feat: publish standalone worker

Separate worker packaging and service lifecycle from the control plane.

checks/cdns/local_query.go

@@ -0,0 +1,67 @@
+package cdns
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"strings"
+
+	"github.com/miekg/dns"
+)
+
+func localQuery(mychan chan DNSreply, qname string, qtype uint16) {
+	if debug {
+		fmt.Printf("DEBUG: start of DNS request \"%s\" / %d\n", qname, qtype)
+	}
+	var result DNSreply
+	var trials uint
+	result.qname = qname
+	result.qtype = qtype
+	result.r = nil
+	result.err = errors.New("no name server to answer the question")
+	localm := new(dns.Msg)
+	localm.Id = dns.Id()
+	localm.RecursionDesired = true
+	localm.Question = make([]dns.Question, 1)
+	localm.SetEdns0(bufsize, false) // Even if no EDNS requested, see #9 May be we should retry without it if timeout?
+	localc := new(dns.Client)
+	localc.ReadTimeout = timeout
+	localm.Question[0] = dns.Question{Name: qname, Qtype: qtype, Qclass: dns.ClassINET}
+Tests:
+	for trials = 0; trials < uint(maxTrials); trials++ {
+		for serverIndex := range conf.Servers {
+			server := conf.Servers[serverIndex]
+			result.nameserver = server
+			// Brackets around the server address are necessary for IPv6 name servers
+			// Brackets required for IPv6; do not use net.JoinHostPort (see check-soa commit 3e4edb1)
+			r, rtt, err := localc.Exchange(localm, "["+server+"]:"+conf.Port)
+			if r == nil {
+				result.r = nil
+				result.err = err
+				log.Println(err.Error())
+				if strings.Contains(err.Error(), "timeout") {
+					// Try another resolver
+					continue
+				}
+				// We give in
+				break Tests
+			}
+			result.rtt = rtt
+			if r.Rcode == dns.RcodeSuccess {
+				// TODO: NODATA (NOERROR/ANSWER=0) are silently ignored (e.g. name exists but no IP address)
+				// TODO: for rcodes like SERVFAIL, trying another resolver could make sense
+				result.r = r
+				result.err = nil
+				break Tests
+			}
+			// All the other codes are errors
+			result.r = r
+			result.err = errors.New(dns.RcodeToString[r.Rcode])
+			break Tests
+		}
+	}
+	if debug {
+		fmt.Printf("DEBUG: end of DNS request \"%s\" / %d\n", qname, qtype)
+	}
+	mychan <- result
+}