How are parameters sent in an HTTP POST request

Question

In an HTTP GET request  parameters are sent as a query string   http   example com page parameter value also another  In an HTTP POST request  the parameters are not sent along with the URI   Where are the values  In the request header  In the request body  What does it look like

User · Accepted Answer

The values are sent in the request body  in the format that the content type specifies   Usually the content type is application x-www-form-urlencoded  so the request body uses the same format as the query string   parameter value amp also another   When you use a file upload in the form  you use the multipart form-data encoding instead  which has a different format  It s more complicated  but you usually don t need to care what it looks like  so I won t show an example  but it can be good to know that it exists

User · Answer

The default media type in a POST request is application x-www-form-urlencoded  This is a format for encoding key-value pairs  The keys can be duplicate  Each key-value pair is separated by an  amp  character  and each key is separated from its value by an   character   For example   Name  John Smith Grade  19   Is encoded as   Name John Smith amp Grade 19   This is placed in the request body after the HTTP headers

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Some of the webservices require you to place request data and metadata separately  For example a remote function may expect that the signed metadata string is included in a URI  while the data is posted in a HTTP-body   The POST request may semantically look like this   POST   AuthId YOURKEY amp Action WebServiceAction amp Signature rcLXfkPldrYm04 HTTP 1 1 Content-Type  text tab-separated-values  charset iso-8859-1 Content-Length     Host  webservices domain com Accept  text html application xhtml xml application xml q 0 9     q 0 8 Accept-Encoding  identity User-Agent  Mozilla 3 0  compatible  Indy Library   name    id John    G12N Sarah   J87M Bob     N33Y   This approach logically combines QueryString and Body-Post using a single Content-Type which is a  parsing-instruction  for a web-server   Please note  HTTP 1 1 is wrapped with the  32  space  on the left and with  10  Line feed  on the right

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The content is put after the HTTP headers   The format of an HTTP POST is to have the HTTP headers  followed by a blank line  followed by the request body   The POST variables are stored as key-value pairs in the body   You can see this in the raw content of an HTTP Post  shown below   POST  path script cgi HTTP 1 0 From  frog jmarshall com User-Agent  HTTPTool 1 0 Content-Type  application x-www-form-urlencoded Content-Length  32  home Cosby amp favorite flavor flies   You can see this using a tool like Fiddler  which you can use to watch the raw HTTP request and response payloads being sent across the wire

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You cannot type it directly on the browser URL bar   You can see how POST data is sent on the Internet with Live HTTP Headers for example  Result will be something like that  http   127 0 0 1 pass php POST  pass php HTTP 1 1  Host  127 0 0 1 User-Agent  Mozilla 5 0  Windows NT 6 1  WOW64  rv 18 0  Gecko 20100101 Firefox 18 0 Accept  text html application xhtml xml application xml q 0 9     q 0 8 Accept-Language  en-US en q 0 5 Accept-Encoding  gzip  deflate DNT  1 Referer  http   127 0 0 1 pass php Cookie  passx 87e8af376bc9d9bfec2c7c0193e6af70  PHPSESSID l9hk7mfh0ppqecg8gialak6gt5 Connection  keep-alive Content-Type  application x-www-form-urlencoded Content-Length  30 username zurfyx amp pass password   Where it says   Content-Length  30     username zurfyx amp pass password   will be the post values

User · Answer

Form values in HTTP POSTs are sent in the request body  in the same format as the querystring   For more information  see the spec

User · Answer

First of all  let s differentiate between GET and POST   Get  It is the default HTTP request that is made to the server and is used to retrieve the data from the server and query string that comes after   in a URI is used to retrieve a unique resource   this is the format  GET  someweb asp data value HTTP 1 0   here data value is the query string value passed   POST  It is used to send data to the server safely so anything that is needed  this is the format of a POST request  POST  somweb aspHTTP 1 0 Host  localhost Content-Type  application x-www-form-urlencoded   you can put any format here Content-Length  11   it depends Name  somename   Why POST over GET   In GET the value being sent to the servers are usually appended to the base URL in the query string now there are 2 consequences of this   The GET requests are saved in browser history with the parameters  So your passwords remain un-encrypted in browser history  This was a real issue for Facebook back in the days  Usually servers have a limit on how long a URI can be  If have too many parameters being sent you might receive 414 Error - URI too long    In case of post request your data from the fields are added to the body instead  Length of request params is calculated  and added to the header for content-length and no important data is directly appended to the URL   You can use the Google Developer Tools  network section to see basic information about how requests are made to the servers   and you can always add more values in your Request Headers like Cache-Control   Origin   Accept

User · Answer

Short answer  in POST requests  values are sent in the  body  of the request  With web-forms they are most likely sent with a media type of application x-www-form-urlencoded or multipart form-data  Programming languages or frameworks which have been designed to handle web-requests usually do  The Right Thing     with such requests and provide you with easy access to the readily decoded values  like   REQUEST or   POST in PHP  or cgi FieldStorage    flask request form in Python      Now let s digress a bit  which may help understand the difference     The difference between GET and POST requests are largely semantic  They are also  used  differently  which explains the difference in how values are passed   GET  relevant RFC section   When executing a GET request  you ask the server for one  or a set of entities  To allow the client to filter the result  it can use the so called  query string  of the URL  The query string is the part after the    This is part of the URI syntax   So  from the point of view of your application code  the part which receives the request   you will need to inspect the URI query part to gain access to these values   Note that the keys and values are part of the URI  Browsers may impose a limit on URI length  The HTTP standard states that there is no limit  But at the time of this writing  most browsers do limit the URIs  I don t have specific values   GET requests should never be used to submit new information to the server  Especially not larger documents  That s where you should use POST or PUT   POST  relevant RFC section   When executing a POST request  the client is actually submitting a new document to the remote host  So  a query string does not  semantically  make sense  Which is why you don t have access to them in your application code   POST is a little bit more complex  and way more flexible    When receiving a POST request  you should always expect a  payload   or  in HTTP terms  a message body  The message body in itself is pretty useless  as there is no standard  as far as I can tell  Maybe application octet-stream   format  The body format is defined by the Content-Type header  When using a HTML FORM element with method  POST   this is usually application x-www-form-urlencoded  Another very common type is multipart form-data if you use file uploads  But it could be anything  ranging from text plain  over application json or even a custom application octet-stream   In any case  if a POST request is made with a Content-Type which cannot be handled by the application  it should return a 415 status-code   Most programming languages  and or web-frameworks  offer a way to de encode the message body from to the most common types  like application x-www-form-urlencoded  multipart form-data or application json   So that s easy  Custom types require potentially a bit more work   Using a standard HTML form encoded document as example  the application should perform the following steps    Read the Content-Type field If the value is not one of the supported media-types  then return a response with a 415 status code otherwise  decode the values from the message body    Again  languages like PHP  or web-frameworks for other popular languages will probably handle this for you  The exception to this is the 415 error  No framework can predict which content-types your application chooses to support and or not support  This is up to you   PUT  relevant RFC section   A PUT request is pretty much handled in the exact same way as a POST request  The big difference is that a POST request is supposed to let the server decide how to  and if at all  create a new resource  Historically  from the now obsolete RFC2616 it was to create a new resource as a  subordinate   child  of the URI where the request was sent to    A PUT request in contrast is supposed to  deposit  a resource exactly at that URI  and with exactly that content  No more  no less  The idea is that the client is responsible to craft the complete resource before  PUTting  it  The server should accept it as-is on the given URL   As a consequence  a POST request is usually not used to replace an existing resource  A PUT request can do both create and replace   Side-Note  There are also  path parameters  which can be used to send additional data to the remote  but they are so uncommon  that I won t go into too much detail here  But  for reference  here is an excerpt from the RFC      Aside from dot-segments in hierarchical paths  a path segment is considered   opaque by the generic syntax   URI producing applications often use the   reserved characters allowed in a segment to delimit scheme-specific or   dereference-handler-specific subcomponents   For example  the semicolon         and equals       reserved characters are often used to delimit parameters and   parameter values applicable to that segment   The comma       reserved   character is often used for similar purposes   For example  one URI producer   might use a segment such as  name v 1 1  to indicate a reference to version   1 1 of  name   whereas another might use a segment such as  name 1 1  to   indicate the same   Parameter types may be defined by scheme-specific   semantics  but in most cases the syntax of a parameter is specific   to the implementation of the URIs dereferencing algorithm

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