WebSockets protocol vs HTTP

Question

There are many blogs and discussions about WebSocket and HTTP  and many developers and sites strongly advocate WebSockets  but I still can not understand why  for example  arguments of WebSocket lovers     HTML5 Web Sockets represents the next evolution of web communications   a full-duplex  bidirectional communications channel that operates through a single socket over the Web    http   www websocket org quantum html     HTTP supports streaming  request body streaming you are using it while uploading large files  and response body streaming    During making the connection with WebSocket  client  and server exchange data per frame which is 2 bytes each  compared to 8 kilobytes of HTTP header when you do continuous polling    Why do that 2 bytes not include TCP and under TCP protocols overhead  GET  about html HTTP 1 1 Host  example org  This is  48 bytes HTTP header  HTTP chunked encoding - https   en wikipedia org wiki Chunked transfer encoding   23 This is the data in the first chunk 1A and this is the second one 3 con 8 sequence 0   So  the overhead per each chunk is not big   Also  both protocols work over TCP  so all TCP issues with long-live connections are still there  Questions   Why is the WebSockets protocol better  Why was it implemented instead of updating the HTTP protocol

User · Answer

For the TL DR  here are 2 cents and a simpler version for your questions   WebSockets provides these benefits over HTTP   Persistent stateful connection for the duration of the connection Low latency  near-real-time communication between server client due to no overhead of reestablishing connections for each request as HTTP requires  Full duplex  both server and client can send receive simultaneously   WebSocket and HTTP protocol have been designed to solve different problems  I E  WebSocket was designed to improve bi-directional communication whereas HTTP was designed to be stateless  distributed using a request response model  Other than sharing the ports for legacy reasons  firewall proxy penetration   there isn t much common ground to combine them into one protocol

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The other answers do not seem to touch on a key aspect here  and that is you make no mention of requiring supporting a web browser as a client  Most of the limitations of plain HTTP above are assuming you would be working with browser  JS implementations  The HTTP protocol is fully capable of full-duplex communication  it is legal to have a client perform a POST with a chunked encoding transfer  and a server to return a response with a chunked-encoding body  This would remove the header overhead to just at init time  So if all you re looking for is full-duplex  control both client and server  and are not interested in extra framing features of WebSockets  then I would argue that HTTP is a simpler approach with lower latency CPU  although the latency would really only differ in microseconds or less for either

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A regular REST API uses HTTP as the underlying protocol for communication  which follows the request and response paradigm  meaning the communication involves the client requesting some data or resource from a server  and the server responding back to that client  However  HTTP is a stateless protocol  so every request-response cycle will end up having to repeat the header and metadata information  This incurs additional latency in case of frequently repeated request-response cycles   With WebSockets  although the communication still starts off as an initial HTTP handshake  it is further upgraded to follow the WebSockets protocol  i e  if both the server and the client are compliant with the protocol as not all entities support the WebSockets protocol   Now with WebSockets  it is possible to establish a full-duplex and persistent connection between the client and a server  This means that unlike a request and a response  the connection stays open for as long as the application is running  i e  it   s persistent   and since it is full-duplex  two-way simultaneous communication is possible i e now the server is capable of initiating communication and  push  some data to the client when new data  that the client is interested in  becomes available   The WebSockets protocol is stateful and allows you to implement the Publish-Subscribe  or Pub Sub  messaging pattern which is the primary concept used in the real-time technologies where you are able to get new updates in the form of server push without the client having to request  refresh the page  repeatedly  Examples of such applications are Uber car s location tracking  Push Notifications  Stock market prices updating in real-time  chat  multiplayer games  live online collaboration tools  etc  You can check out a deep dive article on Websockets which explains the history of this protocol  how it came into being  what it   s used for and how you can implement it yourself  Here s a video from a presentation I did about WebSockets and how they are different from using the regular REST APIs  Standardisation and leveraging the exponential rise in data streaming

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You seem to assume that WebSocket is a replacement for HTTP  It is not  It s an extension  The main use-case of WebSockets are Javascript applications which run in the web browser and receive real-time data from a server  Games are a good example  Before WebSockets  the only method for Javascript applications to interact with a server was through XmlHttpRequest  But these have a major disadvantage  The server can t send data unless the client has explicitly requested it  But the new WebSocket feature allows the server to send data whenever it wants  This allows to implement browser-based games with a much lower latency and without having to use ugly hacks like AJAX long-polling or browser plugins  So why not use normal HTTP with streamed requests and responses In a comment to another answer you suggested to just stream the client request and response body asynchronously  In fact  WebSockets are basically that  An attempt to open a WebSocket connection from the client looks like a HTTP request at first  but a special directive in the header  Upgrade  websocket  tells the server to start communicating in this asynchronous mode  First drafts of the WebSocket protocol weren t much more than that and some handshaking to ensure that the server actually understands that the client wants to communicate asynchronously  But then it was realized that proxy servers would be confused by that  because they are used to the usual request response model of HTTP  A potential attack scenario against proxy servers was discovered  To prevent this it was necessary to make WebSocket traffic look unlike any normal HTTP traffic  That s why the masking keys were introduced in the final version of the protocol

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1  Why is the WebSockets protocol better   WebSockets is better for situations that involve low-latency communication especially for low latency for client to server messages  For server to client data you can get fairly low latency using long-held connections and chunked transfer  However  this doesn t help with client to server latency which requires a new connection to be established for each client to server message   Your 48 byte HTTP handshake is not realistic for real-world HTTP browser connections where there is often several kilobytes of data sent as part of the request  in both directions  including many headers and cookie data  Here is an example of a request response to using Chrome   Example request  2800 bytes including cookie data  490 bytes without cookie data    GET   HTTP 1 1 Host  www cnn com Connection  keep-alive Cache-Control  no-cache Pragma  no-cache Accept  text html application xhtml xml application xml q 0 9     q 0 8 User-Agent  Mozilla 5 0  X11  Linux x86 64  AppleWebKit 537 17  KHTML  like Gecko  Chrome 24 0 1312 68 Safari 537 17 Accept-Encoding  gzip deflate sdch Accept-Language  en-US en q 0 8 Accept-Charset  ISO-8859-1 utf-8 q 0 7   q 0 3 Cookie     2428 byte of cookie data      Example response  355 bytes    HTTP 1 1 200 OK Server  nginx Date  Wed  13 Feb 2013 18 56 27 GMT Content-Type  text html Transfer-Encoding  chunked Connection  keep-alive Set-Cookie  CG US TX Arlington  path   Last-Modified  Wed  13 Feb 2013 18 55 22 GMT Vary  Accept-Encoding Cache-Control  max-age 60  private Expires  Wed  13 Feb 2013 18 56 54 GMT Content-Encoding  gzip   Both HTTP and WebSockets have equivalent sized initial connection handshakes  but with a WebSocket connection the initial handshake is performed once and then small messages only have 6 bytes of overhead  2 for the header and 4 for the mask value   The latency overhead is not so much from the size of the headers  but from the logic to parse handle store those headers  In addition  the TCP connection setup latency is probably a bigger factor than the size or processing time for each request   2  Why was it implemented instead of updating HTTP protocol   There are efforts to re-engineer the HTTP protocol to achieve better performance and lower latency such as SPDY  HTTP 2 0 and QUIC  This will improve the situation for normal HTTP requests  but it is likely that WebSockets and or WebRTC DataChannel will still have lower latency for client to server data transfer than HTTP protocol  or it will be used in a mode that looks a lot like WebSockets anyways    Update    Here is a framework for thinking about web protocols    TCP  low-level  bi-directional  full-duplex  and guaranteed order transport layer  No browser support  except via plugin Flash   HTTP 1 0  request-response transport protocol layered on TCP  The client makes one full request  the server gives one full response  and then the connection is closed  The request methods  GET  POST  HEAD  have specific transactional meaning for resources on the server  HTTP 1 1  maintains the request-response nature of HTTP 1 0  but allows the connection to stay open for multiple full requests full responses  one response per request   Still has full headers in the request and response but the connection is re-used and not closed  HTTP 1 1 also added some additional request methods  OPTIONS  PUT  DELETE  TRACE  CONNECT  which also have specific transactional meanings  However  as noted in the introduction to the HTTP 2 0 draft proposal  HTTP 1 1 pipelining is not widely deployed so this greatly limits the utility of HTTP 1 1 to solve latency between browsers and servers  Long-poll  sort of a  hack  to HTTP  either 1 0 or 1 1  where the server does not respond immediately  or only responds partially with headers  to the client request  After a server response  the client immediately sends a new request  using the same connection if over HTTP 1 1   HTTP streaming  a variety of techniques  multipart chunked response  that allow the server to send more than one response to a single client request  The W3C is standardizing this as Server-Sent Events using a text event-stream MIME type  The browser API  which is fairly similar to the WebSocket API  is called the EventSource API  Comet server push  this is an umbrella term that includes both long-poll and HTTP streaming  Comet libraries usually support multiple techniques to try and maximize cross-browser and cross-server support  WebSockets  a transport layer built-on TCP that uses an HTTP friendly Upgrade handshake  Unlike TCP  which is a streaming transport  WebSockets is a message based transport  messages are delimited on the wire and are re-assembled in-full before delivery to the application  WebSocket connections are bi-directional  full-duplex and long-lived  After the initial handshake request response  there is no transactional semantics and there is very little per message overhead  The client and server may send messages at any time and must handle message receipt asynchronously  SPDY  a Google initiated proposal to extend HTTP using a more efficient wire protocol but maintaining all HTTP semantics  request response  cookies  encoding   SPDY introduces a new framing format  with length-prefixed frames  and specifies a way to layering HTTP request response pairs onto the new framing layer  Headers can be compressed and new headers can be sent after the connection has been established  There are real world implementations of SPDY in browsers and servers  HTTP 2 0  has similar goals to SPDY  reduce HTTP latency and overhead while preserving HTTP semantics  The current draft is derived from SPDY and defines an upgrade handshake and data framing that is very similar the the WebSocket standard for handshake and framing  An alternate HTTP 2 0 draft proposal  httpbis-speed-mobility  actually uses WebSockets for the transport layer and adds the SPDY multiplexing and HTTP mapping as an WebSocket extension  WebSocket extensions are negotiated during the handshake   WebRTC CU-WebRTC  proposals to allow peer-to-peer connectivity between browsers  This may enable lower average and maximum latency communication because as the underlying transport is SDP datagram rather than TCP  This allows out-of-order delivery of packets messages which avoids the TCP issue of latency spikes caused by dropped packets which delay delivery of all subsequent packets  to guarantee in-order delivery   QUIC  is an experimental protocol aimed at reducing web latency over that of TCP  On the surface  QUIC is very similar to TCP TLS SPDY implemented on UDP  QUIC provides multiplexing and flow control equivalent to HTTP 2  security equivalent to TLS  and connection semantics  reliability  and congestion control equivalentto TCP  Because TCP is implemented in operating system kernels  and middlebox firmware  making significant changes to TCP is next to impossible  However  since QUIC is built on top of UDP  it suffers from no such limitations  QUIC is designed and optimised for HTTP 2 semantics     References    HTTP    Wikipedia HTTP Page W3C List of HTTP related Drafts Protocols List of IETF HTTP 1 1 and HTTP 2 0 Drafts  Server-Sent Event    W3C Server-Sent Events EventSource Candidate Recommendation W3C Server-Sent Events EventSource Draft  WebSockets    IETF RFC 6455 WebSockets Protocol IETF RFC 6455 WebSocket Errata  SPDY    IETF SPDY Draft  HTTP 2 0     IETF HTTP 2 0 httpbis-http2 Draft IETF HTTP 2 0 httpbis-speed-mobility Draft IETF httpbis-network-friendly Draft - an older HTTP 2 0 related proposal  WebRTC    W3C WebRTC API Draft List of IETF WebRTC Drafts IETF WebRTC Overview Draft IETF WebRTC DataChannel Draft Microsoft CU-WebRTC Proposal Start Page  QUIC    QUIC Chrominum Project IETF QUIC Draft

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Why is the WebSockets protocol better  I don t think we can compare them side by side like who is better  That won t be a fair comparison simply because they are solving two different problems  Their requirements are different  It will be like comparing apples to oranges  They are different  HTTP is a request-response protocol  The client  browser  wants something  the server gives it  That is  If the data client wants is big  the server might send streaming data to void unwanted buffer problems  Here the main requirement or problem is how to make the request from clients and how to response the resources hypertext  they request  That is where HTTP shine   In HTTP  only client requests  The server only responds   WebSocket is not a request-response protocol where only the client can request  It is a socket very similar to TCP socket   Mean once the connection is open  either side can send data until the underlining TCP connection is closed  It is just like a normal socket  The only difference with TCP socket is WebSocket can be used on the web  On the web  we have many restrictions on a normal socket  Most firewalls will block other ports than 80 and 433 that HTTP used  Proxies and intermediaries will be problematic as well  So to make the protocol easier to deploy to existing infrastructures WebSocket use HTTP handshake to upgrade  That means when the first time connection is going to open  the client sent an HTTP request to tell the server saying  quot That is not HTTP request  please upgrade to WebSocket protocol quot   Upgrade  websocket Connection  Upgrade Sec-WebSocket-Key  x3JJHMbDL1EzLkh9GBhXDw   Sec-WebSocket-Protocol  chat  superchat Sec-WebSocket-Version  13  Once the server understands the request and upgraded to WebSocket protocol  none of the HTTP protocols applied anymore  So my answer is Neither one is better than each other  They are completely different  Why was it implemented instead of updating the HTTP protocol  Well  we can make everything under the name called HTTP as well  But shall we  If they are two different things  I will prefer two different names  So do Hickson and Michael Carter

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