Problem: Need to start refactoring the transaction-related code (BEP-9)

9/README.md

@@ -0,0 +1,80 @@
+```
+shortname: BEP-9
+name: Transaction Code Refactoring, Phase 1
+type: Standard
+status: Raw
+editor: Troy McConaghy <[email protected]>
+contributors: Vanshdeep Singh <[email protected]>, Alberto Granzotto <[email protected]>
+```
+
+# Abstract
+
+This document describes a set of small, specific changes that could be made to transaction-related BigchainDB code, to get the process of refactoring that code started, and to get BigchainDB developers familiar with that code again. Each thing could be done in one pull request.
+
+# Motivation
+
+- We want BigchainDB Server to be able to check if a transaction is valid, even if it conforms to an older version of the transaction spec.
+- We want to be able reuse some Python code in both BigchainDB Server and the BigchainDB Python driver, without importing the entire server codebase into the driver codebase, and without manually copying & pasting code from the sever codebase into the driver codebase (as we do now).
+- We want a given BigchainDB network to be able to support RBAC and other specialized business logic. The operators of a particular network should be able to decide what to support and what not to support in their network.
+- We want the transaction-related code to be easier to work with in general.
+
+Getting our transaction code to the point where it has everything wanted will take a lot of effort, but one must start somewhere. This BEP lists some specific things that could be done _to get started_.
+
+# Specification
+
+## Long-Term Goals
+
+While these long-term goals won’t be achieved completely by the steps specified in this BEP, they guide what is proposed (and not proposed).
+
+1. Have separate, mutually exclusive code for:
+   - transaction construction
+   - checking the validity of a transaction
+1. Have transaction validation plugins for:
+   - checking things that don’t depend on the state (e.g. checking against a JSON Schema), for each version of the transaction spec.
+   - checking things that DO depend on the state (e.g. checking if a transaction is attempting to double spend), for each version of the transaction spec.
+   - RBAC
+   - more!
+
+The idea is that the BigchainDB node operator can decide which transaction validation plugins they will enable. The codebase already has something like a “pluggable validation” system, which is inappropriately named “pluggable consensus”. It only supports one plugin at a time?
+
+## Strategy
+
+We will:
+
+1. Revive and improve the existing pluggable validation system, right from the start. Define a validation interface that can be reused by the validation plugins.
+1. Stop checking the validity of partially-constructed transactions (i.e. during transaction construction).
+1. Leave existing transaction-validation code alone, as much as possible. Isolate it in a specific module. Have a [façade](https://en.wikipedia.org/wiki/Facade_pattern) to interface with the legacy validation code.
+
+We will not:
+
+1. Write transaction validation code (plugins) for v3 transactions. That will happen later. (We _can_ start thinking about what v3 transactions might look like, though.)
+
+## Specific Tasks Proposed
+
+Below is a partial list of specific tasks, with no particular order. Additional tasks will be required to implement the above strategy.
+
+- Change the pluggable validation code so that it runs through an ordered _list_ of transaction-validation plugins (not just one plugin.)
+- Move the code for checking the MongoDB-specific things (listed in https://github.com/bigchaindb/BEPs/blob/master/13/README.md#bigchaindb-server-deviations ) from the webserver code to the transaction-validation code. Maybe only do those checks if the backend database is MongoDB? ([Suggested by Alberto](https://github.com/bigchaindb/bigchaindb/issues/2317#issuecomment-393228308)) We might be able to check for `$` at the start of keys during JSON Schema validation, using "[Pattern Properties](https://spacetelescope.github.io/understanding-json-schema/reference/object.html?highlight=patternproperties#pattern-properties)."
+- (Suggested by Vanshdeep) De-couple database-dependent validation from database-independent validation.
+- Look at [the spec for checking if a version 2.0 transaction is valid](https://github.com/bigchaindb/BEPs/blob/master/13/README.md#transaction-validation). Are all those checks _actually done_? Is _all_ the code for doing those checks in transaction-validation plugins?
+
+# References
+
+- [How to construct a valid version 2.0 transaction](https://github.com/bigchaindb/BEPs/blob/master/13/README.md#how-to-construct-a-transaction)
+- [How to check if a version 2.0 transaction is valid](https://github.com/bigchaindb/BEPs/blob/master/13/README.md#transaction-validation)
+
+# Change Process
+
+Changes to this document are governed by [BEP-2 (COSS)](../2/README.md).
+
+# Copyright Waiver
+
+<p xmlns:dct="http://purl.org/dc/terms/">
+  <a rel="license"
+     href="http://creativecommons.org/publicdomain/zero/1.0/">
+    <img src="http://i.creativecommons.org/p/zero/1.0/88x31.png" style="border-style: none;" alt="CC0" />
+  </a>
+  <br />
+  To the extent possible under law, all contributors to this BEP
+  have waived all copyright and related or neighboring rights to this BEP.
+</p>

README.md

@@ -20,6 +20,7 @@ Short Name   | Title                                                         | T
 [BEP-6](6)   | Shared Workspace Protocol                                     | Meta     | Draft      | Alberto Granzotto
 [BEP-7](7)   | Definition of the BigchainDB Public API                       | Informational | Raw   | Troy McConaghy
 [BEP-8](8)   | Restore system state after crash                              | Standard | Raw        | Vanshdeep Singh
+[BEP-9](9)   | Transaction Code Refactoring, Phase 1                         | Standard | Raw        | Troy McConaghy
 [BEP-10](10) | A Strangler Application Approach to Rewriting Some Code in Go | Informational | Raw   | Alberto Granzotto
 [BEP-11](11) | ORM Implementation for Official BigchainDB Python Driver      | Standard | Raw        | Manan Patel
 [BEP-12](12) | BigchainDB Transaction Spec v1                                | Standard | Stable     | Troy McConaghy