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Dns fetch with slices instead of map for predictability of the order #1672

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merged 2 commits into from
Oct 24, 2023
Merged

Dns fetch with slices instead of map for predictability of the order #1672

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aecaf56
use slices to collect dns servers
hellt Oct 24, 2023
d5bdc65
added rn
hellt Oct 24, 2023
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2 changes: 1 addition & 1 deletion docs/rn/0.47.md
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Original file line number Diff line number Diff line change
Expand Up @@ -39,4 +39,4 @@ Containerlab now [generates an SSH config](../manual/inventory.md#ssh-config) fi

### 0.47.1

* Do not extract more than 3 DNS servers from the host's resolv.conf #1671
* Do not extract more than 3 DNS servers from the host's resolv.conf #1671, #1672
26 changes: 13 additions & 13 deletions utils/resolve.go
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Expand Up @@ -7,13 +7,17 @@ import (
"strings"

log "github.com/sirupsen/logrus"
"golang.org/x/exp/slices"
)

// ExtractDNSServersFromResolvConf extracts IP addresses
// of the DNS servers from the resolv.conf-formatted files passed in filenames list.
// Returns a list of IP addresses of the DNS servers.
func ExtractDNSServersFromResolvConf(filesys fs.FS, filenames []string) ([]string, error) {
DNSServersMap := map[string]struct{}{}
// list of DNS servers up to 10 elements
// since realistically there should be no more than 3
// DNS servers, we leave some room for duplicates
DNSServers := make([]string, 0, 10)

for _, filename := range filenames {
readFile, err := filesys.Open(filename)
Expand All @@ -39,27 +43,23 @@ func ExtractDNSServersFromResolvConf(filesys fs.FS, filenames []string) ([]strin
continue
}

DNSServersMap[ip.String()] = struct{}{}
DNSServers = append(DNSServers, ip.String())
}
}

readFile.Close()
}

if len(DNSServersMap) == 0 {
if len(DNSServers) == 0 {
return nil, nil
}

DNSServers := make([]string, 0, len(DNSServersMap))
var count int
for k := range DNSServersMap {
if count == 3 {
// keep only the first three DNS servers
// since C DNS resolver can't handle more
break
}
DNSServers = append(DNSServers, k)
count++
// remove duplicates
slices.Sort(DNSServers)
DNSServers = slices.Compact(DNSServers)

if len(DNSServers) > 3 {
DNSServers = DNSServers[:3]
}

return DNSServers, nil
Expand Down
16 changes: 3 additions & 13 deletions utils/resolve_test.go
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Expand Up @@ -2,12 +2,10 @@ package utils

import (
"io/fs"
"strings"
"testing"
"testing/fstest"

"github.com/google/go-cmp/cmp"
"github.com/google/go-cmp/cmp/cmpopts"
)

func TestExtractDNSServersFromResolvConf(t *testing.T) {
Expand Down Expand Up @@ -132,6 +130,7 @@ search .
"etc/someother/resolv.conf": &fstest.MapFile{
Data: []byte(
`
nameserver 2.2.2.2
nameserver 8.8.8.8
options edns0 trust-ad
search .
Expand All @@ -141,7 +140,7 @@ search .
},
filenames: []string{"etc/resolv.conf", "etc/someother/resolv.conf"},
},
want: []string{"1.1.1.1", "8.8.8.8"},
want: []string{"1.1.1.1", "2.2.2.2", "8.8.8.8"},
wantErr: false,
},
{
Expand All @@ -163,16 +162,7 @@ search .
return
}

if diff := cmp.Diff(got, tt.want, cmpopts.SortSlices(func(s1, s2 string) bool {
switch strings.Compare(s1, s2) {
case -1:
return false
case 0:
return true
}
return true
},
)); diff != "" {
if diff := cmp.Diff(got, tt.want); diff != "" {
t.Errorf(diff)
}
})
Expand Down