DRIVERS-2884: CSOT avoid connection churn when operations timeout

Author: sanych-sun

source/connection-monitoring-and-pooling/connection-monitoring-and-pooling.md

@@ -593,7 +593,7 @@ response data is drained and the connection is ready to send the next command.
 
 1. **Persist and update timestamp**: The connection must record the current time immediately after the original timeout.
     This timestamp MUST be updated to the current time whenever any bytes are successfully read, received, or consumed
-    while draining of the pending response as part of checking out the connection.
+    while draining of the pending response.
 2. **Aliveness check**: If driver uses synchronous read from the socket and the timestamp is older than 3 seconds, the
     driver MUST perform aliveness check either performing a non-blocking read or using the minimal possible timeout to
     check if at least one byte can be read/received. If at least one byte can be read the timestamp must be updated and

source/connection-monitoring-and-pooling/tests/README.md

@@ -23,16 +23,12 @@ The following tests have not yet been automated, but MUST still be tested:
 
 ### Pending Response
 
-If a connection with a pending response is idle for > 3 seconds, then drivers are expected to perform an aliveness check
-by attempting a non-blocking read of 1 byte from the inbound TCP buffer. The following two cases test both a successful
-read and a failed one.
-
 Due to the complexity of managing a proxy layer, the following qualifying tests should only be run for non-ssl,
 non-auth, and non-compression connections.
 
-#### Recover Partial Header Response
+#### Recover Partially Read Response
 
-This test verifies that if only part of a response header arrives before a timeout, the driver can drain the rest of the
+This test verifies that if only part of a response was read before the timeout, the driver can drain the rest of the
 response and reuse the connection for the next operation.
 
 1. Connect to the proxy server with `maxPoolSize=1` and `direct=true`, subscribing to the following CMAP events:
@@ -41,30 +37,9 @@ response and reuse the connection for the next operation.
     - `PendingResponseFailed`
     - `ConnectionClosed`
 2. Send a command (e.g. an insert) with a 200 millisecond timeout and the following `proxyTest` actions:
-    - `sendBytes`: any value between 1 and 3
-    - `delayMS`: 400 ( to exceed the 200 ms timeout)
-    - `sendAll`: `true`
-3. Assert that the operation failed with timeout error.
-4. Issue another operation (e.g. another insert) and assert that it does not return an error.
-5. Verify that the following sequence of events was observed:
-    - `ConnectionPendingResponseStarted`
-    - `ConnectionPendingResponseSucceeded`
-6. Verify that NONE the following events was observed:
-    - `ConnectionPendingResponseFailed`
-    - `ConnectionClosed`
-
-#### Recover Partial Body Response
-
-This test verifies that if only part of a response body arrives before a socket timeout, the driver can drain the rest
-of the response and reuse the connection for the next operation.
-
-1. Connect to the proxy server with `maxPoolSize=1` and `direct=true`, subscribing to the following CMAP events:
-    - `PendingResponseStarted`
-    - `PendingResponseSucceeded`
-    - `PendingResponseFailed`
-    - `ConnectionClosed`
-2. Send a command (e.g. an insert) with a 200 millisecond timeout and the following `proxyTest` actions:
-    - `sendBytes`: Any value > 16
+    - `sendBytes`: We have 3 possible states here: a) Message size was partially read: random value between 1 and 3
+        inclusive b) Message size was read, body was not read at all: use 4 c) Message size was read, body read
+        partially: random value between 5 and 100 inclusive
     - `delayMS`: 400 ( to exceed the 200 ms timeout)
     - `sendAll`: `true`
 3. Assert that the operation failed with timeout error.