What s the Content-Length field in HTTP header

Question

What does it mean    Byte count of encoded content string with encoding specified in header  Character count of content string    Especially in case of Content-Type  application x-www-form-urlencoded

User · Answer

One octet is 8 bits  Content-length is the number of octets that the message body represents

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rfc2616     The Content-Length entity-header field indicates the size of the   entity-body  in decimal number of OCTETs  sent to the recipient or  in   the case of the HEAD method  the size of the entity-body that would   have been sent had the request been a GET    It doesn t matter what the content-type is   Extension at post below

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Consider if you have headers such as   content-encoding  gzip content-length  52098 content-type  text javascript  charset UTF-8   The content-length is the size of the compressed message body  in  octets   i e  in units of 8 bits  which happen to be  bytes  for all modern computers     The size of the actual message body can be something else  perhaps 150280 bytes    The number of characters can be different again  perhaps 150231 characters  because some unicode characters use multiple bytes  note UTF-8 is a standard encoding    So  different numbers depending on whether you care how much data is transmitted  or how much data is held  or how many symbols are seen  Of course  there is no guarantee that these headers will be provided

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It s the number of bytes of data in the body of the request or response   The body is the part that comes after the blank line below the headers

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The Content-Length entity-header field indicates the size of the entity-body  in decimal number of OCTETs  sent to the recipient or  in the case of the HEAD method  the size of the entity-body that would have been sent had the request been a GET      Content-Length       Content-Length      1 DIGIT   An example is     Content-Length  1024   Applications SHOULD use this field to indicate the transfer-length of the message-body   In PHP you would use something like this   header  Content-Length    filesize  filename      In case of  Content-Type  application x-www-form-urlencoded  the encoded data is sent to the processing agent designated so you can set the length or size of the data you are going to post

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The Content-Length header is a number denoting an the exact byte length of the HTTP body  The HTTP body starts immediately after the first empty line that is found after the start-line and headers   Generally the Content-Length header is used for HTTP 1 1 so that the receiving party knows when the current response  has finished  so the connection can be reused for another request        or request  in the case of request methods that have a body  such as POST  PUT or PATCH  Alternatively  Content-Length header can be omitted and a chunked Transfer-Encoding header can be used    If both Content-Length and Transfer-Encoding headers are missing  then at the end of the response the connection must be closed   The following resource is a guide that I found very useful when learning about HTTP    HTTP Made Really Easy

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According to the spec   The Content-Length entity-header field indicates the size of the entity-body  in decimal number of OCTETs  sent to the recipient or  in the case of the HEAD method  the size of the entity-body that would have been sent had the request been a GET  Content-Length       quot Content-Length quot   quot   quot  1 DIGIT  An example is Content-Length  3495  Applications SHOULD use this field to indicate the transfer-length of the message-body  unless this is prohibited by the rules in section 4 4  Any Content-Length greater than or equal to zero is a valid value  Section 4 4 describes how to determine the length of a message-body if a Content-Length is not given  Note that the meaning of this field is significantly different from the corresponding definition in MIME  where it is an optional field used within the  quot message external-body quot  content-type  In HTTP  it SHOULD be sent whenever the message s length can be determined prior to being transferred  unless this is prohibited by the rules in section 4 4

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From this page     The most common use of POST  by far    is to submit HTML form data to CGI   scripts  In this case  the   Content-Type  header is usually   application x-www-form-urlencoded     and the Content-Length  header gives   the length of the URL-encoded form   data  here s a note on URL-encoding     The CGI script receives the message   body through STDIN  and  decodes it    Here s a typical form submission    using POST   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

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From here      The Content-Length entity-header field   indicates the size of the entity-body    in decimal number of OCTETs  sent to   the recipient or  in the case of the   HEAD method  the size of the   entity-body that would have been sent   had the request been a GET       Content-Length       Content-Length      1 DIGIT       An example is      Content-Length  3495       Applications SHOULD use this field to   indicate the transfer-length of the   message-body  unless this is   prohibited by the rules in section   4 4        Any Content-Length greater than or   equal to zero is a valid value    Section 4 4 describes how to determine   the length of a message-body if a   Content-Length is not given        Note that the meaning of this field is   significantly different from the   corresponding definition in MIME    where it is an optional field used   within the  message external-body    content-type  In HTTP  it SHOULD be   sent whenever the message s length can   be determined prior to being   transferred  unless this is prohibited   by the rules in section 4 4    My interpretation is that this means the length  on the wire   i e  the length of the  encoded  content

[http-headers] What's the "Content-Length" field in HTTP header?

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