net/http: add to deadlines only when positive

The existing implementation allows read / write deadlines to exist
in the past. This updates conditionals to only add to the deadline
when the value is positive.

Fixes: #39177
Change-Id: I841c30ba2849a337e7bc98c8aa136c4527c314ed
Reviewed-on: https://go-review.googlesource.com/c/go/+/235437
Reviewed-by: Emmanuel Odeke <[email protected]>
Reviewed-by: Damien Neil <[email protected]>
Run-TryBot: Emmanuel Odeke <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Trust: Damien Neil <[email protected]>

Author: jharshman

src/net/http/server.go

@@ -964,14 +964,14 @@ func (c *conn) readRequest(ctx context.Context) (w *response, err error) {
 		hdrDeadline      time.Time // or zero if none
 	)
 	t0 := time.Now()
-	if d := c.server.readHeaderTimeout(); d != 0 {
+	if d := c.server.readHeaderTimeout(); d > 0 {
 		hdrDeadline = t0.Add(d)
 	}
-	if d := c.server.ReadTimeout; d != 0 {
+	if d := c.server.ReadTimeout; d > 0 {
 		wholeReqDeadline = t0.Add(d)
 	}
 	c.rwc.SetReadDeadline(hdrDeadline)
-	if d := c.server.WriteTimeout; d != 0 {
+	if d := c.server.WriteTimeout; d > 0 {
 		defer func() {
 			c.rwc.SetWriteDeadline(time.Now().Add(d))
 		}()
@@ -1831,10 +1831,10 @@ func (c *conn) serve(ctx context.Context) {
 	}()
 
 	if tlsConn, ok := c.rwc.(*tls.Conn); ok {
-		if d := c.server.ReadTimeout; d != 0 {
+		if d := c.server.ReadTimeout; d > 0 {
 			c.rwc.SetReadDeadline(time.Now().Add(d))
 		}
-		if d := c.server.WriteTimeout; d != 0 {
+		if d := c.server.WriteTimeout; d > 0 {
 			c.rwc.SetWriteDeadline(time.Now().Add(d))
 		}
 		if err := tlsConn.HandshakeContext(ctx); err != nil {
@@ -2567,7 +2567,8 @@ type Server struct {
 	TLSConfig *tls.Config
 
 	// ReadTimeout is the maximum duration for reading the entire
-	// request, including the body.
+	// request, including the body. A zero or negative value means
+	// there will be no timeout.
 	//
 	// Because ReadTimeout does not let Handlers make per-request
 	// decisions on each request body's acceptable deadline or
@@ -2587,6 +2588,7 @@ type Server struct {
 	// writes of the response. It is reset whenever a new
 	// request's header is read. Like ReadTimeout, it does not
 	// let Handlers make decisions on a per-request basis.
+	// A zero or negative value means there will be no timeout.
 	WriteTimeout time.Duration
 
 	// IdleTimeout is the maximum amount of time to wait for the