rename all remaining packages to internal/ (#12418)

This is to ensure that there are no projects
that try to import `minio/minio/pkg` into
their own repo. Any such common packages should
go to `https://github.com/minio/pkg`

internal/http/dial_dnscache.go

@@ -0,0 +1,199 @@
+// 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"
+	"math/rand"
+	"net"
+	"sync"
+	"time"
+)
+
+var randPerm = func(n int) []int {
+	return rand.Perm(n)
+}
+
+// DialContextWithDNSCache is a helper function which returns `net.DialContext` function.
+// It randomly fetches an IP from the DNS cache and dials it by the given dial
+// function. 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 DialContextWithDNSCache(cache *DNSCache, baseDialCtx DialContext) DialContext {
+	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, host string) (net.Conn, error) {
+		h, p, err := net.SplitHostPort(host)
+		if err != nil {
+			return nil, err
+		}
+
+		// Fetch DNS result from cache.
+		//
+		// ctxLookup is only used for canceling DNS Lookup.
+		ctxLookup, cancelF := context.WithTimeout(ctx, cache.lookupTimeout)
+		defer cancelF()
+		addrs, err := cache.Fetch(ctxLookup, h)
+		if err != nil {
+			return nil, err
+		}
+
+		var firstErr error
+		for _, randomIndex := range randPerm(len(addrs)) {
+			conn, err := baseDialCtx(ctx, "tcp", net.JoinHostPort(addrs[randomIndex], p))
+			if err == nil {
+				return conn, nil
+			}
+			if firstErr == nil {
+				firstErr = err
+			}
+		}
+
+		return nil, firstErr
+	}
+}
+
+const (
+	// cacheSize is initial size of addr and IP list cache map.
+	cacheSize = 64
+)
+
+// defaultFreq is default frequency a resolver refreshes DNS cache.
+var (
+	defaultFreq          = 3 * time.Second
+	defaultLookupTimeout = 10 * time.Second
+)
+
+// DNSCache is DNS cache resolver which cache DNS resolve results in memory.
+type DNSCache struct {
+	sync.RWMutex
+
+	lookupHostFn  func(ctx context.Context, host string) ([]string, error)
+	lookupTimeout time.Duration
+	loggerOnce    func(ctx context.Context, err error, id interface{}, errKind ...interface{})
+
+	cache    map[string][]string
+	doneOnce sync.Once
+	doneCh   chan struct{}
+}
+
+// NewDNSCache initializes DNS cache resolver and starts auto refreshing
+// in a new goroutine. To stop auto refreshing, call `Stop()` function.
+// Once `Stop()` is called auto refreshing cannot be resumed.
+func NewDNSCache(freq time.Duration, lookupTimeout time.Duration, loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{})) *DNSCache {
+	if freq <= 0 {
+		freq = defaultFreq
+	}
+
+	if lookupTimeout <= 0 {
+		lookupTimeout = defaultLookupTimeout
+	}
+
+	r := &DNSCache{
+		lookupHostFn:  net.DefaultResolver.LookupHost,
+		lookupTimeout: lookupTimeout,
+		loggerOnce:    loggerOnce,
+		cache:         make(map[string][]string, cacheSize),
+		doneCh:        make(chan struct{}),
+	}
+
+	rnd := rand.New(rand.NewSource(time.Now().UnixNano()))
+
+	timer := time.NewTimer(freq)
+	go func() {
+		defer timer.Stop()
+
+		for {
+			select {
+			case <-timer.C:
+				// Make sure that refreshes on DNS do not be attempted
+				// at the same time, allows for reduced load on the
+				// DNS servers.
+				timer.Reset(time.Duration(rnd.Float64() * float64(freq)))
+
+				r.Refresh()
+			case <-r.doneCh:
+				return
+			}
+		}
+	}()
+
+	return r
+}
+
+// LookupHost lookups address list from DNS server, persist the results
+// in-memory cache. `Fetch` is used to obtain the values for a given host.
+func (r *DNSCache) LookupHost(ctx context.Context, host string) ([]string, error) {
+	addrs, err := r.lookupHostFn(ctx, host)
+	if err != nil {
+		return nil, err
+	}
+
+	r.Lock()
+	r.cache[host] = addrs
+	r.Unlock()
+
+	return addrs, nil
+}
+
+// Fetch fetches IP list from the cache. If IP list of the given addr is not in the cache,
+// then it lookups from DNS server by `Lookup` function.
+func (r *DNSCache) Fetch(ctx context.Context, host string) ([]string, error) {
+	r.RLock()
+	addrs, ok := r.cache[host]
+	r.RUnlock()
+	if ok {
+		return addrs, nil
+	}
+	return r.LookupHost(ctx, host)
+}
+
+// Refresh refreshes IP list cache, automatically.
+func (r *DNSCache) Refresh() {
+	r.RLock()
+	hosts := make([]string, 0, len(r.cache))
+	for host := range r.cache {
+		hosts = append(hosts, host)
+	}
+	r.RUnlock()
+
+	for _, host := range hosts {
+		ctx, cancelF := context.WithTimeout(context.Background(), r.lookupTimeout)
+		if _, err := r.LookupHost(ctx, host); err != nil {
+			r.loggerOnce(ctx, err, host)
+		}
+		cancelF()
+	}
+}
+
+// Stop stops auto refreshing.
+func (r *DNSCache) Stop() {
+	r.doneOnce.Do(func() {
+		close(r.doneCh)
+	})
+}