diff --git a/src/rsfilesink.rs b/src/rsfilesink.rs
index f1848510..e690ce67 100644
--- a/src/rsfilesink.rs
+++ b/src/rsfilesink.rs
@@ -62,10 +62,10 @@ impl Sink for FileSink {
     }
 
     fn get_uri(&self) -> Option<String> {
-        match self.location {
-            None => None,
-            Some(ref location) => Url::from_file_path(&location).map(|u| u.into_string()).ok()
-        }
+        self.location.as_ref()
+            .map(|l| Url::from_file_path(l).ok())
+            .and_then(|i| i) // join()
+            .map(|u| u.into_string())
     }
 
     fn start(&mut self) -> bool {
@@ -96,7 +96,7 @@ impl Sink for FileSink {
         true
     }
 
-    fn render(&mut self, data: &mut [u8]) -> GstFlowReturn {
+    fn render(&mut self, data: &[u8]) -> GstFlowReturn {
         match self.file {
             None => return GstFlowReturn::Error,
             Some(ref mut f) => {
diff --git a/src/rssink.rs b/src/rssink.rs
index 13f2fbdc..601b0bd9 100644
--- a/src/rssink.rs
+++ b/src/rssink.rs
@@ -1,4 +1,4 @@
-use libc::{c_char};
+use libc::c_char;
 use std::ffi::{CStr, CString};
 use std::slice;
 use std::ptr;
@@ -10,7 +10,7 @@ pub trait Sink {
     fn get_uri(&self) -> Option<String>;
     fn start(&mut self) -> bool;
     fn stop(&mut self) -> bool;
-    fn render(&mut self, data: &mut [u8]) -> GstFlowReturn;
+    fn render(&mut self, data: &[u8]) -> GstFlowReturn;
 }
 
 #[no_mangle]
@@ -26,8 +26,8 @@ pub extern "C" fn sink_set_uri(ptr: *mut Box<Sink>, uri_ptr: *const c_char) -> G
 }
 
 #[no_mangle]
-pub extern "C" fn sink_get_uri(ptr: *mut Box<Sink>) -> *mut c_char {
-    let source: &mut Box<Sink> = unsafe { &mut *ptr };
+pub extern "C" fn sink_get_uri(ptr: *const Box<Sink>) -> *mut c_char {
+    let source: &Box<Sink> = unsafe { &*ptr };
 
     match source.get_uri() {
         Some(ref uri) =>
@@ -38,10 +38,10 @@ pub extern "C" fn sink_get_uri(ptr: *mut Box<Sink>) -> *mut c_char {
 }
 
 #[no_mangle]
-pub extern "C" fn sink_render(ptr: *mut Box<Sink>, data_ptr: *mut u8, data_len: usize) -> GstFlowReturn {
+pub extern "C" fn sink_render(ptr: *mut Box<Sink>, data_ptr: *const u8, data_len: usize) -> GstFlowReturn {
     let source: &mut Box<Sink> = unsafe { &mut *ptr };
 
-    let mut data = unsafe { slice::from_raw_parts_mut(data_ptr, data_len) };
+    let data = unsafe { slice::from_raw_parts(data_ptr, data_len) };
     source.render(data)
 }
 
diff --git a/src/rssource.rs b/src/rssource.rs
index 51ef5231..ed059f3a 100644
--- a/src/rssource.rs
+++ b/src/rssource.rs
@@ -1,4 +1,4 @@
-use libc::{c_char};
+use libc::c_char;
 use std::ffi::{CStr, CString};
 use std::slice;
 use std::ptr;
@@ -63,8 +63,8 @@ pub extern "C" fn source_fill(ptr: *mut Box<Source>, offset: u64, data_ptr: *mut
 }
 
 #[no_mangle]
-pub extern "C" fn source_get_size(ptr: *mut Box<Source>) -> u64 {
-    let source: &mut Box<Source> = unsafe { &mut *ptr };
+pub extern "C" fn source_get_size(ptr: *const Box<Source>) -> u64 {
+    let source: &Box<Source> = unsafe { & *ptr };
 
     return source.get_size();
 }
@@ -84,8 +84,8 @@ pub extern "C" fn source_stop(ptr: *mut Box<Source>) -> GBoolean {
 }
 
 #[no_mangle]
-pub extern "C" fn source_is_seekable(ptr: *mut Box<Source>) -> GBoolean {
-    let source: &mut Box<Source> = unsafe { &mut *ptr };
+pub extern "C" fn source_is_seekable(ptr: *const Box<Source>) -> GBoolean {
+    let source: &Box<Source> = unsafe { & *ptr };
 
     GBoolean::from_bool(source.is_seekable())
 }