feat: add rest sse streaming adapter

crates/crank-adapter-rest/src/client.rs

@@ -7,7 +7,7 @@ use reqwest::{
 };
 use serde_json::Value;
 
-use crate::{RestAdapterError, RestRequest, RestResponse};
+use crate::{RestAdapterError, RestRequest, RestResponse, RestWindowRequest, RestWindowResponse};
 
 #[derive(Clone, Debug)]
 pub struct RestAdapter {
@@ -62,6 +62,61 @@ impl RestAdapter {
             body,
         })
     }
+
+    pub async fn execute_window(
+        &self,
+        target: &RestTarget,
+        request: &RestWindowRequest,
+    ) -> Result<RestWindowResponse, RestAdapterError> {
+        let url = build_url(target, &request.request)?;
+        let mut headers = build_headers(target, &request.request)?;
+        headers.insert(
+            reqwest::header::ACCEPT,
+            HeaderValue::from_static("text/event-stream"),
+        );
+
+        let mut builder = self
+            .client
+            .request(to_reqwest_method(target.method), url)
+            .headers(headers)
+            .timeout(Duration::from_millis(request.request.timeout_ms));
+
+        if let Some(body) = &request.request.body {
+            builder = builder.json(body);
+        }
+
+        let response = builder.send().await?;
+        let status = response.status();
+
+        if !status.is_success() {
+            let headers = normalize_headers(response.headers());
+            let body = decode_body(response).await?;
+            return Err(RestAdapterError::UnexpectedStatus {
+                status: status.as_u16(),
+                body: Value::Object(
+                    [
+                        (
+                            "headers".to_owned(),
+                            serde_json::to_value(headers).unwrap_or(Value::Null),
+                        ),
+                        ("body".to_owned(), body),
+                    ]
+                    .into_iter()
+                    .collect(),
+                ),
+            });
+        }
+
+        let (status_code, headers, body) =
+            crate::sse::collect_sse_window(response, request.window_duration_ms, request.max_items)
+                .await?;
+
+        Ok(RestWindowResponse {
+            status_code,
+            headers,
+            body,
+        })
+    }
 }
 
 fn build_url(target: &RestTarget, request: &RestRequest) -> Result<reqwest::Url, RestAdapterError> {
@@ -172,13 +227,15 @@ mod tests {
         Json, Router,
         extract::{Path, Query},
         http::HeaderMap,
+        response::sse::{Event, KeepAlive, Sse},
         routing::{get, post},
     };
     use crank_core::{HttpMethod, RestTarget};
+    use futures_util::stream;
     use serde_json::{Value, json};
     use tokio::net::TcpListener;
 
-    use crate::{RestAdapter, RestAdapterError, RestRequest};
+    use crate::{RestAdapter, RestAdapterError, RestRequest, RestWindowRequest};
 
     #[tokio::test]
     async fn executes_rest_request_and_normalizes_json_response() {
@@ -242,10 +299,104 @@ mod tests {
         ));
     }
 
+    #[tokio::test]
+    async fn collects_sse_events_with_window_bounds() {
+        let base_url = spawn_test_server().await;
+        let adapter = RestAdapter::new();
+        let target = RestTarget {
+            base_url,
+            method: HttpMethod::Get,
+            path_template: "/events".to_owned(),
+            static_headers: BTreeMap::new(),
+        };
+        let request = RestWindowRequest {
+            request: RestRequest {
+                path_params: BTreeMap::new(),
+                query_params: BTreeMap::new(),
+                headers: BTreeMap::new(),
+                body: None,
+                timeout_ms: 1_000,
+            },
+            window_duration_ms: 1_000,
+            max_items: Some(2),
+        };
+
+        let response = adapter.execute_window(&target, &request).await.unwrap();
+
+        assert_eq!(response.status_code, 200);
+        assert_eq!(
+            response.body,
+            json!({
+                "items": [
+                    { "message": "one" },
+                    { "message": "two" }
+                ],
+                "done": false
+            })
+        );
+    }
+
+    #[tokio::test]
+    async fn returns_timeout_window_when_no_events_arrive_before_deadline() {
+        let base_url = spawn_test_server().await;
+        let adapter = RestAdapter::new();
+        let target = RestTarget {
+            base_url,
+            method: HttpMethod::Get,
+            path_template: "/events-idle".to_owned(),
+            static_headers: BTreeMap::new(),
+        };
+        let request = RestWindowRequest {
+            request: RestRequest {
+                path_params: BTreeMap::new(),
+                query_params: BTreeMap::new(),
+                headers: BTreeMap::new(),
+                body: None,
+                timeout_ms: 1_000,
+            },
+            window_duration_ms: 50,
+            max_items: Some(10),
+        };
+
+        let response = adapter.execute_window(&target, &request).await.unwrap();
+
+        assert_eq!(response.body, json!({ "items": [], "done": true }));
+    }
+
+    #[tokio::test]
+    async fn rejects_malformed_sse_payloads() {
+        let base_url = spawn_test_server().await;
+        let adapter = RestAdapter::new();
+        let target = RestTarget {
+            base_url,
+            method: HttpMethod::Get,
+            path_template: "/events-broken".to_owned(),
+            static_headers: BTreeMap::new(),
+        };
+        let request = RestWindowRequest {
+            request: RestRequest {
+                path_params: BTreeMap::new(),
+                query_params: BTreeMap::new(),
+                headers: BTreeMap::new(),
+                body: None,
+                timeout_ms: 1_000,
+            },
+            window_duration_ms: 1_000,
+            max_items: Some(10),
+        };
+
+        let error = adapter.execute_window(&target, &request).await.unwrap_err();
+
+        assert!(matches!(error, RestAdapterError::InvalidSseEvent));
+    }
+
     async fn spawn_test_server() -> String {
         let app = Router::new()
             .route("/users/{user_id}", post(create_user))
-            .route("/fail", get(fail));
+            .route("/fail", get(fail))
+            .route("/events", get(sse_events))
+            .route("/events-idle", get(sse_idle))
+            .route("/events-broken", get(sse_broken));
         let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
         let address = listener.local_addr().unwrap();
 
@@ -286,4 +437,27 @@ mod tests {
             Json(json!({ "error": "upstream failed" })),
         )
     }
+
+    async fn sse_events()
+    -> Sse<impl futures_util::Stream<Item = Result<Event, std::convert::Infallible>>> {
+        let events = vec![
+            Ok(Event::default().data("{\"message\":\"one\"}")),
+            Ok(Event::default().data("{\"message\":\"two\"}")),
+            Ok(Event::default().data("{\"message\":\"three\"}")),
+        ];
+
+        Sse::new(stream::iter(events)).keep_alive(KeepAlive::default())
+    }
+
+    async fn sse_idle()
+    -> Sse<impl futures_util::Stream<Item = Result<Event, std::convert::Infallible>>> {
+        Sse::new(stream::pending()).keep_alive(KeepAlive::default())
+    }
+
+    async fn sse_broken()
+    -> Sse<impl futures_util::Stream<Item = Result<Event, std::convert::Infallible>>> {
+        let events = vec![Ok(Event::default().data("{broken-json}"))];
+
+        Sse::new(stream::iter(events)).keep_alive(KeepAlive::default())
+    }
 }

crates/crank-adapter-rest/src/error.rs

@@ -15,6 +15,10 @@ pub enum RestAdapterError {
     InvalidHeaderValue { header: String },
     #[error("request failed")]
     Transport(#[from] reqwest::Error),
+    #[error("sse collection window expired before stream completed")]
+    WindowExpired,
     #[error("rest endpoint returned status {status}")]
     UnexpectedStatus { status: u16, body: Value },
+    #[error("sse stream produced malformed event payload")]
+    InvalidSseEvent,
 }

crates/crank-adapter-rest/src/lib.rs

@@ -1,7 +1,8 @@
 mod client;
 mod error;
 mod model;
+mod sse;
 
 pub use client::RestAdapter;
 pub use error::RestAdapterError;
-pub use model::{RestRequest, RestResponse};
+pub use model::{RestRequest, RestResponse, RestWindowRequest, RestWindowResponse};

crates/crank-adapter-rest/src/model.rs

@@ -23,3 +23,20 @@ pub struct RestResponse {
     pub headers: BTreeMap<String, String>,
     pub body: Value,
 }
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Default)]
+pub struct RestWindowRequest {
+    #[serde(flatten)]
+    pub request: RestRequest,
+    pub window_duration_ms: u64,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub max_items: Option<u32>,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct RestWindowResponse {
+    pub status_code: u16,
+    #[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
+    pub headers: BTreeMap<String, String>,
+    pub body: Value,
+}

crates/crank-adapter-rest/src/sse.rs

@@ -0,0 +1,160 @@
+use std::collections::BTreeMap;
+
+use futures_util::StreamExt;
+use reqwest::header::HeaderMap;
+use serde_json::{Value, json};
+use tokio::time::{Duration, Instant, timeout_at};
+
+use crate::RestAdapterError;
+
+pub async fn collect_sse_window(
+    response: reqwest::Response,
+    window_duration_ms: u64,
+    max_items: Option<u32>,
+) -> Result<(u16, BTreeMap<String, String>, Value), RestAdapterError> {
+    let status = response.status();
+    let headers = normalize_headers(response.headers());
+    let deadline = Instant::now() + Duration::from_millis(window_duration_ms);
+    let mut stream = response.bytes_stream();
+    let mut buffer = String::new();
+    let mut items = Vec::new();
+    let mut done = true;
+
+    loop {
+        if max_items.is_some_and(|limit| items.len() >= limit as usize) {
+            done = false;
+            break;
+        }
+
+        let next_chunk = match timeout_at(deadline, stream.next()).await {
+            Ok(next_chunk) => next_chunk,
+            Err(_) => break,
+        };
+
+        let Some(next_chunk) = next_chunk else {
+            break;
+        };
+
+        let chunk = next_chunk?;
+        buffer.push_str(&String::from_utf8_lossy(&chunk));
+
+        while let Some(event_end) = find_event_boundary(&buffer) {
+            let event = buffer[..event_end].to_owned();
+            let boundary_len = boundary_length(&buffer[event_end..]);
+            buffer = buffer[event_end + boundary_len..].to_owned();
+
+            if let Some(item) = parse_sse_event(&event)? {
+                items.push(item);
+
+                if max_items.is_some_and(|limit| items.len() >= limit as usize) {
+                    done = false;
+                    break;
+                }
+            }
+        }
+
+        if !done {
+            break;
+        }
+    }
+
+    Ok((
+        status.as_u16(),
+        headers,
+        json!({
+            "items": items,
+            "done": done
+        }),
+    ))
+}
+
+fn parse_sse_event(raw: &str) -> Result<Option<Value>, RestAdapterError> {
+    let mut data_lines = Vec::new();
+
+    for line in raw.lines() {
+        if line.is_empty() || line.starts_with(':') {
+            continue;
+        }
+
+        if let Some(value) = line.strip_prefix("data:") {
+            data_lines.push(value.trim_start().to_owned());
+        }
+    }
+
+    if data_lines.is_empty() {
+        return Ok(None);
+    }
+
+    let payload = data_lines.join("\n");
+    if payload.is_empty() {
+        return Ok(None);
+    }
+
+    serde_json::from_str::<Value>(&payload)
+        .map(Some)
+        .or_else(|_| {
+            if payload.starts_with('{') || payload.starts_with('[') {
+                Err(RestAdapterError::InvalidSseEvent)
+            } else {
+                Ok(Some(Value::String(payload)))
+            }
+        })
+}
+
+fn find_event_boundary(buffer: &str) -> Option<usize> {
+    buffer
+        .find("\r\n\r\n")
+        .or_else(|| buffer.find("\n\n"))
+        .or_else(|| buffer.find("\r\r"))
+}
+
+fn boundary_length(boundary: &str) -> usize {
+    if boundary.starts_with("\r\n\r\n") {
+        4
+    } else {
+        2
+    }
+}
+
+fn normalize_headers(headers: &HeaderMap) -> BTreeMap<String, String> {
+    headers
+        .iter()
+        .filter_map(|(name, value)| {
+            value
+                .to_str()
+                .ok()
+                .map(|value| (name.as_str().to_owned(), value.to_owned()))
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use serde_json::json;
+
+    use super::parse_sse_event;
+    use crate::RestAdapterError;
+
+    #[test]
+    fn parses_json_event_payload() {
+        let event = "event: message\ndata: {\"message\":\"ok\"}\n\n";
+
+        let parsed = parse_sse_event(event).unwrap();
+
+        assert_eq!(parsed, Some(json!({ "message": "ok" })));
+    }
+
+    #[test]
+    fn ignores_comment_only_events() {
+        let parsed = parse_sse_event(": keepalive\n\n").unwrap();
+
+        assert_eq!(parsed, None);
+    }
+
+    #[test]
+    fn rejects_malformed_json_like_payload() {
+        let error = parse_sse_event("data: {broken-json}\n\n").unwrap_err();
+
+        assert!(matches!(error, RestAdapterError::InvalidSseEvent));
+    }
+}