Version 1.1 Released together with Documents API 1.0. BCF API GitHub repository

Contributing

The Open CDE workgroup develops the Foundation API standard.

Table of Contents

• 1. Introduction
  • 1.1 Paging, Sorting and Filtering
  • 1.2 Caching
  • 1.3 Updating Resources via HTTP PUT
  • 1.4 Cross Origin Resource Sharing (CORS)
  • 1.5 Http Status Codes
    • 1.5.1 Conflict on creation
  • 1.6 Error Response Body Format
  • 1.7 DateTime Format
  • 1.8 Additional Response and Request Object Properties
  • 1.9 Binary File Uploads
  • 1.10 Differences Between null and Empty Lists
  • 1.11 HTTPS/TLS
• 2. Public Services
  • 2.1 Versions Service
  • 2.2 Authentication Services
    • 2.2.1 Obtaining Authentication Information
    • 2.2.2 OAuth2 Example
    • 2.2.3 OAuth2 Protocol Flow - Dynamic Client Registration
• 3. Directory Services
  • 3.1 User Services
    • 3.1.1 Get current user

1. Introduction

The OpenCDE Foundation API includes a small number of services and a few conventions that are common to all OpenCDE APIs.

OpenCDE APIs support the exchange of information between software applications via a RESTful web interface, which means that data is exchanged via HTTP query parameters and JSON payloads. URL schemas in this README are relative to the OpenCDE API servers' base-URL unless an absolute value is provided.

1.1 Paging, Sorting and Filtering

When requesting collections of items, the Server should offer URL parameters according to the OData v4 specification.

1.2 Caching

ETags, or entity-tags, are an important part of HTTP, being a critical part of caching, and also used in "conditional" requests.

The ETag response-header field value, an entity tag, provides for an "opaque" cache validator. The easiest way to think of an etag is as an MD5 or SHA1 hash of all the bytes in a representation. If just one byte in the representation changes, the etag will change.

ETags are returned in a response to a GET:

joe@joe-laptop:~$ curl --include http://bitworking.org/news/
HTTP/1.1 200 Ok
Date: Wed, 21 Mar 2007 15:06:15 GMT
Server: Apache
ETag: "078de59b16c27119c670e63fa53e5b51"
Content-Length: 23081
…

The client may send an "If-None-Match" HTTP Header containing the last retrieved etag. If the content has not changed the server returns a status code 304 (not modified) and no response body.

1.3 Updating Resources via HTTP PUT

Whenever a resource offers the HTTP PUT method, it is to be updated as a whole.

This means that there is no partial update mechanism for objects but every PUT request is sending the whole object representation.

1.4 Cross Origin Resource Sharing (CORS)

To work with browser based API clients using Cross Origin Resource Sharing (Cors), servers will put the Access-Control-Allow' headers in the response headers and specify who can access the servers JSON resources. The client can look for these values and proceed with accessing the resources.

In a CORS scenario, web clients expect the following headers:

• Access-Control-Allow-Headers: Authorization, Content-Type, Accept to allow the Authorization, Content-Type and Accept headers to be used via XHR requests
• Access-Control-Allow-Methods: GET, POST, PUT, OPTIONS to allow the Http methods the API needs
• Access-Control-Allow-Origin: example.com to allow XHR requests from the example.com domain to the API server

For example, Asp.Net applications in IIS need the following entries in their web.config file. * means the server allows any values.

<httpProtocol>
    <customHeaders>
        <add name="Access-Control-Allow-Headers" value="Content-Type, Accept, X-Requested-With,  Authorization" />
        <add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE, OPTIONS" />
        <add name="Access-Control-Allow-Origin" value="*" />
    </customHeaders>
</httpProtocol>

1.5 Http Status Codes

Web-based APIs rely on the regular Http Status Code definitions. Good sources are Wikipedia or the HTTP/1.1 Specification.

Generally, these response codes shall be used in the API:

• 200 - OK for GET requests that return data or PUT requests that update data
• 201 - Created for POST requests that create data
• 401 - Unauthorized for requests that have errors when the user is not authenticated
• 403 - Forbidden for requests when the user is authenticated but not authorized to perform the operation

POST and PUT requests do usually include the created/modified resource in the response body. Exceptions to this rule are described in the specific section for the resource.

1.5.1 Conflict on creation

For resource creation by POST with optional GUID specified, if the GUID already exists in the target system, status code 409 - Conflict will be returned.

1.6 Error Response Body Format

All OpenCDE APIs have a specified error response body format error.json.

1.7 DateTime Format

DateTime values must be rfc3339 compliant.

Examples:

• 2016-04-28T16:31:12Z would represent Thursday, April 28th, 2016, 16:31:12 (0ms) in UTC timezone.
• 2016-04-28T16:31:12.270Z would represent Thursday, April 28th, 2016, 16:31:12 (270ms) in UTC timezone.
• 2016-04-28T16:31:12.270+02:00 would represent Thursday, April 28th, 2016, 16:31:12 (270ms) with a time zone offset of +2 hours relative to UTC.

1.8 Additional Response and Request Object Properties

All API response and request JSON objects may contain additional properties that are not part of the specified exchange for that endpoint. This is to allow server and client implementations freedom to add additional functionality. Servers and clients shall ignore those properties and must not produce errors on additional properties. Servers and clients are not required to preserve these properties.

1.9 Binary File Uploads

Some endpoints may expect binary file uploads, such as the BCF Document Service and the BCF BIM Snippet Service.

In such cases, files should be sent with the following Http headers:

Headers:
Content-Type: application/octet-stream;
Content-Length: {Size of file in bytes};
Content-Disposition: attachment; filename="{Filename.extension}";

1.10 Differences Between null and Empty Lists

Some array or list properties and responses can be interpreted differently if they are either null or empty. In general, there are two cases to consider.

For collection resources:

• A collection resource that does not exist should return Http error 404 - Not Found, e.g. the list of topics for an invalid project id.
• If the resource exists but there are no elements, the returned response should be an empty array [], e.g. the list of topics for a project where no topics exist.

For properties:

• If a list property is null (by explicitly setting it to null or not returning it in the response object at all), the client should not assume that this represents an empty list but instead the property is not present on the response object. Depending on the response object, this can have the same meaning as an empty list (e.g. no components in a viewpoint is the same as an empty list of components), but this can also mean the property is just omitted for optional properties (e.g. no topic_actions in an authorization object can mean no restrictions).

1.11 HTTPS/TLS

To ensure the security of API exchanges servers should only expose API endpoints over HTTPS with a minimal TLS version of 1.2.

---

2. Public Services

2.1 Versions Service

versions_GET.json

The Versions service is used to discover the available OpenCDE APIs and where to find them. The api_base_url field specifies the base path for each API.

To clarify, the Versions service allows specifying api_base_url for the Foundation API. However, to ensure discoverability, the Versions service is always served from the /foundation/versions base path regardless of the api_base_url parameter value.

Resource URL (public resource)

GET /foundation/versions

Parameters

Parameter	Type	Description	Required
api_id	string	Identifier of the API	true
version_id	string	Identifier of the version	true
detailed_version	string	URL of the specification on GitHub	false
api_base_url	string	An optional, fully qualified URL, to allow servers to relocate the API	false

Returns a list of all supported OpenCDE APIs and their versions.

Example Request

GET /foundation/versions

Example Response

Response Code: 200 - OK
Body:
{
    "versions": [{
        "api_id": "foundation",
        "version_id": "1.1",
        "detailed_version": "https://github.com/BuildingSMART/foundation-API/tree/release_1_1"
        "api_base_url": "https://server.base.url/foundation/1.1"
    }, {
        "api_id": "bcf",
        "version_id": "2.1",
        "detailed_version": "https://github.com/buildingSMART/BCF-API/tree/release_2_1",
        "api_base_url": "https://server.base.url/bcf/2.1"
    }, {
        "api_id": "bcf",
        "version_id": "3.0",
        "detailed_version": "https://github.com/buildingSMART/BCF-API/tree/release_3_0",
        "api_base_url": "https://server.base.url/somepath/bcf/3.0"
    }, {
        "api_id": "documents",
        "version_id": "1.0",
        "detailed_version": "https://github.com/buildingSMART/documents-API/tree/release_1_0",
        "api_base_url": "https://server.base.url/somepath/documents/1.0"
    }]
}

2.2 Authentication Services

2.2.1 Obtaining Authentication Information

auth_GET.json

Authentication is based on the OAuth 2.0 Protocol.

Resource URL (public resource)

GET /foundation/{version}/auth

Parameters

Parameter	Type	Description	Required
oauth2_auth_url	string	URL to authorization page (used for Authorization Code Grant and Implicit Grant OAuth2 flows)	false
oauth2_token_url	string	URL for token requests	false
oauth2_dynamic_client_reg_url	string	URL for automated client registration	false
http_basic_supported	boolean	Indicates if Http Basic Authentication is supported	false
supported_oauth2_flows	string[]	array of supported OAuth2 flows	true

If oauth2_auth_url is present, then oauth2_token_url must also be present and vice versa. If properties are not present in the response, clients should assume that the functionality is not supported by the server, e.g. a missing http_basic_supported property would indicate that Http basic authentication is not available on the server.

OAuth2 flows are described in detail in the OAuth2 specification. OpenCDE API servers may support the following flows:

• authorization_code_grant - 4.1 - Authorization Code Grant
• implicit_grant - 4.2 - Implicit Grant
• resource_owner_password_credentials_grant - 4.3 - Resource Owner Password Credentials Grant

The OAuth2 Client Credentials Grant (section 4.4) is not supported since it does not contain any user identity. Also the Extension Grants (section 4.5) are not supported.

Example Request

GET /foundation/{version}/auth

Example Response

Response Code: 200 - OK
Body:
{
    "oauth2_auth_url": "https://example.com/foundation/oauth2/auth",
    "oauth2_token_url": "https://example.com/foundation/oauth2/token",
    "oauth2_dynamic_client_reg_url": "https://example.com/foundation/oauth2/reg",
    "http_basic_supported": true,
    "supported_oauth2_flows": [
        "authorization_code_grant",
        "implicit_grant",
        "resource_owner_password_credentials_grant"
    ]
}

2.2.2 OAuth2 Example

An example for the OAuth2 Authorization Grant workflow can be found here.

2.2.3 OAuth2 Protocol Flow - Dynamic Client Registration

dynRegClient_POST.json

dynRegClient_GET.json

The following part describes the optional dynamic registration process of a client. OpenCDE API Servers may offer additional processes registering clients, for example allowing a client application developer to register his client on the servers website.

The resource url for this service is server specific and is returned as oauth2_dynamic_client_reg_url in the GET /foundation/{version}/auth resource.

Register a new client :

Parameters

JSON encoded body using the application/json content type.

parameter	type	description
client_name	string	The client name
client_description	string	The client description
client_url	string	An URL providing additional information about the client
redirect_url	string	An URL where users are redirected after granting access to the client

Example Request

POST https://example.com/foundation/oauth2/reg
Body:
{
    "client_name": "Example Application",
    "client_description": "Example CAD desktop application",
    "client_url": "http://example.com",
    "redirect_url": "http://localhost:8080"
}

Example Response

Response Code: 201 - Created
Body:
{
    "client_id": "cGxlYXN1cmUu",
    "client_secret": "ZWFzdXJlLg=="
}

---

3. Directory Services

3.1 User Services

3.1.1 Get current user

user_GET.json

Resource URL

GET /foundation/{version}/current-user

Example Request

GET /foundation/1.0/current-user

Example Response

Response Code: 200 - OK
Body:
{
    "id": "Architect@example.com",
    "name": "John Doe"
}