Add mount command to implement FUSE mounting of remotes #494

This enables any rclone remote to be mounted and used as a filesystem
with some limitations.

Only supported for Linux, FreeBSD and OS X

cmd/mount/read_test.go

@@ -0,0 +1,75 @@
+// +build linux darwin freebsd
+
+package mount
+
+import (
+	"io"
+	"os"
+	"syscall"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// Read by byte including don't read any bytes
+func TestReadByByte(t *testing.T) {
+	var data = []byte("hellohello")
+	run.createFile(t, "testfile", string(data))
+	run.checkDir(t, "testfile 10")
+
+	for i := 0; i < len(data); i++ {
+		fd, err := os.Open(run.path("testfile"))
+		assert.NoError(t, err)
+		for j := 0; j < i; j++ {
+			buf := make([]byte, 1)
+			n, err := io.ReadFull(fd, buf)
+			assert.NoError(t, err)
+			assert.Equal(t, 1, n)
+			assert.Equal(t, buf[0], data[j])
+		}
+		err = fd.Close()
+		assert.NoError(t, err)
+	}
+
+	run.rm(t, "testfile")
+}
+
+// Test double close
+func TestReadFileDoubleClose(t *testing.T) {
+	run.createFile(t, "testdoubleclose", "hello")
+
+	in, err := os.Open(run.path("testdoubleclose"))
+	assert.NoError(t, err)
+	fd := in.Fd()
+
+	fd1, err := syscall.Dup(int(fd))
+	assert.NoError(t, err)
+
+	fd2, err := syscall.Dup(int(fd))
+	assert.NoError(t, err)
+
+	// close one of the dups - should produce no error
+	err = syscall.Close(fd1)
+	assert.NoError(t, err)
+
+	// read from the file
+	buf := make([]byte, 1)
+	_, err = in.Read(buf)
+	assert.NoError(t, err)
+
+	// close it
+	err = in.Close()
+	assert.NoError(t, err)
+
+	// read from the other dup - should produce no error as this
+	// file is now buffered
+	n, err := syscall.Read(fd2, buf)
+	assert.NoError(t, err)
+	assert.Equal(t, 1, n)
+
+	// close the dup - should produce an error
+	err = syscall.Close(fd2)
+	assert.Error(t, err, "input/output error")
+
+	run.rm(t, "testdoubleclose")
+}