pages-server/server/dns/dns.go

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package dns
import (
"net"
"strings"
"time"
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"github.com/hashicorp/golang-lru/v2/expirable"
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)
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)
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// 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) {
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// Get CNAME or TXT
var cname string
var err error
if entry, ok := lookupCache.Get(domain); ok {
cname = entry
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} 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), ".")
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if strings.HasSuffix(name, mainDomainSuffix) {
cname = name
break
}
}
}
}
_ = lookupCache.Add(domain, cname)
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}
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
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}
if targetBranch == "" && targetRepo != defaultPagesRepo {
targetBranch = firstDefaultBranch
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}
// if targetBranch is still empty, the caller must find the default branch
return
}