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We still actively developing the protocol. It could change significantly
Syncmaven components communicate through a JSON-based protocol. While currently all Syncmaven components are entirely written in TypeScript, our goal is to allow users to develop destinations in any language using Docker. In other words, a destination could be implemented in any language you prefer, packaged into a Docker image, and set up to interact with Syncmaven using a JSON protocol via standard inputs and outputs. The protocol operates with two entities: the destination and the enrichment. Both destination and enrichment can be bundled in a single package, sharing the same Connection credentials. The protocol also incorporates additional components such as logging and error reporting. Destinations and enrichments communicate with Syncmaven using messages, each represented by a JSON object. There are two types of messages:
  1. Incoming messages: Sent from Syncmaven to enrichment or destination.
  2. Reply messages: Sent from destination or enrichment to Syncmaven.
In addition, Syncmaven establishes a parallel communication channel for state management. State can be used by destinations to implement incremental synchronization through checkpointing the status of previous runs. However, state is optional and should not be relied upon by destinations. In the absence of state, a full synchronization should be run. For Docker container executions, the state manager is passed in as two environment variables: RPC_URL and RPC_SECRET. Destinations should make a POST request to ${RPC_URL}/<method> with Authorization: Bearer ${RPC_SECRET} in the header.

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Destination flow

Here is the sequence diagram detailing the message interactions within the sync process.

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Message References

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log reply message

Used for destination and enrichment
A system message that can be sent by a destination or enrichment at any point to log information.

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halt reply message

Used for destination and enrichment
An equivalent of an exception. It signals the sync process to stop processing. Destination should use this message if credentials are invalid, if the destination is misconfigured or if any unrecoverable error occured during the sync process.

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describe Incoming Message

Used for destination and enrichment
The message request spec is for an enrichment or destination, with only one parameter - {"type": "describe"}. Upon request, the destination or enrichment responds with a spec message.

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spec reply message

Used for destination and enrichment
Defines a specification of a destination or enrichment. credentialsSchema maybe a Zod-schema or JSON-schema. 
{
  "type": "connection-spec",
  "credentialsSchema": {...} //JSON schema of credentials
}

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describe-streams incoming message

Used for destination

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start-stream incoming message

Used for destination

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start-enrichment incoming message

Used for enrichment

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enrichment-request incoming message

Used for enrichment

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enrichment-reply reply message

Used for enrichment

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row incoming message

Used for destination

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end-stream incoming message

Used for destination

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State management

State is used by destination to cache the artifacts of the previous run to remember what was synced to optimize subsequent runs. It could also be used by enrichment to cache the calls to remote APIs.
State should be treated as optimization cache. Sync shouldn’t rely on it’s presence. If state is empty, a full sync should be run.
If destination or enrichment written in TypeScript, the state manager is passed as a parameter. For docker containers, the state manager is passed in as two environment variables: RPC_URL and RPC_SECRET. Destinations should make a POST request to ${RPC_URL}/<method> with Authorization: Bearer ${RPC_SECRET} in the header. Each call must an JSON body, reply is also a JSON object.

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Keys and values

State is a key-value store. Keys are tuples of segments which are strings. If key contains one segment, it can be represented as a string instead of an array size of 1. Values are arbitrary JSON objects. Example of the key: ["syncId=123", "type=cursor"]
You should always include a syncId in the key to avoid conflicts between different syncs. syncId is a unique identifier of the sync configuration and is passed along with start-stream or start-enrichment messages.

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state.get

Get a value by key. 
{"key": ["segment1", "segment2"]}

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state.set

Sets a value for a key. 
{"key": ["segment1", "segment2"], value: {}}

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state.delete

Deletes a value by key. 
{"key": ["segment1", "segment2"]}

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state.deleteAll

Deletes all values with keys starting with the given prefix. Include both ["segment1", "segment2"] and ["segment1", "segment2", "segment3"] 
{"prefix": ["segment1", "segment2"]}

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state.list

List all key-value pairs with keys starting with the given prefix (e.g. ["segment1", "segment2"] or ["segment1", "segment2", "segment3"]). The response is streamed since the response can be large. It’s advised to use a streaming JSON parser to process the response. 
{"prefix": ["segment1", "segment2"]}