fix(on-call): handle empty 200 body in pages get

GET /api/v2/on-call/pages/{id} can return HTTP 200 with an empty body
(content-length: 0). parse_response_json fed the empty body straight to
serde_json, producing "EOF while parsing value at line 1 column 0" and
failing `pup on-call pages get`.

Treat an empty or whitespace-only success body as JSON null in the shared
parse_response_json helper, so every raw_* caller (raw_get/raw_post/etc.)
degrades gracefully instead of crashing, mirroring the existing 204
No Content handling.

- Guard empty/whitespace bodies in raw_client::parse_response_json
- Add raw_get unit tests (empty, whitespace-only, valid JSON)
- Add pages_get regression test for empty 200 body

Closes #638

Author: datadog-bits

src/commands/on_call.rs

@@ -830,6 +830,29 @@ mod tests {
         cleanup_env();
     }
 
+    // Regression test for #638: the on-call pages GET endpoint can return a 200
+    // with an empty body (content-length: 0). pages_get must succeed instead of
+    // failing with "EOF while parsing value at line 1 column 0".
+    #[tokio::test]
+    async fn test_on_call_pages_get_empty_body() {
+        let _lock = lock_env().await;
+        let mut s = mockito::Server::new_async().await;
+        let cfg = test_config(&s.url());
+        s.mock("GET", "/api/v2/on-call/pages/12345")
+            .with_status(200)
+            .with_header("content-type", "application/json")
+            .with_body("")
+            .create_async()
+            .await;
+        let result = super::pages_get(&cfg, "12345").await;
+        assert!(
+            result.is_ok(),
+            "pages_get with empty body failed: {:?}",
+            result.err()
+        );
+        cleanup_env();
+    }
+
     #[tokio::test]
     async fn test_on_call_pages_get_not_found() {
         let _lock = lock_env().await;

src/raw_client.rs

@@ -37,6 +37,13 @@ impl std::error::Error for HttpError {}
 async fn parse_response_json(resp: reqwest::Response) -> anyhow::Result<serde_json::Value> {
     use serde::Deserialize;
     let bytes = resp.bytes().await?;
+    // Some endpoints return a success status (e.g. 200) with an empty body, such
+    // as GET /api/v2/on-call/pages/{id} which responds with content-length: 0.
+    // Treat an empty or whitespace-only body as JSON null rather than failing
+    // with "EOF while parsing value at line 1 column 0".
+    if bytes.iter().all(u8::is_ascii_whitespace) {
+        return Ok(serde_json::Value::Null);
+    }
     let mut de = serde_json::Deserializer::from_slice(&bytes);
     de.disable_recursion_limit();
     let de = serde_stacker::Deserializer::new(&mut de);
@@ -1106,4 +1113,72 @@ mod tests {
         );
         cleanup_env();
     }
+
+    /// Regression test: a 200 response with an empty body must parse as JSON null
+    /// instead of failing with "EOF while parsing value at line 1 column 0".
+    #[tokio::test]
+    async fn test_raw_get_empty_body_returns_null() {
+        let _lock = lock_env().await;
+        let mut server = mockito::Server::new_async().await;
+        let cfg = test_config(&server.url());
+        let _mock = server
+            .mock("GET", "/api/v2/on-call/pages/12345")
+            .with_status(200)
+            .with_header("content-type", "application/json")
+            .with_body("")
+            .create_async()
+            .await;
+        let resp = super::raw_get(&cfg, "/api/v2/on-call/pages/12345", &[]).await;
+        assert!(
+            resp.is_ok(),
+            "raw_get with empty body failed: {:?}",
+            resp.err()
+        );
+        assert_eq!(resp.unwrap(), serde_json::Value::Null);
+        cleanup_env();
+    }
+
+    /// A whitespace-only body is also unparseable JSON and must be treated as null.
+    #[tokio::test]
+    async fn test_raw_get_whitespace_body_returns_null() {
+        let _lock = lock_env().await;
+        let mut server = mockito::Server::new_async().await;
+        let cfg = test_config(&server.url());
+        let _mock = server
+            .mock("GET", "/api/v2/on-call/pages/12345")
+            .with_status(200)
+            .with_header("content-type", "application/json")
+            .with_body("  \n\t ")
+            .create_async()
+            .await;
+        let resp = super::raw_get(&cfg, "/api/v2/on-call/pages/12345", &[]).await;
+        assert!(
+            resp.is_ok(),
+            "raw_get with whitespace body failed: {:?}",
+            resp.err()
+        );
+        assert_eq!(resp.unwrap(), serde_json::Value::Null);
+        cleanup_env();
+    }
+
+    /// A non-empty JSON body must still parse normally (the empty-body guard must
+    /// not shadow the regular parse path).
+    #[tokio::test]
+    async fn test_raw_get_nonempty_body_parses() {
+        let _lock = lock_env().await;
+        let mut server = mockito::Server::new_async().await;
+        let cfg = test_config(&server.url());
+        let _mock = server
+            .mock("GET", "/api/v2/on-call/pages/12345")
+            .with_status(200)
+            .with_header("content-type", "application/json")
+            .with_body(r#"{"data": {"id": "12345"}}"#)
+            .create_async()
+            .await;
+        let resp = super::raw_get(&cfg, "/api/v2/on-call/pages/12345", &[])
+            .await
+            .expect("raw_get with JSON body should succeed");
+        assert_eq!(resp["data"]["id"], "12345");
+        cleanup_env();
+    }
 }