What is the technology behind wechat whatsapp and other messenger apps

Question

I am eager to know about the architecture of different real-time messenger apps  Are they using any generic protocol architecture

User · Answer

To my knowledge  Ejabberd  http   www ejabberd im   is the parent  this is XMPP server which provide quite good features of open source  Whatsapp uses some modified version of this  facebook messaging also uses a modified version of this  Some more chat applications likes Samsung s ChatOn  Nimbuzz messenger all use ejabberd based ones and Erlang solutions also have modified version of this ejabberd which they claim to be highly scalable and well tested with more performance improvements and renamed as MongooseIM    Ejabberd is the server which has most of the featured implemented when compared to other  Since it is build in Erlang it is highly scalable horizontally

User · Answer

The WhatsApp Architecture Facebook Bought For  19 Billion explains the architecture involved in design of whatsapp   Here is the general explanation from the link  WhatsApp server is almost completely implemented in Erlang   Server systems that do the backend message routing are done in Erlang   Great achievement is that the number of active users is managed with a really small server footprint  Team consensus is that it is largely because of Erlang   Interesting to note Facebook Chat was written in Erlang in 2009  but they went away from it because it was hard to find qualified programmers   WhatsApp server has started from ejabberd  Ejabberd is a famous open source Jabber server written in Erlang   Originally chosen because its open  had great reviews by developers  ease of start and the promise of Erlang   s long term suitability for large communication system   The next few years were spent re-writing and modifying quite a few parts of ejabberd  including switching from XMPP to internally developed protocol  restructuring the code base and redesigning some core components  and making lots of important modifications to Erlang VM to optimize server performance   To handle 50 billion messages a day the focus is on making a reliable system that works  Monetization is something to look at later  it   s far far down the road   A primary gauge of system health is message queue length  The message queue length of all the processes on a node is constantly monitored and an alert is sent out if they accumulate backlog beyond a preset threshold  If one or more processes falls behind that is alerted on  which gives a pointer to the next bottleneck to attack   Multimedia messages are sent by uploading the image  audio or video to be sent to an HTTP server and then sending a link to the content along with its Base64 encoded thumbnail  if applicable    Some code is usually pushed every day  Often  it   s multiple times a day  though in general peak traffic times are avoided  Erlang helps being aggressive in getting fixes and features into production  Hot-loading means updates can be pushed without restarts or traffic shifting  Mistakes can usually be undone very quickly  again by hot-loading  Systems tend to be much more loosely-coupled which makes it very easy to roll changes out incrementally   What protocol is used in Whatsapp app  SSL socket to the WhatsApp server pools  All messages are queued on the server until the client reconnects to retrieve the messages  The successful retrieval of a message is sent back to the whatsapp server which forwards this status back to the original sender  which will see that as a  quot checkmark quot  icon next to the message   Messages are wiped from the server memory as soon as the client has accepted the message  How does the registration process work internally in Whatsapp  WhatsApp used to create a username password based on the phone IMEI number  This was changed recently  WhatsApp now uses a general request from the app to send a unique 5 digit PIN  WhatsApp will then send a SMS to the indicated phone number  this means the WhatsApp client no longer needs to run on the same phone   Based on the pin number the app then request a unique key from WhatsApp  This key is used as  quot password quot  for all future calls   this  quot permanent quot  key is stored on the device   This also means that registering a new device will invalidate the key on the old device

User · Answer

WhatsApp has chosen Erlang a language built for writing scalable applications that are designed to withstand errors  Erlang uses an abstraction called the Actor model for it s concurrency - http   en wikipedia org wiki Actor  programming language  Instead of the more traditional shared memory approach  actors communicate by sending each other messages  Actors unlike threads are designed to be lightweight  Actors could be on the same machine or on different machines and the message passing abstractions works for both  A simple implementation of WhatsApp could be  Each user device is represented as an actor  This actor is responsible for handling the inbox of the user  how it gets serialized to disk  the messages that the user sends and the messages that the user receives  Let s assume that Alice and Bob are friends on WhatsApp  So there is an an Alice actor and a Bob actor   Let s trace a series of messages flowing back and forth           Alice decides to message Bob  Alice s phone establishes a connection to the WhatsApp server and it is established that this connection is definitely from Alice s phone  Alice now sends via TCP the following message   For Bob  A giant monster is attacking the Golden Gate Bridge   One of the WhatsApp front end server deserializes this message and delivers this message to the actor called Alice                  Alice the actor decides to serialize this and store it in a file called  Alice s Sent Messages   stored on a replicated file system to prevent data loss due to unpredictable monster rampage  Alice the actor then decides to forward this message to Bob the actor by passing it a message  Msg1 from Alice  A giant monster is attacking the Golden Gate Bridge   Alice the actor can retry with exponential back-off till Bob the actor acknowledges receiving the message                        Bob the actor eventually receives the message from  2  and decides to store this message in a file called  Bob s Inbox   Once it has stored this message durably Bob the actor will acknowledge receiving the message by sending Alice the actor a message of it s own saying  I received Msg1   Alice the actor can now stop it s retry efforts  Bob the actor then checks to see if Bob s phone has an active connection to the server  It does and so Bob the actor streams this message to the device via TCP                              Bob sees this message and replies with   For Alice  Let s create giant robots to fight them   This is now received by Bob the actor as outlined in Step 1  Bob the actor then repeats Step 2 and 3 to make sure Alice eventually receives the idea that will save mankind                            WhatsApp actually uses the XMPP protocol instead of the vastly superior protocol that I outlined above  but you get the point

[architecture] What is the technology behind wechat, whatsapp and other messenger apps?

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