Refactor pkg/networkfs

Solves #11591

Signed-off-by: bobby abbott <ttobbaybbob@gmail.com>

resolvconf/resolvconf.go

@@ -0,0 +1,190 @@
+package resolvconf
+
+import (
+	"bytes"
+	"io/ioutil"
+	"regexp"
+	"strings"
+	"sync"
+
+	log "github.com/Sirupsen/logrus"
+	"github.com/docker/docker/utils"
+)
+
+var (
+	// Note: the default IPv4 & IPv6 resolvers are set to Google's Public DNS
+	defaultIPv4Dns = []string{"nameserver 8.8.8.8", "nameserver 8.8.4.4"}
+	defaultIPv6Dns = []string{"nameserver 2001:4860:4860::8888", "nameserver 2001:4860:4860::8844"}
+	ipv4NumBlock   = `(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)`
+	ipv4Address    = `(` + ipv4NumBlock + `\.){3}` + ipv4NumBlock
+	// This is not an IPv6 address verifier as it will accept a super-set of IPv6, and also
+	// will *not match* IPv4-Embedded IPv6 Addresses (RFC6052), but that and other variants
+	// -- e.g. other link-local types -- either won't work in containers or are unnecessary.
+	// For readability and sufficiency for Docker purposes this seemed more reasonable than a
+	// 1000+ character regexp with exact and complete IPv6 validation
+	ipv6Address = `([0-9A-Fa-f]{0,4}:){2,7}([0-9A-Fa-f]{0,4})`
+	ipLocalhost = `((127\.([0-9]{1,3}.){2}[0-9]{1,3})|(::1))`
+
+	localhostIPRegexp = regexp.MustCompile(ipLocalhost)
+	localhostNSRegexp = regexp.MustCompile(`(?m)^nameserver\s+` + ipLocalhost + `\s*\n*`)
+	nsIPv6Regexp      = regexp.MustCompile(`(?m)^nameserver\s+` + ipv6Address + `\s*\n*`)
+	nsRegexp          = regexp.MustCompile(`^\s*nameserver\s*((` + ipv4Address + `)|(` + ipv6Address + `))\s*$`)
+	searchRegexp      = regexp.MustCompile(`^\s*search\s*(([^\s]+\s*)*)$`)
+)
+
+var lastModified struct {
+	sync.Mutex
+	sha256   string
+	contents []byte
+}
+
+func Get() ([]byte, error) {
+	resolv, err := ioutil.ReadFile("/etc/resolv.conf")
+	if err != nil {
+		return nil, err
+	}
+	return resolv, nil
+}
+
+// Retrieves the host /etc/resolv.conf file, checks against the last hash
+// and, if modified since last check, returns the bytes and new hash.
+// This feature is used by the resolv.conf updater for containers
+func GetIfChanged() ([]byte, string, error) {
+	lastModified.Lock()
+	defer lastModified.Unlock()
+
+	resolv, err := ioutil.ReadFile("/etc/resolv.conf")
+	if err != nil {
+		return nil, "", err
+	}
+	newHash, err := utils.HashData(bytes.NewReader(resolv))
+	if err != nil {
+		return nil, "", err
+	}
+	if lastModified.sha256 != newHash {
+		lastModified.sha256 = newHash
+		lastModified.contents = resolv
+		return resolv, newHash, nil
+	}
+	// nothing changed, so return no data
+	return nil, "", nil
+}
+
+// retrieve the last used contents and hash of the host resolv.conf
+// Used by containers updating on restart
+func GetLastModified() ([]byte, string) {
+	lastModified.Lock()
+	defer lastModified.Unlock()
+
+	return lastModified.contents, lastModified.sha256
+}
+
+// FilterResolvDns has two main jobs:
+// 1. It looks for localhost (127.*|::1) entries in the provided
+//    resolv.conf, removing local nameserver entries, and, if the resulting
+//    cleaned config has no defined nameservers left, adds default DNS entries
+// 2. Given the caller provides the enable/disable state of IPv6, the filter
+//    code will remove all IPv6 nameservers if it is not enabled for containers
+//
+// It also returns a boolean to notify the caller if changes were made at all
+func FilterResolvDns(resolvConf []byte, ipv6Enabled bool) ([]byte, bool) {
+	changed := false
+	cleanedResolvConf := localhostNSRegexp.ReplaceAll(resolvConf, []byte{})
+	// if IPv6 is not enabled, also clean out any IPv6 address nameserver
+	if !ipv6Enabled {
+		cleanedResolvConf = nsIPv6Regexp.ReplaceAll(cleanedResolvConf, []byte{})
+	}
+	// if the resulting resolvConf has no more nameservers defined, add appropriate
+	// default DNS servers for IPv4 and (optionally) IPv6
+	if len(GetNameservers(cleanedResolvConf)) == 0 {
+		log.Infof("No non-localhost DNS nameservers are left in resolv.conf. Using default external servers : %v", defaultIPv4Dns)
+		dns := defaultIPv4Dns
+		if ipv6Enabled {
+			log.Infof("IPv6 enabled; Adding default IPv6 external servers : %v", defaultIPv6Dns)
+			dns = append(dns, defaultIPv6Dns...)
+		}
+		cleanedResolvConf = append(cleanedResolvConf, []byte("\n"+strings.Join(dns, "\n"))...)
+	}
+	if !bytes.Equal(resolvConf, cleanedResolvConf) {
+		changed = true
+	}
+	return cleanedResolvConf, changed
+}
+
+// getLines parses input into lines and strips away comments.
+func getLines(input []byte, commentMarker []byte) [][]byte {
+	lines := bytes.Split(input, []byte("\n"))
+	var output [][]byte
+	for _, currentLine := range lines {
+		var commentIndex = bytes.Index(currentLine, commentMarker)
+		if commentIndex == -1 {
+			output = append(output, currentLine)
+		} else {
+			output = append(output, currentLine[:commentIndex])
+		}
+	}
+	return output
+}
+
+// returns true if the IP string matches the localhost IP regular expression.
+// Used for determining if nameserver settings are being passed which are
+// localhost addresses
+func IsLocalhost(ip string) bool {
+	return localhostIPRegexp.MatchString(ip)
+}
+
+// GetNameservers returns nameservers (if any) listed in /etc/resolv.conf
+func GetNameservers(resolvConf []byte) []string {
+	nameservers := []string{}
+	for _, line := range getLines(resolvConf, []byte("#")) {
+		var ns = nsRegexp.FindSubmatch(line)
+		if len(ns) > 0 {
+			nameservers = append(nameservers, string(ns[1]))
+		}
+	}
+	return nameservers
+}
+
+// GetNameserversAsCIDR returns nameservers (if any) listed in
+// /etc/resolv.conf as CIDR blocks (e.g., "1.2.3.4/32")
+// This function's output is intended for net.ParseCIDR
+func GetNameserversAsCIDR(resolvConf []byte) []string {
+	nameservers := []string{}
+	for _, nameserver := range GetNameservers(resolvConf) {
+		nameservers = append(nameservers, nameserver+"/32")
+	}
+	return nameservers
+}
+
+// GetSearchDomains returns search domains (if any) listed in /etc/resolv.conf
+// If more than one search line is encountered, only the contents of the last
+// one is returned.
+func GetSearchDomains(resolvConf []byte) []string {
+	domains := []string{}
+	for _, line := range getLines(resolvConf, []byte("#")) {
+		match := searchRegexp.FindSubmatch(line)
+		if match == nil {
+			continue
+		}
+		domains = strings.Fields(string(match[1]))
+	}
+	return domains
+}
+
+func Build(path string, dns, dnsSearch []string) error {
+	content := bytes.NewBuffer(nil)
+	for _, dns := range dns {
+		if _, err := content.WriteString("nameserver " + dns + "\n"); err != nil {
+			return err
+		}
+	}
+	if len(dnsSearch) > 0 {
+		if searchString := strings.Join(dnsSearch, " "); strings.Trim(searchString, " ") != "." {
+			if _, err := content.WriteString("search " + searchString + "\n"); err != nil {
+				return err
+			}
+		}
+	}
+
+	return ioutil.WriteFile(path, content.Bytes(), 0644)
+}