Add possibility to get first line

src/inputfile.rs

@@ -7,17 +7,31 @@ const THEME_PREVIEW_FILE: &[u8] = include_bytes!("../assets/theme_preview.rs");
 
 pub struct InputFileReader<'a> {
     inner: Box<dyn BufRead + 'a>,
+    buffer: Vec<u8>,
 }
 
 impl<'a> InputFileReader<'a> {
     fn new<R: BufRead + 'a>(reader: R) -> InputFileReader<'a> {
         InputFileReader {
             inner: Box::new(reader),
+            buffer: vec![],
         }
     }
 
+    pub fn get_first_line(&mut self) -> io::Result<Vec<u8>> {
+        assert!(self.buffer.is_empty());
+
+        self.inner.read_until(b'\n', &mut self.buffer)?;
+        Ok(self.buffer.clone())
+    }
+
     pub fn read_line(&mut self, buf: &mut Vec<u8>) -> io::Result<bool> {
-        self.inner.read_until(b'\n', buf).map(|size| size > 0)
+        if self.buffer.is_empty() {
+            self.inner.read_until(b'\n', buf).map(|size| size > 0)
+        } else {
+            buf.append(&mut self.buffer);
+            return Ok(true);
+        }
     }
 }
 
@@ -48,22 +62,26 @@ impl<'a> InputFile<'a> {
 
 #[test]
 fn basic() {
-    let content = b"hello\nworld";
+    let content = b"#!/bin/bash\necho hello";
     let mut reader = InputFileReader::new(&content[..]);
 
+    let first_line = reader.get_first_line();
+    assert!(first_line.is_ok());
+    assert_eq!(b"#!/bin/bash\n", &first_line.unwrap()[..]);
+
     let mut buffer = vec![];
 
     let res = reader.read_line(&mut buffer);
     assert!(res.is_ok());
     assert_eq!(true, res.unwrap());
-    assert_eq!(b"hello\n", &buffer[..]);
+    assert_eq!(b"#!/bin/bash\n", &buffer[..]);
 
     buffer.clear();
 
     let res = reader.read_line(&mut buffer);
     assert!(res.is_ok());
     assert_eq!(true, res.unwrap());
-    assert_eq!(b"world", &buffer[..]);
+    assert_eq!(b"echo hello", &buffer[..]);
 
     buffer.clear();