Retry GitHub queries with exponential backoff (#699)

Summary:
This patch adds independent exponential backoff to each individual
GitHub GraphQL query. We remove the fixed `GITHUB_DELAY_MS` delay before
each query in favor of this solution, which requires no additional
configuration (thus resolving a TODO in the process).

We use the NPM module `retry` with its default settings: namely, a
maximum of 10 retries with factor-2 backoff starting at 1000ms.
Empirically, it seems very unlikely that we should require much more
than 2 retries for a query. (See Test Plan for more details.)

This is both a short-term unblocker and a good kind of thing to have in
the long term.

Test Plan:
Note that `yarn test --full` passes, including `fetchGithubRepoTest.sh`.
Consider manual testing as follows.

Add `console.info` statements in `retryGithubFetch`, then load a large
repository like TensorFlow, and observe the output:

```shell
$ node bin/sourcecred.js load --plugin github tensorflow/tensorflow 2>&1 | ts -s '%.s'
0.252566 Fetching repo...
0.258422 Trying...
5.203014 Trying...
[snip]
1244.521197 Trying...
1254.848044 Will retry (n=1)...
1260.893334 Trying...
1271.547368 Trying...
1282.094735 Will retry (n=1)...
1283.349192 Will retry (n=2)...
1289.188728 Trying...
[snip]
1741.026869 Ensuring no more pages...
1742.139978 Creating view...
1752.023697 Stringifying...
1754.697116 Writing...
1754.697772 Done.
```

This took just under half an hour, with 264 queries total, of which:
  - 225 queries required 0 retries;
  - 38 queries required exactly 1 retry;
  - 1 query required exactly 2 retries; and
  - 0 queries required 3 or more retries.

wchargin-branch: github-backoff

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ## [Unreleased]
+- Execute GraphQL queries with exponential backoff (#699)
 - Introduce a simplified Git plugin that only tracks commits (#685)
 - Rename cred explorer table columns (#680)
 - Display version string in the app's footer

package.json

@@ -23,6 +23,7 @@
     "react": "^16.4.1",
     "react-dom": "^16.4.1",
     "react-router": "3.2.1",
+    "retry": "^0.12.0",
     "tmp": "^0.0.33",
     "whatwg-fetch": "2.0.3"
   },

src/plugins/github/fetchGithubRepo.js

@@ -5,6 +5,7 @@
  */
 
 import fetch from "isomorphic-fetch";
+import retry from "retry";
 
 import {stringify, inlineLayout} from "../../graphql/queries";
 import {createQuery, createVariables, postQueryExhaustive} from "./graphql";
@@ -49,6 +50,75 @@ export default function fetchGithubRepo(
 
 const GITHUB_GRAPHQL_SERVER = "https://api.github.com/graphql";
 
+type GithubResponseError =
+  | {|+type: "FETCH_ERROR", retry: false, error: Error|}
+  | {|+type: "GRAPHQL_ERROR", retry: false, error: mixed|}
+  | {|+type: "GITHUB_INTERNAL_EXECUTION_ERROR", retry: true, error: mixed|}
+  | {|+type: "NO_DATA", retry: true, error: mixed|};
+
+// Fetch against the GitHub API with the provided options, returning a
+// promise that either resolves to the GraphQL result data or rejects
+// to a `GithubResponseError`.
+function tryGithubFetch(fetch, fetchOptions): Promise<any> {
+  return fetch(GITHUB_GRAPHQL_SERVER, fetchOptions).then(
+    (x) =>
+      x.json().then((x) => {
+        if (x.errors) {
+          if (
+            x.errors.length === 1 &&
+            x.errors[0].message.includes("it could be a GitHub bug")
+          ) {
+            return Promise.reject(
+              ({
+                type: "GITHUB_INTERNAL_EXECUTION_ERROR",
+                retry: true,
+                error: x,
+              }: GithubResponseError)
+            );
+          } else {
+            return Promise.reject(
+              ({
+                type: "GRAPHQL_ERROR",
+                retry: false,
+                error: x,
+              }: GithubResponseError)
+            );
+          }
+        }
+        if (x.data === undefined) {
+          // See https://github.com/sourcecred/sourcecred/issues/350.
+          return Promise.reject(
+            ({type: "NO_DATA", retry: true, error: x}: GithubResponseError)
+          );
+        }
+        return Promise.resolve(x.data);
+      }),
+    (e) =>
+      Promise.reject(
+        ({type: "FETCH_ERROR", retry: false, error: e}: GithubResponseError)
+      )
+  );
+}
+
+function retryGithubFetch(fetch, fetchOptions) {
+  return new Promise((resolve, reject) => {
+    const operation = retry.operation();
+    operation.attempt(() => {
+      tryGithubFetch(fetch, fetchOptions)
+        .then((result) => {
+          resolve(result);
+        })
+        .catch((error) => {
+          if (error.retry && operation.retry(true)) {
+            return;
+          } else {
+            reject(error);
+          }
+        });
+    });
+  });
+}
+
 async function postQuery({body, variables}, token): Promise<any> {
   // TODO(#638): Find a more principled way to ingest this parameter.
   const delayMs: number = parseInt(process.env.GITHUB_DELAY_MS || "0", 10) || 0;
@@ -57,20 +127,21 @@ async function postQuery({body, variables}, token): Promise<any> {
       resolve();
     }, delayMs);
   });
-  const payload = {
+  const postBody = JSON.stringify({
     query: stringify.body(body, inlineLayout()),
     variables: variables,
-  };
-  return fetch(GITHUB_GRAPHQL_SERVER, {
+  });
+  const fetchOptions = {
     method: "POST",
-    body: JSON.stringify(payload),
+    body: postBody,
     headers: {
       Authorization: `bearer ${token}`,
     },
-  })
-    .then((x) => x.json())
-    .then((x) => {
-      if (x.errors || x.data === undefined) {
+  };
+  return retryGithubFetch(fetch, fetchOptions).catch((error) => {
+    switch (error.type) {
+      case "GITHUB_INTERNAL_EXECUTION_ERROR":
+      case "NO_DATA":
         console.error(
           "GitHub query failed! We're tracking these issues at " +
             "https://github.com/sourcecred/sourcecred/issues/350.\n" +
@@ -79,10 +150,22 @@ async function postQuery({body, variables}, token): Promise<any> {
             "The actual failed response can be found below:\n" +
             "================================================="
         );
-        return Promise.reject(x);
-      }
-      return Promise.resolve(x.data);
-    });
+        console.error(error.error);
+        break;
+      case "GRAPHQL_ERROR":
+        console.error(
+          "Unexpected GraphQL error; this may be a bug in SourceCred: ",
+          JSON.stringify({postBody: postBody, error: error.error})
+        );
+        break;
+      case "FETCH_ERROR":
+        // Network error; no need for additional commentary.
+        break;
+      default:
+        throw new Error((error.type: empty));
+    }
+    return Promise.reject(error);
+  });
 }
 
 function ensureNoMorePages(result: any, path = []) {

yarn.lock

@@ -6792,6 +6792,10 @@ ret@~0.1.10:
   version "0.1.15"
   resolved "https://registry.yarnpkg.com/ret/-/ret-0.1.15.tgz#b8a4825d5bdb1fc3f6f53c2bc33f81388681c7bc"
 
+retry@^0.12.0:
+  version "0.12.0"
+  resolved "https://registry.yarnpkg.com/retry/-/retry-0.12.0.tgz#1b42a6266a21f07421d1b0b54b7dc167b01c013b"
+
 right-align@^0.1.1:
   version "0.1.3"
   resolved "https://registry.yarnpkg.com/right-align/-/right-align-0.1.3.tgz#61339b722fe6a3515689210d24e14c96148613ef"