PayloadSerialization can emit additional headers (zio-archive#120)

This can be used to sign the payload cryptographically and pass it as a header onto the request.

.gitignore

@@ -467,3 +467,4 @@ website/node_modules
 website/build
 website/i18n/en.json
 website/static/api
+.idea

webhooks-test/src/test/scala/zio/webhooks/WebhookServerSpec.scala

@@ -882,7 +882,7 @@ object WebhookServerSpecUtil {
       )
     }
 
-  val jsonContentHeaders: Chunk[(String, String)] = Chunk(("Accept", "*/*"), ("Content-Type", "application/json"))
+  val jsonContentHeaders: Chunk[HttpHeader] = Chunk(("Accept", "*/*"), ("Content-Type", "application/json"))
 
   val jsonPayloadPattern: String =
     """(?:\[\{\"event\":\"payload\d+\"}(?:,\{\"event\":\"payload\d+\"})*\])"""
@@ -909,7 +909,7 @@ object WebhookServerSpecUtil {
         WebhooksProxy.live
       )
 
-  val plaintextContentHeaders: Chunk[(String, String)] = Chunk(("Accept", "*/*"), ("Content-Type", "text/plain"))
+  val plaintextContentHeaders: Chunk[HttpHeader] = Chunk(("Accept", "*/*"), ("Content-Type", "text/plain"))
 
   sealed trait ScenarioInterest[A]
   object ScenarioInterest {

webhooks/src/main/scala/zio/webhooks/WebhookServer.scala

@@ -47,8 +47,8 @@ final class WebhookServer private (
    * marked failed.
    */
   private def deliver(dispatch: WebhookDispatch): UIO[Unit] = {
-    val request =
-      WebhookHttpRequest(dispatch.url, serializePayload(dispatch.payload, dispatch.contentType), dispatch.headers)
+    val (payload, headers) = serializePayload(dispatch.payload, dispatch.contentType)
+    val request            = WebhookHttpRequest(dispatch.url, payload, dispatch.headers ++ headers)
     for {
       response <- httpClient.post(request).either
       _        <- (dispatch.deliverySemantics, response) match {

webhooks/src/main/scala/zio/webhooks/backends/JsonPayloadSerialization.scala

@@ -1,6 +1,6 @@
 package zio.webhooks.backends
 
-import zio.{ Has, ULayer, ZLayer }
+import zio.{ Chunk, Has, ULayer, ZLayer }
 import zio.webhooks._
 
 object JsonPayloadSerialization {
@@ -11,16 +11,16 @@ object JsonPayloadSerialization {
         case Some(WebhookContentMimeType(contentType)) if contentType.toLowerCase == "application/json" =>
           webhookPayload match {
             case WebhookPayload.Single(event)   =>
-              event.content
+              (event.content, Chunk.empty)
             case WebhookPayload.Batched(events) =>
-              "[" + events.map(_.content).mkString(",") + "]"
+              ("[" + events.map(_.content).mkString(",") + "]", Chunk.empty)
           }
         case _                                                                                          =>
           webhookPayload match {
             case WebhookPayload.Single(event)   =>
-              event.content
+              (event.content, Chunk.empty)
             case WebhookPayload.Batched(events) =>
-              events.map(_.content).mkString
+              (events.map(_.content).mkString, Chunk.empty)
           }
       }
     }

webhooks/src/main/scala/zio/webhooks/internal/RetryDispatcher.scala

@@ -72,8 +72,8 @@ private[webhooks] final case class RetryDispatcher(
    * for retries when the endpoint begins to return `200` status codes.
    */
   private def retryEvents(dispatch: WebhookDispatch, batchQueue: Option[Queue[WebhookEvent]]): UIO[Unit] = {
-    val request =
-      WebhookHttpRequest(dispatch.url, serializePayload(dispatch.payload, dispatch.contentType), dispatch.headers)
+    val (payload, headers) = serializePayload(dispatch.payload, dispatch.contentType)
+    val request            = WebhookHttpRequest(dispatch.url, payload, dispatch.headers ++ headers)
     for {
       response <- httpClient.post(request).either
       _        <- response match {

webhooks/src/main/scala/zio/webhooks/internal/WebhookDispatch.scala

@@ -31,5 +31,5 @@ private[webhooks] final case class WebhookDispatch(
         events
     }
 
-  lazy val headers: Chunk[(String, String)] = payload.headers
+  lazy val headers: Chunk[HttpHeader] = payload.headers
 }

webhooks/src/main/scala/zio/webhooks/package.scala

@@ -32,9 +32,12 @@ package object webhooks {
       .mergeTerminateRight(UStream.fromEffect(shutdownSignal.await.map(Right(_))))
       .collectLeft
 
+  type HttpHeader = (String, String)
+
   /**
    * [[SerializePayload]] is a function that takes a [[WebhookPayload]] and an optional
-   * [WebhookContentMimeType] and serializes it into a `String`.
+   * [WebhookContentMimeType] and serializes it into a pair of `String` and a chunk of [[HttpHeader]] to append
+   * to the outgoing request.
    */
-  type SerializePayload = (WebhookPayload, Option[WebhookContentMimeType]) => String
+  type SerializePayload = (WebhookPayload, Option[WebhookContentMimeType]) => (String, Chunk[HttpHeader])
 }