sdp: Fix up SDPMedia API that accesses indexed fields

It's forbidden to provide an index higher than the number of elements in
the array, and will cause crashes or other undesired outcomes.

Also the insert() API should take an Option<u32> instead of an i32 that
might also be -1 for appending. It's awful API otherwise.

gstreamer-sdp/src/sdp_media.rs

@@ -210,6 +210,10 @@ impl SDPMediaRef {
     }
 
     pub fn get_attribute(&self, idx: u32) -> Option<&SDPAttribute> {
+        if idx >= self.attributes_len() {
+            return None;
+        }
+
         unsafe {
             let ptr = ffi::gst_sdp_media_get_attribute(&self.0, idx);
             if ptr.is_null() {
@@ -251,6 +255,10 @@ impl SDPMediaRef {
     }
 
     pub fn get_bandwidth(&self, idx: u32) -> Option<&SDPBandwidth> {
+        if idx >= self.bandwidths_len() {
+            return None;
+        }
+
         unsafe {
             let ptr = ffi::gst_sdp_media_get_bandwidth(&self.0, idx);
             if ptr.is_null() {
@@ -266,6 +274,10 @@ impl SDPMediaRef {
     }
 
     pub fn get_connection(&self, idx: u32) -> Option<&SDPConnection> {
+        if idx >= self.connections_len() {
+            return None;
+        }
+
         unsafe {
             let ptr = ffi::gst_sdp_media_get_connection(&self.0, idx);
             if ptr.is_null() {
@@ -277,6 +289,10 @@ impl SDPMediaRef {
     }
 
     pub fn get_format(&self, idx: u32) -> Option<&str> {
+        if idx >= self.formats_len() {
+            return None;
+        }
+
         unsafe {
             let ptr = ffi::gst_sdp_media_get_format(&self.0, idx);
             if ptr.is_null() {
@@ -355,7 +371,14 @@ impl SDPMediaRef {
         }
     }
 
-    pub fn insert_attribute(&mut self, idx: i32, mut attr: SDPAttribute) -> Result<(), ()> {
+    pub fn insert_attribute(&mut self, idx: Option<u32>, mut attr: SDPAttribute) -> Result<(), ()> {
+        if let Some(idx) = idx {
+            if idx >= self.attributes_len() {
+                return Err(());
+            }
+        }
+
+        let idx = idx.map(|idx| idx as i32).unwrap_or(-1);
         let result = unsafe { ffi::gst_sdp_media_insert_attribute(&mut self.0, idx, &mut attr.0) };
         mem::forget(attr);
         match result {
@@ -364,7 +387,14 @@ impl SDPMediaRef {
         }
     }
 
-    pub fn insert_bandwidth(&mut self, idx: i32, mut bw: SDPBandwidth) -> Result<(), ()> {
+    pub fn insert_bandwidth(&mut self, idx: Option<u32>, mut bw: SDPBandwidth) -> Result<(), ()> {
+        if let Some(idx) = idx {
+            if idx >= self.bandwidths_len() {
+                return Err(());
+            }
+        }
+
+        let idx = idx.map(|idx| idx as i32).unwrap_or(-1);
         let result = unsafe { ffi::gst_sdp_media_insert_bandwidth(&mut self.0, idx, &mut bw.0) };
         mem::forget(bw);
         match result {
@@ -373,7 +403,18 @@ impl SDPMediaRef {
         }
     }
 
-    pub fn insert_connection(&mut self, idx: i32, mut conn: SDPConnection) -> Result<(), ()> {
+    pub fn insert_connection(
+        &mut self,
+        idx: Option<u32>,
+        mut conn: SDPConnection,
+    ) -> Result<(), ()> {
+        if let Some(idx) = idx {
+            if idx >= self.connections_len() {
+                return Err(());
+            }
+        }
+
+        let idx = idx.map(|idx| idx as i32).unwrap_or(-1);
         let result = unsafe { ffi::gst_sdp_media_insert_connection(&mut self.0, idx, &mut conn.0) };
         mem::forget(conn);
         match result {
@@ -382,7 +423,14 @@ impl SDPMediaRef {
         }
     }
 
-    pub fn insert_format(&mut self, idx: i32, format: &str) -> Result<(), ()> {
+    pub fn insert_format(&mut self, idx: Option<u32>, format: &str) -> Result<(), ()> {
+        if let Some(idx) = idx {
+            if idx >= self.formats_len() {
+                return Err(());
+            }
+        }
+
+        let idx = idx.map(|idx| idx as i32).unwrap_or(-1);
         let result =
             unsafe { ffi::gst_sdp_media_insert_format(&mut self.0, idx, format.to_glib_none().0) };
         match result {
@@ -404,6 +452,10 @@ impl SDPMediaRef {
     }
 
     pub fn remove_attribute(&mut self, idx: u32) -> Result<(), ()> {
+        if idx >= self.attributes_len() {
+            return Err(());
+        }
+
         let result = unsafe { ffi::gst_sdp_media_remove_attribute(&mut self.0, idx) };
         match result {
             ffi::GST_SDP_OK => Ok(()),
@@ -412,6 +464,10 @@ impl SDPMediaRef {
     }
 
     pub fn remove_bandwidth(&mut self, idx: u32) -> Result<(), ()> {
+        if idx >= self.bandwidths_len() {
+            return Err(());
+        }
+
         let result = unsafe { ffi::gst_sdp_media_remove_bandwidth(&mut self.0, idx) };
         match result {
             ffi::GST_SDP_OK => Ok(()),
@@ -420,6 +476,10 @@ impl SDPMediaRef {
     }
 
     pub fn remove_connection(&mut self, idx: u32) -> Result<(), ()> {
+        if idx >= self.connections_len() {
+            return Err(());
+        }
+
         let result = unsafe { ffi::gst_sdp_media_remove_connection(&mut self.0, idx) };
         match result {
             ffi::GST_SDP_OK => Ok(()),
@@ -428,6 +488,10 @@ impl SDPMediaRef {
     }
 
     pub fn remove_format(&mut self, idx: u32) -> Result<(), ()> {
+        if idx >= self.formats_len() {
+            return Err(());
+        }
+
         let result = unsafe { ffi::gst_sdp_media_remove_format(&mut self.0, idx) };
         match result {
             ffi::GST_SDP_OK => Ok(()),
@@ -436,6 +500,10 @@ impl SDPMediaRef {
     }
 
     pub fn replace_attribute(&mut self, idx: u32, mut attr: SDPAttribute) -> Result<(), ()> {
+        if idx >= self.attributes_len() {
+            return Err(());
+        }
+
         let result = unsafe { ffi::gst_sdp_media_replace_attribute(&mut self.0, idx, &mut attr.0) };
         mem::forget(attr);
         match result {
@@ -445,6 +513,10 @@ impl SDPMediaRef {
     }
 
     pub fn replace_bandwidth(&mut self, idx: u32, mut bw: SDPBandwidth) -> Result<(), ()> {
+        if idx >= self.bandwidths_len() {
+            return Err(());
+        }
+
         let result = unsafe { ffi::gst_sdp_media_replace_bandwidth(&mut self.0, idx, &mut bw.0) };
         mem::forget(bw);
         match result {
@@ -454,6 +526,10 @@ impl SDPMediaRef {
     }
 
     pub fn replace_connection(&mut self, idx: u32, mut conn: SDPConnection) -> Result<(), ()> {
+        if idx >= self.connections_len() {
+            return Err(());
+        }
+
         let result =
             unsafe { ffi::gst_sdp_media_replace_connection(&mut self.0, idx, &mut conn.0) };
         mem::forget(conn);
@@ -464,6 +540,10 @@ impl SDPMediaRef {
     }
 
     pub fn replace_format(&mut self, idx: u32, format: &str) -> Result<(), ()> {
+        if idx >= self.formats_len() {
+            return Err(());
+        }
+
         let result =
             unsafe { ffi::gst_sdp_media_replace_format(&mut self.0, idx, format.to_glib_none().0) };
         match result {