Http status codes

The 100 (Continue) status code indicates that the initial part of a request 
has been received and has not yet been rejected by the server.  
The server intends to send a final response after the request has been fully 
received and acted upon.

When the request contains an Expect header field that includes a
100-continue expectation, the 100 response indicates that the server wishes 
to receive the request payload body, as described in Section 5.1.1. 
The client ought to continue sending the request and discard the 100 response.

If the request did not contain an Expect header field containing the 
100-continue expectation, the client can simply discard this interim response.

The 101 (Switching Protocols) status code indicates that the server
understands and is willing to comply with the client's request, via
the Upgrade header field (Section 6.7 of [RFC7230]), for a change in
the application protocol being used on this connection.  The server 
MUST generate an Upgrade header field in the response that indicates
which protocol(s) will be switched to immediately after the empty
line that terminates the 101 response.

It is assumed that the server will only agree to switch protocols
when it is advantageous to do so.  For example, switching to a newer
version of HTTP might be advantageous over older versions, and
switching to a real-time, synchronous protocol might be advantageous
when delivering resources that use such features

The 200 (OK) status code indicates that the request has succeeded.
   The payload sent in a 200 response depends on the request method.
   For the methods defined by this specification, the intended meaning
   of the payload can be summarized as:

   GET  a representation of the target resource;

   HEAD  the same representation as GET, but without the representation
      data;

   POST  a representation of the status of, or results obtained from,
      the action;

   PUT, DELETE  a representation of the status of the action;

   OPTIONS  a representation of the communications options;

   TRACE  a representation of the request message as received by the end
      server.

   Aside from responses to CONNECT, a 200 response always has a payload,
   though an origin server MAY generate a payload body of zero length.
   If no payload is desired, an origin server ought to send 204 (No
   Content) instead.  For CONNECT, no payload is allowed because the
   successful result is a tunnel, which begins immediately after the 200
   response header section.

   A 200 response is cacheable by default; i.e., unless otherwise
   indicated by the method definition or explicit cache controls (see
   Section 4.2.2 of [RFC7234]).

The 201 (Created) status code indicates that the request has been
   fulfilled and has resulted in one or more new resources being
   created.  The primary resource created by the request is identified
   by either a Location header field in the response or, if no Location
   field is received, by the effective request URI.

   The 201 response payload typically describes and links to the
   resource(s) created.  See Section 7.2 for a discussion of the meaning
   and purpose of validator header fields, such as ETag and
   Last-Modified, in a 201 response.

The 202 (Accepted) status code indicates that the request has been
   accepted for processing, but the processing has not been completed.
   The request might or might not eventually be acted upon, as it might
   be disallowed when processing actually takes place.  There is no
   facility in HTTP for re-sending a status code from an asynchronous
   operation.

   The 202 response is intentionally noncommittal.  Its purpose is to
   allow a server to accept a request for some other process (perhaps a
   batch-oriented process that is only run once per day) without
   requiring that the user agent's connection to the server persist
   until the process is completed.  The representation sent with this
   response ought to describe the request's current status and point to
   (or embed) a status monitor that can provide the user with an
   estimate of when the request will be fulfilled.

The 203 (Non-Authoritative Information) status code indicates that
   the request was successful but the enclosed payload has been modified
   from that of the origin server's 200 (OK) response by a transforming
   proxy (Section 5.7.2 of [RFC7230]).  This status code allows the
   proxy to notify recipients when a transformation has been applied,
   since that knowledge might impact later decisions regarding the
   content.  For example, future cache validation requests for the
   content might only be applicable along the same request path (through
   the same proxies).

   The 203 response is similar to the Warning code of 214 Transformation
   Applied (Section 5.5 of [RFC7234]), which has the advantage of being
   applicable to responses with any status code.

A 203 response is cacheable by default; i.e., unless otherwise
   indicated by the method definition or explicit cache controls (see
   Section 4.2.2 of [RFC7234]).

   The 204 (No Content) status code indicates that the server has
   successfully fulfilled the request and that there is no additional
   content to send in the response payload body.  Metadata in the
   response header fields refer to the target resource and its selected
   representation after the requested action was applied.

   For example, if a 204 status code is received in response to a PUT
   request and the response contains an ETag header field, then the PUT
   was successful and the ETag field-value contains the entity-tag for
   the new representation of that target resource.

   The 204 response allows a server to indicate that the action has been
   successfully applied to the target resource, while implying that the
   user agent does not need to traverse away from its current "document
   view" (if any).  The server assumes that the user agent will provide
   some indication of the success to its user, in accord with its own
   interface, and apply any new or updated metadata in the response to
   its active representation.

   For example, a 204 status code is commonly used with document editing
   interfaces corresponding to a "save" action, such that the document
   being saved remains available to the user for editing.  It is also
   frequently used with interfaces that expect automated data transfers
   to be prevalent, such as within distributed version control systems.

   A 204 response is terminated by the first empty line after the header
   fields because it cannot contain a message body.

   A 204 response is cacheable by default; i.e., unless otherwise
   indicated by the method definition or explicit cache controls (see
   Section 4.2.2 of [RFC7234]).

The 205 (Reset Content) status code indicates that the server has
   fulfilled the request and desires that the user agent reset the
   "document view", which caused the request to be sent, to its original
   state as received from the origin server.

   This response is intended to support a common data entry use case
   where the user receives content that supports data entry (a form,
   notepad, canvas, etc.), enters or manipulates data in that space,

causes the entered data to be submitted in a request, and then the
   data entry mechanism is reset for the next entry so that the user can
   easily initiate another input action.

   Since the 205 status code implies that no additional content will be
   provided, a server MUST NOT generate a payload in a 205 response.  In
   other words, a server MUST do one of the following for a 205
   response: a) indicate a zero-length body for the response by
   including a Content-Length header field with a value of 0; b)
   indicate a zero-length payload for the response by including a
   Transfer-Encoding header field with a value of chunked and a message
   body consisting of a single chunk of zero-length; or, c) close the
   connection immediately after sending the blank line terminating the
   header section.