fork from codeberg.org

server/dns/dns.go

@@ -0,0 +1,66 @@
+package dns
+
+import (
+	"net"
+	"strings"
+	"time"
+
+	"github.com/hashicorp/golang-lru/v2/expirable"
+)
+
+const (
+	lookupCacheValidity = 30 * time.Second
+	defaultPagesRepo    = "pages"
+)
+
+// TODO(#316): refactor to not use global variables
+var lookupCache *expirable.LRU[string, string] = expirable.NewLRU[string, string](4096, nil, lookupCacheValidity)
+
+// GetTargetFromDNS searches for CNAME or TXT entries on the request domain ending with MainDomainSuffix.
+// If everything is fine, it returns the target data.
+func GetTargetFromDNS(domain, mainDomainSuffix, firstDefaultBranch string) (targetOwner, targetRepo, targetBranch string) {
+	// Get CNAME or TXT
+	var cname string
+	var err error
+
+	if entry, ok := lookupCache.Get(domain); ok {
+		cname = entry
+	} else {
+		cname, err = net.LookupCNAME(domain)
+		cname = strings.TrimSuffix(cname, ".")
+		if err != nil || !strings.HasSuffix(cname, mainDomainSuffix) {
+			cname = ""
+			// TODO: check if the A record matches!
+			names, err := net.LookupTXT(domain)
+			if err == nil {
+				for _, name := range names {
+					name = strings.TrimSuffix(strings.TrimSpace(name), ".")
+					if strings.HasSuffix(name, mainDomainSuffix) {
+						cname = name
+						break
+					}
+				}
+			}
+		}
+		_ = lookupCache.Add(domain, cname)
+	}
+	if cname == "" {
+		return
+	}
+	cnameParts := strings.Split(strings.TrimSuffix(cname, mainDomainSuffix), ".")
+	targetOwner = cnameParts[len(cnameParts)-1]
+	if len(cnameParts) > 1 {
+		targetRepo = cnameParts[len(cnameParts)-2]
+	}
+	if len(cnameParts) > 2 {
+		targetBranch = cnameParts[len(cnameParts)-3]
+	}
+	if targetRepo == "" {
+		targetRepo = defaultPagesRepo
+	}
+	if targetBranch == "" && targetRepo != defaultPagesRepo {
+		targetBranch = firstDefaultBranch
+	}
+	// if targetBranch is still empty, the caller must find the default branch
+	return
+}