Reuse storage when converting Vec to String in Communicator::read_str…

…ing()

src/communicate.rs

@@ -508,10 +508,7 @@ impl Communicator {
     /// replacement character.
     pub fn read_string(&mut self) -> Result<(Option<String>, Option<String>), CommunicateError> {
         let (o, e) = self.read()?;
-        Ok((
-            o.map(|v| String::from_utf8_lossy(&v).into()),
-            e.map(|v| String::from_utf8_lossy(&v).into()),
-        ))
+        Ok((o.map(from_utf8_lossy), e.map(from_utf8_lossy)))
     }
 
     /// Limit the amount of data the next `read()` will read from the
@@ -529,6 +526,15 @@ impl Communicator {
     }
 }
 
+/// Like String::from_utf8_lossy(), but takes `Vec<u8>` and reuses its storage if
+/// possible.
+fn from_utf8_lossy(v: Vec<u8>) -> String {
+    match String::from_utf8(v) {
+        Ok(s) => s,
+        Err(e) => String::from_utf8_lossy(e.as_bytes()).into(),
+    }
+}
+
 pub fn communicate(
     stdin: Option<File>,
     stdout: Option<File>,