1 files changed, 35 insertions, 15 deletions
diff --git a/gopher/request.go b/gopher/request.go
index fdd7480..3aeaf74 100644
--- a/gopher/request.go
+++ b/gopher/request.go
@@ -11,6 +11,11 @@ import (
 	"tildegit.org/tjp/sliderule/internal/types"
 )
 
+const (
+	maxSelectorLen = 255
+	maxRequestLen  = 4096
+)
+
 // ParseRequest parses a gopher protocol request into a sliderule.Request object.
 func ParseRequest(rdr io.Reader) (*types.Request, error) {
 	selector, search, err := readFullRequest(rdr)
@@ -34,9 +39,7 @@ func ParseRequest(rdr io.Reader) (*types.Request, error) {
 }
 
 func readFullRequest(rdr io.Reader) (string, string, error) {
-	// The vast majority of requests will fit in this size:
-	// the specified 255 byte max for selector, then CRLF.
-	buf := make([]byte, 257)
+	buf := make([]byte, maxSelectorLen+len("\r\n"))
 
 	n, err := rdr.Read(buf)
 	if err != nil && !errors.Is(err, io.EOF) {
@@ -44,29 +47,46 @@ func readFullRequest(rdr io.Reader) (string, string, error) {
 	}
 	buf = buf[:n]
 
-	// Full-text search transactions are the exception, they
-	// may be longer because there is an additional search string
-	if n == 257 && buf[256] != '\n' {
-		intake := buf[n:cap(buf)]
-		total := n
+	if lineEnd := bytes.IndexByte(buf, '\n'); lineEnd >= 0 {
+		buf = buf[:lineEnd+1]
+	} else if tab := bytes.IndexByte(buf, '\t'); tab >= 0 {
+		// Full-text search transactions append TAB and a search string.
+		// RFC 1436 still caps the selector at 255 bytes, but gives no
+		// search-string limit, so keep a small implementation cap.
 		for {
-			intake = append(intake, 0)
-			intake = intake[:cap(intake)]
+			if len(buf) >= maxRequestLen {
+				return "", "", errors.New("gopher request too long")
+			}
 
+			intake := make([]byte, maxRequestLen-len(buf))
 			n, err = rdr.Read(intake)
 			if err != nil && err != io.EOF {
 				return "", "", err
 			}
-			total += n
 
-			if n < cap(intake) || intake[cap(intake)-1] == '\n' {
+			buf = append(buf, intake[:n]...)
+			if lineEnd := bytes.IndexByte(intake[:n], '\n'); lineEnd >= 0 {
+				buf = buf[:len(buf)-n+lineEnd+1]
+				break
+			}
+			if err == io.EOF {
 				break
 			}
-			intake = intake[n:]
 		}
-		buf = buf[:total]
+	} else if len(buf) > maxSelectorLen {
+		return "", "", errors.New("gopher selector too long")
 	}
 
 	selector, search, _ := bytes.Cut(buf, []byte{'\t'})
-	return strings.TrimRight(string(selector), "\r\n"), strings.TrimRight(string(search), "\r\n"), nil
+	selector = bytes.TrimRight(selector, "\r\n")
+	search = bytes.TrimRight(search, "\r\n")
+
+	if len(selector) > maxSelectorLen {
+		return "", "", errors.New("gopher selector too long")
+	}
+	if bytes.ContainsAny(selector, "\x00\r\n") || bytes.ContainsAny(search, "\x00\t\r\n") {
+		return "", "", errors.New("malformed gopher request")
+	}
+
+	return string(selector), string(search), nil
 }