v2api/reverse: implement Read

1 files changed, 70 insertions, 0 deletions

diff --git a/internal/fusefrontend_reverse/file.go b/internal/fusefrontend_reverse/file.go
new file mode 100644
index 0000000..55f5f80
--- /dev/null
+++ b/internal/fusefrontend_reverse/file.go
@@ -0,0 +1,70 @@
+package fusefrontend_reverse
+
+import (
+	"bytes"
+	"context"
+	"os"
+	"syscall"
+
+	"github.com/hanwen/go-fuse/v2/fs"
+	"github.com/hanwen/go-fuse/v2/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/contentenc"
+)
+
+type File struct {
+	// Backing FD
+	fd *os.File
+	// File header (contains the IV)
+	header contentenc.FileHeader
+	// IV for block 0
+	block0IV []byte
+	// Content encryption helper
+	contentEnc *contentenc.ContentEnc
+}
+
+// Read - FUSE call
+func (f *File) Read(ctx context.Context, buf []byte, ioff int64) (resultData fuse.ReadResult, errno syscall.Errno) {
+	length := uint64(len(buf))
+	off := uint64(ioff)
+	out := bytes.NewBuffer(buf[:0])
+	var header []byte
+
+	// Synthesize file header
+	if off < contentenc.HeaderLen {
+		header = f.header.Pack()
+		// Truncate to requested part
+		end := int(off) + len(buf)
+		if end > len(header) {
+			end = len(header)
+		}
+		header = header[off:end]
+		// Write into output buffer and adjust offsets
+		out.Write(header)
+		hLen := uint64(len(header))
+		off += hLen
+		length -= hLen
+	}
+
+	// Read actual file data
+	if length > 0 {
+		fileData, err := f.readBackingFile(off, length)
+		if err != nil {
+			return nil, fs.ToErrno(err)
+		}
+		if len(fileData) == 0 {
+			// If we could not read any actual data, we also don't want to
+			// return the file header. An empty file stays empty in encrypted
+			// form.
+			return nil, 0
+		}
+		out.Write(fileData)
+	}
+
+	return fuse.ReadResultData(out.Bytes()), 0
+}
+
+// Release - FUSE call, close file
+func (f *File) Release(context.Context) syscall.Errno {
+	return fs.ToErrno(f.fd.Close())
+}