CHANGELOG and doc updates for content-type

Further document the content-type middleware.

Author: plexus

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### New features
+
+* [#548](https://github.com/clojure-emacs/cider-nrepl/pull/548): Make the content-type middleware extensible via multimethod
+
 ## 0.27.4 (2021-12-15)
 
 ### Bugs fixed

doc/modules/ROOT/pages/nrepl-api/ops.adoc

@@ -158,7 +158,9 @@ Returns::
 
 === `content-type-middleware`
 
-Enhances the ``eval`` op by adding ``content-type`` and friends to some responses. Not an op in itself.
+Enhances the ``eval`` op by adding ``content-type`` and ``body`` to certain ``eval`` responses. Not an op in itself.
+
+Depending on the type of the return value of the evaluation this middleware may kick in and include a representation of the result in the response, together with a MIME/Media type to indicate how it should be handled by the client. Comes with implementations for ``URI``, ``URL``, ``File``, and ``java.awt.Image``. More type handlers can be provided by the user by extending the ``cider.nrepl.middleware.content-type/content-type-response`` multimethod. This dispatches using ``clojure.core/type``, so ``:type`` metadata on plain Clojure values can be used to provide custom handling.
 
 Required parameters::
 {blank}
@@ -168,7 +170,9 @@ Optional parameters::
 
 
 Returns::
-{blank}
+* `:body` The rich response document, if applicable.
+* `:content-type` The Media type (MIME type) of the reponse, structured as a pair, `[type {:as attrs}]`
+* `:content-transfer-encoding` The encoding of the response body (Optional, currently only one possible value `"base64"`)
 
 
 === `debug-input`

doc/modules/ROOT/pages/nrepl-api/supplied_middleware.adoc

@@ -27,6 +27,12 @@
 | `complete`
 | Code completion.
 
+| `wrap-content-type`
+| -
+| No
+| `eval`
+| Rich content handling, return multimedia results beyond plain text from `eval`.
+
 | `wrap-debug`
 | -
 | No

src/cider/nrepl/middleware/content_type.clj

@@ -112,7 +112,7 @@
 (defmethod content-type-response java.awt.Image [{^java.awt.Image image :value :as response}]
   (with-open [bos (ByteArrayOutputStream.)]
     (ImageIO/write image "png" ^OutputStream bos)
-    (merge response (when (ImageIO/write ^RenderedImage value "png" ^OutputStream bos)
+    (merge response (when (ImageIO/write ^RenderedImage image "png" ^OutputStream bos)
                       (slurp-reply "" ["image/png" {}] (.toByteArray bos))))))
 
 (defn content-type-transport
@@ -126,7 +126,7 @@
     (recv [_this timeout]
       (.recv transport timeout))
 
-    (send [this response]
+    (send [_this response]
       (.send transport (content-type-response response)))))
 
 (defn handle-content-type