ipld-eth-server/documentation/composeAndExecute.md

composeAndExecute

The composeAndExecute command is used to compose and execute over an arbitrary set of custom transformers. This is accomplished by generating a Go pluggin which allows the vulcanizedb binary to link to external transformers, so long as they abide by one of the standard interfaces.

This command requires Go 1.11+ and Go plugins only work on Unix-based systems.

Writing custom transformers

Storage Transformers

• Guide
• Example

Event Transformers

• Guide
• Example

Preparing transformers to work as a plugin for composeAndExecute

To plug in an external transformer we need to:

1. Create a package that exports a variable TransformerInitializer, StorageTransformerInitializer, or ContractTransformerInitializer that are of type TransformerInitializer or StorageTransformerInitializer, or ContractTransformerInitializer, respectively
2. Design the transformers to work in the context of their event, storage, or contract watcher execution modes
3. Create db migrations to run against vulcanizeDB so that we can store the transformer output
   • Do not goose fix the transformer migrations
   • Specify migration locations for each transformer in the config with the exporter.transformer.migrations fields
   • If the base vDB migrations occupy this path as well, they need to be in their goose fixed form as they are here

To update a plugin repository with changes to the core vulcanizedb repository, replace the vulcanizedb vendored in the plugin repo (plugin_repo/vendor/github.com/vulcanize/vulcanizedb) with the newly updated version

• The entire vendor lib within the vendored vulcanizedb needs to be deleted (plugin_repo/vendor/github.com/vulcanize/vulcanizedb/vendor)
• These complications arise due to this conflict between dep and Go plugins

Configuration

A .toml config file is specified when executing the command: ./vulcanizedb composeAndExecute --config=./environments/config_name.toml

The config provides information for composing a set of transformers:

[database]
    name     = "vulcanize_public"
    hostname = "localhost"
    user     = "vulcanize"
    password = "vulcanize"
    port     = 5432

[client]
    ipcPath  = "/Users/user/Library/Ethereum/geth.ipc"

[exporter]
    home     = "github.com/vulcanize/vulcanizedb"
    name     = "exampleTransformerExporter"
    save     = false
    transformerNames = [
        "transformer1",
        "transformer2",
        "transformer3",
        "transformer4",
    ]
    [exporter.transformer1]
        path = "path/to/transformer1"
        type = "eth_event"
        repository = "github.com/account/repo"
        migrations = "db/migrations"
        rank = "0"
    [exporter.transformer2]
        path = "path/to/transformer2"
        type = "eth_contract"
        repository = "github.com/account/repo"
        migrations = "db/migrations"
        rank = "0"
    [exporter.transformer3]
        path = "path/to/transformer3"
        type = "eth_event"
        repository = "github.com/account/repo"
        migrations = "db/migrations"
        rank = "0"
    [exporter.transformer4]
        path = "path/to/transformer4"
        type = "eth_storage"
        repository = "github.com/account2/repo2"
        migrations = "to/db/migrations"
        rank = "1"

• home is the name of the package you are building the plugin for, in most cases this is github.com/vulcanize/vulcanizedb
• name is the name used for the plugin files (.so and .go)
• save indicates whether or not the user wants to save the .go file instead of removing it after .so compilation. Sometimes useful for debugging/trouble-shooting purposes.
• transformerNames is the list of the names of the transformers we are composing together, so we know how to access their submaps in the exporter map
• exporter.<transformerName>s are the sub-mappings containing config info for the transformers
  • repository is the path for the repository which contains the transformer and its TransformerInitializer
  • path is the relative path from repository to the transformer's TransformerInitializer directory (initializer package).
    • Transformer repositories need to be cloned into the user's $GOPATH (go get)
  • type is the type of the transformer; indicating which type of watcher it works with (for now, there are only two options: eth_event and eth_storage)
    • eth_storage indicates the transformer works with the storage watcher that fetches state and storage diffs from an ETH node (instead of, for example, from IPFS)
    • eth_event indicates the transformer works with the event watcher that fetches event logs from an ETH node
    • eth_contract indicates the transformer works with the contract watcher that is made to work with contract_watcher pkg based transformers which work with either a light or full sync vDB to watch events and poll public methods (example1, example2)
  • migrations is the relative path from repository to the db migrations directory for the transformer
  • rank determines the order that migrations are ran, with lower ranked migrations running first
    • this is to help isolate any potential conflicts between transformer migrations
    • start at "0"
    • use strings
    • don't leave gaps
    • transformers with identical migrations/migration paths should share the same rank
• Note: If any of the imported transformers need additional config variables those need to be included as well

This information is used to write and build a Go plugin which exports the configured transformers. These transformers are loaded onto their specified watchers and executed.

Transformers of different types can be run together in the same command using a single config file or in separate instances using different config files

The general structure of a plugin .go file, and what we would see built with the above config is shown below

package main

import (
	interface1 "github.com/vulcanize/vulcanizedb/libraries/shared/transformer"
	transformer1 "github.com/account/repo/path/to/transformer1"
	transformer2 "github.com/account/repo/path/to/transformer2"
	transformer3 "github.com/account/repo/path/to/transformer3"
	transformer4 "github.com/account2/repo2/path/to/transformer4"
)

type exporter string

var Exporter exporter

func (e exporter) Export() []interface1.EventTransformerInitializer, []interface1.StorageTransformerInitializer, []interface1.ContractTransformerInitializer {
	return []interface1.TransformerInitializer{
            transformer1.TransformerInitializer,
            transformer3.TransformerInitializer,
        },     []interface1.StorageTransformerInitializer{
            transformer4.StorageTransformerInitializer,
        },     []interface1.ContractTransformerInitializer{
            transformer2.TransformerInitializer,
        }
}