dont use line buffering when using json protocol

1 files changed, 105 insertions, 0 deletions

diff --git a/src/utils.rs b/src/utils.rs
new file mode 100644
index 0000000..2ed1868
--- /dev/null
+++ b/src/utils.rs
@@ -0,0 +1,105 @@
+//! Some usefull functions
+
+use serde::Deserialize;
+use serde_json::{Deserializer, Error as JsonError};
+
+/// Retuns (`last_line`, `remaining`). See tests for examples.
+pub fn last_line(s: &[u8]) -> Option<(&[u8], &[u8])> {
+    let mut it = memchr::memrchr_iter(b'\n', s);
+    let last = it.next()?;
+    let rem = &s[(last + 1)..];
+    if let Some(pre_last) = it.next() {
+        Some((&s[(pre_last + 1)..last], rem))
+    } else {
+        Some((&s[..last], rem))
+    }
+}
+
+/// Deserialize the last complete object. Returns (`object`, `remaining`). See tests for examples.
+pub fn de_last_json<'a, T: Deserialize<'a>>(
+    mut s: &'a [u8],
+) -> Result<(Option<T>, &'a [u8]), JsonError> {
+    let mut last = None;
+    let mut tmp;
+    loop {
+        (tmp, s) = de_first_json(s)?;
+        last = match tmp {
+            Some(obj) => Some(obj),
+            None => return Ok((last, s)),
+        };
+    }
+}
+
+/// Deserialize the first complete object. Returns (`object`, `remaining`). See tests for examples.
+pub fn de_first_json<'a, T: Deserialize<'a>>(
+    mut s: &'a [u8],
+) -> Result<(Option<T>, &'a [u8]), JsonError> {
+    while s
+        .first()
+        .map_or(false, |&x| x == b' ' || x == b',' || x == b'\n')
+    {
+        s = &s[1..];
+    }
+    let mut de = Deserializer::from_slice(s).into_iter();
+    match de.next() {
+        Some(Ok(obj)) => Ok((Some(obj), &s[de.byte_offset()..])),
+        Some(Err(e)) if e.is_eof() => Ok((None, &s[de.byte_offset()..])),
+        Some(Err(e)) => Err(e),
+        None => Ok((None, &s[de.byte_offset()..])),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    macro_rules! str {
+        ($str:expr) => {
+            &$str.as_bytes()[..]
+        };
+    }
+
+    #[test]
+    fn streaming_json() {
+        let s = b",[2]\n, [3], [4, 3],[32][3] ";
+        assert_eq!(
+            de_first_json::<Vec<u8>>(s).unwrap(),
+            (Some(vec![2]), str!("\n, [3], [4, 3],[32][3] "))
+        );
+        assert_eq!(
+            de_last_json::<Vec<u8>>(s).unwrap(),
+            (Some(vec![3]), str!(""))
+        );
+
+        let s = b",[2]\n, [3], [4, 3],[32][3] [2, 4";
+        assert_eq!(
+            de_last_json::<Vec<u8>>(s).unwrap(),
+            (Some(vec![3]), str!("[2, 4"))
+        );
+
+        let s = b",[2]\n, [3], [4, 3],[32] invalid";
+        assert_eq!(
+            de_first_json::<Vec<u8>>(s).unwrap(),
+            (Some(vec![2]), str!("\n, [3], [4, 3],[32] invalid"))
+        );
+        assert!(de_last_json::<Vec<u8>>(s).is_err());
+    }
+
+    #[test]
+    fn test_last_line() {
+        let s = b"hello";
+        assert_eq!(last_line(s), None);
+
+        let s = b"hello\n";
+        assert_eq!(last_line(s), Some((str!("hello"), str!(""))));
+
+        let s = b"hello\nworld";
+        assert_eq!(last_line(s), Some((str!("hello"), str!("world"))));
+
+        let s = b"hello\nworld\n";
+        assert_eq!(last_line(s), Some((str!("world"), str!(""))));
+
+        let s = b"hello\nworld\n...";
+        assert_eq!(last_line(s), Some((str!("world"), str!("..."))));
+    }
+}