Synchronize olliesrv fid read state

cmd/olliesrv/server.go

@@ -55,6 +55,7 @@ func (g *GroupTable) IsMember(group, user string) bool {
 }
 
 type fid struct {
+	mu        sync.Mutex
 	path      string
 	qid       plan9.Qid
 	mode      uint8
@@ -517,16 +518,27 @@ func read(root *fs.Tree, cs *connState, fc *plan9.Fcall, ctx context.Context) *p
 		cs.mu.RUnlock()
 		return errFcall(fc, "bad fid")
 	}
+	f.mu.Lock()
 	path := f.path
 	isDir := f.qid.Type&QTDir != 0
 	entry := f.entry
+	f.mu.Unlock()
 	cs.mu.RUnlock()
 
 	if isDir {
-		if fc.Offset == 0 || f.dirCache == nil {
-			f.dirCache = buildDirData(root, path)
+		f.mu.Lock()
+		cached := f.dirCache
+		f.mu.Unlock()
+		if fc.Offset == 0 || cached == nil {
+			cached = buildDirData(root, path)
+			f.mu.Lock()
+			if fc.Offset == 0 || f.dirCache == nil {
+				f.dirCache = cached
+			}
+			cached = f.dirCache
+			f.mu.Unlock()
 		}
-		data := sliceDirData(f.dirCache, fc.Offset, fc.Count)
+		data := sliceDirData(cached, fc.Offset, fc.Count)
 		return &plan9.Fcall{Type: plan9.Rread, Tag: fc.Tag, Count: uint32(len(data)), Data: data}
 	}
 
@@ -536,11 +548,14 @@ func read(root *fs.Tree, cs *connState, fc *plan9.Fcall, ctx context.Context) *p
 
 	if entry.BlockingReadMode() {
 		// Serve from cache if we already have content (multi-Tread paging).
-		if f.readCache != nil {
-			if int(fc.Offset) >= len(f.readCache) {
+		f.mu.Lock()
+		cached := f.readCache
+		f.mu.Unlock()
+		if cached != nil {
+			if int(fc.Offset) >= len(cached) {
 				return &plan9.Fcall{Type: plan9.Rread, Tag: fc.Tag, Count: 0}
 			}
-			return readSlice(fc, f.readCache)
+			return readSlice(fc, cached)
 		}
 		// First Tread: block for content.
 		cs.mu.RLock()
@@ -563,11 +578,15 @@ func read(root *fs.Tree, cs *connState, fc *plan9.Fcall, ctx context.Context) *p
 		if nextBase != "" {
 			cs.mu.Lock()
 			if f, ok := cs.fids[fc.Fid]; ok {
+				f.mu.Lock()
 				f.waitBase = nextBase
+				f.mu.Unlock()
 			}
 			cs.mu.Unlock()
 		}
+		f.mu.Lock()
 		f.readCache = content
+		f.mu.Unlock()
 		return readSlice(fc, content)
 	}
 
@@ -588,7 +607,9 @@ func read(root *fs.Tree, cs *connState, fc *plan9.Fcall, ctx context.Context) *p
 		if nextBase != "" {
 			cs.mu.Lock()
 			if f, ok := cs.fids[fc.Fid]; ok {
+				f.mu.Lock()
 				f.waitBase = nextBase
+				f.mu.Unlock()
 			}
 			cs.mu.Unlock()
 		}
@@ -599,11 +620,17 @@ func read(root *fs.Tree, cs *connState, fc *plan9.Fcall, ctx context.Context) *p
 		return &plan9.Fcall{Type: plan9.Rread, Tag: fc.Tag, Count: uint32(count), Data: content[:count]}
 	}
 
-	// Normal file read: cache content on first Tread, serve via readSlice.
-	// This handles the case where io.ReadAll issues multiple Treads at
-	// increasing offsets (buffer starts at 512 bytes and grows).
-	if f.readCache != nil {
-		return readSlice(fc, f.readCache)
+	cs.mu.RLock()
+	f, ok = cs.fids[fc.Fid]
+	cs.mu.RUnlock()
+	if !ok {
+		return errFcall(fc, "bad fid")
+	}
+	f.mu.Lock()
+	cached := f.readCache
+	f.mu.Unlock()
+	if cached != nil {
+		return readSlice(fc, cached)
 	}
 
 	type result struct {
@@ -622,8 +649,11 @@ func read(root *fs.Tree, cs *connState, fc *plan9.Fcall, ctx context.Context) *p
 		if r.err != nil {
 			return errFcall(fc, r.err.Error())
 		}
+		f.mu.Lock()
 		f.readCache = r.data
-		return readSlice(fc, r.data)
+		cached := f.readCache
+		f.mu.Unlock()
+		return readSlice(fc, cached)
 	case <-ctx.Done():
 		entry.Close()
 		return errFcall(fc, ctx.Err().Error())