sgl-router: experimental Rust HTTP router for SGLang worker pools (#25851)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

experimental/sgl-router/tests/proxy/common/streaming.rs

@@ -0,0 +1,61 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 The SGLang Authors
+// SPDX-License-Identifier: Apache-2.0
+
+//! SSE parsing and body-collection helpers for integration tests.
+
+use bytes::Bytes;
+
+/// Parse an SSE stream's `data: …` payloads (one per event).
+#[allow(dead_code)]
+pub fn parse_sse_data(raw: &[u8]) -> Vec<String> {
+    let s = std::str::from_utf8(raw).unwrap_or("");
+    s.lines()
+        .filter_map(|l| l.strip_prefix("data: "))
+        .map(|l| l.to_string())
+        .collect()
+}
+
+/// Collect an axum Body to bytes in tests.
+#[allow(dead_code)]
+pub async fn collect_body(body: axum::body::Body) -> Bytes {
+    use http_body_util::BodyExt;
+    body.collect().await.unwrap().to_bytes()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Ported from SMG tests/api/streaming_tests.rs::test_sse_format_parsing.
+    /// Verifies that parse_sse_data:
+    ///   1. Extracts standard `data: …` lines.
+    ///   2. Silently ignores SSE `event: …` type fields (not data lines).
+    ///   3. Silently ignores SSE `: …` comment lines.
+    ///   4. Correctly parses `[DONE]` sentinel.
+    ///
+    /// These edge-cases matter because SGLang workers may emit `event: message`
+    /// fields in their SSE frames. A parser that accidentally leaks those into
+    /// the payload list would cause clients to fail on JSON-parse.
+    #[test]
+    fn parse_sse_data_extracts_data_lines_only() {
+        // Basic: three data lines including the [DONE] sentinel.
+        let basic =
+            b"data: {\"text\":\"Hello\"}\n\ndata: {\"text\":\" world\"}\n\ndata: [DONE]\n\n";
+        let events = parse_sse_data(basic);
+        assert_eq!(events.len(), 3, "expected 3 data events, got: {events:?}");
+        assert_eq!(events[0], "{\"text\":\"Hello\"}");
+        assert_eq!(events[1], "{\"text\":\" world\"}");
+        assert_eq!(events[2], "[DONE]");
+
+        // Mixed: event: type field + comment line — neither must appear in output.
+        let mixed = b"event: message\ndata: {\"test\":true}\n\n: comment line\ndata: [DONE]\n\n";
+        let events = parse_sse_data(mixed);
+        assert_eq!(
+            events.len(),
+            2,
+            "event: and : comment lines must be ignored; got: {events:?}"
+        );
+        assert_eq!(events[0], "{\"test\":true}");
+        assert_eq!(events[1], "[DONE]");
+    }
+}