Content Service

Page Summary

• Apps Script's Content service allows scripts to act as "services" by responding to GET and POST requests with raw textual content of various MIME types instead of a user interface.

• A simple example demonstrates returning "Hello, world!" as plain text using ContentService.createTextOutput().

• The Content service can be used for more complex tasks like modifying and serving RSS feeds by fetching external data, processing it, and setting the appropriate MIME type.

• Scripts can serve JSON data to other scripts or services, as shown with an example that checks calendar availability and returns a JSON object.

• By adding a prefix parameter and setting the MIME type to JAVASCRIPT, JSON services can be transformed into JSONP to be called from JavaScript in a browser, though caution is advised due to security risks.

that return raw textual content of various MIME types.

When a script is published as a web app, the callback functions doGet and doPost execute whenever a request is made to the script's URL. Instead of returning a user interface object created with the HTML service, the Content service can return raw textual content. Write scripts that act as services, responding to GET and POST requests and serving data of various MIME types.

The basics

The following example shows how to use the Content service:

function doGet() {
  return ContentService.createTextOutput('Hello, world!');
}

Deploy the script as a web app. Follow the same steps as serving a user interface. When a GET request is made to the script's URL, the text Hello, world! returns. In addition to plain text, the service supports returning ATOM, CSV, iCal, JavaScript, JSON, RSS, vCard, and XML content.

Serve RSS feeds

Filter an RSS feed to modify its content. For example, edit an XKCD feed to include alt text directly in the feed for better mobile viewing.

function doGet() {
  var feed = UrlFetchApp.fetch('http://xkcd.com/rss.xml').getContentText();
  feed = feed.replace(
    /(<img.*?alt="(.*?)".*?>)/g,
    '$1' + new Array(10).join('<br />') + '$2');
  return ContentService.createTextOutput(feed)
    .setMimeType(ContentService.MimeType.RSS);
}

The code consists of the following components. Use the URL Fetch service to fetch the original XKCD RSS feed. Use a standard JavaScript regular expression to make the substitutions. Wrap the edited feed in a TextOutput object and set the MIME type to RSS.

To see this in action, publish the script as a web app and allow anonymous access. Add the URL of the service to your RSS reader or visit it directly in a web browser.

Serve JSON from scripts

Use the Content service to serve JSON to other scripts, websites, and services. The following script implements a service that checks if a calendar slot is open at a specific time.

function doGet(request) {
  var events = CalendarApp.getEvents(
    new Date(Number(request.parameters.start) * 1000),
    new Date(Number(request.parameters.end) * 1000));
  var result = {
    available: events.length == 0
  };
  return ContentService.createTextOutput(JSON.stringify(result))
    .setMimeType(ContentService.MimeType.JSON);
}

Publish this as an anonymous web app. Users can add URL parameters to the end of the service URL. The start and end parameters specify a time range in the standard Unix epoch.

curl -L URL_OF_YOUR_SCRIPT?start=1325437200&end=1325439000

The service returns JSON that reports if the calendar is open in that range.

{"available":true}

Serve JSONP in web pages

With a slight change, your JSON service can become JSONP to be called from JavaScript in a browser.

function doGet(request) {
  var events = CalendarApp.getEvents(
    new Date(Number(request.parameters.start) * 1000),
    new Date(Number(request.parameters.end) * 1000));
  var result = {
    available: events.length == 0
  };
  return ContentService.createTextOutput(
    request.parameters.prefix + '(' + JSON.stringify(result) + ')')
    .setMimeType(ContentService.MimeType.JAVASCRIPT);
}

To call this service from a browser, create a script tag with a src attribute set to the service URL and an additional prefix parameter. This is the name of the function in your client-side JavaScript that is called with the value returned by the service.

<script src="URL_OF_YOUR_SCRIPT?start=1325437200&end=1325439000&prefix=alert"></script>

This example shows a message box in the browser with the service output, using the browser's built-in alert function as the prefix. The JavaScript code returned looks like:

alert({"available":true})

Be careful when using JSONP. Because anyone can embed the script tag in their web page, you can be tricked into executing the script when visiting a malicious website, which can then capture returned data. Ensure JSONP scripts are read-only and only return non-sensitive information.

Redirects

For security, content returned by the Content service is redirected to a one-time URL at script.googleusercontent.com. If you use the Content service to return data to another application, ensure the HTTP client is configured to follow redirects. For the curl command-line utility, add the flag -L. Check the documentation for your HTTP client for more information.