Create Adapters.md

Adapters.md

@@ -0,0 +1,42 @@
+# Adapters
+
+## What is an Adapter
+
+* They are used to process work in a sub task (off-chain, within the ChainLink node)
+* They can be used to communicate with external services
+* Two categories of adapters: core and external
+* Utilize a minimal REST API
+
+## Core Adapters
+* **bitcoinComparisonJSON** Returns a signed Bitcoin transaction. Signs either a completion transaction or a failure transaction based on a value comparison of the input.
+* **ethereumBytes32** Formats the input as Ethereum bytes32 value and writes it into the specified contract. Returns the unformatted value that was provided as input.
+* **ethereumInt256** Formats the input as Ethereum int256 value and writes it into the specified contract. Returns the unformatted value that was provided as input.
+* **ethereumUint256** Formats the input as Ethereum uint256 value and writes it into the specified contract. Returns the unformatted value that was provided as input.
+* **ethereumFormatted** Writes a preformatted Ethereum hexadecimal value into the blockchain as configured. Returns the preformatted value that was provided as input.
+* **ethereumLogWatcher** Returns the data field of an Ethereum event log, if one is provided. Otherwise, returns the value that was provided as the input. (Requires WeiWatchers integration.)
+* **httpGetJSON** Retrieves JSON and returns the specific field selected in the configuration.
+* **jsonReceiver** Generates a URL for the oracle to receive JSON push notifications. Parses the pushed JSON and returns the specific field selected in the configuration.
+
+## External Adapters
+* Can be written in any language as long as they return data conforming to the oracle schema
+* Expand functionality of services offered by the oracle
+* Can take input (from a separate API) and provide output (either to another adapter or to the core ChainLink software)
+* URLs can be provided to specify where to parse data from
+* Data can be passed into an adapter (including results from previous sub tasks)
+
+## Adapter Workflow
+* Perform request to an external API
+* Process response and either:
+* Return to the core (ChainLink node software), or
+* Pass value to the next adapter
+
+## Future changes planned for adapters
+* Allow for adapters to pull data from sub tasks other than the immediate predecessor
+* Allow for sub task pipeline to fan out and in to allow for sub tasks to rely on multiple processes
+* Create a DSL to make specifications simpler and more composable
+
+## Sources
+* https://github.com/smartcontractkit/chainlink#adapters
+* https://github.com/smartcontractkit/schemas#assignments-and-adapters
+* https://chainlink-docs.smartcontract.com/#external-adapters
+* https://link.smartcontract.com/whitepaper