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/// SSE (Server-Sent Events) parser that properly buffers incomplete chunks.
///
/// HTTP chunks don't guarantee alignment with SSE event boundaries. This parser
/// buffers incoming data and only yields complete events (those ending with `\n\n`).
/// Represents a parsed SSE event
#[derive(Debug, Clone)]
pub struct SseEvent {
/// The event type (from `event:` line), if present
pub event_type: Option<String>,
/// The data payload (from `data:` line)
pub data: String,
}
/// An SSE parser that buffers incomplete chunks and yields complete events.
pub struct SseParser {
buffer: String,
}
impl SseParser {
pub fn new() -> Self {
Self {
buffer: String::new(),
}
}
/// Feed a chunk of data into the parser and return any complete events.
///
/// This properly handles:
/// - Events split across multiple chunks
/// - Multiple events in a single chunk
/// - Partial events that need to wait for more data
pub fn feed(&mut self, chunk: &str) -> Vec<SseEvent> {
self.buffer.push_str(chunk);
let mut events = Vec::new();
// SSE events are separated by double newlines
// We need to handle both \n\n and \r\n\r\n
loop {
// Find the next complete event (ends with \n\n or \r\n\r\n)
let split_pos = if let Some(pos) = self.buffer.find("\n\n") {
Some((pos, 2)) // Unix-style
} else if let Some(pos) = self.buffer.find("\r\n\r\n") {
Some((pos, 4)) // Windows-style
} else {
None
};
match split_pos {
Some((pos, delim_len)) => {
// Extract the complete event
let event_str: String = self.buffer.drain(..pos + delim_len).collect();
// Parse the event
if let Some(event) = Self::parse_event(&event_str) {
events.push(event);
}
}
None => {
// No complete event yet, wait for more data
break;
}
}
}
events
}
/// Parse a single SSE event string into an SseEvent
fn parse_event(event_str: &str) -> Option<SseEvent> {
let mut event_type = None;
let mut data_parts = Vec::new();
for line in event_str.lines() {
let line = line.trim();
if line.is_empty() {
continue;
}
if let Some(value) = line.strip_prefix("event:") {
event_type = Some(value.trim().to_string());
} else if let Some(value) = line.strip_prefix("data:") {
data_parts.push(value.trim().to_string());
}
// Ignore other fields like id:, retry:, comments (:)
}
if data_parts.is_empty() {
return None;
}
// Join multiple data lines with newlines (per SSE spec)
let data = data_parts.join("\n");
Some(SseEvent { event_type, data })
}
/// Check if there's any remaining buffered data
pub fn has_remaining(&self) -> bool {
!self.buffer.is_empty()
}
/// Get remaining buffer content (useful for debugging)
#[allow(dead_code)]
pub fn remaining(&self) -> &str {
&self.buffer
}
}
impl Default for SseParser {
fn default() -> Self {
Self::new()
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_complete_event() {
let mut parser = SseParser::new();
let events = parser.feed("event: message\ndata: hello\n\n");
assert_eq!(events.len(), 1);
assert_eq!(events[0].event_type.as_deref(), Some("message"));
assert_eq!(events[0].data, "hello");
}
#[test]
fn test_split_event() {
let mut parser = SseParser::new();
// First chunk - incomplete
let events = parser.feed("event: message\ndata: hel");
assert_eq!(events.len(), 0);
// Second chunk - completes the event
let events = parser.feed("lo world\n\n");
assert_eq!(events.len(), 1);
assert_eq!(events[0].data, "hello world");
}
#[test]
fn test_multiple_events_in_one_chunk() {
let mut parser = SseParser::new();
let events = parser.feed("data: first\n\ndata: second\n\n");
assert_eq!(events.len(), 2);
assert_eq!(events[0].data, "first");
assert_eq!(events[1].data, "second");
}
#[test]
fn test_json_split_midway() {
// This simulates the exact issue: JSON cut off mid-value
let mut parser = SseParser::new();
let events = parser.feed(r#"event: response.created
data: {"type":"response.created","instructions":nul"#);
assert_eq!(events.len(), 0);
// Complete the JSON
let events = parser.feed(r#"l,"status":"ok"}
"#);
assert_eq!(events.len(), 1);
assert_eq!(
events[0].data,
r#"{"type":"response.created","instructions":null,"status":"ok"}"#
);
}
#[test]
fn test_done_event() {
let mut parser = SseParser::new();
let events = parser.feed("data: [DONE]\n\n");
assert_eq!(events.len(), 1);
assert_eq!(events[0].data, "[DONE]");
}
}