node, rpc: add ReadHeaderTimeout config option (#25338)

This change makes http.Server.ReadHeaderTimeout configurable separately
from ReadTimeout for RPC servers. The default is set to the same as
ReadTimeout, which in order to cause no change in existing deployments.

rpc/http.go

@@ -87,6 +87,14 @@ type HTTPTimeouts struct {
 	// ReadHeaderTimeout. It is valid to use them both.
 	ReadTimeout time.Duration
 
+	// ReadHeaderTimeout is the amount of time allowed to read
+	// request headers. The connection's read deadline is reset
+	// after reading the headers and the Handler can decide what
+	// is considered too slow for the body. If ReadHeaderTimeout
+	// is zero, the value of ReadTimeout is used. If both are
+	// zero, there is no timeout.
+	ReadHeaderTimeout time.Duration
+
 	// WriteTimeout is the maximum duration before timing out
 	// writes of the response. It is reset whenever a new
 	// request's header is read. Like ReadTimeout, it does not
@@ -103,9 +111,10 @@ type HTTPTimeouts struct {
 // DefaultHTTPTimeouts represents the default timeout values used if further
 // configuration is not provided.
 var DefaultHTTPTimeouts = HTTPTimeouts{
-	ReadTimeout:  30 * time.Second,
-	WriteTimeout: 30 * time.Second,
-	IdleTimeout:  120 * time.Second,
+	ReadTimeout:       30 * time.Second,
+	ReadHeaderTimeout: 30 * time.Second,
+	WriteTimeout:      30 * time.Second,
+	IdleTimeout:       120 * time.Second,
 }
 
 // DialHTTPWithClient creates a new RPC client that connects to an RPC server over HTTP