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A Distributed Hash Table

The below is an HTTP-based riff on Kademlia.

Requests and responses to any of the endpoints below also include Doenet-Node: which is a URL to the Doenet node's DHT endpoint. This URL is converted to a node ID by computing the sha256 of its URL. This must end in DOENET_STRENGTH many zero bits to be accepted on Doenet. This prevents nodes from freely choosing their ID (to prevent an eclipse attack) and prevents an adversary from producing very large numbers of nodes (to prevent a sybil attack). This suggestion is based off S/Kademlia.

Environment variables

DOENET_NODE is the url for the node.

DOENET_STRENGTH is the number of zero bits required for a node ID to be accepted on the network. In particular, sha256 of DOENET_NODE must end in DOENET_STRENGTH zero bits.

DOENET_BOOTSTRAP is a space-separated list of URLs which may be used to bootstrap our node.

DOENET_K is the size of the k-buckets. This defaults to 20.

DOENET_ALPHA is the desired concurrency parameter. This defaults to 3.

RPC endpoints

These endpoints are relative to DOENET_NODE. For instance, in order to satisfy the DOENET_STRENGTH requirement, the server hosted at doenet.cloud may use the base https://doenet.cloud/557935472 because as verified by

echo -ne https://doenet.cloud/557935472 | sha256sum

this URL ends with many zero bits. One can ping this server via https://doenet.cloud/557935472/ping.

GET /status

Some information about the status of the network. Currently this dumps information about the routing table.

GET /ping

Verify that a Doenet node is alive. This is used to update the routing table, i.e., to decide whether to keep an long-running server in the bucket, or to replace it with a newly seen node.

GET /nodes/:id

This is Kademlia's FIND_NODE. The :id is a 64-byte (hex-encoded) node id.

The response is a JSON array of the k nodes with their id closest to the given id, with each node represented by its URL. The content-type is application/vnd.doenet.nodes+json.

PUT /keys/:key

Store the request body (probably encoded as JSON) at the given :key, which is a 64-byte (hex-encoded) id.

GET /keys/:key

If there is previousy PUT content at the given key, return it with content-type application/json. Otherwise this amounts to a GET /nodes/:id.

Redis representation

The 256 buckets are stored as sorted sets. Bucket n for node with id id is stored with key bucket:id:n with the score being the last-seen time.

dht:key stores the content.