136 lines
3.3 KiB
Go
136 lines
3.3 KiB
Go
package dns
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import (
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"bufio"
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"io"
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"os"
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"strconv"
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"strings"
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)
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// ClientConfig wraps the contents of the /etc/resolv.conf file.
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type ClientConfig struct {
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Servers []string // servers to use
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Search []string // suffixes to append to local name
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Port string // what port to use
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Ndots int // number of dots in name to trigger absolute lookup
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Timeout int // seconds before giving up on packet
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Attempts int // lost packets before giving up on server, not used in the package dns
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}
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// ClientConfigFromFile parses a resolv.conf(5) like file and returns
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// a *ClientConfig.
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func ClientConfigFromFile(resolvconf string) (*ClientConfig, error) {
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file, err := os.Open(resolvconf)
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if err != nil {
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return nil, err
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}
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defer file.Close()
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return ClientConfigFromReader(file)
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}
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// ClientConfigFromReader works like ClientConfigFromFile but takes an io.Reader as argument
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func ClientConfigFromReader(resolvconf io.Reader) (*ClientConfig, error) {
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c := new(ClientConfig)
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scanner := bufio.NewScanner(resolvconf)
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c.Servers = make([]string, 0)
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c.Search = make([]string, 0)
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c.Port = "53"
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c.Ndots = 1
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c.Timeout = 5
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c.Attempts = 2
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for scanner.Scan() {
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if err := scanner.Err(); err != nil {
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return nil, err
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}
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line := scanner.Text()
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f := strings.Fields(line)
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if len(f) < 1 {
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continue
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}
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switch f[0] {
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case "nameserver": // add one name server
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if len(f) > 1 {
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// One more check: make sure server name is
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// just an IP address. Otherwise we need DNS
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// to look it up.
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name := f[1]
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c.Servers = append(c.Servers, name)
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}
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case "domain": // set search path to just this domain
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if len(f) > 1 {
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c.Search = make([]string, 1)
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c.Search[0] = f[1]
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} else {
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c.Search = make([]string, 0)
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}
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case "search": // set search path to given servers
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c.Search = append([]string(nil), f[1:]...)
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case "options": // magic options
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for _, s := range f[1:] {
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switch {
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case len(s) >= 6 && s[:6] == "ndots:":
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n, _ := strconv.Atoi(s[6:])
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if n < 0 {
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n = 0
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} else if n > 15 {
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n = 15
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}
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c.Ndots = n
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case len(s) >= 8 && s[:8] == "timeout:":
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n, _ := strconv.Atoi(s[8:])
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if n < 1 {
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n = 1
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}
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c.Timeout = n
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case len(s) >= 9 && s[:9] == "attempts:":
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n, _ := strconv.Atoi(s[9:])
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if n < 1 {
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n = 1
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}
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c.Attempts = n
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case s == "rotate":
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/* not imp */
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}
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}
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}
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}
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return c, nil
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}
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// NameList returns all of the names that should be queried based on the
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// config. It is based off of go's net/dns name building, but it does not
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// check the length of the resulting names.
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func (c *ClientConfig) NameList(name string) []string {
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// if this domain is already fully qualified, no append needed.
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if IsFqdn(name) {
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return []string{name}
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}
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// Check to see if the name has more labels than Ndots. Do this before making
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// the domain fully qualified.
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hasNdots := CountLabel(name) > c.Ndots
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// Make the domain fully qualified.
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name = Fqdn(name)
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// Make a list of names based off search.
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names := []string{}
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// If name has enough dots, try that first.
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if hasNdots {
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names = append(names, name)
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}
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for _, s := range c.Search {
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names = append(names, Fqdn(name+s))
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}
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// If we didn't have enough dots, try after suffixes.
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if !hasNdots {
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names = append(names, name)
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}
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return names
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}
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