Add a server-sent-events reader to loopd

Implemented-By: Laguna S 2.1 (OpenCode)

crates/loopd/src/sse.rs

@@ -0,0 +1,140 @@
+//! A server-sent-events reader: turns a streamed body into `data:` payloads.
+//!
+//! `llama-server` streams a completion as SSE — one JSON object per `data:` line, then
+//! `data: [DONE]`. Lines end in `\n` or `\r\n`. Blank lines, comment lines (`:`) and any field
+//! other than `data` carry nothing and are skipped. After `data:` one leading space is dropped, and
+//! only one. Every byte the peer sends is read in bounded chunks; a line is only UTF-8 decoded once
+//! its whole length has arrived.
+
+use std::io::{ErrorKind, Read};
+
+use crate::http::is_timeout;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum SseItem {
+    /// The text after `data:`, without the line ending.
+    Data(String),
+    Done,
+}
+
+#[derive(Debug)]
+pub enum SseError {
+    Io(std::io::Error),
+    Timeout,
+    Truncated,
+    LineTooLong,
+    NotUtf8,
+}
+
+impl std::fmt::Display for SseError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            SseError::Io(e) => write!(f, "io error: {e}"),
+            SseError::Timeout => write!(f, "read timed out before the line arrived"),
+            SseError::Truncated => write!(f, "the body ended in the middle of a line"),
+            SseError::LineTooLong => write!(f, "a line exceeded the limit"),
+            SseError::NotUtf8 => write!(f, "a line was not valid UTF-8"),
+        }
+    }
+}
+
+impl std::error::Error for SseError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            SseError::Io(e) => Some(e),
+            _ => None,
+        }
+    }
+}
+
+pub struct Events<R> {
+    reader: R,
+    buf: Vec<u8>,
+    max_line: usize,
+    ended: bool,
+}
+
+impl<R: Read> Events<R> {
+    pub fn new(reader: R, max_line: usize) -> Self {
+        Events {
+            reader,
+            buf: Vec::new(),
+            max_line,
+            ended: false,
+        }
+    }
+
+    /// The next item, or `None` when the stream has ended cleanly between lines.
+    pub fn next_item(&mut self) -> Result<Option<SseItem>, SseError> {
+        loop {
+            if self.ended {
+                return Ok(None);
+            }
+            let line = match self.read_line() {
+                Ok(None) => {
+                    self.ended = true;
+                    return Ok(None);
+                }
+                Ok(Some(line)) => line,
+                Err(e) => return Err(e),
+            };
+            match self.process_line(line)? {
+                Some(item) => return Ok(Some(item)),
+                None => continue,
+            }
+        }
+    }
+
+    /// Reads one complete line, without its ending. Returns `None` on a clean end with nothing
+    /// buffered, and `Truncated` on a clean end with a partial line left over.
+    fn read_line(&mut self) -> Result<Option<Vec<u8>>, SseError> {
+        loop {
+            if let Some(pos) = self.buf.iter().position(|&b| b == b'\n') {
+                let mut line: Vec<u8> = self.buf.drain(..=pos).collect();
+                line.pop(); // drop the '\n'
+                if line.last() == Some(&b'\r') {
+                    line.pop();
+                }
+                if line.len() > self.max_line {
+                    return Err(SseError::LineTooLong);
+                }
+                return Ok(Some(line));
+            }
+            if self.buf.len() > self.max_line {
+                return Err(SseError::LineTooLong);
+            }
+            let mut tmp = [0u8; 4096];
+            let n = match self.reader.read(&mut tmp) {
+                Ok(0) => {
+                    if self.buf.is_empty() {
+                        return Ok(None);
+                    }
+                    return Err(SseError::Truncated);
+                }
+                Ok(n) => n,
+                Err(e) if e.kind() == ErrorKind::Interrupted => continue,
+                Err(e) if is_timeout(&e) => return Err(SseError::Timeout),
+                Err(e) if e.kind() == ErrorKind::UnexpectedEof => return Err(SseError::Truncated),
+                Err(e) => return Err(SseError::Io(e)),
+            };
+            self.buf.extend_from_slice(&tmp[..n]);
+        }
+    }
+
+    fn process_line(&self, line: Vec<u8>) -> Result<Option<SseItem>, SseError> {
+        let rest = match line.strip_prefix(b"data:") {
+            Some(rest) => rest,
+            None => return Ok(None),
+        };
+        let rest = match rest.split_first() {
+            Some((&b' ', rest)) => rest,
+            _ => rest,
+        };
+        let text = std::str::from_utf8(rest).map_err(|_| SseError::NotUtf8)?;
+        if text == "[DONE]" {
+            Ok(Some(SseItem::Done))
+        } else {
+            Ok(Some(SseItem::Data(text.to_string())))
+        }
+    }
+}