by heroku

GitHub Readme.md


Data URIs over HTTP.



Data URIs are great for encoding small amounts of data directly in a URI without requiring a server or storage; however, they are mostly only supported in web browsers. URInception allows Data URIs to be used with any HTTP client, such as curl.

For example, this is a Data URI of an image of a red dot:


Modern web browsers can load this directly, but many clients don't understand the data scheme. URInception is a simple service that serves Data URIs over HTTP. Here is the same image over HTTP:



This is primarily used for integration testing file downloads with contents that can be dynamically generated by the tests themselves. Instead of creating static test fixtures, hosting them somewhere, and hard coding the URI in tests, this service allows the tests to generate Data URIs on the fly without having the host the file anywhere. If clients like curl supported Data URIs directly, this service would not be needed, but this acts an adapter for such clients.


URIs for use with this service can be constructed by the client or server. It is more efficient and simple enough to create them client-side, but a server-side URI builder is provided as convenience and for RESTful symmetry. The urinceptiontest package is also included that runs URInception locally for use with tests in other Go applications that need to test HTTP callouts without external dependencies or network latency.


  1. Create a Data URI as described in RFC 2397.
  2. URL encode the Data URI as described in RFC 2396.
  3. Create a URI with encoded Data URI as the value of the uri query parameter on any path this service.

See the syntax below for details.


POST data to any path on this service and a URI will be returned as a text/uri-list of one. If a Content-Type header is include, it will be used as the Data URI's mediatype; otherwise, the mediatype will be guessed from the data.

For example, to create the URI of the red dot above:

$ curl http://example.com -X POST --data-binary @reddot.png

The mediatype will automatically be detected as image/png; however, if you want to specify it yourself, set the Content-Type header

$ curl http://example.com -X POST --data-binary '<tag/>' -H 'Content-Type: text/xml'

So far these example have not specified a path; however, if one is specified, it will be returned in the URI. This is helpful for clients that expect certain paths or file extensions. The XML example again with a path:

$ curl http://example.com/example.xml -X POST --data-binary '<tag/>' -H 'Content-Type: text/xml'

Testing Go with urinceptiontest package

Package urinceptiontest provides other Go applications a way to run URInception locally for use in tests. Importing urinceptiontest automatically starts an HTTP server on a random port on the local machine. Several methods are provided to create URI fixtures that can be be passed the system under test which will call the local server.

For example, if a test that wants to assert http.Get works, urinceptiontest can be used to create a URI that will return a given response body:

import "github.com/heroku/urinception/urinceptiontest"

// create the URI fixture
txt := "hello world"
uri := urinceptiontest.StringUri(txt)

// pass the URI to the system under test
res, _ := http.Get(uri)
defer res.Body.Close()
bytes, _ := ioutil.ReadAll(res.Body)

// assert the result
obtained := string(bytes)
expected := txt
if obtained != expected {
    t.Errorf("Obtained: '%v'; Expected: '%v'", obtained, expected)

Custom HTTP Statuses

By default, all URIs return an HTTP status of 200 OK; however, this can be overridden with the status parameter.


httpuri    := "http" [ "s" ] "://" host *urlchar "?uri=" datauri [ "&status=" httpstatus ]
datauri    := "data:" [ mediatype ] [ ";base64" ] "," data
mediatype  := [ type "/" subtype ] *( ";" parameter )
data       := *urlchar
parameter  := attribute "=" value
httpstatus := int 


$ go test


$ heroku create
$ git push heroku master

... or just: