server: handle session/new write+read in server (rdwr pattern), bypass FileConfig

cmd/olliesrv/server.go

@@ -50,6 +50,7 @@ type fid struct {
 	completeResult []byte // for /complete: result of last write (per-fid state)
 	generateResult []byte // for /generate: result of last write (per-fid state)
 	routeResult    []byte // for /route: result of last write (per-fid state)
+	sessionResult  []byte // for /session/new: session name from last write
 }
 
 // connState tracks all open fids for a single 9P connection.
@@ -842,6 +843,12 @@ func (s *Server) read(cs *connState, fc *plan9.Fcall, ctx context.Context) *plan
 			return s.readDNS(fc, &f.routeResult)
 		}
 
+		// /session/new: return per-fid result from previous write
+		if path == "/session/new" {
+			s.log.Debug("Tread path=%q offset=%d count=%d", path, fc.Offset, fc.Count)
+			return s.readDNS(fc, &f.sessionResult)
+		}
+
 		s.log.Debug("Tread path=%q offset=%d count=%d", path, fc.Offset, fc.Count)
 	entry, err := s.openEntry(path)
 	if err != nil {
@@ -1014,6 +1021,17 @@ func (s *Server) write(cs *connState, fc *plan9.Fcall) *plan9.Fcall {
 			return &plan9.Fcall{Type: plan9.Rwrite, Tag: fc.Tag, Count: uint32(len(fc.Data))}
 		}
 
+		// /session/new: synchronous create-session (per-fid state, like /net/dns)
+		if f.path == "/session/new" {
+			cs.mu.Unlock()
+			name, err := fs.CreateFromRoot(s.sessionTree, strings.Fields(strings.TrimSpace(string(fc.Data))))
+			if err != nil {
+				return errFcall(fc, err.Error())
+			}
+			f.sessionResult = []byte(name)
+			return &plan9.Fcall{Type: plan9.Rwrite, Tag: fc.Tag, Count: uint32(len(fc.Data))}
+		}
+
 		// Accumulate; the 9P client may split large writes across multiple Twrite messages.
 	end := int(fc.Offset) + len(fc.Data)
 	if end > len(f.writeBuf) {

fs/session/root.go

@@ -423,24 +423,15 @@ func rootOpen(rs *rootState, name string) (File, error) {
 			IsBlocking_: true,
 		}, nil
 	case "new":
-			var sessResult string
 		return &FileConfig{
 			StatFn: func() (os.FileInfo, error) {
 				return &SyntheticFileInfo{Name_: "new", Mode_: Perms[PathSessions].Files["new"]}, nil
 			},
 			ReadFn: func() ([]byte, error) {
-					if sessResult != "" {
-						return []byte(sessResult + "\n"), nil
-					}
 				return []byte("name=\n"), nil
 			},
 			WriteFn: func(data []byte) error {
-					name, err := Create(rs, strings.Fields(strings.TrimSpace(string(data))))
-					if err != nil {
-						return err
-					}
-					sessResult = name
-					return nil
+				return fmt.Errorf("use ollie-9p rdwr session/new")
 			},
 			BlockingReadFn: notBlocking,
 		}, nil