paho_mqtt_redis/lib.rs
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// mqtt.rust.redis/src/lib.rs
//
// Main library source file for 'mqtt-redis'.
//
// --------------------------------------------------------------------------
// Copyright (c) 2017-2023 Frank Pagliughi <fpagliughi@mindspring.com>
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// 1. Redistributions of source code must retain the above copyright notice,
// this list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// 3. Neither the name of the copyright holder nor the names of its
// contributors may be used to endorse or promote products derived from this
// software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
//! This is a small example of using Redis as the persistence store for the
//! Paho MQTT Rust client.
//!
//! It is an add-on library for use with the Eclipse Paho Rust MQTT Client
//! <https://github.com/eclipse/paho.mqtt.rust>
//!
//! The MQTT client library provides several mechanisms to persist QoS 1 & 2
//! messages while they are in transit. This helps to ensure that even if the
//! client application crashes, upon restart those messages can be retrieved
//! from the persistence store and re-sent to the server.
//!
//! The Paho library contains file/disk based persistence out of the box.
//! That is very useful, but on a Flash-based Embedded device, like an IoT
//! gateway, but continuous writes to the flash chip will wear it out
//! prematurely.
//!
//! So it would be nice to use a RAM-based cache that is outside the client
//! application's process. An instance of Redis, running locally, is a
//! nice solution.
//!
//! The Paho library allows the application to create a user-supplied
//! persistence object and register that with the client. The object simply
//! needs to implement the `paho_mqtt::ClientPersistence` trait. These
//! callbacks map to the operations on a key/value store, so Redis is a
//! perfect candidate to match the persistence API and act as a store.
//!
//! The MQTT callbacks map nearly 1:1 to Redis Hash commands:
//!
//! ```ignore
//! open() -> conect
//! close() -> disconnect
//!
//! put() -> HSET
//! get() -> HGET
//! remove() -> HDEL
//! keys() -> HKEYS
//! clear() -> DEL
//! contains_key() -> HEXISTS
//!```
//!
//! NOTE: Using Redis as an MQTT persistence store is an extremely viable
//! solution in a production IoT device or gateway, but it really only makes
//! sense to use it if the Redis server is running locally on the device
//! and connected via localhost or a UNIX socket. It _does not make sense_ to
//! use a remote Redis server for this purpose.
//!
#[macro_use]
extern crate log;
use paho_mqtt as mqtt;
use redis::{Client, Commands, Connection, RedisResult};
// --------------------------------------------------------------------------
/// The MQTT Redis persistence object.
/// An instance of this stuct can be residtered with an MQTT client to hold
/// messgaes in a Redis server until they are properly acknowledged by the
/// remote MQTT server. An instance of this object maps to a single hash
/// on a specific Redis server.
pub struct RedisPersistence {
/// The name of the Redis hash object.
/// This is formed as a combination of the MQTT server name/address
/// and the client ID string.
name: String,
/// The Redis client
client: Client,
/// The connection to the Redis client.
/// This is opened and closed on instruction from the MQTT client.
conn: Option<Connection>,
}
impl RedisPersistence {
/// Create a new persistence object to connect to a local Redis server.
pub fn new() -> Self {
Self::default()
}
}
impl Default for RedisPersistence {
/// Create a new persistence object to connect to the Redis server
/// on localhost.
fn default() -> Self {
Self {
name: "".to_string(),
client: Client::open("redis://localhost/").unwrap(),
conn: None,
}
}
}
impl mqtt::ClientPersistence for RedisPersistence {
/// Opena the connection to the Redis client.
fn open(&mut self, client_id: &str, server_uri: &str) -> mqtt::Result<()> {
self.name = format!("{}:{}", client_id, server_uri);
match self.client.get_connection() {
Ok(conn) => {
trace!("Redis persistence [{}]: open", self.name);
self.conn = Some(conn);
Ok(())
}
Err(e) => {
warn!("Redis persistence connect error: {:?}", e);
Err(mqtt::PersistenceError)
}
}
}
/// Close the connection to the Redis client.
fn close(&mut self) -> mqtt::Result<()> {
trace!("Client persistence [{}]: close", self.name);
if let Some(conn) = self.conn.take() {
drop(conn);
}
trace!("Redis close complete");
Ok(())
}
/// Store a persistent value to Redis.
/// We get a vector of buffer references for the data to store, which we
/// can concatenate into a single byte buffer to send to the server.
fn put(&mut self, key: &str, buffers: Vec<&[u8]>) -> mqtt::Result<()> {
trace!("Client persistence [{}]: put key '{}'", self.name, key);
let conn = self.conn.as_mut().ok_or(mqtt::PersistenceError)?;
let buf: Vec<u8> = buffers.concat();
debug!("Putting key '{}' with {} bytes", key, buf.len());
redis::cmd("HSET")
.arg(&self.name)
.arg(key)
.arg(buf)
.execute(conn);
Ok(())
}
/// Get the data buffer for the requested key.
/// Although the value sent to the server was a collection of buffers,
/// we can return them as a single, concatenated buffer.
fn get(&mut self, key: &str) -> mqtt::Result<Vec<u8>> {
trace!("Client persistence [{}]: get key '{}'", self.name, key);
let conn = self.conn.as_mut().ok_or(mqtt::PersistenceError)?;
if let Ok(v) = conn.hget(&self.name, key) as RedisResult<Vec<u8>> {
debug!("Found key {} with {} bytes", key, v.len());
Ok(v)
} else {
Err(mqtt::PersistenceError)
}
}
/// Remove the value with the specified `key` from the store.
fn remove(&mut self, key: &str) -> mqtt::Result<()> {
trace!("Client persistence [{}]: remove key '{}'", self.name, key);
let conn = self.conn.as_mut().ok_or(mqtt::PersistenceError)?;
if let Ok(res) = conn.hdel(&self.name, key) as RedisResult<usize> {
if res != 0 {
debug!("Removed key: {}", key);
} else {
debug!("Key not found (assuming OK): {}", key);
}
// Either way, if key is not in the store we report success.
return Ok(());
}
Err(mqtt::PersistenceError)
}
/// Return a collection of all the keys in the store for this client.
fn keys(&mut self) -> mqtt::Result<Vec<String>> {
trace!("Client persistence [{}]: keys", self.name);
let conn = self.conn.as_mut().ok_or(mqtt::PersistenceError)?;
if let Ok(v) = conn.hkeys(&self.name) as RedisResult<Vec<String>> {
debug!("Found keys: {:?}", v);
Ok(v)
} else {
warn!("Error looking for keys");
Err(mqtt::PersistenceError)
}
}
/// Remove all the data for this client from the store.
fn clear(&mut self) -> mqtt::Result<()> {
trace!("Client persistence [{}]: clear", self.name);
let conn = self.conn.as_mut().unwrap(); // TODO: Check for error?
if let Ok(_res) = conn.del(&self.name) as RedisResult<usize> {
// res==1 means hash/store deleted, 0 means it wasn't found.
// Either way, it's gone, so return success
return Ok(());
}
Err(mqtt::PersistenceError)
}
/// Determines if the store for this client contains the specified `key`.
fn contains_key(&mut self, key: &str) -> bool {
trace!("Client persistence [{}]: contains key '{}'", self.name, key);
let conn = match self.conn.as_mut() {
Some(conn) => conn,
None => return false,
};
if let Ok(res) = conn.hexists(&self.name, key) as RedisResult<usize> {
debug!("'contains' query returned: {:?}", res);
res != 0
} else {
false
}
}
}