v2api/reverse: implement Read

1 files changed, 117 insertions, 0 deletions

diff --git a/internal/fusefrontend_reverse/virtualnode.go b/internal/fusefrontend_reverse/virtualnode.go
new file mode 100644
index 0000000..2ee9548
--- /dev/null
+++ b/internal/fusefrontend_reverse/virtualnode.go
@@ -0,0 +1,117 @@
+package fusefrontend_reverse
+
+import (
+	"context"
+	"log"
+	"syscall"
+
+	"github.com/hanwen/go-fuse/v2/fs"
+	"github.com/hanwen/go-fuse/v2/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/configfile"
+	"github.com/rfjakob/gocryptfs/internal/inomap"
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+)
+
+const (
+	// virtualFileMode is the mode to use for virtual files (gocryptfs.diriv and
+	// *.name). They are always readable, as stated in func Access
+	virtualFileMode = syscall.S_IFREG | 0444
+	// We use inomap's `Tag` feature to generate unique inode numbers for
+	// virtual files. These are the tags we use.
+	inoTagDirIV    = 1
+	inoTagNameFile = 2
+)
+
+type fileType int
+
+// Values returned by lookupFileType
+const (
+	// A real file/directory/symlink in the backing plaintext directory
+	typeReal fileType = iota
+	// A DirIV (gocryptfs.diriv) file
+	typeDiriv
+	// A gocryptfs.longname.*.name file for a file with a long name
+	typeName
+	// The config file gocryptfs.conf
+	typeConfig
+)
+
+// lookupFileType returns the type of child file name
+// (one of the fileType constants above). Called from Lookup().
+func (n *Node) lookupFileType(cName string) fileType {
+	rn := n.rootNode()
+	// In -plaintextname mode, neither diriv nor longname files exist.
+	if !rn.args.PlaintextNames {
+		// Is it a gocryptfs.diriv file?
+		if cName == nametransform.DirIVFilename {
+			return typeDiriv
+		}
+		// Is it a gocryptfs.longname.*.name file?
+		if t := nametransform.NameType(cName); t == nametransform.LongNameFilename {
+			return typeName
+		}
+	}
+	// gocryptfs.conf in the root directory. This is passed through to
+	// .gocryptfs.reverse.conf in the backing plaintext directory.
+	if n.isRoot() && !rn.args.ConfigCustom && cName == configfile.ConfDefaultName {
+		return typeConfig
+	}
+	return typeReal
+}
+
+// VirtualMemNode is an in-memory node that does not have a representation
+// on disk.
+type VirtualMemNode struct {
+	fs.Inode
+
+	// file content
+	content []byte
+	// attributes for Getattr()
+	attr fuse.Attr
+}
+
+// newVirtualMemNode creates a new in-memory file that does not have a representation
+// on disk. "content" is the file content. Timestamps and file owner are copied
+// from "parentFile" (file descriptor).
+// For a "gocryptfs.diriv" file, you would use the parent directory as
+// "parentFile".
+func (n *Node) newVirtualMemNode(content []byte, parentStat *syscall.Stat_t, inoTag uint8) (vf *VirtualMemNode, errno syscall.Errno) {
+	if inoTag == 0 {
+		log.Panicf("BUG: inoTag for virtual file is zero - this will cause ino collisions!")
+	}
+
+	// Adjust inode number and size
+	rn := n.rootNode()
+	st := parentStat
+	q := inomap.NewQIno(uint64(st.Dev), inoTag, uint64(st.Ino))
+	st.Ino = rn.inoMap.Translate(q)
+	st.Size = int64(len(content))
+	st.Mode = virtualFileMode
+	st.Nlink = 1
+	var a fuse.Attr
+	a.FromStat(st)
+
+	vf = &VirtualMemNode{content: content, attr: a}
+	return
+}
+
+// Open - FUSE call
+func (f *VirtualMemNode) Open(ctx context.Context, flags uint32) (fh fs.FileHandle, fuseFlags uint32, errno syscall.Errno) {
+	return nil, fuse.FOPEN_KEEP_CACHE, 0
+}
+
+// GetAttr - FUSE call
+func (f *VirtualMemNode) Getattr(ctx context.Context, fh fs.FileHandle, out *fuse.AttrOut) syscall.Errno {
+	out.Attr = f.attr
+	return 0
+}
+
+// Read - FUSE call
+func (f *VirtualMemNode) Read(ctx context.Context, fh fs.FileHandle, dest []byte, off int64) (fuse.ReadResult, syscall.Errno) {
+	end := int(off) + len(dest)
+	if end > len(f.content) {
+		end = len(f.content)
+	}
+	return fuse.ReadResultData(f.content[off:end]), 0
+}