Implemented memFS.ReadFile.

samples/memfs/fs.go

@@ -459,6 +459,28 @@ func (fs *memFS) OpenFile(
 	return
 }
 
+func (fs *memFS) ReadFile(
+	ctx context.Context,
+	req *fuse.ReadFileRequest) (resp *fuse.ReadFileResponse, err error) {
+	resp = &fuse.ReadFileResponse{}
+
+	fs.mu.RLock()
+	defer fs.mu.RUnlock()
+
+	// Find the inode in question.
+	inode := fs.getInodeForReadingOrDie(req.Inode)
+	defer inode.mu.RUnlock()
+
+	// Serve the request.
+	//
+	// TODO(jacobsa): Add tests involving EOF matching posix_test.go.
+	resp.Data = make([]byte, req.Size)
+	n, err := inode.ReadAt(resp.Data, req.Offset)
+	resp.Data = resp.Data[:n]
+
+	return
+}
+
 func (fs *memFS) WriteFile(
 	ctx context.Context,
 	req *fuse.WriteFileRequest) (resp *fuse.WriteFileResponse, err error) {
@@ -472,6 +494,8 @@ func (fs *memFS) WriteFile(
 	defer inode.mu.Unlock()
 
 	// Serve the request.
+	//
+	// TODO(jacobsa): Add tests involving EOF matching posix_test.go.
 	_, err = inode.WriteAt(req.Data, req.Offset)
 
 	return

samples/memfs/inode.go

@@ -16,6 +16,7 @@ package memfs
 
 import (
 	"fmt"
+	"io"
 	"os"
 
 	"github.com/jacobsa/fuse"
@@ -290,6 +291,30 @@ func (inode *inode) ReadDir(offset int, size int) (data []byte, err error) {
 	return
 }
 
+// Read from the file's contents. See documentation for ioutil.ReaderAt.
+//
+// REQUIRES: !inode.dir
+// SHARED_LOCKS_REQUIRED(inode.mu)
+func (inode *inode) ReadAt(p []byte, off int64) (n int, err error) {
+	if inode.dir {
+		panic("ReadAt called on directory.")
+	}
+
+	// Ensure the offset is in range.
+	if off > int64(len(inode.contents)) {
+		err = io.EOF
+		return
+	}
+
+	// Read what we can.
+	n = copy(p, inode.contents[off:])
+	if n < len(p) {
+		err = io.EOF
+	}
+
+	return
+}
+
 // Write to the file's contents. See documentation for ioutil.WriterAt.
 //
 // REQUIRES: !inode.dir