From 5fd86e682bea3f6ff9256c8f67de21125805c0f6 Mon Sep 17 00:00:00 2001
From: steve-chavez <stevechavezast@gmail.com>
Date: Mon, 10 Feb 2020 12:00:04 -0500
Subject: [PATCH] Add setting headers via pre-request

---
 api.rst               | 37 +++++++++++++++++++++++++++++++++++++
 releases/upcoming.rst | 12 ++++++------
 2 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/api.rst b/api.rst
index 506cf35b9..dd234b769 100644
--- a/api.rst
+++ b/api.rst
@@ -1415,6 +1415,43 @@ PostgREST reads the ``response.headers`` SQL variable to add extra headers to th
 
 Notice that the variable should be set to an *array* of single-key objects rather than a single multiple-key object. This is because headers such as ``Cache-Control`` or ``Set-Cookie`` need to be repeated when setting multiple values and an object would not allow the repeated key.
 
+.. _pre_req_headers:
+
+Setting headers via pre-request
+-------------------------------
+
+By using a :ref:`pre-request` function, you can add headers to GET/POST/PATCH/PUT/DELETE responses.
+As an example, let's add some cache headers for all requests that come from an Internet Explorer(6 or 7) browser.
+
+.. code-block:: postgresql
+
+   create or replace function custom_headers() returns void as $$
+   declare
+     user_agent text := current_setting('request.header.user-agent', true);
+   begin
+     if user_agent similar to '%MSIE (6.0|7.0)%' then
+       perform set_config('response.headers',
+         '[{"Cache-Control": "no-cache, no-store, must-revalidate"}]', false);
+     end if;
+   end; $$ language plpgsql;
+
+   -- set this function on postgrest.conf
+   -- pre-request = custom_headers
+
+Now when you make a GET request to a table or view, you'll get the cache headers.
+
+.. code-block:: http
+
+  GET /people HTTP/1.1
+  User-Agent: Mozilla/4.01 (compatible; MSIE 6.0; Windows NT 5.1)
+
+  HTTP/1.1 200 OK
+  Content-Type: application/json; charset=utf-8
+  Cache-Control: no-cache, no-store, must-revalidate
+
+  ...
+
+
 Errors and HTTP Status Codes
 ----------------------------
 
diff --git a/releases/upcoming.rst b/releases/upcoming.rst
index cf8bb706c..4da513f6e 100644
--- a/releases/upcoming.rst
+++ b/releases/upcoming.rst
@@ -10,18 +10,18 @@ These are changes yet unreleased. If you'd like to try them out before a new off
 Added
 -----
 
-* Support for HTTP HEAD requests.
-  |br| -- `@steve-chavez <https://github.com/steve-chavez>`_
-
-* Add GUCs for :ref:`guc_req_path_method`.
-  |br| -- `@steve-chavez <https://github.com/steve-chavez>`_
-
 * Support for :ref:`planned_count` and :ref:`estimated_count`.
   |br| -- `@steve-chavez <https://github.com/steve-chavez>`_
 
 * Support for :ref:`Resource Embedding Disambiguation <embed_disamb>`.
   |br| -- `@steve-chavez <https://github.com/steve-chavez>`_
 
+* HTTP improvements -- `@steve-chavez <https://github.com/steve-chavez>`_
+
+   + Support for HTTP HEAD requests.
+   + GUCs for :ref:`guc_req_path_method`.
+   + Support for :ref:`pre_req_headers`.
+
 * Documentation reference for :ref:`s_proc_embed`.
 
 * Documentation reference for :ref:`mutation_embed`.