Fix write path

cryptfs/cryptfile.go

@@ -115,14 +115,26 @@ func (ib *intraBlock) IsPartial() bool {
 	return false
 }
 
-// ciphertextRange - get byte range in ciphertext file corresponding to BlockNo
+// CiphertextRange - get byte range in ciphertext file corresponding to BlockNo
+// (complete block)
 func (ib *intraBlock) CiphertextRange() (offset int64, length int64) {
 	return ib.BlockNo * ib.fs.cipherBS, ib.fs.cipherBS
 }
 
-// CropBlock - crop a full plaintext block down to the relevant part
+// PlaintextRange - get byte range in plaintext corresponding to BlockNo
+// (complete block)
+func (ib *intraBlock) PlaintextRange() (offset int64, length int64) {
+	return ib.BlockNo * ib.fs.plainBS, ib.fs.plainBS
+}
+
+// CropBlock - crop a potentially larger plaintext block down to the relevant part
 func (ib *intraBlock) CropBlock(d []byte) []byte{
-	return d[ib.Offset:ib.Offset+ib.Length]
+	lenHave := len(d)
+	lenWant := int(ib.Offset+ib.Length)
+	if lenHave < lenWant {
+		return d[ib.Offset:lenHave]
+	}
+	return d[ib.Offset:lenWant]
 }
 
 // Split a plaintext byte range into (possible partial) blocks

cryptfs/cryptfs.go

@@ -55,6 +55,10 @@ func (fs *CryptFS) NewFile(f *os.File) *CryptFile {
 	}
 }
 
+func (be *CryptFS) PlainBS() int64 {
+	return be.plainBS
+}
+
 // DecryptName - decrypt filename
 func (be *CryptFS) decryptName(cipherName string) (string, error) {
 

frontend/dir.go

@@ -103,6 +103,9 @@ func (d *Dir) Remove(ctx context.Context, req *fuse.RemoveRequest) error {
 
 func (d *Dir) Create(ctx context.Context, req *fuse.CreateRequest, resp *fuse.CreateResponse) (fusefs.Node, fusefs.Handle, error) {
 	fmt.Printf("Create\n")
+
+	req.Flags, _ = fixFlags(req.Flags)
+
 	req.Name = d.crfs.EncryptPath(req.Name)
 	n, _, err := d.Dir.Create(ctx, req, resp)
 	if err != nil {

frontend/file.go

@@ -10,13 +10,40 @@ import (
 	"golang.org/x/net/context"
 )
 
+func fixFlags(flags fuse.OpenFlags) (fuse.OpenFlags, bool) {
+	fmt.Printf("fixFlags: Before: %s\n", flags.String())
+	var writeOnly bool
+	// We always need read access to do read-modify-write cycles
+	if flags & fuse.OpenWriteOnly > 0 {
+		flags = flags &^ fuse.OpenWriteOnly
+		flags = flags | fuse.OpenReadWrite
+		writeOnly = true
+	}
+	// We also cannot open the file in append mode, we need to seek back for RMW
+	flags = flags &^ fuse.OpenAppend
+	fmt.Printf("fixFlags: After: %s\n", flags.String())
+	return flags, writeOnly
+}
+
+func max(x int, y int) int {
+	if x > y {
+		return x
+	}
+	return y
+}
+
 type File struct {
 	*cluefs.File
 	crfs *cryptfs.CryptFS
+	// Remember if the file is supposed to be write-only
+	writeOnly bool
 }
 
 func (f *File) Open(ctx context.Context, req *fuse.OpenRequest, resp *fuse.OpenResponse) (fusefs.Handle, error) {
-	fmt.Printf("File.Open: f.crfs=%p\n", f.crfs)
+	fmt.Printf("File.Open\n")
+
+	req.Flags, f.writeOnly = fixFlags(req.Flags)
+
 	h, err := f.File.Open(ctx, req, resp)
 	if err != nil {
 		return nil, err
@@ -29,32 +56,68 @@ func (f *File) Open(ctx context.Context, req *fuse.OpenRequest, resp *fuse.OpenR
 }
 
 func (f *File) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) error {
-	fmt.Printf("File.Read: f.crfs=%p\n", f.crfs)
 	iblocks := f.crfs.SplitRange(req.Offset, int64(req.Size))
 	for _, ib := range iblocks {
 		var partReq fuse.ReadRequest
 		var partResp fuse.ReadResponse
 		o, l := ib.CiphertextRange()
+		partReq.Offset = o
 		partReq.Size = int(l)
 		partResp.Data = make([]byte, int(l))
-		partReq.Offset = o
 		err := f.File.Read(ctx, &partReq, &partResp)
 		if err != nil {
 			return err
 		}
 		plaintext, err := f.crfs.DecryptBlock(partResp.Data)
 		if err != nil {
-			fmt.Printf("Read: Block %d: %s\n", ib.BlockNo, err.Error())
+			fmt.Printf("Read: Error reading block %d: %s\n", ib.BlockNo, err.Error())
 			return err
 		}
-		plaintext = ib.CropBlock(partResp.Data)
+		plaintext = ib.CropBlock(plaintext)
 		resp.Data = append(resp.Data, plaintext...)
 	}
 	return nil
 }
 
 func (f *File) Write(ctx context.Context, req *fuse.WriteRequest, resp *fuse.WriteResponse) error {
+	fmt.Printf("File.Write\n")
+	resp.Size = 0
 	iblocks := f.crfs.SplitRange(req.Offset, int64(len(req.Data)))
-	iblocks = iblocks
+	var blockData []byte
+	for _, ib := range iblocks {
+		if ib.IsPartial() {
+			// RMW
+			blockData = make([]byte, f.crfs.PlainBS())
+			var readReq fuse.ReadRequest
+			var readResp fuse.ReadResponse
+			o, l := ib.PlaintextRange()
+			readReq.Offset = o
+			readReq.Size = int(l)
+			err := f.Read(ctx, &readReq, &readResp)
+			if err != nil {
+				return err
+			}
+			copy(blockData, readResp.Data)
+			copy(blockData[ib.Offset:ib.Offset+ib.Length], req.Data)
+			blockLen := max(len(readResp.Data), int(ib.Offset+ib.Length))
+			blockData = blockData[0:blockLen]
+		} else {
+			blockData = req.Data[0:f.crfs.PlainBS()]
+		}
+		ciphertext := f.crfs.EncryptBlock(blockData)
+		var partReq fuse.WriteRequest
+		var partResp fuse.WriteResponse
+		o, _ := ib.CiphertextRange()
+		partReq.Data = ciphertext
+		partReq.Offset = o
+		err := f.File.Write(ctx, &partReq, &partResp)
+		if err != nil {
+			fmt.Printf("Write failure: %s\n", err.Error())
+			return err
+		}
+		// Remove written data from the front of the request
+		req.Data = req.Data[len(blockData):len(req.Data)]
+		resp.Size += len(blockData)
+	}
 	return nil
 }