1 files changed, 58 insertions, 6 deletions
diff --git a/internal/fusefrontend_reverse/rfile.go b/internal/fusefrontend_reverse/rfile.go
index 746a0d6..15f2764 100644
--- a/internal/fusefrontend_reverse/rfile.go
+++ b/internal/fusefrontend_reverse/rfile.go
@@ -1,27 +1,79 @@
 package fusefrontend_reverse
 
 import (
+	"fmt"
+	"io"
 	"os"
 
 	"github.com/hanwen/go-fuse/fuse"
 	"github.com/hanwen/go-fuse/fuse/nodefs"
 
 	"github.com/rfjakob/gocryptfs/internal/contentenc"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
 
-type file struct {
+var zeroFileId []byte
+
+func init() {
+	zeroFileId = make([]byte, 16)
+}
+
+type reverseFile struct {
+	// Embed nodefs.defaultFile for a ENOSYS implementation of all methods
+	nodefs.File
+	// Backing FD
 	fd *os.File
 	// Content encryption helper
 	contentEnc *contentenc.ContentEnc
-
-	// nodefs.defaultFile returns ENOSYS for all operations
-	nodefs.File
 }
 
 func NewFile(fd *os.File, contentEnc *contentenc.ContentEnc) (nodefs.File, fuse.Status) {
-	return &file{
+	return &reverseFile{
+		File:       nodefs.NewDefaultFile(),
 		fd:         fd,
 		contentEnc: contentEnc,
-		File:       nodefs.NewDefaultFile(),
 	}, fuse.OK
 }
+
+// GetAttr - FUSE call
+func (rf *reverseFile) GetAttr(*fuse.Attr) fuse.Status {
+	fmt.Printf("reverseFile.GetAttr fd=%d\n", rf.fd.Fd())
+	return fuse.ENOSYS
+}
+
+// Read - FUSE call
+func (rf *reverseFile) Read(buf []byte, off int64) (resultData fuse.ReadResult, status fuse.Status) {
+	// TODO prefix file header
+
+	length := uint64(len(buf))
+	blocks := rf.contentEnc.ExplodeCipherRange(uint64(off), length)
+
+	// Read the backing plaintext in one go
+	alignedOffset, alignedLength := contentenc.JointPlaintextRange(blocks)
+	tlog.Warn.Printf("alignedOffset=%d, alignedLength=%d\n", alignedOffset, alignedLength)
+	plaintext := make([]byte, int(alignedLength))
+	n, err := rf.fd.ReadAt(plaintext, int64(alignedOffset))
+	if err != nil && err != io.EOF {
+		tlog.Warn.Printf("reverseFile.Read: ReadAt: %s", err.Error())
+		return nil, fuse.ToStatus(err)
+	}
+	// Truncate buffer down to actually read bytes
+	plaintext = plaintext[0:n]
+
+	// Encrypt blocks
+	ciphertext := rf.contentEnc.EncryptBlocks(plaintext, blocks[0].BlockNo, zeroFileId)
+
+	// Crop down to the relevant part
+	var out []byte
+	lenHave := len(ciphertext)
+	skip := blocks[0].Skip
+	endWant := int(skip + length)
+	if lenHave > endWant {
+		out = plaintext[skip:endWant]
+	} else if lenHave > int(skip) {
+		out = plaintext[skip:lenHave]
+	}
+	// else: out stays empty, file was smaller than the requested offset
+
+	return fuse.ReadResultData(out), fuse.OK
+}