Add example payload modification plugin.
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add_subdirectory(message-timestamp)
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add_subdirectory(message-timestamp)
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add_subdirectory(payload-modification)
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DIRS= \
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DIRS= \
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message-timestamp
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message-timestamp \
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payload-modification
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.PHONY : all binary check clean reallyclean test install uninstall
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.PHONY : all binary check clean reallyclean test install uninstall
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15
plugins/README.md
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plugins/README.md
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# Plugins
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This directory contains plugins for use with Mosquitto.
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## Message timestamp
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This is an **example** plugin to demonstrate how it is possible to attach MQTT v5 properties to messages after they have been received, and before they are sent on to subscribers.
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This plugin attaches a user-property property to each message which contains the ISO-8601 timestamp of the time the message was received by the broker. This means it is possible for MQTT v5 clients to see how old a retained message is, for example.
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## Payload modification
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This is an **example** plugin to demonstrate how it is possible to modify the payload of messages after they have been received, and before they are sent on to subscribers.
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If you are considering using this feature, you should be very certain you have verified the payload is the correct format before modifying it.
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This plugin adds the text string "hello " to the beginning of each payload, so with anything other than simple plain text messages it will corrupt the payload contents.
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10
plugins/payload-modification/CMakeLists.txt
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plugins/payload-modification/CMakeLists.txt
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include_directories(${mosquitto_SOURCE_DIR} ${mosquitto_SOURCE_DIR}/include
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${STDBOOL_H_PATH} ${STDINT_H_PATH})
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add_library(mosquitto_payload_modification SHARED mosquitto_payload_modification.c)
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set_target_properties(mosquitto_payload_modification PROPERTIES
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POSITION_INDEPENDENT_CODE 1
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)
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set_target_properties(mosquitto_payload_modification PROPERTIES PREFIX "")
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install(TARGETS mosquitto_payload_modification RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}" LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}")
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26
plugins/payload-modification/Makefile
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plugins/payload-modification/Makefile
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include ../../config.mk
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.PHONY : all binary check clean reallyclean test install uninstall
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PLUGIN_NAME=mosquitto_payload_modification
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all : binary
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binary : ${PLUGIN_NAME}.so
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${PLUGIN_NAME}.so : ${PLUGIN_NAME}.c
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$(CROSS_COMPILE)$(CC) $(PLUGIN_CPPFLAGS) $(PLUGIN_CFLAGS) $(PLUGIN_LDFLAGS) -fPIC -shared $< -o $@
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reallyclean : clean
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clean:
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-rm -f *.o ${PLUGIN_NAME}.so *.gcda *.gcno
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check: test
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test:
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install: ${PLUGIN_NAME}.so
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$(INSTALL) -d "${DESTDIR}$(prefix)/lib"
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$(INSTALL) ${STRIP_OPTS} ${PLUGIN_NAME}.so "${DESTDIR}${prefix}/lib/${PLUGIN_NAME}.so"
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uninstall :
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-rm -f "${DESTDIR}${prefix}/lib/${PLUGIN_NAME}.so"
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/*
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Copyright (c) 2020 Roger Light <roger@atchoo.org>
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All rights reserved. This program and the accompanying materials
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are made available under the terms of the Eclipse Public License v1.0
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and Eclipse Distribution License v1.0 which accompany this distribution.
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The Eclipse Public License is available at
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http://www.eclipse.org/legal/epl-v10.html
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and the Eclipse Distribution License is available at
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http://www.eclipse.org/org/documents/edl-v10.php.
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Contributors:
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Roger Light - initial implementation and documentation.
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*/
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/*
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* This is an *example* plugin which demonstrates how to modify the payload of
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* a message after it is received by the broker and before it is sent on to
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* other clients.
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*
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* You should be very sure of what you are doing before making use of this feature.
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*
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* Compile with:
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* gcc -I<path to mosquitto-repo/include> -fPIC -shared mosquitto_payload_modification.c -o mosquitto_payload_modification.so
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*
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* Use in config with:
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*
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* plugin /path/to/mosquitto_payload_modification.so
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*
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* Note that this only works on Mosquitto 2.0 or later.
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*/
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#include <stdio.h>
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#include <string.h>
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#include "mosquitto_broker.h"
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#include "mosquitto_plugin.h"
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#include "mosquitto.h"
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#include "mqtt_protocol.h"
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static mosquitto_plugin_id_t *mosq_pid = NULL;
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static int callback_message(int event, void *event_data, void *userdata)
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{
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struct mosquitto_evt_message *ed = event_data;
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char *new_payload;
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int new_payloadlen;
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/* This simply adds "hello " to the front of every payload. You can of
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* course do much more complicated message processing if needed. */
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/* Calculate the length of our new payload */
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new_payloadlen = ed->payloadlen + strlen("hello ")+1;
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/* Allocate some memory - use
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* mosquitto_calloc/mosquitto_malloc/mosquitto_strdup when allocating, to
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* allow the broker to track memory usage */
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new_payload = mosquitto_calloc(1, new_payloadlen);
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if(new_payload == NULL){
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return MOSQ_ERR_NOMEM;
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}
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/* Print "hello " to the payload */
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snprintf(new_payload, new_payloadlen, "hello ");
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memcpy(new_payload+strlen("hello "), ed->payload, ed->payloadlen);
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/* Assign the new payload and payloadlen to the event data structure. You
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* must *not* free the original payload, it will be handled by the
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* broker. */
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ed->payload = new_payload;
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ed->payloadlen = new_payloadlen;
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return MOSQ_ERR_SUCCESS;
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}
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int mosquitto_plugin_version(void)
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{
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return 5;
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}
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int mosquitto_plugin_init(mosquitto_plugin_id_t *identifier, void **user_data, struct mosquitto_opt *opts, int opt_count)
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{
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mosq_pid = identifier;
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return mosquitto_callback_register(mosq_pid, MOSQ_EVT_MESSAGE, callback_message, NULL, NULL);
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}
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int mosquitto_plugin_cleanup(void *user_data, struct mosquitto_opt *opts, int opt_count)
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{
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return mosquitto_callback_unregister(mosq_pid, MOSQ_EVT_MESSAGE, callback_message, NULL);
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}
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