Are you getting the same error when you don´t set a converter factory?

I didn't test without the converter. I guess it will not fail because GsonResponseBodyConverter.convert will not run. Is there any reason why i should check without the converter?

What behavior do you expect when the body is empty then?

You are telling Retrofit to deserialize the response as a certain object and Retrofit tells Gson to parse the stream into that type and the type is empty. This behavior already seems very reasonable to me.

Just return an "empty" pojo response (Like it was until now)... all fields null? It's a real problem...for example I didn't write the server side, just the Android App...The server side returns 200 with empty body...but there are times that the same call will return a 200 with a body message. I have nothing to do in situations like that

An empty pojo is {} in JSON.

You can write a delegating converter that does this, the behavior will not be added to Retrofit by default.

class NullOnEmptyConverterFactory implements Converter.Factory {
  @Override public Converter<ResponseBody, ?> responseBody(Type type, Annotation[] annotations, Retrofit retrofit) {
    final Converter<ResponseBody, ?> delegate = retrofit.nextResponseBodyConverter(this, type, annotations);
    return new Converter<>() {
      @Override public void convert(ResponseBody body) {
        if (body.contentLength() == 0) return null;
        return delegate.convert(body);
      }
    };
  }
}

Retrofit retrofit = new Retrofit.Builder()
    .endpoint(..)
    .addConverterFactory(new NullOnEmptyConverterFactory())
    .addConverterFactory(GsonConverterFactory.create())
    .build();

I had to implement this for a requirement from my services team. Here is the updated code I used for release version of Retrofit 2.0 that seems to be working in case anyone else comes across the issue.

public class NullOnEmptyConverterFactory extends Converter.Factory {

    @Override
    public Converter<ResponseBody, ?> responseBodyConverter(Type type, Annotation[] annotations, Retrofit retrofit) {
        final Converter<ResponseBody, ?> delegate = retrofit.nextResponseBodyConverter(this, type, annotations);
            return new Converter<ResponseBody, Object>() {
                @Override
                public Object convert(ResponseBody body) throws IOException {
                    if (body.contentLength() == 0) return null;
                    return delegate.convert(body);                }
            };
    }
}

body.contentLength() always returns -1 on me. What to do?

Just read it. That means unknown content length.

On Wed, May 11, 2016, 11:51 PM nAkhmedov notifications@github.com wrote:

body.contentLength() always returns -1 on me. What to do?

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#1554 (comment)

05-12 11:57:35.040 12039-13092/com.sms.sendsms D/OkHttp: <-- 200 OK http://www.yesplease.co.il/app/login.asp?username=zolim2&password=123456g (554ms)
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: Cache-Control: must-revalidate,no-cache,private
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: Content-Type: text/html; Charset=utf-8
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: Expires: Wed, 11 May 2016 06:58:56 GMT
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: Vary: Accept-Encoding
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: Server: Microsoft-IIS/7.5
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: X-Powered-By: Yes Please
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: Server: Server
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: Date: Thu, 12 May 2016 06:58:56 GMT
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: Connection: Keep-Alive
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: Set-Cookie: source=; path=/
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: Set-Cookie: ASPSESSIONIDCSASTAQA=NCLNDGIBMFFIEGMOBHIABCEC; path=/
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: OkHttp-Sent-Millis: 1463036254545
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: OkHttp-Received-Millis: 1463036255040
05-12 11:57:35.041 12039-13092/com.sms.sendsms D/OkHttp: <-- END HTTP (0-byte body)
05-12 11:57:35.081 12039-12039/com.sms.sendsms W/System.err: java.io.EOFException: End of input at line 1 column 1

HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();//If need to logging, just uncomment
interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
OkHttpClient client = new OkHttpClient.Builder()
.addInterceptor(interceptor)
.build();
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(ContextConstants.APP_URL)
.addConverterFactory(new NullOnEmptyConverterFactory())
.addConverterFactory(GsonConverterFactory.create())
.client(client)
.build();

I add the NullOnEmptyConverterFactory to the retrofit, and still gets the error.Then I find the order is important.

Retrofit retrofit = new Retrofit.Builder()
    .endpoint(..)
    .addConverterFactory(new NullOnEmptyConverterFactory()) //this should come first
    .addConverterFactory(GsonConverterFactory.create())
    .build();

help for Kotlin devs

val nullOnEmptyConverterFactory = object : Converter.Factory() {
    fun converterFactory() = this
    override fun responseBodyConverter(type: Type, annotations: Array<out Annotation>, retrofit: Retrofit) = object : Converter<ResponseBody, Any?> {
        val nextResponseBodyConverter = retrofit.nextResponseBodyConverter<Any?>(converterFactory(), type, annotations)
        override fun convert(value: ResponseBody) = if (value.contentLength() != 0L) nextResponseBodyConverter.convert(value) else null
    }
}