fix: interceptor back-pressure

Refs: #3368
Refs: #3370

lib/dispatcher/agent.js

@@ -79,7 +79,7 @@ class Agent extends DispatcherBase {
     return ret
   }
 
-  [kDispatch] (opts, handler) {
+  [kDispatch] (opts, handler, onDrain) {
     let key
     if (opts.origin && (typeof opts.origin === 'string' || opts.origin instanceof URL)) {
       key = String(opts.origin)
@@ -102,7 +102,7 @@ class Agent extends DispatcherBase {
       this[kClients].set(key, dispatcher)
     }
 
-    return dispatcher.dispatch(opts, handler)
+    return dispatcher.dispatch(opts, handler, onDrain)
   }
 
   async [kClose] () {

lib/dispatcher/client.js

@@ -62,6 +62,7 @@ const connectH2 = require('./client-h2.js')
 let deprecatedInterceptorWarned = false
 
 const kClosedResolve = Symbol('kClosedResolve')
+const kDrainQueue = Symbol('kDrainQueue')
 
 function getPipelining (client) {
   return client[kPipelining] ?? client[kHTTPContext]?.defaultPipelining ?? 1
@@ -243,6 +244,13 @@ class Client extends DispatcherBase {
     this[kMaxConcurrentStreams] = maxConcurrentStreams != null ? maxConcurrentStreams : 100 // Max peerConcurrentStreams for a Node h2 server
     this[kHTTPContext] = null
 
+    this[kDrainQueue] = []
+    this.on('drain', () => {
+      for (const callback of this[kDrainQueue].splice(0)) {
+        callback(null)
+      }
+    })
+
     // kQueue is built up of 3 sections separated by
     // the kRunningIdx and kPendingIdx indices.
     // |   complete   |   running   |   pending   |
@@ -299,26 +307,31 @@ class Client extends DispatcherBase {
     this.once('connect', cb)
   }
 
-  [kDispatch] (opts, handler) {
+  [kDispatch] (opts, handler, onDrain) {
     const origin = opts.origin || this[kUrl].origin
     const request = new Request(origin, opts, handler)
 
-    this[kQueue].push(request)
-    if (this[kResuming]) {
-      // Do nothing.
-    } else if (util.bodyLength(request.body) == null && util.isIterable(request.body)) {
-      // Wait a tick in case stream/iterator is ended in the same tick.
-      this[kResuming] = 1
-      queueMicrotask(() => resume(this))
+    if (this[kBusy] && onDrain) {
+      this[kDrainQueue].push(onDrain)
+      return false
     } else {
-      this[kResume](true)
+      this[kQueue].push(request)
+      if (this[kResuming]) {
+        // Do nothing.
+      } else if (util.bodyLength(request.body) == null && util.isIterable(request.body)) {
+        // Wait a tick in case stream/iterator is ended in the same tick.
+        this[kResuming] = 1
+        queueMicrotask(() => resume(this))
+      } else {
+        this[kResume](true)
+      }
     }
 
     if (this[kResuming] && this[kNeedDrain] !== 2 && this[kBusy]) {
       this[kNeedDrain] = 2
     }
 
-    return this[kNeedDrain] < 2
+    return onDrain ? true : this[kNeedDrain] < 2
   }
 
   async [kClose] () {
@@ -341,6 +354,10 @@ class Client extends DispatcherBase {
         util.errorRequest(this, request, err)
       }
 
+      for (const callback of this[kDrainQueue].splice(0)) {
+        callback(err)
+      }
+
       const callback = () => {
         if (this[kClosedResolve]) {
           // TODO (fix): Should we error here with ClientDestroyedError?

lib/dispatcher/dispatcher-base.js

@@ -142,21 +142,21 @@ class DispatcherBase extends Dispatcher {
     })
   }
 
-  [kInterceptedDispatch] (opts, handler) {
+  [kInterceptedDispatch] (opts, handler, onDrain) {
     if (!this[kInterceptors] || this[kInterceptors].length === 0) {
       this[kInterceptedDispatch] = this[kDispatch]
-      return this[kDispatch](opts, handler)
+      return this[kDispatch](opts, handler, onDrain)
     }
 
     let dispatch = this[kDispatch].bind(this)
     for (let i = this[kInterceptors].length - 1; i >= 0; i--) {
       dispatch = this[kInterceptors][i](dispatch)
     }
     this[kInterceptedDispatch] = dispatch
-    return dispatch(opts, handler)
+    return dispatch(opts, handler, onDrain)
   }
 
-  dispatch (opts, handler) {
+  dispatch (opts, handler, onDrain) {
     if (!handler || typeof handler !== 'object') {
       throw new InvalidArgumentError('handler must be an object')
     }
@@ -174,7 +174,7 @@ class DispatcherBase extends Dispatcher {
         throw new ClientClosedError()
       }
 
-      return this[kInterceptedDispatch](opts, handler)
+      return this[kInterceptedDispatch](opts, handler, onDrain)
     } catch (err) {
       if (typeof handler.onError !== 'function') {
         throw new InvalidArgumentError('invalid onError method')

lib/dispatcher/dispatcher.js

@@ -49,8 +49,15 @@ class ComposedDispatcher extends Dispatcher {
     this.#dispatch = dispatch
   }
 
-  dispatch (...args) {
-    this.#dispatch(...args)
+  dispatch (opts, handler, onDrain) {
+    // Allocating a closure here every time is not great...
+    return this.#dispatch(opts, handler, onDrain ?? (err, ...args) => {
+      if (err) {
+        handler.onError(err)
+      } else {
+        this.emit('drain', ...args)
+      }
+    })
   }
 
   close (...args) {

lib/dispatcher/pool-base.js

@@ -17,6 +17,7 @@ const kGetDispatcher = Symbol('get dispatcher')
 const kAddClient = Symbol('add client')
 const kRemoveClient = Symbol('remove client')
 const kStats = Symbol('stats')
+const kDrainQueue = Symbol('kDrainQueue')
 
 class PoolBase extends DispatcherBase {
   constructor () {
@@ -69,6 +70,13 @@ class PoolBase extends DispatcherBase {
     }
 
     this[kStats] = new PoolStats(this)
+
+    this[kDrainQueue] = []
+    this.on('drain', () => {
+      for (const callback of this[kDrainQueue].splice(0)) {
+        callback(null)
+      }
+    })
   }
 
   get [kBusy] () {
@@ -122,6 +130,10 @@ class PoolBase extends DispatcherBase {
   }
 
   async [kDestroy] (err) {
+    for (const callback of this[kDrainQueue].splice(0)) {
+      callback(err)
+    }
+
     while (true) {
       const item = this[kQueue].shift()
       if (!item) {
@@ -133,10 +145,13 @@ class PoolBase extends DispatcherBase {
     return Promise.all(this[kClients].map(c => c.destroy(err)))
   }
 
-  [kDispatch] (opts, handler) {
+  [kDispatch] (opts, handler, onDrain) {
     const dispatcher = this[kGetDispatcher]()
 
-    if (!dispatcher) {
+    if (!dispatcher && onDrain) {
+      this[kDrainQueue].push(onDrain)
+      return false
+    } else if (!dispatcher) {
       this[kNeedDrain] = true
       this[kQueue].push({ opts, handler })
       this[kQueued]++
@@ -145,7 +160,7 @@ class PoolBase extends DispatcherBase {
       this[kNeedDrain] = !this[kGetDispatcher]()
     }
 
-    return !this[kNeedDrain]
+    return onDrain ? true : !this[kNeedDrain]
   }
 
   [kAddClient] (client) {

lib/dispatcher/proxy-agent.js

@@ -107,7 +107,7 @@ class ProxyAgent extends DispatcherBase {
     })
   }
 
-  dispatch (opts, handler) {
+  dispatch (opts, handler, onDrain) {
     const headers = buildHeaders(opts.headers)
     throwIfProxyAuthIsSent(headers)
 
@@ -121,7 +121,8 @@ class ProxyAgent extends DispatcherBase {
         ...opts,
         headers
       },
-      handler
+      handler,
+      onDrain
     )
   }
 

lib/dispatcher/retry-agent.js

@@ -4,23 +4,24 @@ const Dispatcher = require('./dispatcher')
 const RetryHandler = require('../handler/retry-handler')
 
 class RetryAgent extends Dispatcher {
-  #agent = null
-  #options = null
+  #agent
+  #options
+
   constructor (agent, options = {}) {
     super(options)
     this.#agent = agent
     this.#options = options
   }
 
-  dispatch (opts, handler) {
+  dispatch (opts, handler, onDrain) {
     const retry = new RetryHandler({
       ...opts,
       retryOptions: this.#options
     }, {
       dispatch: this.#agent.dispatch.bind(this.#agent),
       handler
     })
-    return this.#agent.dispatch(opts, retry)
+    return this.#agent.dispatch(opts, retry, onDrain)
   }
 
   close () {

lib/interceptor/dump.js

@@ -106,7 +106,7 @@ function createDumpInterceptor (
   }
 ) {
   return dispatch => {
-    return function Intercept (opts, handler) {
+    return function Intercept (opts, handler, onDrain) {
       const { dumpMaxSize = defaultMaxSize } =
         opts
 
@@ -115,7 +115,7 @@ function createDumpInterceptor (
         handler
       )
 
-      return dispatch(opts, dumpHandler)
+      return dispatch(opts, dumpHandler, onDrain)
     }
   }
 }

lib/interceptor/redirect-interceptor.js

@@ -4,16 +4,16 @@ const RedirectHandler = require('../handler/redirect-handler')
 
 function createRedirectInterceptor ({ maxRedirections: defaultMaxRedirections }) {
   return (dispatch) => {
-    return function Intercept (opts, handler) {
+    return function Intercept (opts, handler, onDrain) {
       const { maxRedirections = defaultMaxRedirections } = opts
 
       if (!maxRedirections) {
-        return dispatch(opts, handler)
+        return dispatch(opts, handler, onDrain)
       }
 
       const redirectHandler = new RedirectHandler(dispatch, maxRedirections, opts, handler)
       opts = { ...opts, maxRedirections: 0 } // Stop sub dispatcher from also redirecting.
-      return dispatch(opts, redirectHandler)
+      return dispatch(opts, redirectHandler, onDrain)
     }
   }
 }

lib/interceptor/redirect.js

@@ -4,7 +4,7 @@ const RedirectHandler = require('../handler/redirect-handler')
 module.exports = opts => {
   const globalMaxRedirections = opts?.maxRedirections
   return dispatch => {
-    return function redirectInterceptor (opts, handler) {
+    return function redirectInterceptor (opts, handler, onDrain) {
       const { maxRedirections = globalMaxRedirections, ...baseOpts } = opts
 
       if (!maxRedirections) {
@@ -18,7 +18,7 @@ module.exports = opts => {
         handler
       )
 
-      return dispatch(baseOpts, redirectHandler)
+      return dispatch(baseOpts, redirectHandler, onDrain)
     }
   }
 }

lib/interceptor/retry.js

@@ -3,7 +3,7 @@ const RetryHandler = require('../handler/retry-handler')
 
 module.exports = globalOpts => {
   return dispatch => {
-    return function retryInterceptor (opts, handler) {
+    return function retryInterceptor (opts, handler, onDrain) {
       return dispatch(
         opts,
         new RetryHandler(
@@ -12,7 +12,8 @@ module.exports = globalOpts => {
             handler,
             dispatch
           }
-        )
+        ),
+        onDrain
       )
     }
   }