SessionState tracks most recent truncation (#682)

* session state tracks most recent truncation

* add tests for lastTruncation

* clear lastTruncation each flush

* track from and to

Author: chm-diederichs

lib/session-state.js

@@ -36,6 +36,7 @@ module.exports = class SessionState {
     this.signature = treeInfo.signature || null
 
     this.snapshotCompatLength = this.isSnapshot() ? Math.min(this.length, this.core.state.length) : -1
+    this.lastTruncation = null
 
     this.active = 0
 
@@ -230,10 +231,13 @@ module.exports = class SessionState {
     this._activeTx = null
 
     try {
-      return await tx.flush()
+      if (!(await tx.flush())) return false
     } finally {
       this._clearActiveBatch()
     }
+
+    this.lastTruncation = null
+    return true
   }
 
   _precommit () {
@@ -246,6 +250,7 @@ module.exports = class SessionState {
     try {
       const bitfield = this._pendingBitfield
       this._pendingBitfield = null
+      this.lastTruncation = null
       await this.parent._oncommit(this, bitfield)
     } finally {
       this.commiting = false
@@ -576,6 +581,8 @@ module.exports = class SessionState {
   ontruncate (tree, to, from, flushed) {
     const bitfield = { start: to, length: from - to, drop: true }
 
+    this.lastTruncation = { from, to }
+
     if (!flushed) this._updateBitfield(bitfield)
     else if (this.isDefault()) this.core.ontruncate(tree, bitfield)
 

test/core.js

@@ -56,8 +56,13 @@ test('core - append and truncate', async function (t) {
     b4a.from('ooo')
   ])
 
+  t.is(core.state.lastTruncation, null)
+
   await core.state.truncate(3, 1)
 
+  t.is(core.state.lastTruncation.from, 4)
+  t.is(core.state.lastTruncation.to, 3)
+
   t.is(core.state.length, 3)
   t.is(core.state.byteLength, 12)
   t.is(core.state.fork, 1)
@@ -71,30 +76,52 @@ test('core - append and truncate', async function (t) {
 
   await core.state.truncate(3, 2)
 
+  t.is(core.state.lastTruncation.from, 7)
+  t.is(core.state.lastTruncation.to, 3)
+
   t.is(core.state.length, 3)
   t.is(core.state.byteLength, 12)
   t.is(core.state.fork, 2)
 
   await core.state.truncate(2, 3)
+  t.is(core.state.lastTruncation.from, 3)
+  t.is(core.state.lastTruncation.to, 2)
 
   await core.state.append([b4a.from('a')])
+  t.is(core.state.lastTruncation, null)
+
   await core.state.truncate(2, 4)
+  t.is(core.state.lastTruncation.from, 3)
+  t.is(core.state.lastTruncation.to, 2)
 
   await core.state.append([b4a.from('a')])
+  t.is(core.state.lastTruncation, null)
+
   await core.state.truncate(2, 5)
+  t.is(core.state.lastTruncation.from, 3)
+  t.is(core.state.lastTruncation.to, 2)
 
   await core.state.append([b4a.from('a')])
+  t.is(core.state.lastTruncation, null)
+
   await core.state.truncate(2, 6)
+  t.is(core.state.lastTruncation.from, 3)
+  t.is(core.state.lastTruncation.to, 2)
 
   await core.state.append([b4a.from('a')])
+  t.is(core.state.lastTruncation, null)
+
   await core.state.truncate(2, 7)
+  t.is(core.state.lastTruncation.from, 3)
+  t.is(core.state.lastTruncation.to, 2)
 
   // check that it was persisted
   const coreReopen = await reopen()
 
   t.is(coreReopen.state.length, 2)
   t.is(coreReopen.state.byteLength, 10)
   t.is(coreReopen.state.fork, 7)
+  t.is(coreReopen.state.lastTruncation, null)
   // t.is(coreReopen.header.hints.reorgs.length, 4)
 })