1、 Preface

Developers who have experience in mobile terminal development have a deep understanding of it ： Mobile IM Development of , With the traditional PC End IM There's a big difference , Unreliable wireless networks in particular 、 The limitation of mobile hardware resources , Leading to a complete mobile terminal IM Architecture design and implementation are full of a lot of challenges . This article will briefly describe the mobile terminal IM The most important aspects of architecture design and communication protocol selection , Hope for IM Some inspiration from developers .（ This article is published synchronously in ：http://www.52im.net/thread-289-1-1.html）

2、 Exchange of learning

- Instant messaging development communication group ： 215891622 [ recommend ]

- Mobile IM Develop recommended articles ：《 Beginner level one is enough ： Develop mobile from scratch IM》

3、 summary

The advent of the mobile Internet era urges all our developers to start from the perspective of users , Create an application based on a specific scenario , Meet the needs of users . Usually , In these applications , Communication is essential . This requires entrepreneurs not only to spend time and energy to figure out what pain points users need in a particular scenario , Figure out how to address this need , And it may take more energy and time to solve the problems in the product “ communicate ” This technology node .

And to solve communication problems , You need a set IM System （ And it must support mobile terminals ）. As IM Developers may soon become IM The developer's technicians ,IM The value and importance of . But in terms of technical implementation , It's not easy . Of course , Suppose you have 100 Users , Everything is easy , But suppose you have 100 ten thousand 、1000 Wan even 1 Million users , The simplest technical node cannot be solved well , Will become a disaster , Moreover, IM System （ Especially on the mobile end IM System ） There are still many technical difficulties and pits .

4、 About mobile IM Communication protocol

secondly , Let's see IM How to choose the protocol . Usually IM The agreements adopted are xmpp、mqtt、protobuf And other data communication private protocols , Let's analyze their advantages and disadvantages one by one .

1. XMPP agreement ：

advantage ： be based on xml agreement , Easy to understand , Widely used , extensible .
shortcoming ： There's a lot of traffic , The mobile terminal also consumes electricity . The interaction process is complex . Many by pc Product use in the era , Not suitable for the mobile era IM product , Even if we are based on xmpp Improvement , Simplify the handshake process , Improve the file transfer mechanism , But its genes determine how to improve , He is not suitable for the era of mobile Internet IM product . Just like Sister Feng, no matter how cosmetic , Nor can it become a high circle .

2. MQTT agreement ：

advantage ： Adapt to multiple platforms .
shortcoming ： Simple protocol , But you need to expand your friends , Group and other functions .

3. Private agreements ：

advantage ： Follow one's inclinations , Define your own , The flow is small .
shortcoming ： Huge workload , Expandability of , It needs to be considered comprehensively .

4. Protobuf agreement ：

advantage ： A very small 、 Very fast 、 It's simple , For one message data Protobuf The serialized size is JSON Of 1/10、XML Format 1/20、 Is binary serialized 1/10.
shortcoming ： Cannot represent complex data structures , But for IM Speaking of , Enough already . This agreement is highly recommended .

Add 1： For strong columns, it is recommended to use Protobuf, For the following reasons

flexible 、 Efficient ： flexible （ Convenient interface update ）、 Efficient （ Efficiency goes through google The optimization of the , The transmission efficiency is higher than that of ordinary XML Much higher ）;
Easy to use ： Developers define structured message formats by following certain syntax , Then send it to the command line tool , The tool will automatically generate relevant classes , Can support java、c++、python And other language environments . By including these classes in the project , You can easily call relevant methods to complete the serialization and deserialization of business messages .
Language support ： Native support c++、java、python Wait up to 10 More than one language .

Add 2：Protobuf Mainly applicable to

Need to exchange messages with other systems , Very sensitive to message size . that protobuf Fit , It has nothing to do with language , The message space is relatively small xml and json Wait, save a lot .
Small data occasions . If you are big data , It's not suitable for .
The project language is c++、java、python etc. , Because they can use google Source class library , Serialization and deserialization are very efficient . Other languages need to be written by a third party or yourself , The efficiency of serialization and deserialization is not guaranteed .

Overall speaking ,Protobuf It's still very easy to use , Tools used by many open source systems for data communication , stay google It is also the core basic library .

（ More articles ：《 The strong proposal will Protobuf As your IM application data transfer format 》、《 How to choose the data transmission format of instant messaging application 》、《 Combining theory with practice ： A typical set of IM Communication protocol design details 》）

5、 Mobile IM Client's pit

Last , Let's learn more about the difficulties of the mobile terminal that need to be solved .

1. Traffic ：
What kind of agreement 、 Picture thumbnail 、 The compression of attachments determines the size of traffic .

2. Power consumption ：
(1) The smaller the flow , The lower the power consumption .(2) Heartbeat strategy , Reduce the number of heartbeats , Power consumption will be reduced .

3. The duration of the heartbeat ：
wifi,2G,3G,4G, Move 、 telecom 、 Unicom , Different networks , Different operators ,NAT The failure time is different , So the time of heartbeat is different .

4. network connections ：
cmnet and cmwap Lower connection processing mechanism .

5. Network instability ：
The biggest feature of mobile terminal is the instability of network , In an unstable network state , How to ensure that messages arrive at the fastest speed ？ How to avoid reconnection storm ？ These need to be considered from the overall architecture , It also needs to adopt ingenious strategies at the mobile end to avoid .

（ More articles ： Mobile IM The technical problems that development needs to face ）

6、 Mobile IM The pit of architecture design

First , Let's look at the mobile terminal IM Architecture design needs to consider .

1. Connector design ：
The connector is mainly used to manage the long connection of the client . The best single connector at present 8G8 The core server can do 70 ten thousand —100 Wan's connection , And some developers can only do 4000 Left and right connections , There are several orders of magnitude . Where is the mystery here ？

2. The design of middleware ：
Whether communication middleware is adopted ？ What are the benefits of communication middleware ？ If middleware is not used , How to manage the connection relationship between the connector and the logical server ？

3. Logical server ：
Logical servers are usually simpler , It is mainly to divide the minimum granularity according to the business logic . But even so , There are still many developers who put together seemingly relevant but actually irrelevant logic , Such as authentication and message Put the servers together .

4. State server ：
The status server mainly manages users online 、 Offline related status , The scheme of central node needs to be adopted , Otherwise the state will be out of sync . Here, we mainly need to consider the data storage mechanism corresponding to the state server , How to write , How to read ？ In order to maximize the processing capacity and response speed of the status server .

5. Database design ：
Database design is the most difficult , It is also the bottleneck of expansion . Because no matter for sql（ Relational type ） Database or nosql（ Non relational ） database , All have the limits of read-write processing , Then you need to consider how to partition the database （ According to what principle 、 What operation 、 Which users access the database on which node ）. At the same time, we need to consider each atomic operation （ Like landing ） Which libraries need to be read , Write which libraries . Only these indicators are clear , You can assume that there is 100 Million concurrent users ,100 In the case of 10000 concurrent messages , Accurately evaluate how many servers the server needs , How to deploy .

6. other ：
And the processing of device push , What kind of mechanism can ensure that messages are not lost , How to handle offline messages , wait . These are necessary and very complex function points and technical requirements , We need to adopt the correct architecture and strategy to achieve .

（ More articles ：http://www.52im.net/forum.php?mod=collection&action=view&ctid=7）

7、 Conclusion

The above difficulties and pit points are only recorded in a thousand words , But we should really solve these problems and meet the production and application standards , But I don't know how many days and nights it takes 、 How many lines of code to knock down , I'm afraid I've only really done IM Developers have a deeper understanding .（ This article is published synchronously in ：http://www.52im.net/thread-289-1-1.html）

appendix ： more IM Technical articles

author ：Jack Jiang ( Click the author name to enter Github)
Source ：http://www.52im.net/space-uid-1.html
communication ： Welcome to the instant messaging development exchange group 215891622
Discuss ：http://www.52im.net/
Jack Jiang At the same time 【 original Java Swing Appearance engineering BeautyEye】 and 【 Lightweight mobile instant messaging framework MobileIMSDK】 The author of , You can go to download and exchange .