OP#792 initial commit after fork

internal/http/dial_dnscache.go

@@ -0,0 +1,80 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package http
+
+import (
+	"context"
+	"net"
+	"time"
+)
+
+// LookupHost is a function to make custom lookupHost for optional cached DNS requests
+type LookupHost func(ctx context.Context, host string) (addrs []string, err error)
+
+// DialContextWithLookupHost is a helper function which returns `net.DialContext` function.
+// It randomly fetches an IP via custom LookupHost function and dials it by the given dial
+// function. LookupHost may implement an internal DNS caching implementation, lookupHost
+// input if nil then net.DefaultResolver.LookupHost is used.
+//
+// It dials one by one and returns first connected `net.Conn`.
+// If it fails to dial all IPs from cache it returns first error. If no baseDialFunc
+// is given, it sets default dial function.
+//
+// You can use returned dial function for `http.Transport.DialContext`.
+//
+// In this function, it uses functions from `rand` package. To make it really random,
+// you MUST call `rand.Seed` and change the value from the default in your application
+func DialContextWithLookupHost(lookupHost LookupHost, baseDialCtx DialContext) DialContext {
+	if lookupHost == nil {
+		lookupHost = net.DefaultResolver.LookupHost
+	}
+
+	if baseDialCtx == nil {
+		// This is same as which `http.DefaultTransport` uses.
+		baseDialCtx = (&net.Dialer{
+			Timeout:   30 * time.Second,
+			KeepAlive: 30 * time.Second,
+		}).DialContext
+	}
+
+	return func(ctx context.Context, network, addr string) (conn net.Conn, err error) {
+		host, port, err := net.SplitHostPort(addr)
+		if err != nil {
+			return nil, err
+		}
+
+		if net.ParseIP(host) != nil {
+			// For IP only setups there is no need for DNS lookups.
+			return baseDialCtx(ctx, "tcp", addr)
+		}
+
+		ips, err := lookupHost(ctx, host)
+		if err != nil {
+			return nil, err
+		}
+
+		for _, ip := range ips {
+			conn, err = baseDialCtx(ctx, "tcp", net.JoinHostPort(ip, port))
+			if err == nil {
+				break
+			}
+		}
+
+		return conn, err
+	}
+}