Configuration

Compared to other tools that may help you replicate Ethereum state locally, Attestate’s Crawler comes with plenty of configuration options. This page’s purpose is to serve as a reference for all configurable options.

Overview

There are two files which we are using to configure the crawler:

a .env file defines all environmental variables. We’ve built the crawler such that only variables go into it that aren’t supposed to be checked into version control, e.g. your Infura API key.
a config.mjs file that contains a sharable set up of crawler instructions.

First, let’s walk you throught the .env file.

Environment Variables

@attestate/crawler internally uses dotenv to automatically load environment variables from a .env file in the project root into Node.js’s process.env object. However, if necessary, environment variables that have already been set in, e.g., the .env file can be overwritten by passing them before an invoking command.

@attestate/crawler guarantees any downstream plugin or strategy the presence and validity of environment variables. To avoid having to define .env files in applications that programmatically embed the crawler, environment variables can be set in the config file and they’ll be made available through process.env.

The environment variables with an asterisk * are required for @attestate/crawler to run:

RPC_HTTP_HOST* describes the host that Ethereum JSON-RPC extraction request are made against. It must be set to an URL to an Ethereum full node’s JSON-RPC endpoint that starts with https://. ws:// or wss:// prefixes are currently not supported. We support URLs that include the API’s bearer token as is the case with, e.g., Infura or Alchemy.
RPC_API_KEY is the API key for the host extraction requests are made against. It must be set if an Ethereum full node was provisioned behind an HTTP proxy that requires a bearer token authorization via the HTTP Authorization header. In this case, the header is structurally set as follows: Authorization: Bearer ${RPC_API_KEY}.
DATA_DIR* is the directory that stores all results from extraction and transformation of the crawler. It must be set to a file system path (relative or absolute).
IPFS_HTTPS_GATEWAY* describes the host that IPFS extraction requests are made against. A list of publicly accessible IPFS gateways can be found here.
IPFS_HTTPS_GATEWAY_KEY is the API key for the IPFS host extraction requests are made against. It must be set if an IPFS node was provisioned behind an HTTP proxy that requires a bearer token authorization via the HTTP Authorization header. In this case, the header is structurally set as follows: Authorization: Bearer ${IPFS_HTTPS_GATEWAY_KEY}.
ARWEAVE_HTTPS_GATEWAY* describes the host that Arweave extraction requests are made against. A commonly-used Arweave gateway is https://arweave.net.

Note

In some cases, you may only work with Ethereum, however, the crawler will complain if, e.g., IPFS_HTTPS_GATEWAY isn’t defined. Also, some Ethereum full node providers will append the API key in the RPC_HTTP_HOST URI. In those cases it is sufficient to define those variables as an empty string: RPC_API_KEY="".

Overwriting environment variables in the configuration

To use the crawler in downstream applications in JavaScript, we want to avoid leaking the requirement of dotenv, which requires a .env file to be present in the application folder.

Hence, applications don’t need to define the environmental variables in a .env file, they can pass those into the function boot(config) in config.environment. However, those variables’ names will then be mapped to camel case such that RPC_HTTP_HOST becomes rpcHttpHost.

Defining config.environment.rpcHttpHost will take presedence over RPC_HTTP_HOST.

Note

For all downstream applications, like strategies, the environment variables will always be defined, independently of whether the developer choses to write them in the config.mjs or .env file.

Configuration File

The configuration file is a .mjs that, using ESM’s export default, exports a list of tasks to be run. It is normatively specified as a JSON schema in the code base.

The @attestate/crawler repository always contains a pre-defined config.mjs file that you can copy.

Structurally, it is defined as follows:

export default {
  // First, there is the crawl path property, which we'll describe later in
  // this section.
  path: {
    "...": "..."
  },
  // All environment variables can be alternatively defined as properties in
  // the configuration file. However, they're using camel-case format here, such
  // that "RPC_HTTP_HOST" becomes "rpcHttpHost".
  environment: {
    "rpcHttpHost": "https://example.com",
    "...": "..."
  },
  queue: {
    options: {
      // The queue's concurrency controls how many requests are sent to
      // external resources concurrently.
      concurrent: 100
    },
  },
  // In case an external resource implements rate limiting, then the crawler
  // can be rate limited here to not pass any of these limits.
  endpoints: {
    ["https://ipfs.io"]: {
      timeout: 10_000,
      requestsPerUnit: 25,
      unit: "second",
    },
  }
};

Structurally, the path property looks as follows

const path = [
  {
    name: "Task #1",
    extractor: { /* ... */ },
    transformer: { /* ... */ },
    loader: { /* ... */ },
  },
  {
    name: "Task #2",
    "...": "..."
  }
]

The crawler implements an Extract, Transform and Load stage separation which is reflected in the names of a task’s phases. Attestate Crawler executes them sequentially in order: (1) extraction, (2) transformation, (3) loading.

Below is a fully configured crawl path to fetch all Ethereum block logs and the arguments declared as an object {start: 0, end: 1}. The output of the requests are stored in extractor.output.name with the pre-configured DATA_DIR environment variable.

const path = [
  {
    name: "call-block-logs",
    extractor: {
      module: {
        // NOTE: An extractor is an ESM module that exports a function init({
        // args, state, execute }) and a function update({ message }).
        // init: ({ args, state, execute }) => { /* ... */ },
        update: ({ message }) => { /* ... */ },
      },
      // NOTE: The arguments are passed into the module's init function
      args: {start: 0, end: 1},
      output: {
        name: "call-block-logs-extraction",
      },
    },
    "...": "..."
  },
];

Upon completing extraction, a transformation is scheduled to filter events by the EIP-20/EIP-721 transfer signature. A transformer’s module consists of a single function onLine({ state }) that is invoked for each line of the transformer.input.name.

const path = [
  {
    name: "call-block-logs",
    "...": "...",
    transformer: {
      module: {
        // NOTE: onLine gets invoked for each line in `input.name`.
        onLine: ({ state }) => { /* console.log(state.line) */ },
      },
      args: {
        topics: [
          /*
           * NOTE: After the extraction phase, we're filtering all events by topics.
           * We're generating the transfer event's signature using the keccak256 hash
           * function.
           *
           *  keccak256("Transfer(address,address,uint256)") == "0xddf...";
           */
          "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef";
        ]
      },
      // NOTE: A transformer always requires an `input.name` and
      // `output.name` // property to be present.
      input: {
        name: "call-block-logs-extraction",
      },
      output: {
        name: "call-block-logs-transformation",
      },
    },
    "...": "...",
  }
];

Upon completion of the transformation step, the loading phase is initiated. In it the transformation’s output is loaded into LMDB. For that, a strategy must implement a loader.module.direct and loader.module.order generator function. These functions must allocate a key-value relationship between each of the data points:

direct()’s yielded key must be globally unique (like a primary key).
order()’s yielded key must be unique and totally, lexographically orderable.

const path = [
  {
    name: "call-block-logs",
    loader: {
      module: {
        direct: function* ({ state }) {
          const log = JSON.parse(state.line);
          // NOTE: To access a transaction directly by its identifier, in
          // `direct` we select ``transactionHash`` as the key for the entire
          // `log`.
          yield {
            key: log.transactionHash,
            value: log
          }
        },
        order: function* ({ state }) {
          const log = JSON.parse(state.line);
          // NOTE: For LMDB to be able to order the keys properly it is
          // important that they're correctly encoded and padded. To see how
          // this may be implemented, check out the key encoding logic at
          // https://github.com/attestate/crawler-call-block-logs/blob/main/src/loader.mjs
          // yield...
        },
      },
      input: {
        name: "call-block-logs-transformer",
      },
      output: {
        name: "call-block-logs-loader",
      }
    }
  },
];

And that’s all! A full configuration of the Attestate crawler can be found on GitHub.