fix default batch size (#211)

Author: saghm

src/cursor.rs

@@ -36,7 +36,8 @@ use wire_protocol::operations::Message;
 
 use std::collections::vec_deque::VecDeque;
 
-pub const DEFAULT_BATCH_SIZE: i32 = 20;
+// Allows the server to decide the batch size.
+pub const DEFAULT_BATCH_SIZE: i32 = 0;
 
 /// Maintains a connection to the server and lazily returns documents from a
 /// query.
@@ -457,14 +458,31 @@ impl Cursor {
         Ok(vec)
     }
 
+    /// # Return value
+    ///
+    /// Returns a vector containing the BSON documents that were read.
+    #[deprecated(since="0.2.8", note="this method uses 20 as the default batch size instead of letting the server decide; using `drain_current_batch` is recommended instead")]
+    pub fn next_batch(&mut self) -> Result<Vec<bson::Document>> {
+        let batch_size = if self.batch_size == 0 {
+            20
+        } else {
+            self.batch_size
+        };
+
+        self.next_n(batch_size)
+    }
+
     /// Attempts to read a batch of BSON documents from the cursor.
     ///
     /// # Return value
     ///
     /// Returns a vector containing the BSON documents that were read.
-    pub fn next_batch(&mut self) -> Result<Vec<bson::Document>> {
-        let n = self.batch_size;
-        self.next_n(n)
+    pub fn drain_current_batch(&mut self) -> Result<Vec<bson::Document>> {
+        if self.buffer.is_empty() {
+            self.get_from_stream()?;
+        }
+
+        Ok(self.buffer.drain(..).collect())
     }
 
     /// Checks whether there are any more documents for the cursor to return.

src/gridfs/mod.rs

@@ -76,8 +76,8 @@ impl FileCursor {
     }
 
     /// Returns the next batch of files.
-    pub fn next_batch(&mut self) -> Result<Vec<File>> {
-        let docs = try!(self.cursor.next_batch());
+    pub fn drain_current_batch(&mut self) -> Result<Vec<File>> {
+        let docs = try!(self.cursor.drain_current_batch());
         Ok(docs.into_iter()
             .map(|doc| File::with_doc(self.store.clone(), doc))
             .collect())

tests/client/cursor.rs

@@ -43,7 +43,7 @@ fn cursor_features() {
         Err(s) => panic!("{}", s),
     };
 
-    let batch = cursor.next_batch().expect("Failed to get next batch from cursor.");
+    let batch = cursor.drain_current_batch().expect("Failed to get current batch from cursor.");
 
     assert_eq!(batch.len(), 3 as usize);
 

tests/client/gridfs.rs

@@ -56,7 +56,7 @@ fn put_get() {
     // Check chunks
     let mut cursor = fschunks.find(Some(doc!{"files_id" => (id.clone())}), Some(opts)).unwrap();
 
-    let chunks = cursor.next_batch().expect("Failed to get next batch");
+    let chunks = cursor.drain_current_batch().expect("Failed to get current batch");
     assert_eq!(3, chunks.len());
 
     for (i, chunk) in chunks.iter().enumerate().take(3) {
@@ -114,14 +114,14 @@ fn remove() {
     assert!(fsfiles.find_one(Some(doc!{"_id" => (id.clone())}), None).unwrap().is_some());
 
     let mut cursor = fschunks.find(Some(doc!{"files_id" => (id.clone())}), None).unwrap();
-    let results = cursor.next_batch().unwrap();
+    let results = cursor.drain_current_batch().unwrap();
     assert_eq!(2, results.len());
 
     fs.remove(name.to_owned()).unwrap();
     assert!(fsfiles.find_one(Some(doc!{"_id" => (id.clone())}), None).unwrap().is_none());
 
     let mut cursor = fschunks.find(Some(doc!{"files_id" => (id.clone())}), None).unwrap();
-    let results = cursor.next_batch().unwrap();
+    let results = cursor.drain_current_batch().unwrap();
     assert_eq!(0, results.len());
 }
 
@@ -141,12 +141,12 @@ fn remove_id() {
     assert!(fsfiles.find_one(Some(doc!{"_id" => (id.clone())}), None).unwrap().is_some());
 
     let mut cursor = fschunks.find(Some(doc!{"files_id" => (id.clone())}), None).unwrap();
-    let results = cursor.next_batch().unwrap();
+    let results = cursor.drain_current_batch().unwrap();
     assert_eq!(2, results.len());
 
     fs.remove_id(id.clone()).unwrap();
     let mut cursor = fschunks.find(Some(doc!{"files_id" => (id.clone())}), None).unwrap();
-    let results = cursor.next_batch().unwrap();
+    let results = cursor.drain_current_batch().unwrap();
     assert_eq!(0, results.len());
 }
 
@@ -171,7 +171,7 @@ fn find() {
     grid_file2.close().unwrap();
 
     let mut cursor = fs.find(None, None).unwrap();
-    let results = cursor.next_batch().unwrap();
+    let results = cursor.drain_current_batch().unwrap();
     assert_eq!(2, results.len());
     assert_eq!(name, results[0].name.as_ref().unwrap());
     assert_eq!(name2, results[1].name.as_ref().unwrap());