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net/dns/resolvconffile: unify three /etc/resolv.conf parsers into new package

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Change-Id: I2120893ca802d12f1bd0407d49077d3672627d33
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick
2022-02-14 20:17:51 -08:00
committed by Brad Fitzpatrick
parent 1dc4151f8b
commit c988bd6ed1
6 changed files with 227 additions and 126 deletions
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35
net/dns/resolver/tsdns.go
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@@ -8,7 +8,6 @@ package resolver
import (
"bufio"
"bytes"
"context"
"encoding/hex"
"errors"
@@ -23,16 +22,15 @@ import (
"sync/atomic"
"time"
"go4.org/mem"
dns "golang.org/x/net/dns/dnsmessage"
"inet.af/netaddr"
"tailscale.com/net/dns/resolvconffile"
"tailscale.com/net/tsaddr"
"tailscale.com/net/tsdial"
"tailscale.com/types/dnstype"
"tailscale.com/types/logger"
"tailscale.com/util/clientmetric"
"tailscale.com/util/dnsname"
"tailscale.com/util/lineread"
"tailscale.com/wgengine/monitor"
)
@@ -518,7 +516,7 @@ var errEmptyResolvConf = errors.New("resolv.conf has no nameservers")
// stubResolverForOS returns the IP address of the first nameserver in
// /etc/resolv.conf.
func stubResolverForOS() (ip netaddr.IP, err error) {
fi, err := os.Stat("/etc/resolv.conf")
fi, err := os.Stat(resolvconffile.Path)
if err != nil {
return netaddr.IP{}, err
}
@@ -529,37 +527,14 @@ func stubResolverForOS() (ip netaddr.IP, err error) {
if c, ok := resolvConfCacheValue.Load().(resolvConfCache); ok && c.mod == cur.mod && c.size == cur.size {
return c.ip, nil
}
// TODO(bradfitz): unify this /etc/resolv.conf parsing code with readResolv
// in net/dns, which we can't use due to circular dependency reasons.
// Move it to a leaf, including the OSConfig type (perhaps in its own dnstype
// package?)
err = lineread.File("/etc/resolv.conf", func(line []byte) error {
if !ip.IsZero() {
return nil
}
line = bytes.TrimSpace(line)
if len(line) == 0 || line[0] == '#' {
return nil
}
// Normalize tabs to spaces to simplify parsing code later.
for i, b := range line {
if b == '\t' {
line[i] = ' '
}
}
if mem.HasPrefix(mem.B(line), mem.S("nameserver ")) {
s := strings.TrimSpace(strings.TrimPrefix(string(line), "nameserver "))
ip, err = netaddr.ParseIP(s)
return err
}
return nil
})
conf, err := resolvconffile.ParseFile(resolvconffile.Path)
if err != nil {
return netaddr.IP{}, err
}
if !ip.IsValid() {
if len(conf.Nameservers) == 0 {
return netaddr.IP{}, errEmptyResolvConf
}
ip = conf.Nameservers[0]
cur.ip = ip
resolvConfCacheValue.Store(cur)
return ip, nil