One document matched: draft-nottingham-http-problem-02.xml

<?xml version="1.0" encoding="utf-8"?>

<!DOCTYPE rfc SYSTEM "http://xml.resource.org/authoring/rfc2629.dtd" [
   <!ENTITY rfc2119 SYSTEM 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml'>  
   <!ENTITY rfc2616 SYSTEM 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2616.xml'>  
   <!ENTITY rfc3023 SYSTEM 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3023.xml'>  
   <!ENTITY rfc3986 SYSTEM 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3986.xml'>  
   <!ENTITY rfc4627 SYSTEM 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4627.xml'>  
   <!ENTITY rfc5987 SYSTEM 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.5987.xml'>  
   <!ENTITY rfc5988 SYSTEM 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.5988.xml'>  
   <!ENTITY xml SYSTEM 'http://xml.resource.org/public/rfc/bibxml4/reference.W3C.REC-xml-20081126.xml'>  
   <!ENTITY xmls SYSTEM 'http://xml.resource.org/public/rfc/bibxml4/reference.W3C.REC-xmlschema-0-20041028.xml'>  
   <!ENTITY problem-schema SYSTEM 'http-problem-02.xsd'>
]>

<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<?rfc toc="yes" ?>
<?rfc tocdepth="3" ?>
<?rfc tocindent="yes" ?>
<?rfc symrefs="yes" ?>
<?rfc sortrefs="yes"?>
<?rfc iprnotified="no" ?>
<?rfc strict="yes" ?>
<?rfc compact="yes" ?>
<?rfc comments="yes" ?>
<?rfc inline="yes" ?>

<rfc ipr="trust200902" docName="draft-nottingham-http-problem-02" category="info">

	<front>
		<title abbrev="Problem Details">Problem Details for HTTP APIs</title>
		<author initials="M." surname="Nottingham" fullname="Mark Nottingham">
			<organization>Akamai</organization>
			<address>       
				<email>mnot@mnot.net</email> 
				<uri>http://www.mnot.net/</uri>
			</address>
		</author>
		<date year="2012"/>
		<keyword>status</keyword>
		<keyword>HTTP</keyword>
		<keyword>error</keyword>
		<keyword>problem</keyword>
		<abstract>

			<t>This document defines a "problem detail" as an extensible
         way to carry machine-readable details of errors in a HTTP response,
         to avoid the need to invent new response formats for HTTP APIs.</t>

		</abstract>

      <note title="Note to Readers">
			<t>This draft should be discussed on the <eref
         target="https://www.ietf.org/mailman/listinfo/apps-discuss">apps-discuss
         mailing list</eref>.</t>
      </note>

	</front>

	<middle>

		<section title="Introduction">

      <t>While HTTP <xref target="RFC2616"/> defines the status code as the
      primary indicator of generic response semantics, it is sometimes not
      fine-grained enough to convey helpful information about an error,
      particularly to non-human consumers of so-called "HTTP APIs".</t>
      
      <t>Consider a 403 Forbidden response that indicates that the client's
      account doesn't have enough credit. While this can be adequately
      expressed in HTML if presented to a human in front of a Web browser, a
      non-browser client would have difficulty understanding the response,
      because it doesn't understand the structure of the markup.</t>
      
       <t>This specification defines conventions for carrying machine-readable
      details of errors in a response ("problem details"), to avoid the need
      to invent new, application-specific response formats.</t>
      
       <t>Conceptually, problem details are associated with a generic type
      (e.g., "out of credit"). Optionally, the specific occurrence of a
      problem can also be identified (e.g., "when Bob ran out of credit last
      Tuesday at 5:32 pm"). Both use URIs to assure global uniqueness, and
      provide the opportunity to fetch further information.</t>
      
       <t>Problem details are specified as a JSON <xref target="RFC4627"/>
      object; when occurring in a message body, they use the
      "application/api-problem+json" media type. <xref target="xml-syntax"/>
      defines how to translate problem details to an XML format, for those
      APIs that need it.</t>
      
       <t>Note that problem details are (naturally) not the only way to convey
      the details of a problem in HTTP; if the response is still a
      representation of a resource, for example, it's often preferable to
      accommodate describing the relevant details in that format.</t>
      
       <t>Instead, the aim of this specification is to define a common error
       format for those applications that need one, so that they aren't
       required to define their own.</t>

		</section>

		<section title="Requirements">
      <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
      "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
      document are to be interpreted as described in <xref
      target="RFC2119"/>.</t>
		</section>


    <section title="The Problem Details JSON Object">

      <t>The canonical format for problem details is a JSON <xref
      target="RFC4627"/> document, identified with the
      "application/api-problem+json" media type, whose root MUST be an object.</t>

      <t>For example:</t>

     <figure><artwork><![CDATA[
HTTP/1.1 403 Forbidden
Content-Type: application/api-problem+json
Content-Language: en

{
 "describedBy": "http://example.com/probs/out-of-credit",
 "title": "You do not have enough credit.",
 "detail": "Your current balance is 30, but that costs 50.",
 "supportId": "http://example.net/account/12345/msgs/abc",
 "balance": 30,
 "account": "http://example.net/account/12345"
}]]></artwork></figure>

      <t>Here, the out-of-credit problem (identified by its describedBy URI)
      indicates the reason for the 403 in "title", gives a reference for the
      specific problem occurrence with "supportId", gives occurrence-specific
      details in "detail", and adds two extensions; "balance" conveys the
      account's balance, and "account" gives a link where the account can be
      topped up.</t>

      <t>Note that "describedBy" is case-sensitive in the JSON object, as are
      all other member names.</t>

      <section title="Required Members">
       
        <t>The root object MUST have the following members:</t>
       
        <t><list style='symbols'>

          <t>"describedBy" (string) - An absolute URI <xref
          target="RFC3986"/> that identifies the problem type. When
          dereferenced, it SHOULD provide human-readable documentation for
          the problem type (e.g., using HTML).</t>

          <t>"title" (string) - A short, human-readable summary of the
          problem type. It SHOULD NOT change from occurrence to occurrence of
          the problem, except for purposes of localisation.</t>

        </list></t>
          
        <t>Consumers MUST use the describedBy string as the primary
        identifier for the problem type; the title string is advisory, and
        included only for users who are not aware of the semantics of the
        URL, and don’t have the ability to discover them (e.g., offline log
        analysis). Consumers SHOULD NOT automatically dereference the
        describedBy URL.</t>
      
      </section>
      <section title="Optional Members">

        <t>Furthermore, the root object MAY have the following members:</t>

        <t><list style='symbols'>
        
          <t>"httpStatus" (number) - The HTTP status code set by the origin
          server for this occurrence of the problem.</t>
          
           <t>"detail" (string) - An human readable explanation specific to
          this occurance of the problem.</t>
          
           <t>"supportId" (string) - An absolute URI that identifies the
          specific occurrence of the problem. It may or may not yield
          further information if dereferenced.</t>
        
         </list></t>

        <t>The httpStatus member, if present, is only advisory; it conveys the
        HTTP status code used for the convenience of the consumer. Generators
        MUST use the same status code in the actual HTTP response, to assure
        that generic HTTP software that does not understand this format still
        behaves correctly. See <xref target="security-considerations"/> for
        further caveats regarding its use.</t>

        <t>The detail member, if present, SHOULD focus on helping the
        client correct the problem, rather than giving debugging
        information.</t>
        
        <t>Consumers SHOULD NOT be parse the detail member for information;
        extensions are more suitable and less error-prone ways to obtain
        such information.</t>

      </section>
      <section title="Extension Members">
       
        <t>Finally, problem type definitions MAY extend the root object with
        additional members.</t>

        <t>Clients consuming problem details MUST ignore unrecognised
        extensions; this allows problem types to evolve and include additional
        information in the future.</t>

      </section>
    </section>

    <section anchor="defining" title="Defining New Problem Types">

      <t>Before defining a new type of problem detail, it’s important to
      understand what they are good for, and what’s better left to other
      mechanisms.</t>

      <t>Problem details are not a debugging tool for the underlying
      implementation; rather, they are a way to expose greater detail about
      the HTTP interface itself. New problem types need to carefully consider
      the Security Considerations <xref target="security-considerations"/>, in
      particular the risk of exposing attack vectors by exposing
      implementation internals through error messages.</t>
      
      <t>Likewise, truly generic problems – i.e., conditions that could
      potentially apply to any resource on the Web – are usually better
      expressed as plain status codes. For example, a "write access
      disallowed" problem is probably unnecessary, since a 403 Forbidden
      status code on a PUT request is self-explanatory.</t>

      <t>Finally, an application may have a more appropriate way to carry
      an error in a format that it already defines. Problem details
      are intended to avoid the necessity of establishing new "fault" or
      "error" document formats, not to replace existing domain-specific
      formats.</t>

      <t>That said, it is possible to add support for problem details to
      existing HTTP APIs using HTTP content negotiation (e.g., using the
      Accept request header to indicate a preference for this format).</t>

      <t>New problem type definitions MUST document:

      <list style="numbers">
        <t>A describedBy URL (typically, with the "http"
        scheme),</t>
        <t>A title that appropriately describes it (think
        short), and</t>
        <t>The HTTP status code for it to be used with.</t>
      </list></t>

      <t>Problem types MAY specify the use of the Retry-After response
      header in appropriate circumstances.</t>

      <t>A problem’s describedBy URL SHOULD resolve to HTML documentation
      that explains how to resolve the problem.</t>

      <t>A problem type definition MAY specify additional members on the
      Problem Details JSON object. For example, an extension might use
      typed links <xref target="RFC5988"/> to another resource that can be
      used by machines to resolve the problem.</t>

      <t>If such additional members are defined, their names SHOULD conform
      to token <xref target="RFC2616"/>, so that it can be serialised in
      formats other than JSON, and SHOULD be three characters or longer.</t>

      <t>Likewise, problem types defining extensions SHOULD either make their
      values strings, or explain how to map their values to strings, so that
      it's possible to include them in other formats.</t>

    </section>
      
            
		<section anchor="security-considerations" title="Security Considerations">

        <t>When defining a new problem type, the information included must be
        carefully vetted. Likewise, when actually generating a problem –
        however it is serialised – the details given must also be
        scrutinised.</t>
         
        <t>Risks include leaking information that can be exploited to
        compromise the system, access to the system, or the privacy of users
        of the system.</t>
		  
        <t>Generators providing links to occurrence information are encouraged
        to avoid making implementation details such as a stack dump available
        through the HTTP interface, since this can expose sensitive details of
        the server implementation, its data, and so on.</t>
            
        <t>The "httpStatus" member duplicates the information available in the
        HTTP status code itself, thereby bringing the possibility of
        disagreement between the two. Their relative precedence is not clear,
        since a disagreement might indicate that (for example) an intermediary
        has modified the HTTP status code in transit. As such, those defining
        problem types as well as generators and consumers of problems need to
        be aware that generic software (such as proxies, load balancers,
        firewalls, virus scanners) are unlikely to know of or respect the
        status code conveyed in this member.</t>

		</section>

		<section title="IANA Considerations">

<t>This specification defines two new Internet media types:</t>

      <figure><artwork><![CDATA[
   Type name: application
   Subtype name: api-problem+json
   Required parameters: None
   Optional parameters: None; unrecognised parameters 
                        should be ignored
   Encoding considerations: Same as [RFC4627]
   Security considerations: see [this document]
   Interoperability considerations: None.
   Published specification: [this document]
   Applications that use this media type: HTTP
   Additional information:
     Magic number(s): n/a
     File extension(s): n/a
     Macintosh file type code(s): n/a
   Person & email address to contact for further information:
     Mark Nottingham <mnot@mnot.net>
   Intended usage: COMMON
   Restrictions on usage: None.
   Author: Mark Nottingham <mnot@mnot.net>
   Change controller: IESG
]]></artwork></figure>

      <figure><artwork><![CDATA[
   Type name: application
   Subtype name: api-problem+xml
   Required parameters: None
   Optional parameters: None; unrecognised parameters 
                        should be ignored
   Encoding considerations: Same as [RFC3023]
   Security considerations: see [this document]
   Interoperability considerations: None.
   Published specification: [this document]
   Applications that use this media type: HTTP
   Additional information:
     Magic number(s): n/a
     File extension(s): n/a
     Macintosh file type code(s): n/a
   Person & email address to contact for further information:
     Mark Nottingham <mnot@mnot.net>
   Intended usage: COMMON
   Restrictions on usage: None.
   Author: Mark Nottingham <mnot@mnot.net>
   Change controller: IESG
]]></artwork></figure>

		</section>
      
		<section title="Acknowledgements">
			<t>The author would like to thank 
				Jan Algermissen,
				Mike Amundsen,
				Subbu Allamaraju,
				Roy Fielding,
				Sam Johnston,
				Mike McCall,
				Julian Reschke,
				James Snell, and
				Erik Wilde
			for early review of this specification (even if some disagree
			with parts of it).
			</t>
		</section>

	</middle>

	<back>
		<references title="Normative References">
			&rfc2119;
			&rfc2616;
			&rfc3023;
			&rfc3986;
			&rfc4627;
		</references>

      <references title="Informative References">
        &xml;
        &xmls;
  			&rfc5988;         
		</references>

<section anchor="xml-syntax" title="HTTP Problems and XML">
   
   <t>Some HTTP-based APIs use XML <xref
   target="W3C.REC-xml-20081126"/> as their primary format convention. Such
   APIs MAY express HTTP Problems using the format defined in this
   appendix.</t>
      
   <t>The OPTIONAL XML Schema <xref target="W3C.REC-xmlschema-0-20041028"/>
   for the XML format is:</t>
      
<figure><artwork>&problem-schema;</artwork></figure>

   <t>The media type for this format is "application/api-problem+xml".</t>
   
   <t>Extension arrays and objects can be serialised into the XML format by
   considering an element containing a child or children to represent an
   object, except for elements that contain only child element(s) named 'i',
   which are considered arrays. For example, an alternate version of the
   example above:</t>
     
     <figure><artwork><![CDATA[
HTTP/1.1 403 Forbidden
Content-Type: application/api-problem+json
Content-Language: en

{
 "describedBy": "http://example.com/probs/out-of-credit",
 "title": "You do not have enough credit.",
 "detail": "Your current balance is 30, but that costs 50.",
 "supportId": "http://example.net/accounts/12345/msgs/abc",
 "more": {
   "balance": 30,
   "accounts": [
     "http://example.net/account/12345",
     "http://example.net/account/67890"
   ]
 }
}]]></artwork></figure>     

      <t>would appear in XML as:</t>
      
     <figure><artwork><![CDATA[
HTTP/1.1 403 Forbidden
Content-Type: application/api-problem+xml
Content-Language: en

<problem>
  <describedBy>http://example.com/probs/out-of-credit</describedBy>
  <title>You do not have enough credit.</title>
  <detail>Your current balance is 30, but that costs 50.</detail>
  <supportId>http://example.net/account/12345/msgs/abc</supportId>
  <more>
    <balance>30</balance>
    <accounts>
      <i>http://example.net/account/12345</i>
      <i>http://example.net/account/67890</i>
    </accounts>
  </more>
</problem>]]></artwork></figure> 


</section>


	</back>
	

</rfc>