Swallow DNS allowlist parsing errors if at least one record is valid.

src/auth.go

@@ -157,19 +157,35 @@ func authorizeDNSAllowlist(r *http.Request) (*Authorization, error) {
 	}
 
 	allowlistHostname := fmt.Sprintf("_git-pages-repository.%s", host)
-	repoURLs, err := net.LookupTXT(allowlistHostname)
+	records, err := net.LookupTXT(allowlistHostname)
 	if err != nil {
 		return nil, AuthError{http.StatusUnauthorized,
 			fmt.Sprintf("failed to look up DNS repository allowlist: %s TXT", allowlistHostname)}
 	}
 
-	for _, repoURL := range repoURLs {
-		if parsedURL, err := url.Parse(repoURL); err != nil {
-			return nil, AuthError{http.StatusBadRequest,
-				fmt.Sprintf("failed to parse URL: %s TXT %q", allowlistHostname, repoURL)}
+	var (
+		repoURLs []string
+		errs     []error
+	)
+	for _, record := range records {
+		if parsedURL, err := url.Parse(record); err != nil {
+			errs = append(errs, fmt.Errorf("failed to parse URL: %s TXT %q", allowlistHostname, record))
 		} else if !parsedURL.IsAbs() {
-			return nil, AuthError{http.StatusBadRequest,
-				fmt.Sprintf("repository URL is not absolute: %s TXT %q", allowlistHostname, repoURL)}
+			errs = append(errs, fmt.Errorf("repository URL is not absolute: %s TXT %q", allowlistHostname, record))
+		} else {
+			repoURLs = append(repoURLs, record)
+		}
+	}
+
+	if len(repoURLs) == 0 {
+		if len(records) > 0 {
+			errs = append([]error{AuthError{http.StatusUnauthorized,
+				fmt.Sprintf("no valid DNS TXT records for %s", allowlistHostname)}},
+				errs...)
+			return nil, joinErrors(errs...)
+		} else {
+			return nil, AuthError{http.StatusUnauthorized,
+				fmt.Sprintf("no DNS TXT records found for %s", allowlistHostname)}
 		}
 	}
 
@@ -351,7 +367,7 @@ func AuthorizeMetadataRetrieval(r *http.Request) (*Authorization, error) {
 		}
 	}
 
-	return nil, errors.Join(causes...)
+	return nil, joinErrors(causes...)
 }
 
 // Returns `repoURLs, err` where if `err == nil` then the request is authorized to clone from
@@ -421,7 +437,7 @@ func AuthorizeUpdateFromRepository(r *http.Request) (*Authorization, error) {
 		}
 	}
 
-	return nil, errors.Join(causes...)
+	return nil, joinErrors(causes...)
 }
 
 func AuthorizeRepository(repoURL string, auth *Authorization) error {
@@ -511,7 +527,7 @@ func AuthorizeUpdateFromArchive(r *http.Request) (*Authorization, error) {
 		return auth, nil
 	}
 
-	return nil, errors.Join(causes...)
+	return nil, joinErrors(causes...)
 }
 
 func CheckForbiddenDomain(r *http.Request) error {

src/pages.go

@@ -562,9 +562,7 @@ func ServePages(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		var authErr AuthError
 		if errors.As(err, &authErr) {
-			message := fmt.Sprint(err)
-			http.Error(w, strings.ReplaceAll(message, "\n", "\n- "), authErr.code)
-			err = errors.New(strings.ReplaceAll(message, "\n", "; "))
+			http.Error(w, prettyErrMsg(err), authErr.code)
 		}
 		var tooLargeErr *http.MaxBytesError
 		if errors.As(err, &tooLargeErr) {

src/util.go

@@ -1,6 +1,10 @@
 package main
 
-import "io"
+import (
+	"errors"
+	"io"
+	"strings"
+)
 
 type BoundedReader struct {
 	inner io.Reader
@@ -23,3 +27,55 @@ func (reader *BoundedReader) Read(dest []byte) (count int, err error) {
 	reader.fuel -= int64(count)
 	return
 }
+
+type prettyError interface {
+	error
+	Pretty() string
+}
+
+func prettyErrMsg(err error) string {
+	switch cerr := err.(type) {
+	case prettyError:
+		return cerr.Pretty()
+	default:
+		return cerr.Error()
+	}
+}
+
+type prettyJoinError struct {
+	errs []error
+}
+
+func joinErrors(errs ...error) error {
+	if err := errors.Join(errs...); err != nil {
+		wrapErr := err.(interface{ Unwrap() []error })
+		return &prettyJoinError{errs: wrapErr.Unwrap()}
+	}
+	return nil
+}
+
+func (e *prettyJoinError) Error() string {
+	var s strings.Builder
+	for i, err := range e.errs {
+		if i > 0 {
+			s.WriteString("; ")
+		}
+		s.WriteString(err.Error())
+	}
+	return s.String()
+}
+
+func (e *prettyJoinError) Pretty() string {
+	var s strings.Builder
+	for i, err := range e.errs {
+		if i > 0 {
+			s.WriteString("\n- ")
+		}
+		s.WriteString(strings.ReplaceAll(prettyErrMsg(err), "\n", "\n  "))
+	}
+	return s.String()
+}
+
+func (e *prettyJoinError) Unwrap() []error {
+	return e.errs
+}