Akka Http how to add charset utf-8 to the content-type header

[Thibault Meyer]

Hello,

I dont find how to set the content type to "application/json; charset=UTF-8" with the completeOKWithFuture and Jackson marshaller. Currently, Akka Http return the Content-Type "application/json" without specifying the charset. So in some browsers (like Opera or Chrome) the output text is not good.

get(() -> {
  final MessageDispatcher dispatcher = akkaSystem.dispatchers().lookup("application.dispatcher");
  return completeOKWithFuture(CompletableFuture.supplyAsync(() -> {
    final Map<String, Object> result = new HashMap<>();
    result.put("trackingNumber", trackingNumber);
    ArrayList<Map<String, String>> status;
    if (this.cache == null) {
      status = TrackingCrawler.parseDocument(trackingNumber);
    } else {
      status = this.cache.readFromCache("tracking." + trackingNumber);
      if (status == null) {
        status = TrackingCrawler.parseDocument(trackingNumber);
        this.cache.writeToCache(
          "tracking." + trackingNumber,
          status
        );
      }
    }
    result.put("status", status);
    return result;
  }, dispatcher).exceptionally(ex -> {
    LOG.error("Something goes wrong", ex);
    return new HashMap<>();
  }), Jackson.marshaller());
})

Sincerly.

[Alex Cozzi]

funny, I was looking into this yesterday!

I am by no means an expert, but I think that what it is happening is the following: 

application/json implies UTF-8: if you look at the MediaType class from akka http you se the declaration:

val `application/json` = awfc("json", HttpCharsets.`UTF-8`, "json")

second,  get the data from your service with curl/wget and have a look. When I did in my experiment the data in the file was correctly rendered as UTF-8. 

now, why non-ascii characters are messed up when you look at it in the browser? I think that the browser is trying to render json as HTML, and since the data is not html it defaults to HTML default encoding, which is ISO-8859-1 (https://www.w3schools.com/html/html_charset.asp), so it renders your data incorrectly.

In conclusion I believe that is not akka http at fault, but the default behavior of all web browser (I saw it on chrome and safari): your data is fine, it is just displayed wrongly when you look at it in a browser

Alex

[Alan Burlison]

On 05/05/17 18:42, Alex Cozzi wrote:

> funny, I was looking into this yesterday!
> I am by no means an expert, but I think that what it is happening is the
> following:
> application/json implies UTF-8: if you look at the MediaType class from
> akka http you se the declaration:

I believe you are correct, http://www.ietf.org/rfc/rfc4627.txt says:

3. Encoding
JSON text SHALL be encoded in Unicode. The default encoding is UTF-8.

so an explicit MIME type isn't required if the content is UTF-8 - but
other JSON frameworks do often seem to include the UTF-8 charset.

As far as I know there's no "proper" way of forcing the addition of the
charset to the application/json content type in Akka-HTTP but it is
possible to hack around it:

val ct = ContentType(MediaType.custom("application/json",
false).asInstanceOf[MediaType.WithOpenCharset], HttpCharset.custom("utf-8"))

--
Alan Burlison
--

[Greg Methvin]

There is no charset parameter defined for application/json. See https://www.iana.org/assignments/media-types/application/json

The encoding should not be determined by looking at the charset parameter, but rather by looking at the first four octets: https://tools.ietf.org/html/rfc4627#section-3

If you absolutely have to deal with non-conforming parsers, the custom media type is probably the right way to go.

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[Thibault Meyer]

Hi Greg,

how to do this ? I see no arguments in completeOKWithFuture or Jackson.marshaller() to do this. I'm using Java version of akka-http.

Thanks

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[johannes...@lightbend.com]

Hi Thibault,

you are right, there's currently no built-in way to do this. To achieve it, you could e.g. copy the Jackson marshaller from the sources to use a custom media type. See here: https://github.com/akka/akka-http/blob/5932237a86a432d623fafb1e84eeeff56d7485fe/akka-http-marshallers-java/akka-http-jackson/src/main/java/akka/http/javadsl/marshallers/jackson/Jackson.java#L27-L27

Johannes

[Thibault Meyer]

Hi Johannes,

Thanks for the tips. It now working !

Sincerly