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api-sig/guidelines/consuming-catalog/version-discovery.rst

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Version Discovery

The topic document on discoverability describes how REST services can expose version discovery information. However, due to seven years of existence that pre-date the existence of that document, there are a few non-optimal setups in the wild. This document describes the complete algorithm to correctly consume OpenStack version discovery. The intent with this algorithm is that for all clouds that fully implement discoverability guidelines the path through the system should be the most efficient, but that process degrades gracefully for systems that do not yet... ultimately degrading all the way back to being behaviorally the same as the "just use what's in the catalog" method.

Note

This document contains references to dealing with all known forms of things encountered in the wild. Where it doesn't distract from the rest of the description, care is taken to indicate which form is the preferred form and which are supported for legacy reasons. Mention of a form in this document should not be construed as endorsement. Definitions of preferred forms of data will be found in other documents.

Version Discovery Algorithm

The Version Discovery Algorithm is a part of ../consuming-catalog. Its input parameters and return values are a subset of the input parameters and return values described in catalog-user-request. It is expeced at this point that the {catalog-endpoint} is already known, either from the Service Catalog or directly from {endpoint-override}.

The algorithm is as follows:

  1. If the user has omitted {endpoint-version}, follow User Omitted API Version.

  2. Infer the {found-endpoint-version} from the {catalog-endpoint} using the Inferring Version process.

  3. If {found-endpoint-version} exists and {fetch-version-information} is false, STOP. Return {catalog-endpoint} as {service-endpoint}.

  4. If the Inferring Version process returned an error, the {catalog-endpoint} does not match the {endpoint-version}. Attempt to Find a Document.

    Note

    If the discoverability guidelines have been implemented, there will always be a {discovery-document}.

  5. If it is not possible to find a {discovery-document} and {be-strict} is true, STOP. Return an error that version discovery has failed.

  6. Determine {single-or-multiple} for the {discovery-document} (see Single or Multiple Version Documents).

    Note

    If the discoverability guidelines have been implemented, {single-or-multiple} will always be multiple.

At this point, there is a matrix of four possibilities:

  1. If {endpoint-version} is latest and {single-or-multiple} is single, follow Latest Single Version.
  2. If {endpoint-version} is latest and {single-or-multiple} is multiple, follow Latest Multiple Versions.
  3. If {endpoint-version} is a version and {single-or-multiple} is single, follow Requested Single Version.
  4. If {endpoint-version} is a version and {single-or-multiple} is multiple, follow Requested Multiple Versions.

User Omitted API Version

If the user has omitted the API Version, then the user is indicating that they want to use the {catalog-endpoint} as their {service-endpoint}. Discovery is only run to find out version information about that endpoint.

  1. {service-endpoint} is {catalog-endpoint}.
  2. If {fetch-version-information} is false, STOP. Infer the {found-endpoint-version} from {service-endpoint}. (see Inferring Version)
  3. Retrieve {discovery-document} at {service-endpoint}.
  4. If a {discovery-document} is found, STOP. Return the {endpoint-information} in it (see Return Information).
  5. If there is no {discovery-document}, attempt to Find a Document.
  6. If there is no {discovery-document}, STOP Infer the {found-endpoint-version} from {service-endpoint}. (see Inferring Version)
  7. Determine if the {single-or-multiple} of the {discovery-document} is single or multiple (see Single or Multiple Version Documents).
  8. If {single-or-multiple} is single, STOP. Return the {endpoint-information} in it (see Return Information).
  9. If {single-or-multiple} is multiple, find the {endpoint-information} in the {discovery-document} that matches {service-endpoint} (see Matching Endpoints).
  10. If there is no {endpoint-information}, STOP. Infer the {found-endpoint-version} from {catalog-endpoint}. (see Inferring Version)
  11. STOP. Return the information in {endpoint-information} (see Return Information).

Find a Document

In some cases, the {discovery-endpoint} will either not return a document, or will not return the document we want, so we need to look for a new one.

The Unversioned Document is always preferred over the Versioned Document, because the Unversioned Document supplies the list of possible versions, allowing Discovery to process the list and make decisions in one step. The Versioned Document only contains one Version, so additional calls must be made if the version in it does not match the user's request.

The algorithm for finding a new document is as follows:

  1. If there is an existing {discovery-document} and {single-or-multiple} is multiple, STOP. There is no better document.

  2. If

    • there is an existing {discovery-document}
    • {single-or-multiple} is single
    • the collection link in the links section is different than the current {discovery-endpoint}

    make the endpoint at the collection link the new {discovery-endpoint} and fetch a new {discovery-document}. STOP. Return the new {discovery-document}.

  3. Get the curently scoped project_id from the token, if one exists.

  4. If the {discovery-endpoint} ends with a path element that ends with the project_id, remove that path element and make the resulting URL the new {discovery-endpoint}.

  5. If the current {discovery-endpoint} ends with a path element that ends with a version string of the form "v[0-9]+(.[0-9]+)?$", remove that path element but save it as {removed-version-path-element}. Make the resulting URL the new {discovery-endpoint}.

  6. If the {discovery-endpoint} matches the {catalog-endpoint}, STOP. Return an error reporting no working {discovery-document}.

  7. Attempt to fetch a {discovery-document} from the {discovery-endpoint}. If one exists, STOP. Normalize it (see Normalizing Documents) and return it as the {dicovery-document}.

  8. If no new {discovery-document} can be found at the new endpoint but there is a saved value in {removed-version-path-element}, append the {removed-version-path-element} to the {discovery-endpoint} and make the resulting URL the new {discovery-endpoint}.

  9. Attempt to fetch a {discovery-document} from the {discovery-endpoint}. If one exists, STOP. Normalize it (see Normalizing Documents) and return it as the {dicovery-document}.

  10. If no document can be found, return an error reporting no working {discovery-document}.

For example:

# Given a discovery document from the cloud
original_document = {
  "version": {
    "status": "SUPPORTED",
    "id": "v2.0",
    "links": [
      {
        "href": "http://compute.example.com/v2/",
        "rel": "self"
      },
      {
        "href": "http://compute.example.com/",
        "rel": "collection"
      }
    ]
  }
}

# It is a single version document
single_or_multiple = 'single'

# We apply the normalization process
normalized_document = {
  "versions": [
    {
      "status": "SUPPORTED",
      "id": "v2.0",
      "min_version": "",
      "max_version": "",
      "links": [
        {
          "href": "http://compute.example.com/v2/",
          "rel": "self"
        },
        {
          "href": "http://compute.example.com/",
          "rel": "collection"
        }
      ]
    }
  ]
}

# We see that a collection link exists, so we'll use it as the new discovery
# endpoint.
discovery_endpoint = "http://compute.example.com/"

# We fetch the document from that endpoint and normalize it.
normalized_better_discovery_document = {
  "versions": [
    {
      "status": "SUPPORTED",
      "links": [
        {
          "href": "http://compute.example.com/v2/",
          "rel": "self"
        }
      ],
      "min_version": "",
      "max_version": "",
      "id": "v2.0"
    }, {
      "status": "CURRENT",
      "links": [
        {
          "href": "http://compute.example.com/v2.1/",
          "rel": "self"
        }
      ],
      "min_version": "2.1",
      "max_version": "2.38",
      "id": "v2.1"
    }
  ]
}

# single-or-multiple is multiple, so it's better
return normalized_better_discovery_document

Example with project_id:

# The user has requested service-type=file-storage

# The user's token reports the project_id
project_id = '45f0034e8c5a4ef4895b5a87b6b57def'
# The service-catalog contains an entry for filestorage
catalog_endpoint = 'https://file-storage.example.com/v2/45f0034e8c5a4ef4895b5a87b6b57def'

# The catalog_endpoint ends with the user's project_id, so we pop it.
new_endpoint = 'https://file-storage.example.com/v2'

# Fetch the document, normalize it and return it
return {
  "versions": [
    {
      "status": "CURRENT",
      "id": "v2.0",
      "links": [
        {
          "href": "http://file-storage.example.com/v2/",
          "rel": "self"
        },
        {
          "href": "http://file-storage.example.com/",
          "rel": "collection"
        }
      ]
    }
  ]
}

More pathological example:

# The user has requested service-type=file-storage

# The user's token reports the project_id
project_id = '45f0034e8c5a4ef4895b5a87b6b57def'
catalog_endpoint = 'https://file-storage.example.com/v2/45f0034e8c5a4ef4895b5a87b6b57def'

# The catalog_endpoint ends with the user's project_id, so we pop it.
discovery_endpoint = 'https://file-storage.example.com/v2'

# We try to fetch https://file-storage.example.com/v2 but it returns an error

# Pop version string from the endpoint
new_discovery_endpoint = 'https://file-storage.example.com/'

# Fetch the document, normalize and return it
return {
  "versions": [
    {
      "status": "SUPPORTED",
      "links": [
        {
          "href": "http://file-storage.example.com/v1/",
          "rel": "self"
        }
      ],
      "min_version": "",
      "max_version": "",
      "id": "v1.0"
    },
    {
      "status": "CURRENT",
      "links": [
        {
          "href": "http://file-storage.example.com/v2/",
          "rel": "self"
        }
      ],
      "min_version": "2.0",
      "max_version": "2.22",
      "id": "v2.0"
    }
  ]
}

Inferring Version

In most cases the version of the {service-endpoint} should be retrievable from the {discovery-document}, and in those cases it should be considered the version of the service at the {service-endpoint}. In some cases no discovery document can be found corresponding with the {service-endpoint} in question. Alternately, in some cases the {catalog-endpoint} contains version information and the user is not looking for microversion information.

Microversion information will always be empty when this procedure is used.

The algorithm for inferring the version is as follows:

  1. Get the curently scoped project_id from the token, if one exists.
  2. If the endpoint ends with a path element that ends with project_id, remove it.
  3. If the endpoint ends with a path element that is of the form, ^v[0-9]+(\.[0-9]+)?$, strip the v and use the rest of that element as {found-endpoint-version}.
  4. If the endpoint contains no version elements, a version cannot be inferred. Return a null value for {found-endpoint-version}.
  5. If {endpoint-version} was given and does not match {found-endpoint-version}, STOP. Return an error that says that user requested a version and that the version inferred from the URL did not match.
  6. Return {found-endpoint-version}.

For example:

catalog_endpoint = 'https://file-storage.example.com/v2/45f0034e8c5a4ef4895b5a87b6b57def'
# Match path elements - /v2/ matches ...
found_api_version = '2'

catalog_endpoint = 'https://identity-storage.example.com/'
# Match path elements - no matches
found_api_version = None

catalog_endpoint = 'https://object-store.example.com/v1/AUTH_622b11a1-5dfa-43b4-9f58-4ad3c6dbc4a0'
# Match path elements - /v1/ matches ...
found_api_version = '1'

catalog_endpoint = 'https://compute.example.com/v2.1'
# Match path elements - /v2.1/ matches ...
found_api_version = '2.1'

Matching Endpoints

If {single-or-multiple} is multiple and the discovery algorithm has chosen to fall back to the endpoint provided by the catalog, a URL matching the catalog URL should be found so that the version can be extracted.

  1. Sort the endpoints in the {discovery-document} by id in descending order using version comparision.
  2. For each endpoint in the list, expand it (see Expanding Endpoints) and compare it to the catalog endpoint. The first endpoint that matches is the winner.

For example:

catalog_endpoint = 'https://file-storage.example.com/v2/45f0034e8c5a4ef4895b5a87b6b57def'

discovery_document = {
  "versions": [
    {
      "status": "CURRENT",
      "id": "v2.0",
      "links": [
        {
          "href": "http://file-storage.example.com/v2/",
          "rel": "self"
        }
      ],
    }
  ]
}

# Expand endpoint http://file-storage.example.com/v2/
expanded_endpoint = "https://file-storage.example.com/v2/45f0034e8c5a4ef4895b5a87b6b57def"

# expanded_endpoint matches catalog_endpoint - id v2.0 is the match

Expanding Endpoints

Endpoints in discovery documents can be relative and can also be erroneous in known ways. Before using endpoints from discovery documents, they must be expanded. The algorithm is as follows:

  1. Join the endpoint from the discovery document with the endpoint the discovery document was fetched from. If the endpoint in the document is an absolute url, this should result in the endpoint from the document being unchanged. If the endpoint from the document is relative, it should be be appended to the endpoint the document was fetched from following normal relative URL rules. The python module six.moves.urllib.parse.urljoin is an example of an implementation of url joining that behaves as expected.

  2. Replace the scheme and host of the endpoint from the discovery document with the scheme and host from the endpoint it was fetched from. This is to work around older buggy discovery documents seen in the wild.

    For example:

def replace_scheme(endpoint, discovery_url):
     parsed_endpoint = urllib.parse.urlparse(endpoint)
     parsed_discovery_url = urllib.parse.urlparse(discovery_url)

     return urllib.parse.ParseResult(
         parsed_discovery_url.scheme,
         parsed_discovery_url.netloc,
         parsed_endpoint.path,
         parsed_endpoint.params,
         parsed_endpoint.query,
         parsed_endpoint.fragment).geturl()
  1. Get the curently scoped project_id from the token, if one exists.
  2. If the {catalog-endpoint} ends with a path element that ends with project_id but the endpoint does not, append the final element of the path of the {catalog-endpoint} to the end of the endpoint.

Note

Some services prepend a string to the project_id in their endpoint, so just appending the project_id to the catalog-endpoint is not sufficient.

For example:

project_id = '45f0034e8c5a4ef4895b5a87b6b57def'
catalog_endpoint = 'https://file-storage.example.com/v2/45f0034e8c5a4ef4895b5a87b6b57def'

discovery_document = {
  "versions": [
    {
      "status": "CURRENT",
      "id": "v2.0",
      "links": [
        {
          "href": "/v2.0",
          "rel": "self"
        }
      ]
    }
  ]
}

# Pop project_id from catalog_endpoint
shortened_catalog_endpoint = 'https://file-storage.example.com/v2'

# Apply URL join to https://file-storage.example.com/v2 and /v2.0
joined_endpoint = 'https://file-storage.example.com/v2.0'

# catalog_endpoint ends with project_id, append project_id
service_endpoint = 'http://file-storage.example.com/v2.0/45f0034e8c5a4ef4895b5a87b6b57def'

With broken service endpoint in discovery:

project_id = '45f0034e8c5a4ef4895b5a87b6b57def'
catalog_endpoint = 'https://file-storage.example.com/v2/45f0034e8c5a4ef4895b5a87b6b57def'

# This discovery_document is the result of a service with a broken
# configuration. Obviously the service is not on "localhost". Similarly,
# since the discovery endpoint is an https endpoint, it can be assumed
# that the actual service endpoint is https.
discovery_document = {
  "versions": [
    {
      "status": "CURRENT",
      "id": "v2.0",
      "links": [
        {
          "href": "http://localhost/v2.0",
          "rel": "self"
        }
      ],
    }
  ]
}

# Pop project_id from catalog_endpoint
shortened_catalog_endpoint = 'https://file-storage.example.com/v2'

# Apply URL join to https://file-storage.example.com/v2 and
# http://localhost/v2.0 - endpoint from discovery is absolute
joined_endpoint = 'http://localhost/v2.0'

# Replace scheme and host from https://file-storage.example.com/v2
joined_endpoint = 'https://file-storage.example.com/v2.0'

# catalog_endpoint ends with project_id, append project_id
service_endpoint = 'http://file-storage.example.com/v2.0/45f0034e8c5a4ef4895b5a87b6b57def'

Single or Multiple Version Documents

Even with the version documents normalized as per Normalizing Documents into the form described by discoverability, it is still important to know if the document lists all available versions or only a single out of a larger set. As it's also possible that there is only one version, merely looking at the length of the list is not sufficient.

Note

Once all services implement the full recommendations in discoverability there will never be a document with a single version out of a larger set, so this logic will not be needed. However, the logic is upwards compatible with that desired future state.

In order to apply the discovery algorithm, the type of document must be detected.

  • If the document has a link description in the links list with a rel of collection and the href of that link is different than the href of the link with a rel of self, then it is a Single Version Document.
  • Otherwise it is a Multiple Version Document and can be relied on to contain the complete set of available versions.

Note

TODO(mordred) add examples

Normalizing Documents

Note

If the API-SIG recommendations in discoverability are implemented, all of the logic in this section can be skipped.

There are three forms of existing version discovery documents in addition to the one that is preferred and described in discoverability. In order to apply the algorithm sanely, the fetched documents should be normalized to align with the discoverability.

Note

It is not actually required that normalization take place in a client or library. It is described here for the purposes of simplifying other parts of this document and being able to describe the process in terms of the correct document formats.

  • If the document has a key named versions which contains a dict with a key named values, move the list contained in values to be directly under versions. That list is then the list of Version objects.

For example:

{
  "versions": {
    "values": [
      {
        "status": "stable",
        "updated": "2016-10-06T00:00:00Z",
        "id": "v3.7",
        "links": [
          {
            "href": "https://auth.example.com/v3/",
            "rel": "self"
          }
        ]
      },
      {
        "status": "deprecated",
        "updated": "2016-08-04T00:00:00Z",
        "id": "v2.0",
        "links": [
          {
            "href": "https://auth.example.com/v2.0/",
            "rel": "self"
          }
        ]
      }
    ]
  }
}

becomes:

{
  "versions": [
    {
      "status": "stable",
      "updated": "2016-10-06T00:00:00Z",
      "id": "v3.7",
      "links": [
        {
          "href": "https://auth.example.com/v3/",
          "rel": "self"
        }
      ]
    },
    {
      "status": "deprecated",
      "updated": "2016-08-04T00:00:00Z",
      "id": "v2.0",
      "links": [
        {
          "href": "https://auth.example.com/v2.0/",
          "rel": "self"
        }
      ]
    }
  ]
}
  • If the document has a key named id make a key named version and place all of the values under it.

For example:

{
  "status": "CURRENT",
  "id": "v2.0",
  "links": [
    {
      "href": "http://network.example.com/v2.0",
      "rel": "self"
    }
  ]
}

becomes:

{
  "version": {
    "status": "CURRENT",
    "id": "v2.0",
    "links": [
      {
        "href": "http://network.example.com/v2.0",
        "rel": "self"
      }
    ]
  }
}
  • If the document has a key named version, (even if you just created it) look for a collection link in the links list. If one does not exist, grab the href from the self link. If the self link ends with a version string of the form "v[0-9]+(.[0-9]+)?$", pop that version string from the end of the endpoint and add a collection entry to the links list with the resulting endpoint.

For example:

{
  "version": {
    "status": "CURRENT",
    "id": "v2.0",
    "links": [
      {
        "href": "http://network.example.com/v2.0",
        "rel": "self"
      }
    ]
  }
}

becomes:

{
  "version": {
    "status": "CURRENT",
    "id": "v2.0",
    "links": [
      {
        "href": "http://network.example.com/v2.0",
        "rel": "self"
      },
      {
        "href": "http://network.example.com/",
        "rel": "collection"
      }
    ]
  }
}
  • If the document has a key named version, create a top level key called versions that contains a list. Move the contents of version into a dict in the versions list and remove the top level key version.

For example:

{
  "version": {
    "status": "CURRENT",
    "id": "v2.0",
    "links": [
      {
        "href": "http://network.example.com/v2.0",
        "rel": "self"
      },
      {
        "href": "http://network.example.com/",
        "rel": "collection"
      }
    ]
  }
}

becomes:

{
  "versions": [
    {
      "status": "CURRENT",
      "id": "v2.0",
      "links": [
        {
          "href": "http://network.example.com/v2.0",
          "rel": "self"
        },
        {
          "href": "http://network.example.com/",
          "rel": "collection"
        }
      ]
    }
  ]
}

For each Version object in the versions list:

  1. Keys other than id, version, min_version, max_version, status and links can be ignored or removed.
  2. Convert the value in the status field to upper case.
  3. If status is STABLE, change it to CURRENT. (handles keystone)
  4. If there is a version field and not a max_version field, make a max_version field with the value from the version field. (handles nova, cinder, manila and ironic microversions)
  5. The links key should contain a list, and that list should contain one dict with rel equal to self and additionally may contain a second dict with rel equal to collection. Any other entries can be discarded.

Some examples of the total normalization follow.

Original document:

{
  "versions": [
    {
      "status": "stable",
      "updated": "2016-10-06T00:00:00Z",
      "id": "v3.7",
      "links": [
        {
          "href": "https://auth.example.com/v3/",
          "rel": "self"
        }
      ]
    },
    {
      "status": "deprecated",
      "updated": "2016-08-04T00:00:00Z",
      "id": "v2.0",
      "links": [
        {
          "href": "https://auth.example.com/v2.0/",
          "rel": "self"
        }
      ]
    }
  ]
}

becomes:

{
  "versions": [
    {
      "status": "CURRENT",
      "id": "v3.7",
      "links": [
        {
          "href": "https://auth.example.com/v3/",
          "rel": "self"
        }
      ]
    },
    {
      "status": "DEPRECATED",
      "id": "v2.0",
      "links": [
        {
          "href": "https://auth.example.com/v2.0/",
          "rel": "self"
        }
      ]
    }
  ]
}

Original document:

{
  "versions": [
    {
      "status": "SUPPORTED",
      "updated": "2011-01-21T11:33:21Z",
      "links": [
        {
          "href": "http://compute.example.com/v2/",
          "rel": "self"
        }
      ],
      "min_version": "",
      "version": "",
      "id": "v2.0"
    },
    {
      "status": "CURRENT",
      "updated": "2013-07-23T11:33:21Z",
      "links": [
        {
          "href": "http://compute.example.com/v2.1/",
          "rel": "self"
        }
      ],
      "min_version": "2.1",
      "version": "2.38",
      "id": "v2.1"
    }
  ]
}

becomes:

{
  "versions": [
    {
      "status": "SUPPORTED",
      "links": [
        {
          "href": "http://compute.example.com/v2/",
          "rel": "self"
        }
      ],
      "min_version": "",
      "max_version": "",
      "id": "v2.0"
    },
    {
      "status": "CURRENT",
      "links": [
        {
          "href": "http://compute.example.com/v2.1/",
          "rel": "self"
        }
      ],
      "min_version": "2.1",
      "max_version": "2.38",
      "id": "v2.1"
    }
  ]
}

Find Matching Version

Finding a version out of a list of endpoint descriptions is done by comparing {endpoint-version} with the id field of the description to find a list of {candidate-endpoints} (see comparing-major-versions).

If there is more than one {id} that matches the requested {endpoint-version} and one of them has status of CURRENT, it should be returned.

If there is more than one {id} that matches the requested {endpoint-version} and none has the status of CURRENT, the highest should be returned.

If there is more than one {id} that matches the requested {endpoint-version} and more than one has the status of CURRENT, the highest should be returned.

Latest Single Version

{endpoint-version} is latest and {single-or-multiple} is single.

  1. If status in the {discovery-document} is CURRENT, STOP. Return the {endpoint-information} in the {discovery-document} (see Return Information).
  2. Attempt to Find a Document
  3. If there is a new {discovery-document} determine if the {single-or-multiple} is single or multiple (see Single or Multiple Version Documents).
  4. If new {single-or-multiple} is multiple, follow Latest Multiple Versions.
  5. If new {single-or-multiple} is single, or there is no new {discovery-document}, STOP. Return the {endpoint-information} in the {discovery-document} (see Return Information).

Latest Multiple Versions

{endpoint-version} is latest and {single-or-multiple} is multiple.

  1. Find the {endpoint-information} in the {discovery-document} with the latest version, see Find Latest Version.
  2. When {endpoint-information} is found, STOP. Return the information in the {endpoint-information} (see Return Information).

Requested Single Version

{endpoint-version} is a version or range and {single-or-multiple} is single.

  1. Check to see if the version in the {discovery-document} matches the {endpoint-version} by following Find Matching Version.
  2. Find a matching {endpoint-information} in the {discovery-document} that matches the {endpoint-version}. (see Find Matching Version)
  3. If {endpoint-information} is found, STOP. Return the information in the {endpoint-information} (see Return Information).
  4. If the version does not match, attempt to Find a Document.
  5. If there is a new {discovery-document} determine if the {single-or-multiple} is single or multiple (see Single or Multiple Version Documents).
  6. If the {single-or-multiple} is multiple, follow Requested Multiple Versions.
  7. If there is no new {discovery-document}, STOP. Return an error telling the user their requested version could not be found. Include the version that was found in the error.

Requested Multiple Versions

{endpoint-version} is a version or range and {single-or-multiple} is multiple.

  1. Find a matching {endpoint-information} in the {discovery-document} (see Find Matching Version)
  2. If {endpoint-information} is found, STOP. Return the information in the {endpoint-information} (see Return Information).
  3. If no matching {endpoint-information} is found and {be-strict} is True, STOP. Return an error telling the user their requested version could not be found. Include the list of versions that were found in the error.
  4. If no matching {endpoint-information} is found and {be-strict} is False, use the {catalog-endpoint} as the {service-endpoint}. Find the {endpoint-information} in the document that matches the {catalog-endpoint} and use it. (see Matching Endpoints).
  5. If there is no {endpoint-information}, STOP. Infer the {found-endpoint-version} from the {service-endpoint} (see Inferring Version).
  6. STOP. Return the information in {endpoint-information} (see Return Information).

Find Latest Version

If one of the versions in the list has status of CURRENT, use it.

Otherwise, select the version with the highest id, excluding any with status of EXPERIMENTAL or DEPRECATED sorted using version comparison not lexical sorting.

Return Information

When endpoint information has been selected, return the information in the following manner:

  1. Strip the leading "v" from {id} and return it as {found-endpoint-version}.
  2. Expand the href of the entry in links where rel is self and return it as the {service-endpoint} (see Expanding Endpoints).
  3. Return {min-version} and {max-version} if they exist.