drafts are working

index.js

@@ -77,7 +77,7 @@ module.exports = class Hypercore extends EventEmitter {
     this.opened = false
     this.closed = false
     this.snapshotted = !!opts.snapshot
-    this.dryRun = !!opts.dryRun
+    this.draft = !!opts.draft
     this.sparse = opts.sparse !== false
     this.sessions = opts._sessions || [this]
     this.autoClose = !!opts.autoClose
@@ -268,7 +268,7 @@ module.exports = class Hypercore extends EventEmitter {
     this.writable = this._isWritable()
     this.autoClose = o.autoClose
 
-    if (o.state) this.state = this.dryRun ? o.state.memoryOverlay() : this.snapshotted ? o.state.snapshot() : o.state.ref()
+    if (o.state) this.state = this.draft ? o.state.memoryOverlay() : this.snapshotted ? o.state.snapshot() : o.state.ref()
 
     if (o.core) this.tracer.setParent(o.core.tracer)
 
@@ -805,7 +805,7 @@ module.exports = class Hypercore extends EventEmitter {
     if (this.opened === false) await this.opening
     if (!isValidIndex(bytes)) throw ASSERTION('seek is invalid')
 
-    const tree = (opts && opts.tree) || this.core.tree
+    const tree = (opts && opts.tree) || this.state.tree
     const s = tree.seek(bytes, this.padding)
 
     const offset = await s.update()
@@ -1037,7 +1037,7 @@ module.exports = class Hypercore extends EventEmitter {
   async treeHash (length) {
     if (length === undefined) {
       await this.ready()
-      length = this.core.tree.length
+      length = this.state.tree.length
     }
 
     const roots = await this.state.tree.getRoots(length)

lib/core.js

@@ -185,15 +185,16 @@ class SessionState {
   }
 
   memoryOverlay () {
+    const storage = new MemoryOverlay(this.storage)
     const s = new SessionState(
       this.core,
       this.storage,
       this.blocks,
-      this.tree,
+      this.tree.clone(storage),
       this.bitfield,
       this.treeLength,
       null,
-      new MemoryOverlay(this.storage)
+      storage
     )
 
     return s
@@ -871,7 +872,7 @@ module.exports = class Core {
 
     const promises = []
 
-    const reader = state.storage.createReadBatch()
+    const reader = state.createReadBatch()
     for (let i = treeLength; i < length; i++) promises.push(reader.getBlock(i))
     reader.tryFlush()
 

lib/memory-overlay.js

@@ -15,7 +15,7 @@ class MemoryOverlay {
     this.bitfields = null
   }
 
-  createReadBatch (read) {
+  createReadBatch (read = this.storage.createReadBatch()) {
     return new MemoryOverlayReadBatch(this, read)
   }
 
@@ -42,6 +42,10 @@ class TipList {
     this.data = []
   }
 
+  end () {
+    return this.offset + this.data.length
+  }
+
   put (index, value) {
     if (this.data.length === 0) {
       this.offset = index
@@ -62,6 +66,12 @@ class TipList {
     if (index >= this.data.length) return null
     return this.data[index]
   }
+
+  * [Symbol.iterator] () {
+    for (let i = 0; i < this.data.length; i++) {
+      yield [i + this.offset, this.data[i]]
+    }
+  }
 }
 
 module.exports = MemoryOverlay
@@ -233,7 +243,8 @@ function mergeMap (a, b) {
 
 function mergeTip (a, b) {
   if (a === null) return b
-  if (a.offset + a.data.length !== b.offset) throw ASSERTION('Cannot merge tip list')
+  while (a.end() !== b.offset && b.offset >= a.offset && b.end() >= a.end()) a.data.pop()
+  if (a.end() !== b.offset) throw ASSERTION('Cannot merge tip list')
   for (const data of b.data) a.data.push(data)
   return a
 }

lib/merkle-tree.js

@@ -509,6 +509,10 @@ module.exports = class MerkleTree {
     return u.finalise()
   }
 
+  clone (storage) {
+    return new MerkleTree(storage, this.roots.slice(0), this.fork, this.signature, this.prologue)
+  }
+
   batch () {
     return new MerkleTreeBatch(this)
   }
@@ -683,7 +687,7 @@ module.exports = class MerkleTree {
   get (index, error = true, readBatch = null) {
     if (readBatch) return readBatch.getTreeNode(index, error)
 
-    return this.storage.getTreeNode(index, error)
+    return getTreeNode(this.storage, index, error)
   }
 
   clear (writer) {
@@ -847,7 +851,7 @@ module.exports = class MerkleTree {
 
     const roots = []
     for (const index of flat.fullRoots(2 * length)) {
-      roots.push(unslabNode(await storage.getTreeNode(index, true)))
+      roots.push(unslabNode(await getTreeNode(storage, index, true)))
     }
 
     return new MerkleTree(storage, roots, opts.fork || 0, opts.signature || null, opts.prologue || null)
@@ -1274,6 +1278,13 @@ function normalizeIndexed (block, hash) {
   return null
 }
 
+function getTreeNode (storage, index, error) {
+  const batch = storage.createReadBatch()
+  const node = batch.getTreeNode(index, error)
+  batch.tryFlush()
+  return node
+}
+
 async function settleProof (p) {
   const result = [
     p.node && Promise.all(p.node),

test/all.js

@@ -14,6 +14,7 @@ async function runTests () {
   // await import('./compat.js') // todo: how to test compat?
   await import('./conflicts.js')
   await import('./core.js')
+  await import('./draft.js')
   await import('./encodings.js')
   await import('./encryption.js')
   await import('./extension.js')

test/draft.js

@@ -0,0 +1,50 @@
+const { create } = require('./helpers')
+const test = require('brittle')
+const b4a = require('b4a')
+
+test('draft', async function (t) {
+  const core = await create(t)
+
+  await core.append('hello')
+  await core.append('world')
+
+  const draft = core.session({ draft: true })
+
+  await draft.append('edits!')
+
+  t.alike(await draft.get(0), b4a.from('hello'))
+  t.alike(await draft.get(1), b4a.from('world'))
+  t.alike(await draft.get(2), b4a.from('edits!'))
+  t.alike(await draft.seek(11), [2, 1])
+  t.alike(draft.byteLength, 16)
+  t.alike(draft.length, 3)
+
+  await draft.close()
+
+  // nothing changed as it was a draft
+  t.alike(core.byteLength, 10)
+  t.alike(core.length, 2)
+
+  await core.close()
+})
+
+test('draft and then undraft', async function (t) {
+  const core = await create(t)
+
+  await core.append('hello')
+  await core.append('world')
+
+  const draft = core.session({ draft: true })
+
+  await draft.append('edits!')
+
+  await core.core.commit(draft.state)
+
+  await draft.close()
+
+  // nothing changed as it was a draft
+  t.alike(core.byteLength, 16)
+  t.alike(core.length, 3)
+
+  await core.close()
+})