Implement content caching too, and disable due to memory overflow.

unionfs/cachingfs.go

 package unionfs
 
 import (
+	"bytes"
 	"fmt"
 	"github.com/hanwen/go-fuse/fuse"
 	"os"
@@ -31,6 +32,11 @@ type linkResponse struct {
 	fuse.Status
 }
 
+type openResponse struct {
+	fuse.File
+	fuse.Status
+}
+
 // Caches readdir and getattr()
 type CachingFileSystem struct {
 	fuse.FileSystem
@@ -39,6 +45,7 @@ type CachingFileSystem struct {
 	dirs       *TimedCache
 	links      *TimedCache
 	xattr      *TimedCache
+	files      *TimedCache
 }
 
 func readDir(fs fuse.FileSystem, name string) *dirResponse {
@@ -67,6 +74,43 @@ func getAttr(fs fuse.FileSystem, name string) *attrResponse {
 	}
 }
 
+func openFile(fs fuse.FileSystem, name string) (result *openResponse) {
+	result = &openResponse{}
+	flags := uint32(os.O_RDONLY)
+	
+	f, code := fs.Open(name, flags)
+	if !code.Ok() {
+		result.Status = code
+		return
+	}
+	defer f.Release()
+	defer f.Flush()
+
+	buf := bytes.NewBuffer(nil)
+	input := fuse.ReadIn{
+	Offset: 0,
+	Size: 128 * (1<<10),
+	Flags: flags,
+	}
+
+	bp := fuse.NewGcBufferPool()
+	for {
+		data, status := f.Read(&input, bp)
+		buf.Write(data)
+		if !status.Ok() {
+			result.Status = status
+			return 
+		}
+		if len(data) < int(input.Size) {
+			break
+		}
+		input.Offset += uint64(len(data))
+	}
+
+	result.File = fuse.NewReadOnlyFile(buf.Bytes())
+	return
+}
+
 func getXAttr(fs fuse.FileSystem, nameAttr string) *xattrResponse {
 	ns := strings.Split(nameAttr, _XATTRSEP, 2)
 	a, code := fs.GetXAttr(ns[0], ns[1])
@@ -93,6 +137,9 @@ func NewCachingFileSystem(fs fuse.FileSystem, ttlNs int64) *CachingFileSystem {
 	c.xattr = NewTimedCache(func(n string) interface{} {
 		return getXAttr(fs, n)
 	},ttlNs)
+	c.files = NewTimedCache(func(n string) interface{} {
+		return openFile(fs, n)
+	},ttlNs)
 	return c
 }
 
@@ -131,3 +178,13 @@ func (me *CachingFileSystem) OpenDir(name string) (stream chan fuse.DirEntry, st
 
 	return nil, r.Status
 }
+
+// Caching file contents easily overflows available memory.
+func (me *CachingFileSystem) DisabledOpen(name string, flags uint32) (f fuse.File, status fuse.Status) {
+	if flags & fuse.O_ANYWRITE != 0 {
+		return nil, fuse.EPERM
+	}
+
+	r := me.files.Get(name).(*openResponse)
+	return r.File, r.Status
+}