A decentralized quoting service.
The quoting service is capable of storing and distributing "quotes", and tracking when they expire.
Here a "quote" means an MCIP #31 "Signed Contingent Input", which is (informally) a signed offer to trade one cryptocurrency on the Mobilecoin network for another at some price.
See also MCIP #42 which added support for partial fills.
This quoting service can be used to facilitate private peer-to-peer trades.
The DEQS is organized as a decentralized peer-to-peer network for distributing signed quotes. (A quote consists of an Signed Contingent Input (SCI) together with some metadata such as a timestamp, an ID, a and list of involved currencies for convenience.)
The DEQS is somewhat restrictive about what SCIs it accepts. The MCIPs and the consensus network permit SCIs involving potentially many outputs, and as long as the rules are followed, the transaction is valid. However, the DEQS only accepts SCIs with exactly one fractional output, or, with exactly one required output, corresponding to either "partial fill" quotes or "all-or-nothing" quotes for exactly one currency in terms of some other currency. This makes it easy for the DEQS to expose a "quote book" across currency pairs and not have to keep track of and represent any more complex three currency swap offers and so on.
Any MobileCoin network participant is able to take one or more signed quotes, incorporate them into a transaction, and settle that transaction to the MobileCoin blockchain, completing a trade.
This does not reveal the identity of any party to the other, or reveal the volume of the trade, if partial fills are being used. Because a Quote reveals the key image of the input that it signed over, and reveals the public keys of any required TxOut's, it becomes clear to anyone watching the blockchain and the DEQS that this quote was filled.
Filling quotes in this way is inherently racy, if two people try to fill a quote at the same time, only one of them can succeed, because the MobileCoin network prevents the same key image from appearing twice in the blockchain in order to prevent double-spends generally.
The DEQS node offers several features.
The DeqsClient GRPC API:
- Submit quotes
- Get quotes of a desired type, from the node's local quote book
- Subscribe to streaming updates of the available quotes
A gossip network protocol based on libp2p (internal to the server):
- Broadcast a signed quote to peers
- Request all quotes from peers
A local sqllite database that backs up the known quotes:
- Helps the node recover quickly if it is rebooted.
The DEQS node relies on a local copy of the MobileCoin ledger, which it uses to validate quotes
and prune expired quotes. This needs to be synced by a separate process, such as mobilecoind or full-service.
TODO
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Install Rust from https://www.rust-lang.org/tools/install
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Install dependencies.
On Ubuntu:
sudo apt install build-essential protobuf-compiler
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Pull submodule.
git submodule update --init --recursive
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Run cargo as usual
cargo build
This code is available under open-source licenses. Look for the LICENSE file for more information.