add support for appending to header map from rhai

NEXT_CHANGELOG.md

@@ -26,6 +26,23 @@ By [@USERNAME](https://github.com/USERNAME) in https://github.com/apollographql/
 
 # [x.x.x] (unreleased) - 2022-mm-dd
 
+## 🚀 Features
+
+### Add support for setting multi-value header keys to rhai ([Issue #2211](https://github.com/apollographql/router/issues/2211))
+
+Adds support for setting a header map key with an array. This causes the HeaderMap key/values to be appended() to the map, rather than inserted().
+
+Example use from rhai as:
+
+```
+  response.headers["set-cookie"] = [
+    "foo=bar; Domain=localhost; Path=/; Expires=Wed, 04 Jan 2023 17:25:27 GMT; HttpOnly; Secure; SameSite=None",
+    "foo2=bar2; Domain=localhost; Path=/; Expires=Wed, 04 Jan 2023 17:25:27 GMT; HttpOnly; Secure; SameSite=None",
+  ];
+```
+
+By [@garypen](https://github.com/garypen) in https://github.com/apollographql/router/pull/2219
+
 ## 🐛 Fixes
 
 ### Filter nullified deferred responses ([Issue #2213](https://github.com/apollographql/router/issues/2168))

apollo-router/src/plugins/rhai.rs

@@ -1196,6 +1196,18 @@ impl Rhai {
                 );
                 Ok(())
             })
+            // Register an additional setter which allows us to set multiple values for the same
+            // key
+            .register_indexer_set(|x: &mut HeaderMap, key: &str, value: rhai::Array| {
+                let h_key = HeaderName::from_str(key).map_err(|e| e.to_string())?;
+                for v in value {
+                    x.append(
+                        h_key.clone(),
+                        HeaderValue::from_str(&v.into_string()?).map_err(|e| e.to_string())?,
+                    );
+                }
+                Ok(())
+            })
             // Register a Context indexer so we can get/set context
             .register_indexer_get(
                 |x: &mut Context, key: &str| -> Result<Dynamic, Box<EvalAltResult>> {

docs/source/customizations/rhai-api.mdx

@@ -248,6 +248,12 @@ The headers of a request are accessible as a read/write indexed variable. The ke
 // You can interact with request.headers as an indexed variable
 request.headers["x-my-new-header"] = 42.to_string(); // Inserts a new header "x-my-new-header" with value "42"
 print(`${request.headers["x-my-new-header"]}`); // Writes "42" into the router log at info level
+// You can also set an header value from an array. Useful with the "set-cookie" header,
+// Note: It's probably more useful to do this on response headers. Simply illustrating the syntax here.
+request.headers["set-cookie"] = [
+  "foo=bar; Domain=localhost; Path=/; Expires=Wed, 04 Jan 2023 17:25:27 GMT; HttpOnly; Secure; SameSite=None",
+  "foo2=bar2; Domain=localhost; Path=/; Expires=Wed, 04 Jan 2023 17:25:27 GMT; HttpOnly; Secure; SameSite=None",
+];
 // Rhai also supports extended dot notation for indexed variables, so this is equivalent
 request.headers.x-my-new-header = 42.to_string();
 ```