refactor loop

Author: baileympearson

src/sessions.ts

@@ -735,8 +735,35 @@ export class ClientSession
     let committed = false;
     let result: T;
 
+    let lastError: Error | null = null;
+
     try {
-      for (let retry = 0; !committed; ++retry) {
+      retryTransaction: for (let attempt = 0, isRetry = attempt > 0; !committed; ++attempt) {
+        if (isRetry) {
+          const BACKOFF_INITIAL_MS = 5;
+          const BACKOFF_MAX_MS = 500;
+          const BACKOFF_GROWTH = 1.5;
+          const jitter = Math.random();
+          const backoffMS =
+            jitter * Math.min(BACKOFF_INITIAL_MS * BACKOFF_GROWTH ** attempt, BACKOFF_MAX_MS);
+
+          const willExceedTransactionDeadline =
+            (this.timeoutContext?.csotEnabled() &&
+              backoffMS > this.timeoutContext.remainingTimeMS) ||
+            processTimeMS() + backoffMS > startTime + MAX_TIMEOUT;
+
+          if (willExceedTransactionDeadline) {
+            throw (
+              lastError ??
+              new MongoRuntimeError(
+                `Transaction retry did not record an error: should never occur. Please file a bug.`
+              )
+            );
+          }
+
+          await setTimeout(backoffMS);
+        }
+
         this.startTransaction(options); // may throw on error
 
         try {
@@ -774,13 +801,14 @@ export class ClientSession
             fnError.hasErrorLabel(MongoErrorLabel.TransientTransactionError) &&
             (this.timeoutContext?.csotEnabled() || processTimeMS() - startTime < MAX_TIMEOUT)
           ) {
-            continue;
+            lastError = fnError;
+            continue retryTransaction;
           }
 
           throw fnError;
         }
 
-        while (!committed) {
+        retryCommit: while (!committed) {
           try {
             /*
              * We will rely on ClientSession.commitTransaction() to
@@ -809,29 +837,13 @@ export class ClientSession
                  * { ok:0, code: 50, codeName: 'MaxTimeMSExpired' }
                  * { ok:1, writeConcernError: { code: 50, codeName: 'MaxTimeMSExpired' } }
                  */
-                continue;
+                continue retryCommit;
               }
 
               if (commitError.hasErrorLabel(MongoErrorLabel.TransientTransactionError)) {
-                const BACKOFF_INITIAL_MS = 5;
-                const BACKOFF_MAX_MS = 500;
-                const BACKOFF_GROWTH = 1.5;
-                const jitter = Math.random();
-                const backoffMS =
-                  jitter * Math.min(BACKOFF_INITIAL_MS * BACKOFF_GROWTH ** retry, BACKOFF_MAX_MS);
-
-                const willExceedTransactionDeadline =
-                  (this.timeoutContext?.csotEnabled() &&
-                    backoffMS > this.timeoutContext.remainingTimeMS) ||
-                  processTimeMS() + backoffMS > startTime + MAX_TIMEOUT;
-
-                if (willExceedTransactionDeadline) {
-                  break;
-                }
-
-                await setTimeout(backoffMS);
+                lastError = commitError;
 
-                break;
+                continue retryTransaction;
               }
             }