.. Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. .. include:: ../../../common.defs .. _developer-plugins-http-transformations-append: Append Transform Plugin *********************** The append_transform plugin appends text to the body of an HTTP response. It obtains this text from a file; the name of the file containing the append text is a parameter you specify in ``plugin.config``, as follows: :: append_transform.so path/to/file The append_transform plugin is based on ``null_transform.c``. The only difference is that after the plugin feeds the document through the transformation, it adds text to the response. Below is a list of the functions in ``append_transform.c``, in the order they appear in the source code. Below each entry is a description of what the function does: - **``my_data_alloc``** Allocates and initializes a ``MyData`` structure. The plugin defines a struct, ``MyData``, as follows: .. code-block:: c typedef struct { TSVIO output_vio; TSIOBuffer output_buffer; TSIOBufferReader output_reader; int append_needed; } MyData; The ``MyData`` structure is used to represent data that the transformation (vconnection) needs. The transformation's data pointer is set to a ``MyData`` pointer using ``TSContDataSet`` in the ``handle_transform`` routine. - **``my_data_destroy``** Destroys objects of type ``MyData``. To deallocate the transform's data, the ``append_transform`` routine (see below) calls ``my_data_destroy`` when the transformation is complete. - **``handle_transform``** This function does the actual data transformation. The transformation is created in ``transform_add`` (see below). ``handle_transform`` is called by ``append_transform``. - **``append_transform``** This is the handler function for the transformation vconnection created in ``transform_add``. It is the implementation of the vconnection. - If the transformation vconnection has been closed, then ``append_transform`` calls ``my_data_destroy`` to destroy the vonnection. - If ``append_transform`` receives an error event, then it calls back the continuation to let it know it has completed the write operation. - If it receives a ``WRITE_COMPLETE`` event, then it shuts down the write portion of its vconnection. - If it receives a ``WRITE_READY`` or any other event (such as ``TS_HTTP_RESPONSE_TRANSFORM_HOOK``), then it calls ``handle_transform`` to attempt to transform more data. - **``transformable``** The plugin transforms only documents that have a content type of ``text/html``. This function examines the ``Content-Type`` MIME header field in the response header. If the value of the MIME field is ``text/html``, then the function returns 1; otherwise, it returns zero. - **``transform_add``** Creates the transformation for the current transaction and sets up a transformation hook. The handler function for the transformation is ``append_transform``. - **``transform_plugin``** This is the handler function for the main continuation for the plugin. Traffic Server calls this function whenever it reads an HTTP response header. ``transform_plugin`` does the following: - Gets a handle to the HTTP transaction being processed - Calls ``transformable`` to determine whether the response document content is of type ``text/html`` - If the content is transformable, then it calls ``transform_add`` to create the transformation. - Calls ``TSHttpTxnReenable`` to continue the transaction - **``load``** Opens the file containing the text to be appended and loads the contents of the file into an ``TSIOBuffer`` called ``append_buffer``. - **``TSPluginInit``** Does the following: - Checks to make sure that the required configuration information (the append text filename) is entered in ``plugin.config`` correctly. - If there is a filename, then ``TSPluginInit`` calls load to load the text. - Creates a continuation for the plugin. The handler for this continuation is ``transform_plugin``. - Adds the plugin's continuation to ``TS_HTTP_READ_RESPONSE_HDR_HOOK``. In other words, it sets up a callback of the plugin's continuation when Traffic Server reads HTTP response headers.