Bundle up blocks for bigger reads from the backing filesystem

2 files changed, 72 insertions, 21 deletions

diff --git a/cryptfs/cryptfs_content.go b/cryptfs/cryptfs_content.go
index 0ebf34d..512bca9 100644
--- a/cryptfs/cryptfs_content.go
+++ b/cryptfs/cryptfs_content.go
@@ -3,6 +3,7 @@ package cryptfs
 // File content encryption / decryption
 
 import (
+	"bytes"
 	"os"
 	"errors"
 	"crypto/cipher"
@@ -13,7 +14,23 @@ type CryptFile struct {
 	gcm cipher.AEAD
 }
 
-// decryptBlock - Verify and decrypt GCM block
+// DecryptBlocks - Decrypt a number of blocks
+func (be *CryptFS) DecryptBlocks(ciphertext []byte) ([]byte, error) {
+	cBuf := bytes.NewBuffer(ciphertext)
+	var err error
+	var pBuf bytes.Buffer
+	for cBuf.Len() > 0 {
+		cBlock := cBuf.Next(int(be.cipherBS))
+		pBlock, err := be.DecryptBlock(cBlock)
+		if err != nil {
+			break
+		}
+		pBuf.Write(pBlock)
+	}
+	return pBuf.Bytes(), err
+}
+
+// DecryptBlock - Verify and decrypt GCM block
 func (be *CryptFS) DecryptBlock(ciphertext []byte) ([]byte, error) {
 
 	// Empty block?
@@ -92,3 +109,29 @@ func (be *CryptFS) minu64(x uint64, y uint64) uint64 {
 	}
 	return y
 }
+
+// Get the byte range in the ciphertext corresponding to blocks
+// (full blocks!)
+func (be *CryptFS) JoinCiphertextRange(blocks []intraBlock) (uint64, uint64) {
+
+	offset, _ := blocks[0].CiphertextRange()
+	last := blocks[len(blocks)-1]
+	length := (last.BlockNo - blocks[0].BlockNo + 1) * be.cipherBS
+
+	return offset, length
+}
+
+// Crop plaintext that correspons to complete cipher blocks down to what is
+// requested according to "iblocks"
+func (be *CryptFS) CropPlaintext(plaintext []byte, blocks []intraBlock) []byte {
+	offset := blocks[0].Offset
+	last := blocks[len(blocks)-1]
+	length := (last.BlockNo - blocks[0].BlockNo + 1) * be.plainBS
+	var cropped []byte
+	if offset + length > uint64(len(plaintext)) {
+		cropped = plaintext[offset:len(plaintext)]
+	} else {
+		cropped = plaintext[offset:offset+length]
+	}
+	return cropped
+}
diff --git a/frontend/fe_file.go b/frontend/fe_file.go
index 7cc23ad..b417227 100644
--- a/frontend/fe_file.go
+++ b/frontend/fe_file.go
@@ -67,26 +67,32 @@ 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("Read: o=%d l=%d\n", req.Offset, req.Size)
+
+	// Read the backing ciphertext in one go
 	iblocks := f.crfs.SplitRange(uint64(req.Offset), uint64(req.Size))
-	for _, ib := range iblocks {
-		var partReq fuse.ReadRequest
-		var partResp fuse.ReadResponse
-		o, l := ib.CiphertextRange()
-		partReq.Offset = int64(o)
-		partReq.Size = int(l)
-		partResp.Data = make([]byte, int(l))
-		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: Error reading block %d: %s\n", ib.BlockNo, err.Error())
-			return err
-		}
-		plaintext = ib.CropBlock(plaintext)
-		resp.Data = append(resp.Data, plaintext...)
+	var cipherReq fuse.ReadRequest
+	var cipherResp fuse.ReadResponse
+	o, l := f.crfs.JoinCiphertextRange(iblocks)
+	cipherResp.Data = make([]byte, int(l))
+	cipherReq.Offset = int64(o)
+	cipherReq.Size = int(l)
+	cryptfs.Debug.Printf("Read: cipherReq o=%d l=%d\n", o, l)
+	err := f.File.Read(ctx, &cipherReq, &cipherResp)
+	if err != nil {
+		return err
+	}
+
+	// Decrypt it
+	plaintext, err := f.crfs.DecryptBlocks(cipherResp.Data)
+	if err != nil {
+		resp.Data = plaintext
+		return err
 	}
+	// Crop down to relevant part
+	resp.Data = f.crfs.CropPlaintext(plaintext, iblocks)
+
 	return nil
 }
 
@@ -98,6 +104,7 @@ func (f *File) Write(ctx context.Context, req *fuse.WriteRequest, resp *fuse.Wri
 	for _, ib := range iblocks {
 		if ib.IsPartial() {
 			// RMW
+			cryptfs.Debug.Printf("RMW\n")
 			blockData = make([]byte, f.crfs.PlainBS())
 			var readReq fuse.ReadRequest
 			var readResp fuse.ReadResponse
@@ -127,8 +134,9 @@ func (f *File) Write(ctx context.Context, req *fuse.WriteRequest, resp *fuse.Wri
 			return err
 		}
 		// Remove written data from the front of the request
-		req.Data = req.Data[len(blockData):len(req.Data)]
-		resp.Size += len(blockData)
+		cryptfs.Debug.Printf("req.Data[%d:%d]\n", int(ib.Length), len(req.Data))
+		req.Data = req.Data[int(ib.Length):len(req.Data)]
+		resp.Size += int(ib.Length)
 	}
 	return nil
 }