Fix whitespace remover

Previously, if there was enough whitespace to fill the buffer it would
return a read length of zero, even though there is still content to
read.

src/version_prefix.rs

@@ -38,7 +38,7 @@ where
             self.0.has_seen_version = true;
             let mut new_buf = vec![0; buf.len() + 1];
             new_buf[0] = self.0.version;
-            (&mut new_buf[1..]).copy_from_slice(buf);
+            new_buf[1..].copy_from_slice(buf);
             self.0.wrapped.write(&new_buf).map(|n| n - 1)
         }
     }

src/whitespace_remover.rs

@@ -1,3 +1,6 @@
+#[cfg(test)]
+mod test;
+
 use std::io::{Read, Result};
 
 /// Remove all ascii whitespace from an incoming stream.
@@ -20,10 +23,24 @@ where
 {
     fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
         let mut my_buf = vec![0; buf.len()];
-        let n = self.inner.read(&mut my_buf)?;
-        my_buf.truncate(n);
-        my_buf.retain(|d| !d.is_ascii_whitespace());
-        buf[..my_buf.len()].copy_from_slice(&my_buf);
-        Ok(my_buf.len())
+
+        Ok(loop {
+            let n = self.inner.read(&mut my_buf)?;
+            if n == 0 {
+                // the underlying reader is done
+                break 0;
+            }
+
+            my_buf.truncate(n);
+            my_buf.retain(|d| !d.is_ascii_whitespace());
+
+            // keep reading until we get at least a byte to return
+            if !my_buf.is_empty() {
+                buf[..my_buf.len()].copy_from_slice(&my_buf);
+                break my_buf.len();
+            }
+
+            my_buf.resize(buf.len(), 0);
+        })
     }
 }

src/whitespace_remover/test.rs

@@ -0,0 +1,33 @@
+use std::io::Read;
+
+#[test]
+fn test() {
+    const TEST: &str = " t/prau0INWoWUQ0LgQ\tMUdJRcCetBZP\nAyD+DCpn 01yWZT/LBo3Ogk0INwwuAtKNI ";
+
+    let mut stripped = String::new();
+    super::WhitespaceRemover::new(TEST.as_bytes())
+        .read_to_string(&mut stripped)
+        .unwrap();
+
+    assert_eq!(
+        stripped,
+        "t/prau0INWoWUQ0LgQMUdJRcCetBZPAyD+DCpn01yWZT/LBo3Ogk0INwwuAtKNI"
+    );
+}
+
+#[test]
+fn long_whitespace() {
+    let mut test_string = "a".to_owned();
+    test_string.reserve_exact(161);
+    for _ in 0..20 {
+        test_string.push_str("        ");
+    }
+    test_string.push('b');
+
+    let mut stripped = String::new();
+    super::WhitespaceRemover::new(test_string.as_bytes())
+        .read_to_string(&mut stripped)
+        .unwrap();
+
+    assert_eq!(stripped, "ab");
+}