introduce dns-record module (#536)

README.md

@@ -142,6 +142,24 @@ gesundheit -conf /etc/gesundheit/gesundheit.toml
       <td>MinAvailable</td>
       <td>Min available space considered healthy, e.g. <code>"1G"</code></td>
     </tr>
+    <tr>
+      <td rowspan="4"><strong>dns-record</strong></td>
+      <td rowspan="4">Check DNS record</td>
+      <td>Address</td>
+      <td>DNS server address, e.g. <code>"127.0.0.1:53"</code></td>
+    </tr>
+    <tr>
+      <td>Type</td>
+      <td>Record type, e.g. <code>"A"</code></td>
+    </tr>
+    <tr>
+      <td>Name</td>
+      <td>Name to lookup, e.g. <code>"example.com"</code></td>
+    </tr>
+    <tr>
+      <td>Value</td>
+      <td>Expected value, e.g. <code>"1.1.1.1"</code></td>
+    </tr>
     <tr>
       <td rowspan="2"><strong>exec</strong></td>
       <td rowspan="2">Execute check command</td>

check/dns-record/check.go

@@ -0,0 +1,108 @@
+package filemtime
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/ushis/gesundheit/check"
+	"github.com/ushis/gesundheit/result"
+)
+
+type Check struct {
+	Address string
+	Type    string
+	Name    string
+	Value   string
+}
+
+func init() {
+	check.Register("dns-record", New)
+}
+
+func New(_ check.Database, configure func(interface{}) error) (check.Check, error) {
+	check := Check{}
+
+	if err := configure(&check); err != nil {
+		return nil, err
+	}
+	if check.Type == "" {
+		return nil, errors.New("missing Type")
+	}
+	if check.Name == "" {
+		return nil, errors.New("missing Name")
+	}
+	return check, nil
+}
+
+func (c Check) Exec() result.Result {
+	records, err := lookup(resolver(c.Address), c.Type, c.Name)
+
+	if err != nil {
+		return result.Fail("failed to lookup %s: %s", c.Name, err)
+	}
+	for _, r := range records {
+		if r == c.Value {
+			return result.OK("%s %s resolves to %s", c.Type, c.Name, c.Value)
+		}
+	}
+	if len(records) == 0 {
+		return result.Fail("could not find any records for %s %s", c.Type, c.Name)
+	}
+	return result.Fail("%s %s resolves to %s", c.Type, c.Name, records[0])
+}
+
+func resolver(addr string) *net.Resolver {
+	if addr == "" {
+		return net.DefaultResolver
+	}
+	d := &net.Dialer{Timeout: time.Second}
+
+	return &net.Resolver{
+		PreferGo: true,
+		Dial: func(ctx context.Context, network string, _ string) (net.Conn, error) {
+			return d.DialContext(ctx, network, addr)
+		},
+	}
+}
+
+func lookup(r *net.Resolver, typ, name string) (result []string, err error) {
+	switch typ {
+	case "A":
+		records, err := r.LookupIP(context.Background(), "ip4", name)
+
+		if err != nil {
+			return nil, err
+		}
+		return mapToStrings(records), nil
+	case "AAAA":
+		records, err := r.LookupIP(context.Background(), "ip6", name)
+
+		if err != nil {
+			return nil, err
+		}
+		return mapToStrings(records), nil
+	case "CNAME":
+		record, err := r.LookupCNAME(context.Background(), name)
+
+		if err != nil {
+			return nil, err
+		}
+		return []string{record}, nil
+	case "TXT":
+		return r.LookupTXT(context.Background(), name)
+	default:
+		return nil, fmt.Errorf("unsupported record type: %s", typ)
+	}
+}
+
+func mapToStrings[T fmt.Stringer](values []T) []string {
+	s := make([]string, len(values))
+
+	for i, val := range values {
+		s[i] = val.String()
+	}
+	return s
+}

main.go

@@ -16,6 +16,7 @@ import (
 	"time"
 
 	_ "github.com/ushis/gesundheit/check/disk-space"
+	_ "github.com/ushis/gesundheit/check/dns-record"
 	_ "github.com/ushis/gesundheit/check/exec"
 	_ "github.com/ushis/gesundheit/check/file-mtime"
 	_ "github.com/ushis/gesundheit/check/file-presence"

package.json

@@ -22,7 +22,7 @@
     "eslint-plugin-vue": "^8.7.1",
     "sass": "^1.71.1",
     "typescript": "^5.3.3",
-    "vite": "^2.9.16",
+    "vite": "^2.9.17",
     "vue-tsc": "^1.8.27"
   }
 }