# TestSnapshotSucceedViaAppResp regression tests the situation in which a snap-
# shot is sent to a follower at the most recent index (i.e. the snapshot index
# is the leader's last index is the committed index). In that situation, a bug
# in the past left the follower in probing status until the next log entry was
# committed.
#
# See https://github.com/etcd-io/etcd/pull/10308 for additional background.

# Turn off output during the setup of the test.
log-level none
----
ok

# Start with two nodes, but the config already has a third.
add-nodes 2 voters=(1,2,3) index=10
----
ok

campaign 1
----
ok

# Fully replicate everything, including the leader's empty index.
stabilize
----
ok

compact 1 11
----
ok

# Drop inflight messages to n3.
deliver-msgs drop=(3)
----
ok

# Show the Raft log messages from now on.
log-level debug
----
ok

status 1
----
1: StateReplicate match=11 next=12
2: StateReplicate match=11 next=12
3: StateProbe match=0 next=11 paused inactive

# Add the node that will receive a snapshot (it has no state at all, does not
# even have a config).
add-nodes 1
----
INFO 3 switched to configuration voters=()
INFO 3 became follower at term 0
INFO newRaft 3 [peers: [], term: 0, commit: 0, applied: 0, lastindex: 0, lastterm: 0]

# Time passes on the leader so that it will try the previously missing follower
# again.
tick-heartbeat 1
----
ok

process-ready 1
----
Ready MustSync=false:
Messages:
1->2 MsgHeartbeat Term:1 Log:0/0 Commit:11
1->3 MsgHeartbeat Term:1 Log:0/0

# Iterate until no more work is done by the new peer. It receives the heartbeat
# and responds.
stabilize 3
----
> 3 receiving messages
  1->3 MsgHeartbeat Term:1 Log:0/0
  INFO 3 [term: 0] received a MsgHeartbeat message with higher term from 1 [term: 1]
  INFO 3 became follower at term 1
> 3 handling Ready
  Ready MustSync=true:
  Lead:1 State:StateFollower
  HardState Term:1 Commit:0
  Messages:
  3->1 MsgHeartbeatResp Term:1 Log:0/0

# The leader in turn will realize that n3 needs a snapshot, which it initiates.
stabilize 1
----
> 1 receiving messages
  3->1 MsgHeartbeatResp Term:1 Log:0/0
  DEBUG 1 [firstindex: 12, commit: 11] sent snapshot[index: 11, term: 1] to 3 [StateProbe match=0 next=11]
  DEBUG 1 paused sending replication messages to 3 [StateSnapshot match=0 next=12 paused pendingSnap=11]
> 1 handling Ready
  Ready MustSync=false:
  Messages:
  1->3 MsgSnap Term:1 Log:0/0
    Snapshot: Index:11 Term:1 ConfState:Voters:[1 2 3] VotersOutgoing:[] Learners:[] LearnersNext:[] AutoLeave:false

status 1
----
1: StateReplicate match=11 next=12
2: StateReplicate match=11 next=12
3: StateSnapshot match=0 next=12 paused pendingSnap=11

# Follower applies the snapshot. Note how it reacts with a MsgAppResp upon completion.
# The snapshot fully catches the follower up (i.e. there are no more log entries it
# needs to apply after). The bug was that the leader failed to realize that the follower
# was now fully caught up.
stabilize 3
----
> 3 receiving messages
  1->3 MsgSnap Term:1 Log:0/0
    Snapshot: Index:11 Term:1 ConfState:Voters:[1 2 3] VotersOutgoing:[] Learners:[] LearnersNext:[] AutoLeave:false
  INFO log [committed=0, applied=0, applying=0, unstable.offset=1, unstable.offsetInProgress=1, len(unstable.Entries)=0] starts to restore snapshot [index: 11, term: 1]
  INFO 3 switched to configuration voters=(1 2 3)
  INFO 3 [commit: 11, lastindex: 11, lastterm: 1] restored snapshot [index: 11, term: 1]
  INFO 3 [commit: 11] restored snapshot [index: 11, term: 1]
> 3 handling Ready
  Ready MustSync=false:
  HardState Term:1 Commit:11
  Snapshot Index:11 Term:1 ConfState:Voters:[1 2 3] VotersOutgoing:[] Learners:[] LearnersNext:[] AutoLeave:false
  Messages:
  3->1 MsgAppResp Term:1 Log:0/11

# The MsgAppResp lets the leader move the follower back to replicating state.
# Leader sends another MsgAppResp, to communicate the updated commit index.
stabilize 1
----
> 1 receiving messages
  3->1 MsgAppResp Term:1 Log:0/11
  DEBUG 1 recovered from needing snapshot, resumed sending replication messages to 3 [StateSnapshot match=11 next=12 paused pendingSnap=11]

status 1
----
1: StateReplicate match=11 next=12
2: StateReplicate match=11 next=12
3: StateReplicate match=11 next=12

# Let things settle.
stabilize
----
> 2 receiving messages
  1->2 MsgHeartbeat Term:1 Log:0/0 Commit:11
> 2 handling Ready
  Ready MustSync=false:
  Messages:
  2->1 MsgHeartbeatResp Term:1 Log:0/0
> 1 receiving messages
  2->1 MsgHeartbeatResp Term:1 Log:0/0
