This article provides detailed design information about the Web API design object and its configuration options.
Web APIs provide a way to expose Appian data and services to outside systems. Web APIs are created much like expression rules, however there are two main differences between them. First Web APIs also include an end point that can be called by other systems. Second, a designer doesn't configure rule inputs for Web APIs, instead passing values to the Web API via query parameters, headers, a body, or any combination of the three.
To learn about web API authentication, see Web API Authentication.
HTTP requests made by one web site to another are said to be "cross-origin" because the origin (the url) of the first web site is different than the origin of the other site. Web browsers block requests of this nature by default for security reasons. However, web sites that wish to opt into allowing other sites to access their resources can use a standard called "Cross-Origin Resource Sharing", or CORS, to mark resources as being shareable with other sites. To configure this in Appian, you must add any sites you wish to expose data or services to in this manner to the allowed origins list in the Appian Administration Console.
For POST
, PUT
, and DELETE
Web APIs, adding a web site to the allowed origins list will also exempt that site from Appian's built-in cross-site request forgery (CSRF) protection. You should not add sites that you don't trust to the allowed origins list.
HTTP headers allow the designer to pass additional information with the response. Appian will automatically send several response headers, including Content-Length
, Date
, Server
, and more. The designer can pass any additional headers they deem necessary.
When a document is returned in the body, two headers are automatically added: Content-Type
, and Content-Disposition
. The generated Content-Type
header returns the type of the document. For example, if a GIF file is returned, the value of Content-Type
is image/gif
. The generated Content-Disposition
header holds a value of inline
, indicating that the document will be viewed inline in the browser, rather than being downloaded as an attachment for local viewing. This Content-Disposition
header also contains the filename of the returned document. The designer can override these headers by manually setting them in the headers
parameter of a!httpResponse().
When creating or editing a Web API, designers can select from one of the following HTTP methods: GET
, POST
, PUT
, and DELETE
. Additionally, the HTTP methods OPTIONS
and HEAD
are automatically handled by the system based on the Web APIs that exist in the system for a given Endpoint.
HEAD
requests will execute the Web API for the GET
method for the Endpoint and return the result, minus the response body.
OPTIONS
requests will return a list of methods for which Web APIs exist for a given Endpoint.
For example, assuming that you have two Web APIs with the Endpoint field set to customer, one for GET
and one for POST
, and you make an OPTIONS
request to https://www.example.com/suite/webapi/customer
, the response will looks something like the following.
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HTTP/1.1 200 OK
Date: Tue, 19 Apr 2016 15:27:22 GMT
Server: Apache
Pragma: No-cache
Cache-Control: no-cache
Expires: Thu, 01 Jan 1970 00:00:00 GMT
X-Frame-Options: SAMEORIGIN
Allow: GET, POST, OPTIONS
Content-Length: 0
Keep-Alive: timeout=20, max=100
Connection: Keep-Alive
Content-Type: text/plain
Note that the Allow
header contains entries for both GET
and POST
.
Only Web APIs for the POST
, PUT
, and DELETE
methods may execute smart services. Web APIs for the GET
method will not execute any smart services included in their expression. Attempting to do so will result in the following error message: Smart Services cannot be executed in Web APIs that have a method of "GET."
There are several factors that affect what HTTP status code a Web API returns.
Status Code | Condition |
---|---|
404 | There is no Web API with the specified endpoint and HTTP method |
404 | The user is not in the viewer role or higher for the Web API |
500 | There was an error evaluating the Web API's expression |
500 | The result of the expression evaluation was not an HTTP Response object |
Additionally, designers may specify in their expression a status code that the Web API should return. This allows them to do things like return a 404
code if data about a record that does not exist is requested.
A user must have at least Viewer permissions to a web API in order to execute it.
The security role map of a web API controls which users can see or modify it and its properties. By default, only the web API creator and system administrators have access to the web API. See Editing Object Security to modify an web API's security.
The following table outlines the actions that can be completed for each permission level in a web API's security role map:
Actions | Administrator | Editor | Viewer |
---|---|---|---|
Execute the web API* | Yes | Yes | Yes |
View the web API definition | Yes | Yes | Yes |
View the security | Yes | Yes | Yes |
Update the web API definition | Yes | Yes | No |
Update the security | Yes | No | No |
Delete the web API | Yes | No | No |
*The Administrator user may view, edit, and delete Web APIs but may not execute them. This includes testing them inside the Web API Designer.
Each time you modify and save a Web API, a new version is created. All objects that use the Web API will use the latest version. All versions are accessible to designers who can view the Web API, and a Web API can be reverted back to a previous version at any time.
For information on how to manage object versions, see Managing Object Versions.
Web APIs do not support deleting versions.
Web APIs can also be used to upload a document to Appian. The size of this document is limited to 75 MB.
If there is an error executing the expression associated with a Web API, the error message appears in logs/design_errors.csv
rather than in the standard application server error log.
See also: Web API Performance Logs and Web API Metrics Logs
The performance view shows you detailed performance information for your web API. This allows you to identify and address performance bottlenecks and to understand the impact of particular rules and functions.
The performance view can be accessed using the Performance View option in the gear menu in the header. See the Performance View page for more information on how to use the performance view.