Attach fields bson to lifetime of cursor

src/collection.rs

@@ -129,8 +129,9 @@ impl<'a> Collection<'a> {
 
         let default_options = CommandAndFindOptions::default();
         let options         = options.unwrap_or(&default_options);
+        let fields_bsonc    = options.fields_bsonc();
 
-        let inner = unsafe {
+        let cursor_ptr = unsafe {
             bindings::mongoc_collection_command(
                 self.inner,
                 options.query_flags.flags(),
@@ -138,10 +139,8 @@ impl<'a> Collection<'a> {
                 options.limit,
                 options.batch_size,
                 try!(Bsonc::from_document(&command)).inner(),
-                match options.fields {
-                    Some(ref f) => {
-                        try!(Bsonc::from_document(f)).inner()
-                    },
+                match fields_bsonc {
+                    Some(ref f) => f.inner(),
                     None => ptr::null()
                 },
                 match options.read_prefs {
@@ -151,11 +150,15 @@ impl<'a> Collection<'a> {
             )
         };
 
-        if inner.is_null() {
+        if cursor_ptr.is_null() {
             return Err(InvalidParamsError.into())
         }
 
-        Ok(Cursor::new(cursor::CreatedBy::Collection(self), inner))
+        Ok(Cursor::new(
+            cursor::CreatedBy::Collection(self),
+            cursor_ptr,
+            fields_bsonc
+        ))
     }
 
     pub fn count(
@@ -240,8 +243,9 @@ impl<'a> Collection<'a> {
 
         let default_options = CommandAndFindOptions::default();
         let options         = options.unwrap_or(&default_options);
+        let fields_bsonc    = options.fields_bsonc();
 
-        let inner = unsafe {
+        let cursor_ptr = unsafe {
             bindings::mongoc_collection_find(
                 self.inner,
                 options.query_flags.flags(),
@@ -249,10 +253,8 @@ impl<'a> Collection<'a> {
                 options.limit,
                 options.batch_size,
                 try!(Bsonc::from_document(query)).inner(),
-                match options.fields {
-                    Some(ref f) => {
-                        try!(Bsonc::from_document(f)).inner()
-                    },
+                match fields_bsonc {
+                    Some(ref f) => f.inner(),
                     None => ptr::null()
                 },
                 match options.read_prefs {
@@ -262,11 +264,15 @@ impl<'a> Collection<'a> {
             )
         };
 
-        if inner.is_null() {
+        if cursor_ptr.is_null() {
             return Err(InvalidParamsError.into())
         }
 
-        Ok(Cursor::new(cursor::CreatedBy::Collection(self), inner))
+        Ok(Cursor::new(
+            cursor::CreatedBy::Collection(self),
+            cursor_ptr,
+            fields_bsonc
+        ))
     }
 
     pub fn get_name(&self) -> Cow<str> {

src/cursor.rs

@@ -25,20 +25,25 @@ pub struct Cursor<'a> {
     _created_by:       CreatedBy<'a>,
     inner:             *mut bindings::mongoc_cursor_t,
     tailing:           bool,
-    tail_wait_time_ms: u32
+    tail_wait_time_ms: u32,
+    // Become owner of bsonc because the cursor needs it
+    // to be allocated for it's entire lifetime
+    _fields:           Option<bsonc::Bsonc>
 }
 
 impl<'a> Cursor<'a> {
     pub fn new(
         created_by: CreatedBy<'a>,
-        inner:      *mut bindings::mongoc_cursor_t
+        inner:      *mut bindings::mongoc_cursor_t,
+        fields:     Option<bsonc::Bsonc>
     ) -> Cursor<'a> {
         assert!(!inner.is_null());
         Cursor {
             _created_by:       created_by,
             inner:             inner,
             tailing:           false,
-            tail_wait_time_ms: 0
+            tail_wait_time_ms: 0,
+            _fields:           fields
         }
     }
 

src/database.rs

@@ -45,8 +45,9 @@ impl<'a> Database<'a> {
 
         let default_options = CommandAndFindOptions::default();
         let options         = options.unwrap_or(&default_options);
+        let fields_bsonc    = options.fields_bsonc();
 
-        let inner = unsafe {
+        let cursor_ptr = unsafe {
             bindings::mongoc_database_command(
                 self.inner,
                 options.query_flags.flags(),
@@ -54,10 +55,8 @@ impl<'a> Database<'a> {
                 options.limit,
                 options.batch_size,
                 try!(Bsonc::from_document(&command)).inner(),
-                match options.fields {
-                    Some(ref f) => {
-                        try!(Bsonc::from_document(f)).inner()
-                    },
+                match fields_bsonc {
+                    Some(ref f) => f.inner(),
                     None => ptr::null()
                 },
                 match options.read_prefs {
@@ -67,11 +66,15 @@ impl<'a> Database<'a> {
             )
         };
 
-        if inner.is_null() {
+        if cursor_ptr.is_null() {
             return Err(InvalidParamsError.into())
         }
 
-        Ok(Cursor::new(cursor::CreatedBy::Database(self), inner))
+        Ok(Cursor::new(
+            cursor::CreatedBy::Database(self),
+            cursor_ptr,
+            fields_bsonc
+        ))
     }
 
     pub fn create_collection<S: Into<Vec<u8>>>(

src/lib.rs

@@ -58,6 +58,13 @@ impl CommandAndFindOptions {
             read_prefs:  None
         }
     }
+
+    fn fields_bsonc(&self) -> Option<bsonc::Bsonc> {
+        match self.fields {
+            Some(ref f) => Some(bsonc::Bsonc::from_document(f).unwrap()),
+            None => None
+        }
+    }
 }
 
 #[cfg(test)]