How can I capture a Retrofit response error in onResponse?

Question

I'm using Retrofit2 in an Android app. Here's my response code:

override fun onResponse(call: Call<Asset>?, response: Response<Asset>?) {

                val errorStart = response?.errorBody()?.string() // I get "ERROR" here

                if (response != null && response.isSuccessful) {
                    // A successful response was returned
                    completion(response.body(), null)
                } else {
                    // Not success
                    val errorElse = response?.errorBody()?.string() // I get "" here

                    val error = Error(errorText)
                    completion(null,error)
                }
            }

and here's the code I'm using to test my code:

response = Response.Builder()
                            .code(403)
                            .message(responseString)
                            .request(chain.request())
                            .protocol(Protocol.HTTP_1_0)
                            .body(ResponseBody.create(MediaType.parse("application/json"), "ERROR"))
                            .addHeader("content-type", "application/json")
                            .build()

When the code run and a response is returned response?.errorBody()?.string() is a string and I can capture it, as I have in this code as val errorStart. ...But... when I run the IF code/logic and attempt to capture response?.errorBody()?.string() in the else code block it's now blank/gone.

Can someone explain what's going on or what I'm doing wrong? What is the proper way to capture error information in OnResponse?

Answer 1

First of all the errorBody() is of type stream, meaning that it is not read until you call the method. Streams can be read only once, take a look here for a detailed explanation.