From 683b02b06cce0686c75c8703424fbe27ccd83f9c Mon Sep 17 00:00:00 2001
From: Roman Lisagor <rlisagor@gmail.com>
Date: Fri, 8 Jun 2018 13:25:28 +0200
Subject: [PATCH 1/2] Read timeout accounts for total time to receive relevant
 packet, not just any packet

---
 client.go | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/client.go b/client.go
index dfc7e17..7185b06 100644
--- a/client.go
+++ b/client.go
@@ -6,6 +6,7 @@ import (
 	"math/rand"
 	"net"
 	"sync"
+	"syscall"
 	"time"
 
 	"github.com/d2g/dhcp4"
@@ -145,8 +146,15 @@ func (c *Client) SendDiscoverPacket() (dhcp4.Packet, error) {
 //Retreive Offer...
 //Wait for the offer for a specific Discovery Packet.
 func (c *Client) GetOffer(discoverPacket *dhcp4.Packet) (dhcp4.Packet, error) {
+	start := time.Now()
+
 	for {
-		c.connection.SetReadTimeout(c.timeout)
+		timeout := c.timeout - time.Since(start)
+		if timeout < 0 {
+			return dhcp4.Packet{}, syscall.ETIMEDOUT
+		}
+
+		c.connection.SetReadTimeout(timeout)
 		readBuffer, source, err := c.connection.ReadFrom()
 		if err != nil {
 			return dhcp4.Packet{}, err
@@ -186,8 +194,15 @@ func (c *Client) SendRequest(offerPacket *dhcp4.Packet) (dhcp4.Packet, error) {
 //Retreive Acknowledgement
 //Wait for the offer for a specific Request Packet.
 func (c *Client) GetAcknowledgement(requestPacket *dhcp4.Packet) (dhcp4.Packet, error) {
+	start := time.Now()
+
 	for {
-		c.connection.SetReadTimeout(c.timeout)
+		timeout := c.timeout - time.Since(start)
+		if timeout < 0 {
+			return dhcp4.Packet{}, syscall.ETIMEDOUT
+		}
+
+		c.connection.SetReadTimeout(timeout)
 		readBuffer, source, err := c.connection.ReadFrom()
 		if err != nil {
 			return dhcp4.Packet{}, err

From 45101b2b7db70316458cd81730558ac4cb963cf1 Mon Sep 17 00:00:00 2001
From: Michael Stapelberg <stapelberg@google.com>
Date: Fri, 8 Jun 2018 13:47:12 +0200
Subject: [PATCH 2/2] Return friendlier errors on timeout

---
 client.go | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/client.go b/client.go
index 7185b06..510bea2 100644
--- a/client.go
+++ b/client.go
@@ -2,6 +2,7 @@ package dhcp4client
 
 import (
 	"bytes"
+	"fmt"
 	"hash/fnv"
 	"math/rand"
 	"net"
@@ -143,6 +144,15 @@ func (c *Client) SendDiscoverPacket() (dhcp4.Packet, error) {
 	return discoveryPacket, c.SendPacket(discoveryPacket)
 }
 
+// TimeoutError records a timeout when waiting for a DHCP packet.
+type TimeoutError struct {
+	Timeout time.Duration
+}
+
+func (te *TimeoutError) Error() string {
+	return fmt.Sprintf("no DHCP packet received within %v", te.Timeout)
+}
+
 //Retreive Offer...
 //Wait for the offer for a specific Discovery Packet.
 func (c *Client) GetOffer(discoverPacket *dhcp4.Packet) (dhcp4.Packet, error) {
@@ -151,12 +161,15 @@ func (c *Client) GetOffer(discoverPacket *dhcp4.Packet) (dhcp4.Packet, error) {
 	for {
 		timeout := c.timeout - time.Since(start)
 		if timeout < 0 {
-			return dhcp4.Packet{}, syscall.ETIMEDOUT
+			return dhcp4.Packet{}, &TimeoutError{Timeout: c.timeout}
 		}
 
 		c.connection.SetReadTimeout(timeout)
 		readBuffer, source, err := c.connection.ReadFrom()
 		if err != nil {
+			if errno, ok := err.(syscall.Errno); ok && errno == syscall.EAGAIN {
+				return dhcp4.Packet{}, &TimeoutError{Timeout: c.timeout}
+			}
 			return dhcp4.Packet{}, err
 		}
 
@@ -199,12 +212,15 @@ func (c *Client) GetAcknowledgement(requestPacket *dhcp4.Packet) (dhcp4.Packet,
 	for {
 		timeout := c.timeout - time.Since(start)
 		if timeout < 0 {
-			return dhcp4.Packet{}, syscall.ETIMEDOUT
+			return dhcp4.Packet{}, &TimeoutError{Timeout: c.timeout}
 		}
 
 		c.connection.SetReadTimeout(timeout)
 		readBuffer, source, err := c.connection.ReadFrom()
 		if err != nil {
+			if errno, ok := err.(syscall.Errno); ok && errno == syscall.EAGAIN {
+				return dhcp4.Packet{}, &TimeoutError{Timeout: c.timeout}
+			}
 			return dhcp4.Packet{}, err
 		}