Refactor event scraping and add support for scraping ERC20 approval events (#1401)

* Refactor event scraping and add support for scraping ERC20 approval events

* Add tests for data_sources/contract-wrappers/utils

1 files changed, 67 insertions, 0 deletions

diff --git a/packages/pipeline/src/data_sources/contract-wrappers/utils.ts b/packages/pipeline/src/data_sources/contract-wrappers/utils.ts
new file mode 100644
index 000000000..67660a37e
--- /dev/null
+++ b/packages/pipeline/src/data_sources/contract-wrappers/utils.ts
@@ -0,0 +1,67 @@
+import { DecodedLogArgs, LogWithDecodedArgs } from 'ethereum-types';
+
+const NUM_BLOCKS_PER_QUERY = 10000; // Number of blocks to query for events at a time.
+const NUM_RETRIES = 3; // Number of retries if a request fails or times out.
+
+export type GetEventsFunc<ArgsType extends DecodedLogArgs> = (
+    fromBlock: number,
+    toBlock: number,
+) => Promise<Array<LogWithDecodedArgs<ArgsType>>>;
+
+/**
+ * Gets all events between the given startBlock and endBlock by querying for
+ * NUM_BLOCKS_PER_QUERY at a time. Accepts a getter function in order to
+ * maximize code re-use and allow for getting different types of events for
+ * different contracts. If the getter function throws with a retryable error,
+ * it will automatically be retried up to NUM_RETRIES times.
+ * @param getEventsAsync A getter function which will be called for each step during pagination.
+ * @param startBlock The start of the entire block range to get events for.
+ * @param endBlock The end of the entire block range to get events for.
+ */
+export async function getEventsWithPaginationAsync<ArgsType extends DecodedLogArgs>(
+    getEventsAsync: GetEventsFunc<ArgsType>,
+    startBlock: number,
+    endBlock: number,
+): Promise<Array<LogWithDecodedArgs<ArgsType>>> {
+    let events: Array<LogWithDecodedArgs<ArgsType>> = [];
+    for (let fromBlock = startBlock; fromBlock <= endBlock; fromBlock += NUM_BLOCKS_PER_QUERY) {
+        const toBlock = Math.min(fromBlock + NUM_BLOCKS_PER_QUERY - 1, endBlock);
+        const eventsInRange = await _getEventsWithRetriesAsync(getEventsAsync, NUM_RETRIES, fromBlock, toBlock);
+        events = events.concat(eventsInRange);
+    }
+    return events;
+}
+
+/**
+ * Calls the getEventsAsync function and retries up to numRetries times if it
+ * throws with an error that is considered retryable.
+ * @param getEventsAsync a function that will be called on each iteration.
+ * @param numRetries the maximum number times to retry getEventsAsync if it fails with a retryable error.
+ * @param fromBlock the start of the sub-range of blocks we are getting events for.
+ * @param toBlock the end of the sub-range of blocks we are getting events for.
+ */
+export async function _getEventsWithRetriesAsync<ArgsType extends DecodedLogArgs>(
+    getEventsAsync: GetEventsFunc<ArgsType>,
+    numRetries: number,
+    fromBlock: number,
+    toBlock: number,
+): Promise<Array<LogWithDecodedArgs<ArgsType>>> {
+    let eventsInRange: Array<LogWithDecodedArgs<ArgsType>> = [];
+    for (let i = 0; i <= numRetries; i++) {
+        try {
+            eventsInRange = await getEventsAsync(fromBlock, toBlock);
+        } catch (err) {
+            if (isErrorRetryable(err) && i < numRetries) {
+                continue;
+            } else {
+                throw err;
+            }
+        }
+        break;
+    }
+    return eventsInRange;
+}
+
+function isErrorRetryable(err: Error): boolean {
+    return err.message.includes('network timeout');
+}