rust: Add MessageIn::{new_raw_payload, with_content_type} (#1533)

… and add some extra detail to the docs of the kotlin equivalent.

Part of svix/monorepo-private#9470.

kotlin/lib/src/main/kotlin/Message.kt

@@ -76,10 +76,15 @@ class Message internal constructor(token: String, options: SvixOptions) {
 /**
  * Creates a [MessageIn] with the payload already being serialized.
  *
+ * The payload is not normalized on the server (usually whitespace outside
+ * of string literals, unnecessarily escaped characters in string and such
+ * are fixed up by the server), and is not even required to be JSON.
+ *
  * @param payload Serialized message payload
  * @param contentType Content type of the payload to send as a header. Defaults to `application/json`.
  *
  * See the class documentation for details about the other parameters.
+ *
  */
 fun messageInRaw(
     eventType: String,

rust/src/lib.rs

@@ -19,6 +19,7 @@ extern crate serde_derive;
 
 pub mod api;
 pub mod error;
+mod model_ext;
 mod request;
 pub mod webhooks;
 

rust/src/model_ext.rs

@@ -0,0 +1,36 @@
+//! Extensions of the auto-generated "models" (schema structs).
+
+use serde_json::json;
+
+use crate::models::MessageIn;
+
+impl MessageIn {
+    /// Create a new message with a pre-serialized payload.
+    ///
+    /// The payload is not normalized on the server (usually whitespace outside
+    /// of string literals, unnecessarily escaped characters in string and such
+    /// are fixed up by the server), and is not even required to be JSON.
+    ///
+    /// The default `content-type` of `application/json` will still be used,
+    /// unless overwritten with [`with_content_type`][Self::with_content_type].
+    pub fn new_raw_payload(event_type: String, payload: String) -> Self {
+        Self {
+            transformations_params: Some(json!({ "rawPayload": payload })),
+            ..Self::new(event_type, json!({}))
+        }
+    }
+
+    /// Set the `content-type` header to use for the message.
+    pub fn with_content_type(mut self, content_type: String) -> Self {
+        let transformations_params = self.transformations_params.get_or_insert_with(|| json!({}));
+
+        // This will panic if transformations_params, its headers field, or the
+        // headers' content-type field already exists as an array, bool, number
+        // or string.
+        // That would make the whole parameter struct invalid anyways though,
+        // and can hardly happen accidentally.
+        transformations_params["headers"]["content-type"] = content_type.into();
+
+        self
+    }
+}