From dc81eb9c37873e391a927a6f6810239565a91732 Mon Sep 17 00:00:00 2001
From: Ghanan Gowripalan <ghanan@google.com>
Date: Thu, 27 Aug 2020 12:48:19 -0700
Subject: Add function to get error from a tcpip.Endpoint

In an upcoming CL, socket option types are made to implement a marker
interface with pointer receivers. Since this results in calling methods
of an interface with a pointer, we incur an allocation when attempting
to get an Endpoint's last error with the current implementation.

When calling the method of an interface, the compiler is unable to
determine what the interface implementation does with the pointer
(since calling a method on an interface uses virtual dispatch at runtime
so the compiler does not know what the interface method will do) so it
allocates on the heap to be safe incase an implementation continues to
hold the pointer after the functioon returns (the reference escapes the
scope of the object).

In the example below, the compiler does not know what b.foo does with
the reference to a it allocates a on the heap as the reference to a may
escape the scope of a.
```
var a int
var b someInterface
b.foo(&a)
```

This change removes the opportunity for that allocation.

RELNOTES: n/a
PiperOrigin-RevId: 328796559
---
 pkg/tcpip/transport/udp/endpoint.go | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

(limited to 'pkg/tcpip/transport/udp')

diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 0a9d3c6cf..1d5ebe3f2 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -209,7 +209,7 @@ func (e *endpoint) UniqueID() uint64 {
 	return e.uniqueID
 }
 
-func (e *endpoint) takeLastError() *tcpip.Error {
+func (e *endpoint) LastError() *tcpip.Error {
 	e.lastErrorMu.Lock()
 	defer e.lastErrorMu.Unlock()
 
@@ -268,7 +268,7 @@ func (e *endpoint) ModerateRecvBuf(copied int) {}
 // Read reads data from the endpoint. This method does not block if
 // there is no data pending.
 func (e *endpoint) Read(addr *tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
-	if err := e.takeLastError(); err != nil {
+	if err := e.LastError(); err != nil {
 		return buffer.View{}, tcpip.ControlMessages{}, err
 	}
 
@@ -411,7 +411,7 @@ func (e *endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 }
 
 func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-chan struct{}, *tcpip.Error) {
-	if err := e.takeLastError(); err != nil {
+	if err := e.LastError(); err != nil {
 		return 0, nil, err
 	}
 
@@ -962,8 +962,6 @@ func (e *endpoint) GetSockOptInt(opt tcpip.SockOptInt) (int, *tcpip.Error) {
 // GetSockOpt implements tcpip.Endpoint.GetSockOpt.
 func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
 	switch o := opt.(type) {
-	case tcpip.ErrorOption:
-		return e.takeLastError()
 	case *tcpip.MulticastInterfaceOption:
 		e.mu.Lock()
 		*o = tcpip.MulticastInterfaceOption{
-- 
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