add weak session support (#603)

index.js

@@ -64,6 +64,7 @@ class Hypercore extends EventEmitter {
     this.exclusive = false
     this.opened = false
     this.closed = false
+    this.weak = !!opts.weak
     this.snapshotted = !!opts.snapshot
     this.draft = !!opts.draft
     this.onwait = opts.onwait || null
@@ -206,6 +207,7 @@ class Hypercore extends EventEmitter {
     const writable = opts.writable === false ? false : !this._readonly
     const onwait = opts.onwait === undefined ? this.onwait : opts.onwait
     const timeout = opts.timeout === undefined ? this.timeout : opts.timeout
+    const weak = opts.weak === undefined ? this.weak : opts.weak
     const Clz = opts.class || Hypercore
     const s = new Clz(null, this.key, {
       ...opts,
@@ -214,6 +216,7 @@ class Hypercore extends EventEmitter {
       onwait,
       timeout,
       writable,
+      weak,
       parent: this
     })
 

lib/core.js

@@ -22,6 +22,7 @@ module.exports = class Core {
     this.replicator = new Replicator(this, opts)
     this.sessionStates = []
     this.monitors = []
+    this.activeSessions = 0
 
     this.id = opts.key ? z32.encode(opts.key) : null
     this.key = opts.key || null
@@ -86,12 +87,14 @@ module.exports = class Core {
 
   allSessions () {
     const sessions = []
-    for (const state of this.sessionStates) sessions.push(...state.sessions)
+    for (const state of this.sessionStates) {
+      if (state.sessions.length) sessions.push(...state.sessions)
+    }
     return sessions
   }
 
   hasSession () {
-    return this.sessionStates.length > 1 || (this.state !== null && this.state.sessions.length !== 0)
+    return this.activeSessions !== 0
   }
 
   checkIfIdle () {
@@ -719,8 +722,13 @@ module.exports = class Core {
   }
 
   destroy () {
+    if (this.hasSession() === true) throw new Error('Cannot destroy while sessions are open')
     if (this.replicator) this.replicator.destroy()
     if (this.state) this.state.destroy()
+
+    // close all pending weak sessions...
+    const weakSessions = this.allSessions()
+    for (const s of weakSessions) s.close().catch(noop)
   }
 
   async _close () {

lib/session-state.js

@@ -42,14 +42,17 @@ module.exports = class SessionState {
   }
 
   addSession (s) {
+    if (s._stateIndex !== -1) return
     s._stateIndex = this.sessions.push(s) - 1
+    if (s.weak === false) this.core.activeSessions++
   }
 
   removeSession (s) {
     if (s._stateIndex === -1) return
     const head = this.sessions.pop()
     if (head !== s) this.sessions[(head._stateIndex = s._stateIndex)] = head
     s._stateIndex = -1
+    if (s.weak === false) this.core.activeSessions--
     this.core.checkIfIdle()
   }