net: lib: http_server: add static fs resource

adds filesystem as a resource for the http_server which serves static
(gzipped) files from a filesystem to the client.

Signed-off-by: Gerhard Jörges <joerges@metratec.com>

doc/connectivity/networking/api/http_server.rst

@@ -187,6 +187,38 @@ following code to the application's ``CMakeLists.txt`` file:
 
 where ``src/index.html`` is the location of the webpage to be compressed.
 
+Static filesystem resources
+===========================
+
+Static filesystem resource content is defined build-time and is immutable. The following
+example shows how the path can be defined as a static resource in the application:
+
+.. code-block:: c
+
+    struct http_resource_detail_static_fs static_fs_resource_detail = {
+        .common = {
+            .type                              = HTTP_RESOURCE_TYPE_STATIC_FS,
+            .bitmask_of_supported_http_methods = BIT(HTTP_GET),
+        },
+        .fs_path = "/lfs1/www",
+    };
+
+    HTTP_RESOURCE_DEFINE(static_fs_resource, my_service, "*", &static_fs_resource_detail);
+
+All files located in /lfs1/www are made available to the client. If a file is
+gzipped, .gz must be appended to the file name (e.g. index.html.gz), then the
+server delivers index.html.gz when the client requests index.html and adds gzip
+content-encoding to the HTTP header.
+
+The content type is evaluated based on the file extension. The server supports
+.html, .js, .css, .jpg, .png and .svg. More content types can be provided with the
+:c:macro:`HTTP_SERVER_CONTENT_TYPE` macro. All other files are provided with the
+content type text/html.
+
+.. code-block:: c
+
+    HTTP_SERVER_CONTENT_TYPE(json, "application/json")
+
 Dynamic resources
 =================