Before these fixes, it was possible to see errors on new RPCs after a
connection began draining, and before establishing a new connection. There is
an inherent race between choosing a SubConn and attempting to creating a stream
on it. We should be able to avoid application-visible RPC errors due to this
with transparent retry. However, several bugs were preventing this from
working correctly:
1. Non-wait-for-ready RPCs were skipping transparent retry, though the retry
design calls for retrying them.
2. The transport closed itself (and would consequently error new RPCs) before
notifying the SubConn that it was draining.
3. The SubConn wasn't synchronously updating itself once it was notified about
the closing or draining state.
4. The SubConn would go into the TRANSIENT_FAILURE state instantaneously,
causing RPCs to fail instead of queue.
* internal: fix Dial_OneBackoffPerRetryGroup
Instead of mutating global variables, switches getMinConnectDeadline to a
dial option.
Fixes#2687.
* rename getMinConnectTimeoutFunc to minConnectTimeout, ditto dial opt
Previously, the transport was able to reset via the retry loop,
or via the event closures calling resetTransport. This meant
a very large amount of synchronization was necessary: one
reset meant the other had to not reset; state had to be kept
at the addrconn; and very subtle interactions were hard to
reason about.
This change removes the ability for event closures to directly
reset the transport. Instead, they signal to to the retry
loop about the event, and the retry loop is always the single
place that retries occur.
This also allows us to refactor the address switching logic
into a much simpler for loop inside the retry loop instead of
using addrConn state to keep track of an index.
internal: fix client send preface problems
This CL fixes three problems:
- In clientconn_state_transitions_test.go, sometimes tests would flake because there's not enough buffer to send client side settings, causing the connection to unpredictably enter TRANSIENT FAILURE. Each time we set up a server to send SETTINGS, we should also set up the server to read. This allows the client to successfully send its SETTINGS, unflaking the test.
- In clientconn.go, we incorrectly transitioned into TRANSIENT FAILURE when creating an http2client returned an error. This should be handled in the outer resetTransport main reset loop. The reason this became a problem is that the outer resetTransport has very specific conditions around when to transition into TRANSIENT FAILURE that the egregious transition did not have. So, it could transition into TRANSIENT FAILURE after failing to dial, even if it was trying to connect to a non-final address in the list of addresses.
- In clientconn.go, we incorrectly stay in CONNECTING after `createTransport` when a server sends its connection preface but the client is not able to send its connection preface. This CL causes the addrconn to correctly enter TRANSIENT FAILURE when `createTransport` fails, even if a server preface was received. It does so by making ac.successfulHandshake to consider both server preface received as well as client preface sent.
internal: clean up and unflake state transitions test
Switches state transitions test to using a notification from a custom load
balancer, instead of relying on waiting for laggy balancer state updates.
Also generally adds more coverage around state transitions and a framework
for easily adding more of these kinds of tests.
Fixes#2348
