Made DefaultErrorHandler extensible

typedrest/src/main/kotlin/net/typedrest/errors/DefaultErrorHandler.kt

@@ -4,31 +4,35 @@ import kotlinx.serialization.*
 import kotlinx.serialization.json.Json
 import net.typedrest.http.HttpStatusCode
 import okhttp3.Response
-import java.io.IOException
+import okhttp3.ResponseBody
 
 /**
  * Handles errors in HTTP responses by mapping status codes to common exception types.
  */
-class DefaultErrorHandler : ErrorHandler {
+open class DefaultErrorHandler : ErrorHandler {
     @Throws(HttpException::class)
     override fun handle(response: Response) {
         if (response.isSuccessful) return
 
-        val body = response.body?.string()
-        val message = extractJsonMessage(response, body)
+        val message = response.body?.let(::extractJsonMessage)
             ?: "${response.request.url} responded with ${response.code} ${response.message}"
 
         throw mapException(HttpStatusCode.parse(response.code) ?: HttpStatusCode.InternalServerError, message, response)
     }
 
-    private fun extractJsonMessage(response: Response, body: String?): String? {
-        if (body.isNullOrEmpty()) return null
-
-        val mediaType = response.body?.contentType()?.toString()
-        if (mediaType != "application/json" && (mediaType == null || !mediaType.endsWith("+json"))) return null
+    /**
+     * Tries to extract an error message from the response body.
+     *
+     * @param body The response body.
+     */
+    protected open fun extractJsonMessage(body: ResponseBody): String? {
+        val mediaType = body.contentType()?.toString()
+        if (mediaType == null || (mediaType != "application/json" && !mediaType.endsWith("+json"))) {
+            return null
+        }
 
         return try {
-            val decoded = Json.decodeFromString<JsonErrorResponse>(body)
+            val decoded = Json.decodeFromString<JsonErrorResponse>(body.string())
             return decoded.message ?: decoded.details
         } catch (e: SerializationException) {
             null
@@ -38,7 +42,14 @@ class DefaultErrorHandler : ErrorHandler {
     @Serializable
     private class JsonErrorResponse(val message: String?, val details: String? = null)
 
-    private fun mapException(status: HttpStatusCode, message: String, response: Response?) =
+    /**
+     * Maps the HTTP status code to an exception.
+     *
+     * @param status The status code.
+     * @param message An error message to include in the exception.
+     * @param response The HTTP response to include in the exception.
+     */
+    protected open fun mapException(status: HttpStatusCode, message: String, response: Response?) =
         when (status) {
             HttpStatusCode.BadRequest -> BadRequestException(message, status, response)
             HttpStatusCode.Unauthorized -> AuthenticationException(message, status, response)