Issues converting OkHttp request to Retrofit for translation API

[alexj]

I’m having trouble converting my working OkHttp code to use Retrofit instead. I have a working OkHttp implementation that calls a translation service, but when I try to recreate the same request using Retrofit, it doesn’t work properly.

Here’s my current OkHttp code that works fine:

val httpClient = OkHttpClient()

val contentType = MediaType.parse("application/x-www-form-urlencoded")
val requestBody = RequestBody.create(contentType, "text=Good%20morning&lang=fr")
val httpRequest = Request.Builder()
    .url("https://translate-service.p.rapidapi.com/v2/translate")
    .post(requestBody)
    .addHeader("content-type", "application/x-www-form-urlencoded")
    .addHeader("Accept-Encoding", "application/gzip")
    .addHeader("X-RapidAPI-Host", "translate-service.p.rapidapi.com")
    .addHeader("X-RapidAPI-Key", MY_API_KEY)
    .build()

val result = httpClient.newCall(httpRequest).execute()

I’m trying to convert this to Retrofit but not sure about the correct approach. Here’s what I have so far:

interface TranslationService {

    @Headers(
        "content-type: application/x-www-form-urlencoded",
        "Accept-Encoding: application/gzip",
        "X-RapidAPI-Host: translate-service.p.rapidapi.com",
        "X-RapidAPI-Key: MY_API_KEY"
    )
    @POST("v2/translate")
    suspend fun performTranslation(
        @Body text: String,
        @Query("lang") language: String,
        @Query("source") sourceLanguage: String
    ): Response<TranslationResponse>
}

What am I doing wrong with the Retrofit setup?

[Laura219]

The problem is you’re sending form data but Retrofit’s treating it as raw text. Your OkHttp code uses text=Good%20morning&lang=fr as form body, but @Body sends it as a plain string. You need @FormUrlEncoded on the method and swap @Body for @Field("text"). Also change lang from @Query to @Field("lang") since it’s part of the form data.

[benmoore]

You’re mixing form data with query parameters. Your OkHttp code sends text=Good%20morning&lang=fr as form-encoded body data, but your Retrofit interface sends text as a body and lang as a query parameter. Use @FormUrlEncoded on your method and @Field parameters instead of @Body and @Query for proper form encoding. Also, move the API key to an interceptor instead of hardcoding it in headers - it’s cleaner and easier to maintain. I had the same issue migrating from OkHttp to Retrofit and this fixed it immediately.

[Tom_89Paint]

Your problem is that you’re sending form data but Retrofit isn’t set up for it. Your OkHttp code creates a form-encoded request (text=Good%20morning&lang=fr), but your Retrofit method uses @Body which sends raw content instead of form data. Add @FormUrlEncoded to your method and swap @Body and @Query for @Field annotations. Also, Accept-Encoding should probably be application/json, not application/gzip unless the API specifically wants gzip. I hit the same thing migrating old HTTP clients - you’ve got to match the exact request format from your working implementation.