseAddr?: string;
    nodeKey?: string;
    keepAliveInterval?: number;
    relay?: boolean;
    minPeersToPublish?: number
}

Fields:

All fields are optional. If a key is undefined, or null, a default value will be set.

• host: Listening IP address. Default 0.0.0.0.
• port: Libp2p TCP listening port. Default 60000. Use 0 for random.
• advertiseAddr: External address to advertise to other nodes. Can be ip4, ip6 or dns4, dns6. If null, the multiaddress(es) generated from the ip and port specified in the config (or default ones) will be used. Default: null.
• nodeKey: Secp256k1 private key in Hex format (0x123...abc). Default random.
• keepAliveInterval: Interval in seconds for pinging peers to keep the connection alive. Default 20.
• relay: Enable relay protocol. Default true.
• minPeersToPublish: The minimum number of peers required on a topic to allow broadcasting a message. Default 0.

For example:

{
  "host": "0.0.0.0",
  "port": 60000,
  "advertiseAddr": "1.2.3.4",
  "nodeKey": "0x123...567",
  "keepAliveInterval": 20,
  "relay": true,
  "minPeersToPublish": 0
}

extern char* waku_new(char* jsonConfig)

Instantiates a Waku node.

Parameters

1. char* jsonConfig: JSON string containing the options used to initialize a go-waku node. Type JsonConfig. It can be NULL to use defaults.

Returns

A JsonResponse. If the execution is successful, the result field is set to true.

For example:

{
  "result": true
}

extern char* waku_start()

Start a Waku node mounting all the protocols that were enabled during the Waku node instantiation.

Returns

A JsonResponse. If the execution is successful, the result field is set to true.

For example:

{
  "result": true
}

extern char* waku_stop()

Stops a Waku node.

Returns

A JsonResponse. If the execution is successful, the result field is set to true.

For example:

{
  "result": true
}

extern char* waku_peerid()

Get the peer ID of the waku node.

Returns

A JsonResponse. If the execution is successful, the result field contains the peer ID as a string (base58 encoded).

For example:

{
  "result": "QmWjHKUrXDHPCwoWXpUZ77E8o6UbAoTTZwf1AD1tDC4KNP"
}

extern char* waku_listen_addresses()

Get the multiaddresses the Waku node is listening to.

Returns

A JsonResponse. If the execution is successful, the result field contains an array of multiaddresses. The multiaddresses are strings.

For example:

{
  "result": [
    "/ip4/127.0.0.1/tcp/30303",
    "/ip4/1.2.3.4/tcp/30303",
    "/dns4/waku.node.example/tcp/8000/wss"
  ]
}

Connecting to peers

extern char* waku_add_peer(char* address, char* protocolId)

Add a node multiaddress and protocol to the waku node's peerstore.

Parameters

1. char* address: A multiaddress (with peer id) to reach the peer being added.
2. char* protocolId: A protocol we expect the peer to support.

Returns

A JsonResponse. If the execution is successful, the result field contains the peer ID as a base58 string of the peer that was added.

For example:

{
  "result": "QmWjHKUrXDHPCwoWXpUZ77E8o6UbAoTTZwf1AD1tDC4KNP"
}

extern char* waku_connect_peer(char* address, int timeoutMs)

Dial peer using a multiaddress.

Parameters

1. char* address: A multiaddress to reach the peer being dialed.
2. int timeoutMs: Timeout value in milliseconds to execute the call. If the function execution takes longer than this value, the execution will be canceled and an error returned. Use 0 for no timeout.

Returns

A JsonResponse. If the execution is successful, the result field is set to true.

For example:

{
   "result": true
}

extern char* waku_connect_peerid(char* peerId, int timeoutMs)

Dial peer using its peer ID.

Parameters

1char* peerID: Peer ID to dial. The peer must be already known. It must have been added before with waku_add_peer or previously dialed with waku_connect_peer. 2. int timeoutMs: Timeout value in milliseconds to execute the call. If the function execution takes longer than this value, the execution will be canceled and an error returned. Use 0 for no timeout.

Returns

A JsonResponse. If the execution is successful, the result field is set to true.

For example:

{
   "result": true
}

extern char* waku_disconnect_peer(char* peerId)

Disconnect a peer using its peerID

Parameters

1. char* peerID: Peer ID to disconnect.

Returns

A JsonResponse. If the execution is successful, the result field is set to true.

For example:

{
   "result": true
}

extern char* waku_peer_count()

Get number of connected peers.

Returns

A JsonResponse. If the execution is successful, the result field contains an integer which represents the number of connected peers.

For example:

{
  "result": 0
}

extern char* waku_peers()

Retrieve the list of peers known by the Waku node.

Returns

A JsonResponse containing a list of peers. The list of peers has this format:

{
  "result": [
    {
      "peerID": "16Uiu2HAmJb2e28qLXxT5kZxVUUoJt72EMzNGXB47RedcBafeDCBA",
      "protocols": [
        "/ipfs/id/1.0.0",
        "/vac/waku/relay/2.0.0",
        "/ipfs/ping/1.0.0"
      ],
      "addrs": [
        "/ip4/1.2.3.4/tcp/30303"
      ],
      "connected": true
    }
  ]
}

Waku Relay

extern char* waku_content_topic(char* applicationName, unsigned int applicationVersion, char* contentTopicName, char* encoding)

Create a content topic string according to RFC 23.

Parameters

1. char* applicationName
2. unsigned int applicationVersion
3. char* contentTopicName
4. char* encoding: depending on the payload, use proto, rlp or rfc26

Returns

char * containing a content topic formatted according to RFC 23.

/{application-name}/{version-of-the-application}/{content-topic-name}/{encoding}

extern char* waku_pubsub_topic(char* name, char* encoding)

Create a pubsub topic string according to RFC 23.

Parameters

1. char* name
2. char* encoding: depending on the payload, use proto, rlp or rfc26

Returns

char * containing a content topic formatted according to RFC 23.

/waku/2/{topic-name}/{encoding}

extern char* waku_default_pubsub_topic()

Returns the default pubsub topic used for exchanging waku messages defined in RFC 10.

Returns

char * containing the default pubsub topic:

/waku/2/default-waku/proto

extern char* waku_relay_publish(char* messageJson, char* pubsubTopic, int timeoutMs)

Publish a message using Waku Relay.

Parameters

1. char* messageJson: JSON string containing the Waku Message as JsonMessage.
2. char* pubsubTopic: pubsub topic on which to publish the message. If NULL, it uses the default pubsub topic.
3. int timeoutMs: Timeout value in milliseconds to execute the call. If the function execution takes longer than this value, the execution will be canceled and an error returned. Use 0 for no timeout.

Note: messageJson.version is overwritten to 0.

Returns

A JsonResponse. If the execution is successful, the result field contains the message ID.

extern char* waku_relay_publish_enc_asymmetric(char* messageJson, char* pubsubTopic, char* publicKey, char* optionalSigningKey, int timeoutMs)

Optionally sign, encrypt using asymmetric encryption and publish a message using Waku Relay.

Parameters

1. char* messageJson: JSON string containing the Waku Message as JsonMessage.
2. char* pubsubTopic: pubsub topic on which to publish the message. If NULL, it uses the default pubsub topic.
3. char* publicKey: hex encoded public key to be used for encryption.
4. char* optionalSigningKey: hex encoded private key to be used to sign the message.
5. int timeoutMs: Timeout value in milliseconds to execute the call. If the function execution takes longer than this value, the execution will be canceled and an error returned. Use 0 for no timeout.

Note: messageJson.version is overwritten to 1.

Returns

A JsonResponse. If the execution is successful, the result field contains the message ID.

extern char* waku_relay_publish_enc_symmetric(char* messageJson, char* pubsubTopic, char* symmetricKey, char* optionalSigningKey, int timeoutMs)

Optionally sign, encrypt using symmetric encryption and publish a message using Waku Relay.

Parameters

1. char* messageJson: JSON string containing the Waku Message as JsonMessage.
2. char* pubsubTopic: pubsub topic on which to publish the message. If NULL, it uses the default pubsub topic.
3. char* symmetricKey: hex encoded secret key to be used for encryption.
4. char* optionalSigningKey: hex encoded private key to be used to sign the message.
5. int timeoutMs: Timeout value in milliseconds to execute the call. If the function execution takes longer than this value, the execution will be canceled and an error returned. Use 0 for no timeout.

Note: messageJson.version is overwritten to 1.

Returns

A JsonResponse. If the execution is successful, the result field contains the message ID.

extern char* waku_relay_enough_peers(char* pubsubTopic)

Determine if there are enough peers to publish a message on a given pubsub topic.

Parameters

1. char* pubsubTopic: Pubsub topic to verify. If NULL, it verifies the number of peers in the default pubsub topic.

Returns

A JsonResponse. If the execution is successful, the result field contains a boolean indicating whether there are enough peers.

For example:

{
  "result": true
}

extern char* waku_relay_subscribe(char* topic)

Subscribe to a Waku Relay pubsub topic to receive messages.

Parameters

1. char* topic: Pubsub topic to subscribe to. If NULL, it subscribes to the default pubsub topic.

Returns

A JsonResponse. If the execution is successful, the result field is set to true.

For example:

{
  "result": true
}

Events

When a message is received, a ``"message" event is emitted containing the message, pubsub topic, and node ID in which the message was received.

The event type is JsonMessageEvent.

For Example:

{
  "type": "message",
  "event": {
    "subscriptionID": 1,
    "pubsubTopic": "/waku/2/default-waku/proto",
    "messageID": "0x6496491e40dbe0b6c3a2198c2426b16301688a2daebc4f57ad7706115eac3ad1",
    "wakuMessage": {
      "payload": "TODO",
      "contentTopic": "/my-app/1/notification/proto",
      "version": 1,
      "timestamp": 1647826358000000000
    }
  }
}

extern char* waku_relay_unsubscribe(char* topic)

Closes the pubsub subscription to a pubsub topic. No more messages will be received from this pubsub topic.

Parameters

1. char* pusubTopic: Pubsub topic to unsubscribe from. If NULL, unsubscribes from the default pubsub topic.

Returns

A JsonResponse. If the execution is successful, the result field is set to true.

For example:

{
   "result": true
}

Decrypting messages

extern char* waku_decode_symmetric(char* messageJson, char* symmetricKey)

Decrypt a message using a symmetric key

Parameters

1. char* messageJson: JSON string containing the Waku Message as JsonMessage.
2. char* symmetricKey: 32 byte symmetric key hex encoded.

Note: messageJson.version is expected to be 1.

Returns

A JsonResponse. If the execution is successful, the result field contains the decoded payload as a DecodedPayload. An error message otherwise.

{
  "result": {
    "pubkey": "0x......",
    "signature": "0x....",
    "data": "...",
    "padding": "..."
  }
}

extern char* waku_decode_asymmetric(char* messageJson, char* privateKey)

Decrypt a message using a secp256k1 private key

Parameters

1. char* messageJson: JSON string containing the Waku Message as JsonMessage.
2. char* privateKey: secp256k1 private key hex encoded.

Note: messageJson.version is expected to be 1.

Returns

A JsonResponse. If the execution is successful, the result field contains the decoded payload as a DecodedPayload. An error message otherwise.

{
  "result": {
    "pubkey": "0x......",
    "signature": "0x....",
    "data": "...",
    "padding": "..."
  }
}

Utils

extern char* waku_utils_base64_encode(char* data)

Encode a byte array to base64. Useful for creating the payload of a Waku Message in the format understood by waku_relay_publish

Parameters

1. char* data: Byte array to encode

Returns

A char * containing the base64 encoded byte array.

extern char* waku_utils_base64_decode(char* data)

Decode a base64 string (useful for reading the payload from Waku Messages).

Parameters

1. char* data: base64 encoded byte array to decode.

Returns

A JsonResponse. If the execution is successful, the result field contains the decoded payload.

Copyright

Copyright and related rights waived via CC0.