buildkit/executor/oci/resolvconf.go

123 lines
2.6 KiB
Go

package oci
import (
"context"
"io/ioutil"
"os"
"path/filepath"
"github.com/docker/docker/pkg/idtools"
"github.com/docker/libnetwork/resolvconf"
"github.com/docker/libnetwork/types"
"github.com/moby/buildkit/util/flightcontrol"
)
var g flightcontrol.Group
var notFirstRun bool
var lastNotEmpty bool
type DNSConfig struct {
Nameservers []string
Options []string
SearchDomains []string
}
func GetResolvConf(ctx context.Context, stateDir string, idmap *idtools.IdentityMapping, dns *DNSConfig) (string, error) {
p := filepath.Join(stateDir, "resolv.conf")
_, err := g.Do(ctx, stateDir, func(ctx context.Context) (interface{}, error) {
generate := !notFirstRun
notFirstRun = true
if !generate {
fi, err := os.Stat(p)
if err != nil {
if !os.IsNotExist(err) {
return "", err
}
generate = true
}
if !generate {
fiMain, err := os.Stat(resolvconf.Path())
if err != nil {
if !os.IsNotExist(err) {
return nil, err
}
if lastNotEmpty {
generate = true
lastNotEmpty = false
}
} else {
if fi.ModTime().Before(fiMain.ModTime()) {
generate = true
}
}
}
}
if !generate {
return "", nil
}
var dt []byte
f, err := resolvconf.Get()
if err != nil {
if !os.IsNotExist(err) {
return "", err
}
} else {
dt = f.Content
}
if dns != nil {
var (
dnsNameservers = resolvconf.GetNameservers(dt, types.IP)
dnsSearchDomains = resolvconf.GetSearchDomains(dt)
dnsOptions = resolvconf.GetOptions(dt)
)
if len(dns.Nameservers) > 0 {
dnsNameservers = dns.Nameservers
}
if len(dns.SearchDomains) > 0 {
dnsSearchDomains = dns.SearchDomains
}
if len(dns.Options) > 0 {
dnsOptions = dns.Options
}
f, err = resolvconf.Build(p+".tmp", dnsNameservers, dnsSearchDomains, dnsOptions)
if err != nil {
return "", err
}
} else {
// Logic seems odd here: why are we filtering localhost IPs
// only if neither of the DNS configs were specified?
// Logic comes from https://github.com/docker/libnetwork/blob/164a77ee6d24fb2b1d61f8ad3403a51d8453899e/sandbox_dns_unix.go#L230-L269
f, err = resolvconf.FilterResolvDNS(f.Content, true)
if err != nil {
return "", err
}
}
tmpPath := p + ".tmp"
if err := ioutil.WriteFile(tmpPath, f.Content, 0644); err != nil {
return "", err
}
if idmap != nil {
root := idmap.RootPair()
if err := os.Chown(tmpPath, root.UID, root.GID); err != nil {
return "", err
}
}
if err := os.Rename(tmpPath, p); err != nil {
return "", err
}
return "", nil
})
if err != nil {
return "", err
}
return p, nil
}