add userData API

index.js

@@ -91,6 +91,10 @@ class WriteBatch {
     this.write.tryPut(encodeDataIndex(this.dataPointer, DATA.INFO), encode(m.DataInfo, info))
   }
 
+  setUserData (key, value) {
+    this.write.tryPut(encodeUserDataIndex(this.dataPointer, DATA.INFO, key), value)
+  }
+
   putBlock (index, data) {
     this.write.tryPut(encodeDataIndex(this.storage.dataPointer, DATA.BLOCK, index), data)
   }
@@ -161,6 +165,10 @@ class ReadBatch {
     return this._get(encodeDataIndex(this.dataPointer, DATA.INFO), m.DataInfo)
   }
 
+  getUserData (key) {
+    return this._get(encodeUserDataIndex(this.dataPointer, DATA.INFO, key), null)
+  }
+
   async hasBlock (index) {
     return this._has(encodeDataIndex(this.storage.dataPointer, DATA.BLOCK, index))
   }
@@ -387,6 +395,13 @@ class HypercoreStorage {
     return p
   }
 
+  getUserData (key) {
+    const b = this.createReadBatch()
+    const p = b.getUserData(key)
+    b.tryFlush()
+    return p
+  }
+
   getLocalKeyPair () {
     const b = this.createReadBatch()
     const p = b.getLocalKeyPair()
@@ -513,6 +528,17 @@ function encodeDataIndex (pointer, type, index) {
   return state.buffer.subarray(start, state.start)
 }
 
+function encodeUserDataIndex (pointer, type, key) {
+  const state = ensureSlab(128 + key.byteLength)
+  const start = state.start
+  UINT.encode(state, TL.DATA)
+  UINT.encode(state, pointer)
+  UINT.encode(state, type)
+  c.buffer.encode(state, key)
+
+  return state.buffer.subarray(start, state.start)
+}
+
 function encodeDiscoveryKey (discoveryKey) {
   const state = ensureSlab(128)
   const start = state.start

test/basic.js

@@ -549,6 +549,41 @@ test('header', async function (t) {
   t.alike(await c2.getCoreHead(), head)
 })
 
+test('user data', async function (t) {
+  const c = await getCore(t)
+
+  {
+    const b = c.createWriteBatch()
+
+    b.setUserData(Buffer.from('hello'), Buffer.from('world'))
+    b.setUserData(Buffer.from('hej'), Buffer.from('verden'))
+
+    await b.flush()
+  }
+
+  {
+    const b = c.createReadBatch()
+    const data1 = b.getUserData(Buffer.from('hello'))
+    const data2 = b.getUserData(Buffer.from('hej'))
+    b.tryFlush()
+
+    t.alike(await data1, Buffer.from('world'))
+    t.alike(await data2, Buffer.from('verden'))
+  }
+
+  {
+    const b = c.createWriteBatch()
+
+    b.setUserData(Buffer.from('hello'), null)
+    b.setUserData(Buffer.from('hej'), Buffer.from('verden'))
+
+    await b.flush()
+  }
+
+  t.alike(await c.getUserData(Buffer.from('hello')), null)
+  t.alike(await c.getUserData(Buffer.from('hej')), Buffer.from('verden'))
+})
+
 async function getStorage (t, dir) {
   if (!dir) dir = await tmp(t)
   const s = new CoreStorage(dir)