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HTTP Conditional Request

Overview#

HTTP Conditional Requests are defined in RFC 7232 and several HTTP Header Fields are called conditional headers, lead to HTTP Conditional Request.

These are:

  • If-Match - Succeeds if the Etag of the distant resource is equal to one listed in this header. By default, unless the etag is prefixed with 'W/', it performs a strong validation.
  • If-None-Match - Succeeds if the Etag of the distant resource is different to each listed in this header. By default, unless the etag is prefixed with 'W/', it performs a strong validation.
  • If-Modified-Since - Succeeds if the Last-Modified date of the distant resource is more recent than the one given in this header.
  • If-Unmodified-Since - Succeeds if the Last-Modified date of the distant resource is older or the same than the one given in this header.
  • If-Range - Similar to If-Match, or If-Unmodified-Since, but can have only one single etag, or one date. If it fails, the range request fails, and instead of a HTTP 206 Partial Content response, a HTTP 200 OK is sent with the complete resource.

More Information#

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