Fix maxConnectionPoolSize verification

Under high load of sessions, the connection pool is allowing new
connections to be created.
This is happening because, while the development of `AuthTokenManager`
and `connection liveness check`,
the methods do validate connection on acquired and return to the pool
need to be async.
This changes creates a situation of racing condition which doesn't exist
the original code and this introduces this bug.

Increasing the resouce acquired count before validating the connection
solves the issue, since the race condition is removed.
However, the pool needs also to release the resource when the validation
return `false` or fails for some reason.
This is important to avoid broken connection still be count for the max
pool size.

Author: bigmontz

packages/core/src/internal/pool/pool.ts

@@ -251,19 +251,32 @@ class Pool<R extends unknown = unknown> {
           continue
         }
 
+        resourceAcquired(key, this._activeResourceCounts)
+
         if (this._removeIdleObserver != null) {
           this._removeIdleObserver(resource)
         }
 
-        if (await this._validateOnAcquire(acquisitionContext, resource)) {
+        let valid = false
+
+        try {
+          valid = await this._validateOnAcquire(acquisitionContext, resource)
+        } catch (e) {
+          if (this._log.isErrorEnabled()) {
+            // eslint-disable-next-line @typescript-eslint/restrict-template-expressions
+            this._log.error(`Failure on validate ${resource}. This is a bug, please report it. Caused by: ${e.message}`)
+          }
+        }
+
+        if (valid) {
           // idle resource is valid and can be acquired
-          resourceAcquired(key, this._activeResourceCounts)
           if (this._log.isDebugEnabled()) {
             // eslint-disable-next-line @typescript-eslint/restrict-template-expressions
             this._log.debug(`${resource} acquired from the pool ${key}`)
           }
           return { resource, pool }
         } else {
+          resourceReleased(key, this._activeResourceCounts)
           pool.removeInUse(resource)
           await this._destroy(resource)
         }

packages/core/test/internal/pool/pool.test.ts

@@ -905,6 +905,139 @@ describe('#unit Pool', () => {
     expect(conns.length).toEqual(1)
   })
 
+  it('should count connection on validation process when eval max pool size', async () => {
+    const conns: any[] = []
+    const pool = new Pool<any>({
+      // Hook into connection creation to track when and what connections that are
+      // created.
+      create: async (_, server, release) => {
+        // Create a fake connection that makes it possible control when it's connected
+        // and released from the outer scope.
+        const conn: any = {
+          server,
+          release
+        }
+        conns.push(conn)
+        return conn
+      },
+      validateOnAcquire: async (context, resource: any) => {
+        const promise = new Promise<boolean>((resolve, reject) => {
+          if (resource.promises == null) {
+            resource.promises = []
+          }
+          resource.promises.push({
+            resolve,
+            reject
+          })
+        })
+
+        return await promise
+      },
+      // Setup pool to only allow one connection
+      config: new PoolConfig(1, 100000)
+    })
+
+    // Make the first request for a connection, this will return a connection instantaneously
+    const conn0 = await pool.acquire({}, address)
+    expect(conns.length).toEqual(1)
+
+    // Releasing connection back to the pool, so it can be re-acquired.
+    await conn0.release(address, conn0)
+
+    // Request the same connection again, it will wait until resolve get called.
+    const req0 = pool.acquire({}, address)
+    expect(conns.length).toEqual(1)
+
+    // Request other connection, this should also resolve the same connection1.
+    const req1 = pool.acquire({}, address)
+    expect(conns.length).toEqual(1)
+
+    // connection 1 is valid
+    conns[0].promises[0].resolve(true)
+
+    // getting the connection 1
+    const conn1 = await req0
+    expect(conn0).toBe(conn1)
+    await conn1.release(address, conn1)
+
+    // connection 2 is valid
+    conns[0].promises[1].resolve(true)
+
+    // getting the connection 2
+    const conn2 = await req1
+    expect(conn0).toBe(conn2)
+    await conn2.release(address, conn2)
+  })
+
+  it.each([
+    ['is not valid', (promise: any) => promise.resolve(false)],
+    ['validation fails', (promise: any) => promise.reject(new Error('failed'))]
+  ])('should create new connection if the current one when %s', async (_, resolver) => {
+    const conns: any[] = []
+    const pool = new Pool<any>({
+      // Hook into connection creation to track when and what connections that are
+      // created.
+      create: async (_, server, release) => {
+        // Create a fake connection that makes it possible control when it's connected
+        // and released from the outer scope.
+        const conn: any = {
+          server,
+          release
+        }
+        conns.push(conn)
+        return conn
+      },
+      validateOnAcquire: async (context, resource: any) => {
+        const promise = new Promise<boolean>((resolve, reject) => {
+          if (resource.promises == null) {
+            resource.promises = []
+          }
+          resource.promises.push({
+            resolve,
+            reject
+          })
+        })
+
+        return await promise
+      },
+      // Setup pool to only allow one connection
+      config: new PoolConfig(1, 100000)
+    })
+
+    // Make the first request for a connection, this will return a connection instantaneously
+    const conn0 = await pool.acquire({}, address)
+    expect(conns.length).toEqual(1)
+
+    // Releasing connection back to the pool, so it can be re-acquired.
+    await conn0.release(address, conn0)
+
+    // Request the same connection again, it will wait until resolve get called.
+    const req0 = pool.acquire({}, address)
+    expect(conns.length).toEqual(1)
+
+    // Request other connection, this should also resolve the same connection2.
+    const req1 = pool.acquire({}, address)
+    expect(conns.length).toEqual(1)
+
+    // should resolve the promise with the configured value
+    resolver(conns[0].promises[0])
+
+    // getting the connection 1
+    const conn1 = await req0
+    expect(conn0).not.toBe(conn1)
+    await conn1.release(address, conn1)
+    expect(conns.length).toEqual(2)
+
+    // connection 2 is valid
+    conns[1].promises[0].resolve(true)
+
+    // getting the connection 2
+    const conn2 = await req1
+    expect(conn1).toBe(conn2)
+    await conn2.release(address, conn2)
+    expect(conns.length).toEqual(2)
+  })
+
   it('should not time out if max pool size is not set', async () => {
     let counter = 0
 

packages/neo4j-driver-deno/lib/core/internal/pool/pool.ts

@@ -251,19 +251,32 @@ class Pool<R extends unknown = unknown> {
           continue
         }
 
+        resourceAcquired(key, this._activeResourceCounts)
+
         if (this._removeIdleObserver != null) {
           this._removeIdleObserver(resource)
         }
 
-        if (await this._validateOnAcquire(acquisitionContext, resource)) {
+        let valid = false
+
+        try {
+          valid = await this._validateOnAcquire(acquisitionContext, resource)
+        } catch(e) {
+          if (this._log.isErrorEnabled()) {
+            // eslint-disable-next-line @typescript-eslint/restrict-template-expressions
+            this._log.error(`Failure on validate ${resource}. This is a bug, please report it. Caused by: ${e.message}`)
+          } 
+        }
+
+        if (valid) {
           // idle resource is valid and can be acquired
-          resourceAcquired(key, this._activeResourceCounts)
           if (this._log.isDebugEnabled()) {
             // eslint-disable-next-line @typescript-eslint/restrict-template-expressions
             this._log.debug(`${resource} acquired from the pool ${key}`)
           }
           return { resource, pool }
         } else {
+          resourceReleased(key, this._activeResourceCounts)
           pool.removeInUse(resource)
           await this._destroy(resource)
         }