jessequ
/
AMQP-CPP
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Merge pull request #468 from jacksonn-gtc/updated-docs 

Updated README.md
This commit is contained in:
Emiel Bruijntjes 2022-07-16 09:28:25 +02:00 committed by GitHub
parent 4d09ec5a9c 8bd8ad0b7d
commit badc4eafa3
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 295 additions and 223 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

518
README.md
View File

@ -4,30 +4,38 @@ AMQP-CPP
[![Build Status](https://travis-ci.org/CopernicaMarketingSoftware/AMQP-CPP.svg?branch=master)](https://travis-ci.org/CopernicaMarketingSoftware/AMQP-CPP)
[![Build status](https://ci.appveyor.com/api/projects/status/heh4n7gjwgqcugfn/branch/master?svg=true)](https://ci.appveyor.com/project/copernica/amqp-cpp/branch/master)
AMQP-CPP is a C++ library for communicating with a RabbitMQ message broker.
The library can be used to parse incoming data from, and generate frames to, a RabbitMQ server.
OVERVIEW
========
**Are you upgrading from AMQP-CPP 3 to AMQP-CPP 4?** [Please read the upgrade instructions](#upgrading)
AMQP-CPP is a C++ library for communicating with a RabbitMQ message broker. The
library can be used to parse incoming data from a RabbitMQ server, and to
generate frames that can be sent to a RabbitMQ server.
**Note for the reader:** This readme file has a peculiar structure. We start
explaining the pure and hard core low level interface in which you have to
take care of opening socket connections yourself. In reality, you probably want
to use the simpler TCP interface that is being described [later on](#tcp-connections).
<br>
This library has a layered architecture, and allows you - if you like - to
completely take care of the network layer. If you want to set up and manage the
network connections yourself, the AMQP-CPP library will not make a connection to
RabbitMQ by itself, nor will it create sockets and/or perform IO operations. As
a user of this library, you create the socket connection and implement a certain
interface that you pass to the AMQP-CPP library and that the library will use
for IO operations.
a user of this library, you create the socket connection and implement an interface
defined by AMQP-CPP, passing it to the AMQP-CPP library to use for IO operations.
Intercepting this network layer is however optional, the AMQP-CPP library also
comes with a predefined TCP and TLS module that can be used if you trust the AMQP
library to take care of the network (and optional TLS) handling. In that case, the
AMQP-CPP library does all the system and library calls to set up network connections
and send and receive the (possibly encrypted) data.
Intercepting this network layer is optional. The AMQP-CPP library comes with a
predefined TCP and TLS module that can be used if you trust the AMQP library
to take care of the network (and optional TLS) handling. In that case, the
AMQP-CPP library does all the system and library calls to set up network
connections, and send/receive the (possibly encrypted) data.
This layered architecture makes the library extremely flexible and portable: it
This layered architecture makes the library flexible and portable: it
does not necessarily rely on operating system specific IO calls, and can be
easily integrated into any kind of event loop. If you want to implement the AMQP
protocol on top of some [unusual other communication layer](https://tools.ietf.org/html/rfc1149),
protocol on top of some [other unusual communication layer](https://tools.ietf.org/html/rfc1149),
this library can be used for that - but if you want to use it with regular TCP
connections, setting it up is just as easy.
@ -37,14 +45,32 @@ it can be used in high performance applications without the need for threads.
The AMQP-CPP library uses C++11 features, so if you intend to use it, please make
sure that your compiler is up-to-date and supports C++11.
**Note for the reader:** This readme file has a peculiar structure. We start
explaining the pure and hard core low level interface in which you have to
take care of opening socket connections yourself. In reality, you probably want
to use the simpler TCP interface that is being described [later on](#tcp-connections).
TABLE OF CONTENTS
=================
* [Overview](#overview)
* [About](#about)
* [How to install](#how-to-install)
* [How to use AMQP-CPP](#how-to-use-amqp-cpp)
* [Parsing incoming data](#parsing-incoming-data)
* [TCP connections](#tcp-connections)
* [Secure connections](#secure-connections)
* [Existing event loops](#existing-event-loops)
* [Heartbeats](#heartbeats)
* [Channels](#channels)
* [Channel callbacks](#channel-callbacks)
* [Channel errors](#channel-errors)
* [Flags and Tables](#flags-and-tables)
* [Publishing messages](#publishing-messages)
* [Publisher confirms](#publishing-confirms)
* [Consuming messages](#consuming-messages)
* [Upgrading](#upgrading)
* [Work in progress](#work-in-progress)
ABOUT
=====
[Back to Table of Contents](#table-of-contents)
This library is created and maintained by Copernica (www.copernica.com), and is
used inside the MailerQ (www.mailerq.com) and Yothalot (www.yothalot.com) applications.
@ -63,19 +89,27 @@ Then check out our other commercial and open source solutions:
* Yothalot big data processor (www.yothalot.com)
INSTALLING
==========
HOW TO INSTALL
==============
[Back to Table of Contents](#table-of-contents)
Start by cloning the repository and navigating to the `AMQP-CPP` directory.
```bash
git clone https://github.com/CopernicaMarketingSoftware/AMQP-CPP.git
cd AMQP-CPP
```
There are two methods to compile AMQP-CPP: CMake and Make. CMake is platform portable
and works on all systems, while the Makefile only works on Linux. The two methods
create both a shared and a static version of the AMQP-CPP library. Building of a
shared library is currently not supported on Windows.
AMQP-CPP comes with an optional Linux-only TCP module that takes care of the
network part required for the AMQP-CPP core library. If you use this module, you
are required to link with `pthread` and `dl`.
There are two methods to compile AMQP-CPP: CMake and Make. CMake is platform portable
and works on all systems, while the Makefile only works on Linux. The two methods
create both a shared and a static version of the AMQP-CPP library. Building of a
shared library is currently not supported on Windows.
After building there are two relevant files to #include when you use the library.
After building there are two relevant files to `#include` when you use the library.
File | Include when?
---------------------|--------------------------------------------------------
@ -100,40 +134,59 @@ cmake --build . --target install
Option | Default | Meaning
-------------------------|---------|-----------------------------------------------------------------------
AMQP-CPP_BUILD_SHARED | OFF | Static lib(OFF) or shared lib(ON)? Shared is not supported on Windows.
AMQP-CPP_LINUX_TCP | OFF | Should the Linux-only TCP module be built?
AMQP-CPP_BUILD_SHARED | OFF | OFF for static lib, ON for shared lib. Shared is not supported on Windows.
AMQP-CPP_LINUX_TCP | OFF | ON to build TCP module. TCP module is supported for Linux only.
## Using make
Compiling and installing AMQP-CPP with make is as easy as running `make` and
then `make install`. This will install the full version of AMQP-CPP, including
the system specific TCP module. If you do not need the additional TCP module
(because you take care of handling the network stuff yourself), you can also
compile a pure form of the library. Use `make pure` and `make install` for that.
Compiling and installing AMQP-CPP with make is as easy as running:
When you compile an application that uses the AMQP-CPP library, do not
forget to link with the library. For gcc and clang the linker flag is -lamqpcpp.
If you use the fullblown version of AMQP-CPP (with the TCP module), you also
need to pass the -lpthread and -ldl linker flags, because the TCP module uses a
thread for running an asynchronous and non-blocking DNS hostname lookup, and it
must be linked with the "dl" library to allow dynamic lookups for functions from
the openssl library if a secure connection to RabbitMQ has to be set up.
```bash
make
make install
```
This will install the full version of AMQP-CPP, including
the system specific TCP module.
To install without the TCP module (so that you can handle
network connection yourself), run:
```bash
make pure
make install
```
## Compiling a program
When you compile an application that uses the AMQP-CPP library, remember to link
with the library. For gcc and clang the linker flag is `-lamqpcpp`.
If you use the TCP module, you also need to pass the `-lpthread` and `-ldl`
linker flags. The TCP module uses a thread for running an asynchronous
and non-blocking DNS hostname lookup, and it must be linked with the `dl` library to
allow dynamic lookups for functions from the openssl library if a secure connection
to RabbitMQ has to be set up.
An example compilation command for an application using the TCP module:
```bash
g++ -g -Wall -lamqcpp -lpthread -ldl my-amqp-cpp.c -o my-amqp-cpp
```
HOW TO USE AMQP-CPP
===================
[Back to Table of Contents](#table-of-contents)
As we mentioned above, the library can be used in a network-agnostic fashion.
It then does not do any IO by itself, and you need to pass an object to the
library that the library can use for IO. So, before you start using the
library, you first need to create a class that extends from the
ConnectionHandler base class. This is a class with a number of methods that are
called by the library every time it wants to send out data, or when it needs to
inform you that an error occurred.
AMQP-CPP operates in a network-agnostic fashion. It does not do IO by itself.
An object must be provided that defines the IO operations. We have provided the
`ConnectionHandler` base class for you to extend from and create your own object.
This class defines a number of methods called by the library any time it wants
to send data, or if it wants to notify you an error has occurred.
````c++
#include <amqpcpp.h>
// You'll need to extend the ConnectionHandler class and make your own, like this
class MyConnectionHandler : public AMQP::ConnectionHandler
{
/**
@ -198,9 +251,10 @@ class MyConnectionHandler : public AMQP::ConnectionHandler
};
````
After you've implemented the ConnectionHandler class (which is entirely up to
you), you can start using the library by creating a Connection object, and one
or more Channel objects:
After you've implemented the `ConnectionHandler` class the way you like,
you can start using the library by creating a `Connection` object, and one
or more `Channel` objects:
````c++
// create an instance of your own connection handler
@ -218,44 +272,50 @@ channel.declareQueue("my-queue");
channel.bindQueue("my-exchange", "my-queue", "my-routing-key");
````
A number of remarks about the example above. First you may have noticed that we've
created all objects on the stack. You are of course also free to create them
on the heap with the C++ operator 'new'. That works just as well, and is in real
life code probably more useful as you normally want to keep your handlers, connection
and channel objects around for a longer time.
A number of remarks about the example above. You may notice that we've
created all objects on the stack. You are also free to create them
on the heap with the C++ operator `new`. That works just as well, and
in a real project you will likely want to keep your `Handler`, `Connection`,
and `Channel` objects around for a longer time.
But more importantly, you can see in the example above that we instantiated the
channel object directly after we made the connection object, and we also
started declaring exchanges and queues right away. However, under the hood, a handshake
protocol is executed between the server and the client when the Connection
object is first created. During this handshake procedure it is not permitted to send
other instructions (like opening a channel or declaring a queue). It would therefore have been better
if we had first waited for the connection to be ready (implement the MyConnectionHandler::onReady() method),
and create the channel object only then. But this is not strictly necessary.
The methods that are called before the handshake is completed are cached by the
AMQP library and will be executed the moment the handshake is completed and the
connection becomes ready for use.
`Channel` object directly after we made the `Connection` object, and we also
started declaring exchanges and queues right away.
However, under the hood, a handshake protocol is executed between the
server and the client when the `Connection` object is first created.
During this handshake procedure other operations are
not permitted (like opening a channel or declaring a queue).
It would be better practice to wait for the connection to be ready
(implementing the `MyConnectionHandler::OnReady()` method) and creating the
`Channel` object only then.
However, this is not strictly necessary. Methods called during a handshake
are cached by the AMQP library, and will be executed the moment the handshake
is completed and the connection becomes ready for use.
PARSING INCOMING DATA
=====================
[Back to Table of Contents](#table-of-contents)
The ConnectionHandler class has a method onData() that is called by the library
every time that it wants to send out data. We've explained that it is up to you to
implement that method. Inside your ConnectionHandler::onData() method, you can for
example call the "send()" or "write()" system call to send out the data to
The `ConnectionHandler` class has a method `onData()` that is called by the library
every time that it wants to send data. The `onData` method is implemented by you, the user.
For example, you might make system calls to `send()` or `write()` to send data to
the RabbitMQ server. But what about data in the other direction? How does the
library receive data back from RabbitMQ?
library receive data from RabbitMQ?
In this raw setup, the AMQP-CPP library does not do any IO by itself and it is
therefore also not possible for the library to receive data from a
socket. It is again up to you to do this. If, for example, you notice in your
event loop that the socket that is connected with the RabbitMQ server becomes
readable, you should read out that socket (for example by using the recv() system
In this raw setup, the AMQP-CPP library does not do IO by itself, and so does not
receive any data from a socket. You will have to create a socket that connects to
the RabbitMQ server yourself.
Inside your event loop, after checking the socket is readable,
you should read out that socket (for example by using the `recv()` system
call), and pass the received bytes to the AMQP-CPP library. This is done by
calling the parse() method in the Connection object.
calling the `parse()` method in the `Connection` object.
The Connection::parse() method gets two parameters, a pointer to a buffer of
The `Connection::parse()` method gets two parameters, a pointer to a buffer of
data that you just read from the socket, and a parameter that holds the size of
this buffer. The code snippet below comes from the Connection.h C++ header file.
@ -283,40 +343,42 @@ size_t parse(char *buffer, size_t size)
````
You should do all the book keeping for the buffer yourselves. If you for example
call the Connection::parse() method with a buffer of 100 bytes, and the method
call the `Connection::parse()` method with a buffer of 100 bytes, and the method
returns that only 60 bytes were processed, you should later call the method again,
with a buffer filled with the remaining 40 bytes. If the method returns 0, you should
make a new call to parse() when more data is available, with a buffer that contains
make a new call to `parse()` when more data is available, with a buffer that contains
both the old data, and the new data.
To optimize your calls to the parse() method, you _could_ use the Connection::expected()
and Connection::maxFrame() methods. The expected() method returns the number of bytes
that the library prefers to receive next. It is pointless to call the parse() method
To optimize your calls to the `parse()` method, you _could_ use the `Connection::expected()`
and `Connection::maxFrame()` methods. The `expected()` method returns the number of bytes
that the library prefers to receive next. It is pointless to call the `parse()` method
with a smaller buffer, and it is best to call the method with a buffer of exactly this
size. The maxFrame() returns the max frame size for AMQP messages. If you read your
size. The `maxFrame()` returns the max frame size for AMQP messages. If you read your
messages into a reusable buffer, you could allocate this buffer up to this size, so that
you never will have to reallocate.
TCP CONNECTIONS
===============
[Back to Table of Contents](#table-of-contents)
Although the AMQP-CPP library gives you extreme flexibility by letting you setup
your own network connections, the reality is that most if not all AMQP connections
use the TCP protocol. To help you out, the library therefore also comes with a
your own network connections, the reality is that virtually all AMQP connections
use the TCP protocol. To help you out, the library also comes with a
TCP module that takes care of setting up the network connections, and sending
and receiving the data.
If you want to use this TCP module, you should not use the AMQP::Connection
and AMQP::Channel classes that you saw above, but the alternative AMQP::TcpConnection
and AMQP::TcpChannel classes instead. You also do not have to create your own class
that implements the "AMQP::ConnectionHandler" interface - but a class that inherits
from "AMQP::TcpHandler" instead. This AMQP::TcpHandler class contains a set of
methods that you can override to intercept all sort of events that occur during the
TCP and AMQP connection lifetime. Overriding these methods is mostly optional, because
almost all have a default implementation. But you do need to implement the
"monitor()" method, as that is needed by the AMQP-CPP library to interact with
the main event loop:
With the TCP module, you should not use the `AMQP::Connection`
and `AMQP::Channel` classes that you saw above, but the alternative `AMQP::TcpConnection`
and `AMQP::TcpChannel` classes instead. The `AMQP::ConnectionHandler` goes unused here as well;
In a TCP connection, you create a class that extends from `AMQP::TcpHandler` instead.
This `AMQP::TcpHandler` class contains a set of methods that you can override to intercept
all sort of events that occur during the TCP and AMQP connection lifetime. Overriding these
methods is mostly optional, because almost all have a default implementation.
What does need to be implemented by the user is the `monitor()` method,
as that is needed by the AMQP-CPP library to interact with the main event loop.
````c++
#include <amqpcpp.h>
@ -460,22 +522,21 @@ class MyTcpHandler : public AMQP::TcpHandler
};
````
You see that there are many methods in TcpHandler that you can implement. The most important
one is "monitor()". This method is used to integrate the AMQP filedescriptors in your
You see that there are many methods in `TcpHandler` that you can implement. The most important
one is `monitor()`. This method is used to integrate the AMQP filedescriptors in your
application's event loop. For some popular event loops (libev, libuv, libevent), we
have already added example handler objects (see the next section for that). All the
other methods are optional to override. It often is a good idea to override the
onError() method to log or report errors and onDetached() for cleaning up stuff.
AMQP-CPP has it's own buffers if you send instructions prematurely, but if you
`onError()` method to log or report errors and `onDetached()` for cleaning up stuff.
AMQP-CPP has its own buffers if you send instructions prematurely, but if you
intend to send a lot of data over the connection, it also is a good idea to
implement the onReady() method and delay your calls until the AMQP connection
implement the `onReady()` method and delay your calls until the AMQP connection
has been fully set up.
Using the TCP module of the AMQP-CPP library is easier than using the
raw AMQP::Connection and AMQP::Channel objects, because you do not have to
create the sockets and connections yourself, and you also do not have to take
care of buffering network data. The example that we gave above, looks slightly
different if you make use of the TCP module:
raw `AMQP::Connection` and `AMQP::Channel` objects. You do not have to
create the sockets and connections yourself, nor do you handle buffering the data.
The example that we gave above looks slightly different if you make use of the TCP module:
````c++
// create an instance of your own tcp handler
@ -498,6 +559,7 @@ channel.bindQueue("my-exchange", "my-queue", "my-routing-key");
SECURE CONNECTIONS
==================
[Back to Table of Contents](#table-of-contents)
The TCP module of AMQP-CPP also supports setting up secure connections. If your
RabbitMQ server accepts SSL connections, you can specify the address to your
@ -515,13 +577,12 @@ AMQP::TcpConnection connection(&myHandler, address);
````
There are two things to take care of if you want to create a secure connection:
(1) you must link your application with the -lssl flag (or use dlopen()), and (2)
you must initialize the openssl library by calling OPENSSL_init_ssl(). This
initializating must take place before you let you application connect to RabbitMQ.
(1) you must link your application with the `-lssl` flag (or use `dlopen()`), and (2)
you must initialize the openssl library by calling `OPENSSL_init_ssl()`. This
initialization must take place before you connect to RabbitMQ.
This is necessary because AMQP-CPP needs access to the openssl library to set up
secure connections. It can only access this library if you have linked your
application with this library, or if you have loaded this library at runtime
using dlopen()).
secure connections. It can only access this library if you have linked it to your
application, or if you have loaded this library at runtime using `dlopen()`.
Linking openssl is the normal thing to do. You just have to add the `-lssl` flag
to your linker. If you however do not want to link your application with openssl,
@ -540,11 +601,10 @@ AMQP::openssl(handle);
````
By itself, AMQP-CPP does not check if the created TLS connection is sufficient
secure. Whether the certificate is expired, self-signed, missing or invalid: for
AMQP-CPP it all doesn't matter and the connection is simply permitted. If you
want to be more strict (for example: if you want to verify the server's certificate),
you must do this yourself by implementing the "onSecured()" method in your handler
object:
secure. Whether the certificate is expired, self-signed, missing, or invalid:
AMQP-CPP will simply permit the connection. If you want to be more strict (for example:
if you want to verify the server's certificate), you must do this yourself by implementing
the `onSecured()` method in your handler object:
````c++
#include <amqpcpp.h>
@ -575,24 +635,24 @@ class MyTcpHandler : public AMQP::TcpHandler
};
````
The SSL pointer that is passed to the onSecured() method refers to the "SSL"
The SSL pointer that is passed to the `onSecured()` method refers to the "SSL"
structure from the openssl library.
EXISTING EVENT LOOPS
====================
[Back to Table of Contents](#table-of-contents)
Both the pure AMQP::Connection as well as the easier AMQP::TcpConnection class
Both the pure `AMQP::Connection` as well as the easier `AMQP::TcpConnection` class
allow you to integrate AMQP-CPP in your own event loop. Whether you take care
of running the event loop yourself (for example by using the select() system
of running the event loop yourself (for example by using the `select()` system
call), or if you use an existing library for it (like libevent, libev or libuv),
you can implement the "monitor()" method to watch the file descriptors and
you can implement the `monitor()` method to watch the file descriptors and
hand over control back to AMQP-CPP when one of the sockets become active.
For libev, libuv and libevent users, we have even implemented an example
implementation, so that you do not even have to do this. Instead of implementing
the monitor() method yourself, you can use the AMQP::LibEvHandler,
AMQP::LibUvHandler or AMQP:LibEventHandler classes instead:
the `monitor()` method yourself, you can use the `AMQP::LibEvHandler`,
`AMQP::LibUvHandler` or `AMQP:LibEventHandler` classes instead:
````c++
#include <ev.h>
@ -631,14 +691,14 @@ int main()
}
````
The AMQP::LibEvHandler and AMQP::LibEventHandler classes are extended AMQP::TcpHandler
classes, with an implementation of the monitor() method that simply adds the
The `AMQP::LibEvHandler` and `AMQP::LibEventHandler` classes are extended `AMQP::TcpHandler`
classes, with an implementation of the `monitor()` method that simply adds the
filedescriptor to the event loop. If you use this class, it is recommended not to
instantiate it directly (like we did in the example), but to create your own
"MyHandler" class that extends from it, and in which you also implement the
onError() method to report possible connection errors to your end users.
`onError()` method to report possible connection errors to your end users.
Currently, we have example TcpHandler implementations for libev, libuv,
Currently, we have example `TcpHandler` implementations for libev, libuv,
libevent, and Boost's asio. For other event loops we do not yet have
such examples. The quality of the libboostasio is however debatable: it was
not developed and is not maintained by the original AMQP-CPP developers, and
@ -653,6 +713,7 @@ it has a couple of open issues.
HEARTBEATS
==========
[Back to Table of Contents](#table-of-contents)
The AMQP protocol supports *heartbeats*. If this heartbeat feature is enabled, the
client and the server negotiate a heartbeat interval during connection setup, and
@ -671,8 +732,8 @@ lasting algorithms after you've consumed a message from RabbitMQ, without having
to worry about the connection being idle for too long.
You can however choose to enable these heartbeats. If you want to enable heartbeats,
you should implement the onNegotiate() method inside your ConnectionHandler or
TcpHandler class and have it return the interval that you find appropriate.
you should implement the `onNegotiate()` method inside your `ConnectionHandler` or
`TcpHandler` class and have it return the interval that you find appropriate.
````c++
#include <amqpcpp.h>
@ -713,12 +774,13 @@ during the heartbeat interval. It is also your responnsibility to shutdown
the connection if you find out that the server stops sending data during
this period.
If you use the AMQP::LibEvHandler event loop implementation, heartbeats are
If you use the `AMQP::LibEvHandler` event loop implementation, heartbeats are
enabled by default, and all these checks are automatically performed.
CHANNELS
========
[Back to Table of Contents](#table-of-contents)
In the above example we created a channel object. A channel is a sort of virtual
connection, and it is possible to create many channels that all use
@ -733,22 +795,22 @@ C++ header file for a list of all available methods. Every method in it is well
documented.
All operations that you can perform on a channel are non-blocking. This means
that it is not possible for a method (like Channel::declareExchange()) to
immediately return 'true' or 'false'. Instead, almost every method of the Channel
class returns an instance of the 'Deferred' class. This 'Deferred' object can be
that it is not possible for a method (like `Channel::declareExchange()`) to
immediately return `true` or `false`. Instead, almost every method of the `Channel`
class returns an instance of the `Deferred` class. This `Deferred` object can be
used to install handlers that will be called in case of success or failure.
For example, if you call the channel.declareExchange() method, the AMQP-CPP library
For example, if you call the `channel.declareExchange()` method, the AMQP-CPP library
will send a message to the RabbitMQ message broker to ask it to declare the
queue. However, because all operations in the library are asynchronous, the
declareExchange() method can not return 'true' or 'false' to inform you whether
`declareExchange()` method can not return `true` or `false` to inform you whether
the operation was successful or not. Only after a while, after the instruction
has reached the RabbitMQ server, and the confirmation from the server has been
sent back to the client, the library can report the result of the declareExchange()
sent back to the client, the library can report the result of the `declareExchange()`
call.
To prevent any blocking calls, the channel.declareExchange() method returns a
'Deferred' result object, on which you can set callback functions that will be
To prevent any blocking calls, the `channel.declareExchange()` method returns a
`Deferred` result object, on which you can set callback functions that will be
called when the operation succeeds or fails.
````c++
@ -767,34 +829,35 @@ myChannel.declareExchange("my-exchange")
});
````
As you can see in the above example, we call the declareExchange() method, and
As you can see in the above example, we call the `declareExchange()` method, and
treat its return value as an object, on which we immediately install a lambda
callback function to handle success, and to handle failure.
Installing the callback methods is optional. If you're not interested in the
result of an operation, you do not have to install a callback for it. Next
to the onSuccess() and onError() callbacks that can be installed, you can also
install a onFinalize() method that gets called directly after the onSuccess()
and onError() methods, and that can be used to set a callback that should
to the `onSuccess()` and `onError()` callbacks that can be installed, you can also
install a `onFinalize()` method that gets called directly after the `onSuccess()`
and `onError()` methods, and that can be used to set a callback that should
run in either case: when the operation succeeds or when it fails.
The signature for the onError() method is always the same: it gets one parameter
with a human readable error message. The onSuccess() function has a different
signature depending on the method that you call. Most onSuccess() functions
(like the one we showed for the declareExchange() method) do not get any
parameters at all. Some specific onSuccess callbacks receive extra parameters
The signature for the `onError()` method is always the same: it gets one parameter
with a human readable error message. The `onSuccess()` function has a different
signature depending on the method that you call. Most `onSuccess()` functions
(like the one we showed for the `declareExchange()` method) do not get any
parameters at all. Some specific `onSuccess()` callbacks receive extra parameters
with additional information.
CHANNEL CALLBACKS
=================
[Back to Table of Contents](#table-of-contents)
As explained, most channel methods return a 'Deferred' object on which you can
install callbacks using the Deferred::onError() and Deferred::onSuccess() methods.
As explained, most channel methods return a `Deferred` object on which you can
install callbacks using the `Deferred::onError()` and `Deferred::onSuccess()` methods.
The callbacks that you install on a Deferred object, only apply to one specific
The callbacks that you install on a `Deferred` object, only apply to one specific
operation. If you want to install a generic error callback for the entire channel,
you can do so by using the Channel::onError() method. Next to the Channel::onError()
you can do so by using the `Channel::onError()` method. Next to the `Channel::onError()`
method, you can also install a callback to be notified when the channel is ready
for sending the first instruction to RabbitMQ.
@ -818,7 +881,7 @@ myChannel.onReady([]() {
});
````
In theory, you should wait for the onReady() callback to be called before you
In theory, you should wait for the `onReady()` callback to be called before you
send any other instructions over the channel. In practice however, the AMQP library
caches all instructions that were sent too early, so that you can use the
channel object right after it was constructed.
@ -826,23 +889,26 @@ channel object right after it was constructed.
CHANNEL ERRORS
==============
[Back to Table of Contents](#table-of-contents)
It is important to realize that any error that occurs on a channel,
invalidates the entire channel, including all subsequent instructions that
were already sent over it. This means that if you call multiple methods in a row,
and the first method fails, all subsequent methods will not be executed either:
If a channel ever sees an error, the entire channel is invalidated, including
subsequent instructions that were already sent. This means that if you call
multiple methods in a row, and the first method fails, all subsequent methods
will not be executed:
````c++
Channel myChannel(&connection);
myChannel.declareQueue("my-queue");
myChannel.declareExchange("my-exchange");
myChannel.declareQueue("my-queue"); // If this method fails...
myChannel.declareExchange("my-exchange"); // ...this method will not execute.
````
If the first declareQueue() call fails in the example above, the second
myChannel.declareExchange() method will not be executed, even when this
second instruction was already sent to the server. The second instruction will be
ignored by the RabbitMQ server because the channel was already in an invalid
state after the first failure.
If the first `declareQueue()` call fails in the example above, the second
`myChannel.declareExchange()` method will not be executed, even when this
second instruction was already sent to the server.
The second instruction will be ignored by the RabbitMQ server
because the channel became invalid at the first instruction.
You can overcome this by using multiple channels:
@ -885,10 +951,11 @@ void myDeclareMethod(AMQP::Connection *connection)
FLAGS AND TABLES
================
[Back to Table of Contents](#table-of-contents)
Let's take a closer look at one method in the Channel object to explain
Let's take a closer look at one method in the `Channel` object to explain
two other concepts of this AMQP-CPP library: flags and tables. The method that we
will be looking at is the Channel::declareQueue() method - but we could've
will be looking at is the `Channel::declareQueue()` method - but we could've
picked a different method too because flags and
tables are used by many methods.
@ -909,7 +976,7 @@ tables are used by many methods.
* @param flags combination of flags
* @param arguments optional arguments
*/
DeferredQueue &declareQueue(const std::string &name, int flags, const Table &arguments);
DeferredQueue &declareQueue(const std::string &name, int flags, const Table &arguments); // This version is the most extensive
DeferredQueue &declareQueue(const std::string &name, const Table &arguments);
DeferredQueue &declareQueue(const std::string &name, int flags = 0);
DeferredQueue &declareQueue(int flags, const Table &arguments);
@ -921,9 +988,9 @@ As you can see, the method comes in many forms, and it is up to you to choose
the one that is most appropriate. We now take a look at the most complete
one, the method with three parameters.
All above methods returns a 'DeferredQueue' object. The DeferredQueue class
extends from the AMQP::Deferred class and allows you to install a more powerful
onSuccess() callback function. The 'onSuccess' method for the declareQueue()
All above methods returns a `DeferredQueue` object. The `DeferredQueue` class
extends from the `AMQP::Deferred` class and allows you to install a more powerful
`onSuccess()` callback function. The `onSuccess` method for the `declareQueue()`
function gets three arguments:
````c++
@ -938,20 +1005,20 @@ auto callback = [](const std::string &name, int msgcount, int consumercount) {
channel.declareQueue("myQueue").onSuccess(std::move(callback));
````
Just like many others methods in the Channel class, the declareQueue() method
accepts an integer parameter named 'flags'. This is a variable in which you can
Just like many others methods in the `Channel` class, the `declareQueue()` method
accepts an integer parameter named `flags`. This is a variable in which you can
set method-specific options, by summing up all the options that are described in
the documentation above the method. If you for example want to create a durable,
auto-deleted queue, you can pass in the value AMQP::durable + AMQP::autodelete.
auto-deleted queue, you can pass in the value `AMQP::durable + AMQP::autodelete`.
The declareQueue() method also accepts a parameter named 'arguments', which is of type
Table. This Table object can be used as an associative array to send additional
The `declareQueue()` method also accepts a parameter named `arguments`, which is of type
`Table`. This `Table` object can be used as an associative array to send additional
options to RabbitMQ, that are often custom RabbitMQ extensions to the AMQP
standard. For a list of all supported arguments, take a look at the documentation
on the RabbitMQ website. With every new RabbitMQ release more features, and
supported arguments are added.
The Table class is a very powerful class that enables you to build
The `Table` class is a very powerful class that enables you to build
complicated, deeply nested structures full of strings, arrays and even other
tables. In reality, you only need strings and integers.
@ -969,25 +1036,26 @@ channel.declareQueue("my-queue-name", AMQP::durable + AMQP::autodelete, argument
PUBLISHING MESSAGES
===================
[Back to Table of Contents](#table-of-contents)
Publishing messages is easy, and the Channel class has a list of methods that
Publishing messages is easy, and the `Channel` class has a list of methods that
can all be used for it. The most simple one takes three arguments: the name of the
exchange to publish to, the routing key to use, and the actual message that
you're publishing - all these parameters are standard C++ strings.
More extended versions of the publish() method exist that accept additional
arguments, and that enable you to publish entire Envelope objects. An envelope
More extended versions of the `publish()` method exist that accept additional
arguments, and that enable you to publish entire `Envelope` objects. An `Envelope`
is an object that contains the message plus a list of optional meta properties like
the content-type, content-encoding, priority, expire time and more. None of these
meta fields are interpreted by this library, and also the RabbitMQ ignores most
of them, but the AMQP protocol defines them, and they are free for you to use.
meta fields are interpreted by this library, and RabbitMQ ignores most
of them, but the AMQP protocol defines them and are free for you to use.
For an extensive list of the fields that are supported, take a look at the MetaData.h
header file (MetaData is the base class for Envelope). You should also check the
header file (`MetaData` is the base class for `Envelope`). You should also check the
RabbitMQ documentation to find out if an envelope header is interpreted by the
RabbitMQ server (at the time of this writing, only the expire time is being used).
The following snippet is copied from the Channel.h header file and lists all
available publish() methods. As you can see, you can call the publish() method
available `publish()` methods. As you can see, you can call the `publish()` method
in almost any form:
````c++
@ -1063,12 +1131,13 @@ and consuming.
PUBLISHER CONFIRMS
===================
[Back to Table of Contents](#table-of-contents)
RabbitMQ supports a lightweight method of confirming that broker received
and processed a message. When you enable this, RabbitMQ sends back an
'ack' or 'nack' for each publish-operation. For this to work, the channel
needs to be put in _confirm mode_. This is done using the
confirmSelect() method. When the channel is successfully put in confirm mode,
`confirmSelect()` method. When the channel is successfully put in confirm mode,
the server starts counting the received messages (starting from 1) and sends
acknowledgments for every message it processed (it can also acknowledge
multiple message at once).
@ -1076,7 +1145,7 @@ multiple message at once).
If server is unable to process a message, it will send send negative
acknowledgments. Both positive and negative acknowledgments handling are
passed to callbacks that you can install on the object that
is returned by the confirmSelect() method:
is returned by the `confirmSelect()` method:
````c++
// setup confirm mode and ack/nack callbacks (from this moment onwards
@ -1106,10 +1175,10 @@ channel.confirmSelect().onSuccess([&]() {
If you use this feature, you will have to implement your own bookkeeping to
track which messages have already been acked/nacked, and which messages
are still being handled. For your convenience however, the AMQP-CPP library
are still being handled. For your convenience, the AMQP-CPP library
comes with a number of helper classes that can take over this responsibility.
The AMQP::Reliable class is an optional wrapper around channels. When you use
The `AMQP::Reliable` class is an optional wrapper around channels. When you use
it, your underlying channel is automatically put it _confirm method_, and all publish
operations are individually acknowledged:
@ -1149,24 +1218,24 @@ reliable.publish("my-exchange", "my-key", "my first message").onAck([]() {
````
In the above example we have implemented four callback methods. In a real life
application, implementing the onAck() and onLost() is normally sufficient.
application, implementing the `onAck()` and `onLost()` is normally sufficient.
Publisher-confirms are often useful in situations where you need reliability.
If you want to have certainty about whether your message was handled by RabbitMQ
or not, you can enable this feature, either by explicitly calling channel.confirmSelect()
if you want to do your own bookkeeping, or using AMQP::Reliable for a simpler
or not, you can enable this feature. Call `channel.confirmSelect()`
if you want to do your own bookkeeping, or using `AMQP::Reliable` for a simpler
API.
But it also is useful for flood prevention. RabbitMQ turns out not to be very
good at handling big loads of publish-operations. If you publish messages faster
But it also is useful for flood prevention. RabbitMQ is not great
at handling big loads of publish-operations. If you publish messages faster
than RabbitMQ can handle, a server-side buffer builds up, and RabbitMQ gets slow
(which causes the buffer to build up even further, et cetera). With publish-confirms
(which causes the buffer to build up even further, etc). With publish-confirms
you can keep the messages in your own application, and only proceed with publishing
them when your previous messages have been handled. With this approach you
prevent that RabbitMQ gets overloaded. We call it throttling.
You can build your own throttling mechanism using the confirmSelect() approach
or the AMQP::Reliable class. Or you use AMQP::Throttle:
You can build your own throttling mechanism using the `confirmSelect()` approach
or the `AMQP::Reliable` class. Or you use `AMQP::Throttle`:
````c++
// create a channel
@ -1187,9 +1256,9 @@ for (size_t i = 0; i < 100000; ++i)
}
````
The AMQP::Reliable and AMQP::Throttle classes both wrap around a channel.
The `AMQP::Reliable` and `AMQP::Throttle` classes both wrap around a channel.
But what if you want to use both? You want to throttle messages, but also like
to install your own callbacks for onAck and onLost? This is possible too:
to install your own callbacks for `onAck` and `onLost`? This is possible too:
````c++
// create a channel
@ -1220,12 +1289,13 @@ For more information, see http://www.rabbitmq.com/confirms.html.
CONSUMING MESSAGES
==================
[Back to Table of Contents](#table-of-contents)
Fetching messages from RabbitMQ is called consuming, and can be started by calling
the method Channel::consume(). After you've called this method, RabbitMQ starts
the method `Channel::consume()`. After you've called this method, RabbitMQ starts
delivering messages to you.
Just like the publish() method that we just described, the consume() method also
Just like the `publish()` method that we just described, the `consume()` method also
comes in many forms. The first parameter is always the name of the queue you like
to consume from. The subsequent parameters are an optional consumer tag, flags and
a table with custom arguments. The first additional parameter, the consumer tag,
@ -1272,15 +1342,15 @@ DeferredConsumer &consume(const std::string &queue, int flags = 0);
DeferredConsumer &consume(const std::string &queue, const AMQP::Table &arguments);
````
As you can see, the consume method returns a DeferredConsumer. This object is a
regular Deferred, with additions. The onSuccess() method of a
DeferredConsumer is slightly different than the onSuccess() method of a regular
Deferred object: one extra parameter will be supplied to your callback function
As you can see, the consume method returns a `DeferredConsumer`. This object is a
regular `Deferred`, with additions. The `onSuccess()` method of a
`DeferredConsumer` is slightly different than the `onSuccess()` method of a regular
`Deferred` object: one extra parameter will be supplied to your callback function
with the consumer tag.
The onSuccess() callback will be called when the consume operation _has started_,
The `onSuccess()` callback will be called when the consume operation _has started_,
but not when messages are actually consumed. For this you will have to install
a different callback, using the onReceived() method.
a different callback, using the `onReceived()` method.
````c++
// callback function that is called when the consume operation starts
@ -1312,24 +1382,24 @@ channel.consume("my-queue")
````
The Message object holds all information of the delivered message: the actual
content, all meta information from the envelope (in fact, the Message class is
derived from the Envelope class), and even the name of the exchange and the
The `Message` object holds all information of the delivered message: the actual
content, all meta information from the envelope (in fact, the `Message` class is
derived from the `Envelope` class), and even the name of the exchange and the
routing key that were used when the message was originally published. For a full
list of all information in the Message class, you best have a look at the
list of all information in the `Message` class, you best have a look at the
message.h, envelope.h and metadata.h header files.
Another important parameter to the onReceived() method is the deliveryTag parameter.
Another important parameter to the `onReceived()` method is the `deliveryTag` parameter.
This is a unique identifier that you need to acknowledge an incoming message.
RabbitMQ only removes the message after it has been acknowledged, so that if your
application crashes while it was busy processing the message, the message does
not get lost but remains in the queue. But this means that after you've processed
the message, you must inform RabbitMQ about it by calling the Channel:ack() method.
the message, you must inform RabbitMQ about it by calling the `Channel:ack()` method.
This method is very simple and takes in its simplest form only one parameter: the
deliveryTag of the message.
`deliveryTag` of the message.
Consuming messages is a continuous process. RabbitMQ keeps sending messages, until
you stop the consumer, which can be done by calling the Channel::cancel() method.
you stop the consumer, which can be done by calling the `Channel::cancel()` method.
If you close the channel, or the entire TCP connection, consuming also stops.
RabbitMQ throttles the number of messages that are delivered to you, to prevent
@ -1339,35 +1409,37 @@ quality-of-service (QOS). The QOS setting is a numeric value which holds the num
of unacknowledged messages that you are allowed to have. RabbitMQ stops sending
additional messages when the number of unacknowledges messages has reached this
limit, and only sends additional messages when an earlier message gets acknowledged.
To change the QOS, you can simple call Channel::setQos().
To change the QOS, you can simple call `Channel::setQos()`.
UPGRADING
=========
[Back to Table of Contents](#table-of-contents)
AMQP-CPP 4.* is not always compatible with previous versions. Especially some
virtual methods in the ConnectionHandler and TcpHandler classes have been renamed
virtual methods in the `ConnectionHandler` and `TcpHandler` classes have been renamed
or are called during a different stage in the connection lifetime. Check
out this README file and the comments inside the connectionhandler.h and
tcphandler.h files to find out if your application has to be changed. You
should especially check the following:
- ConnectionHandler::onConnected has been renamed to ConnectionHandler::onReady
- TcpHandler::onConnected is now called sooner: when the TCP connection is
- `ConnectionHandler::onConnected` has been renamed to `ConnectionHandler::onReady`
- `TcpHandler::onConnected` is now called sooner: when the TCP connection is
established, instead of when the AMQP connection is ready for instructions.
- The new method TcpHandler::onReady is called when the AMQP connection is
ready to be used (this is the old behavior of TcpHandler::onConnected)
- TcpHandler::onError is no longer the last method that is called (TcpHandler::onLost
could be called and TcpHandler::onDetached will be called after the error too)
- TcpHandler::onClosed is now called to indicate the graceful end of the
- The new method `TcpHandler::onReady` is called when the AMQP connection is
ready to be used (this is the old behavior of `TcpHandler::onConnected`)
- `TcpHandler::onError` is no longer the last method that is called (`TcpHandler::onLost`
could be called and `TcpHandler::onDetached` will be called after the error too)
- `TcpHandler::onClosed` is now called to indicate the graceful end of the
AMQP protocol, and not the end of TCP connection.
- TcpHandler::onLost is called when the TCP connection is lost or closed.
- The new method TcpHandler::onDetached is a better alternative for cleanup
code instead of TcpHandler::onClosed and/or TcpHandler::onError.
- `TcpHandler::onLost` is called when the TCP connection is lost or closed.
- The new method `TcpHandler::onDetached` is a better alternative for cleanup
code instead of `TcpHandler::onClosed` and/or `TcpHandler::onError`.
WORK IN PROGRESS
================
[Back to Table of Contents](#table-of-contents)
Almost all AMQP features have been implemented. But the following things might
need additional attention:
@ -1381,7 +1453,7 @@ valid data). Also, when we now receive an answer from RabbitMQ that does not
match the request that we sent before, we do not report an error (this is also
an issue that only occurs in theory).
It would be nice to have sample implementations for the ConnectionHandler
It would be nice to have sample implementations for the `ConnectionHandler`
class that can be directly plugged into libev, libevent and libuv event loops.
For performance reasons, we need to investigate if we can limit the number of times