src/plugins/http/http_plugin.rst

.. _http_plugin:

.. toctree::

HTTP Plugin
===========

Overview
--------

This plugin adds the HTTP protocol to VPP's Host Stack.
As a result parsing of HTTP/1 request or response is available for internal VPP applications.

Usage
-----

The plugin exposes following inline functions: ``http_validate_abs_path_syntax``, ``http_validate_query_syntax``,
``http_percent_decode``, ``http_path_remove_dot_segments``, ``http_parse_headers``, ``http_get_header``,
``http_free_header_table``.

It relies on the hoststack constructs and uses ``http_msg_data_t`` data structure for passing metadata to/from applications.

Server application
^^^^^^^^^^^^^^^^^^

Server application sets ``TRANSPORT_PROTO_HTTP`` as ``transport_proto`` in session endpoint configuration when registering to listen.

Receiving data
""""""""""""""

HTTP plugin sends message header with metadata for parsing, in form of offset and length, followed by all data bytes as received from transport.

Application will get pre-parsed following items:

* HTTP method
* target form
* target path offset and length
* target query offset and length
* header section offset and length
* body offset and length

The example below reads HTTP message header in ``builtin_app_rx_callback``, which is first step application should do:

.. code-block:: C

  #include <http/http.h>
  http_msg_t msg;
  rv = svm_fifo_dequeue (ts->rx_fifo, sizeof (msg), (u8 *) &msg);
  ASSERT (rv == sizeof (msg));

As next step application might validate message and method type, for example application only expects to receive GET requests:

.. code-block:: C

  if (msg.type != HTTP_MSG_REQUEST || msg.method_type != HTTP_REQ_GET)
    {
      /* your error handling */
    }

Now application can start reading HTTP data. First let's read the target path:

.. code-block:: C

  u8 *target_path;
  vec_validate (target_path, msg.data.target_path_len - 1);
  rv = svm_fifo_peek (ts->rx_fifo, msg.data.target_path_offset, msg.data.target_path_len, target_path);
  ASSERT (rv == msg.data.target_path_len);

Application might also want to know target form which is stored in ``msg.data.target_form``, you can read more about target forms in RFC9112 section 3.2.
In case of origin form HTTP plugin always sets ``target_path_offset`` after leading slash character.

Example bellow validates "absolute-path" rule, as described in RFC9110 section 4.1, in case of target in origin form, additionally application can get information if percent encoding is used and decode path:

.. code-block:: C

  int is_encoded = 0;
  if (msg.data.target_form == HTTP_TARGET_ORIGIN_FORM)
    {
      if (http_validate_abs_path_syntax (target_path, &is_encoded))
        {
          /* your error handling */
        }
      if (is_encoded)
        {
          u8 *decoded = http_percent_decode (target_path);
          vec_free (target_path);
          target_path = decoded;
        }
    }

More on topic when to decode in RFC3986 section 2.4.

When application serves static files, it is highly recommended to sanitize target path by removing dot segments (you don't want to risk path traversal attack):

.. code-block:: C

  u8 *sanitized_path;
  sanitized_path = http_path_remove_dot_segments (target_path);

Let's move to target query which is optional. Percent encoding might be used too, but we skip it for brevity:

.. code-block:: C

  u8 *target_query = 0;
  if (msg.data.target_query_len)
    {
      vec_validate (target_query, msg.data.target_query_len - 1);
      rv = svm_fifo_peek (ts->rx_fifo, msg.data.target_query_offset,
			  msg.data.target_query_len, target_query);
      ASSERT (rv == msg.data.target_query_len);
      if (http_validate_query_syntax (target_query, 0))
        {
          /* your error handling */
        }
    }

And now for something completely different, headers.
Headers are parsed using a generic algorithm, independent of the individual header names.
When header is repeated, its combined value consists of all values separated by comma, concatenated in order as received.
Following example shows how to parse headers:

.. code-block:: C

  if (msg.data.headers_len)
    {
      u8 *headers = 0;
      http_header_table_t *ht;
      vec_validate (headers, msg.data.headers_len - 1);
      rv = svm_fifo_peek (ts->rx_fifo, msg.data.headers_offset,
			  msg.data.headers_len, headers);
      ASSERT (rv == msg.data.headers_len);
      if (http_parse_headers (headers, &ht))
        {
          /* your error handling */
        }
      /* get Accept header */
      const char *accept_value = http_get_header (ht, HTTP_HEADER_ACCEPT);
      if (accept_value)
        {
          /* do something interesting */
        }
      http_free_header_table (ht);
      vec_free (headers);
    }

Finally application reads body:

.. code-block:: C

  u8 *body = 0;
  if (msg.data.body_len)
    {
      vec_validate (body, msg.data.body_len - 1);
      rv = svm_fifo_peek (ts->rx_fifo, msg.data.body_offset, msg.data.body_len, body);
      ASSERT (rv == msg.data.body_len);
    }