*: allow index start from 0 (#353)

This PR removes the modifications of index during initialization, which will
allow raft's log index goes from 0 again. This is important as many existing
test cases rely on it, especially those related to flow control. Those cases
pass on master in an accidental way, checking what are exact broken will be
too much work. Besides upstream patches from etcd also rely on the same
assumption, only forbid growing from 0 in raft-rs will make it hard to port
patches.

Most of the changes are basically revert of index changes introduced from #196
and #214.

Signed-off-by: Jay Lee <[email protected]>

benches/suites/raw_node.rs

@@ -110,7 +110,7 @@ fn test_ready_raft_node(logger: &slog::Logger) -> RawNode<MemStorage> {
         let mut e = Entry::default();
         e.data = vec![0; 32 * 1024];
         e.context = vec![];
-        e.index = i + 1;
+        e.index = i;
         e.term = 1;
         entries.push(e);
     }

examples/five_mem_node/main.rs

@@ -11,7 +11,6 @@ use std::time::{Duration, Instant};
 use std::{str, thread};
 
 use protobuf::Message as PbMessage;
-use raft::eraftpb::ConfState;
 use raft::storage::MemStorage;
 use raft::{prelude::*, StateRole};
 use regex::Regex;
@@ -175,8 +174,15 @@ impl Node {
         let mut cfg = example_config();
         cfg.id = id;
         let logger = logger.new(o!("tag" => format!("peer_{}", id)));
-
-        let storage = MemStorage::new_with_conf_state(ConfState::from((vec![id], vec![])));
+        let mut s = Snapshot::default();
+        // Because we don't use the same configuration to initialize every node, so we use
+        // a non-zero index to force new followers catch up logs by snapshot first, which will
+        // bring all nodes to the same initial state.
+        s.mut_metadata().index = 1;
+        s.mut_metadata().term = 1;
+        s.mut_metadata().mut_conf_state().voters = vec![1];
+        let storage = MemStorage::new();
+        storage.wl().apply_snapshot(s).unwrap();
         let raft_group = Some(RawNode::new(&cfg, storage, &logger).unwrap());
         Node {
             raft_group,

harness/tests/failpoints_cases/mod.rs

@@ -15,7 +15,7 @@ fn test_reject_stale_term_message() {
     let l = default_logger();
     let mut r = new_test_raft(1, vec![1, 2, 3], 10, 1, new_storage(), &l);
     fail::cfg("before_step", "panic").unwrap();
-    r.load_state(&hard_state(2, 1, 0));
+    r.load_state(&hard_state(2, 0, 0));
 
     let mut m = new_message(0, 0, MessageType::MsgAppend, 0);
     m.term = r.term - 1;