perf: zero copy llhttp buffers (#712)

* perf: zero copy llhttp buffers

Fixes: nodejs/llhttp#100
Refs: #711

* fixup

* fixup

* fixup

lib/client.js

@@ -421,20 +421,26 @@ class Parser {
         },
         wasm_on_header_field: (p, at, len) => {
           assert(this.headers.length % 2 === 0)
-          return this.onHeader(this.inst.memory.buffer, at, len) || 0
+          const start = at - this.bufferPtr
+          const end = start + len
+          return this.onHeader(this.bufferRef.slice(start, end)) || 0
         },
         wasm_on_header_value: (p, at, len) => {
           assert(this.headers.length % 2 === 1)
-          return this.onHeader(this.inst.memory.buffer, at, len) || 0
+          const start = at - this.bufferPtr
+          const end = start + len
+          return this.onHeader(this.bufferRef.slice(start, end)) || 0
         },
         wasm_on_headers_complete: p => {
           const statusCode = this.inst.llhttp_get_status_code(p)
           const upgrade = Boolean(this.inst.llhttp_get_upgrade(p))
           const shouldKeepAlive = Boolean(this.inst.llhttp_should_keep_alive(p))
-          return this.onHeadersComplete(statusCode, upgrade, shouldKeepAlive)
+          return this.onHeadersComplete(statusCode, upgrade, shouldKeepAlive) || 0
         },
-        wasm_on_body: (p, at, length) => {
-          return this.onBody(this.inst.memory.buffer, at, length) || 0
+        wasm_on_body: (p, at, len) => {
+          const start = at - this.bufferPtr
+          const end = start + len
+          return this.onBody(this.bufferRef.slice(start, end)) || 0
         },
         wasm_on_message_complete: (p) => {
           return this.onMessageComplete() || 0
@@ -449,6 +455,7 @@ class Parser {
     this.ptr = this.inst.llhttp_alloc(constants.TYPE.RESPONSE)
     this.bufferSize = 0
     this.bufferPtr = null
+    this.bufferRef = null
     this.bufferView = null
     this.client = client
     this.socket = socket
@@ -498,13 +505,16 @@ class Parser {
       this.bufferView = new Uint8Array(this.inst.memory.buffer, this.bufferPtr, this.bufferSize)
     }
 
+    // TODO (perf): Can we avoid this copy somehow?
     this.bufferView.set(data)
 
     // Call `execute` on the wasm parser.
     // We pass the `llhttp_parser` pointer address, the pointer address of buffer view data,
     // and finally the length of bytes to parse.
     // The return value is an error code or `constants.ERROR.OK`.
+    this.bufferRef = data
     const ret = this.inst.llhttp_execute(this.ptr, this.bufferPtr, data.length)
+    this.bufferRef = null
 
     if (ret === constants.ERROR.OK) {
       return
@@ -531,15 +541,10 @@ class Parser {
     }
   }
 
-  onHeader (buf, at, len) {
-    // TODO: we could optimize this further by making this part the responsibility of the user.
-    // Forcing them to consume the buffer synchronously or copy it otherwise.
-    const data = Buffer.allocUnsafe(len)
-    Buffer.from(buf, at, len).copy(data)
+  onHeader (buf) {
+    this.headers.push(buf)
 
-    this.headers.push(data)
-
-    this.headersSize += len
+    this.headersSize += buf.length
     if (this.headersSize >= this.headersMaxSize) {
       util.destroy(this.socket, new HeadersOverflowError())
     }
@@ -722,18 +727,13 @@ class Parser {
     }
   }
 
-  onBody (buf, at, len) {
+  onBody (buf) {
     const { client, socket, statusCode, timeout } = this
 
     if (socket.destroyed) {
       return -1
     }
 
-    // TODO: we could optimize this further by making this part responsibility fo the user.
-    // Forcing them to consume the buffer synchronously or copy it otherwise.
-    const data = Buffer.allocUnsafe(len)
-    Buffer.from(buf, at, len).copy(data)
-
     const request = client[kQueue][client[kRunningIdx]]
     assert(request)
 
@@ -747,7 +747,7 @@ class Parser {
     assert(statusCode >= 200)
 
     try {
-      if (request.onData(data) === false) {
+      if (request.onData(buf) === false) {
         return constants.ERROR.PAUSED
       }
     } catch (err) {