Add contentType and charset extension properties to HttpResponse

Signed-off-by: Graham <gpe@openrs2.org>

http/src/main/kotlin/org/openrs2/http/HttpResponseExtensions.kt

@@ -1,7 +1,10 @@
 package org.openrs2.http
 
+import com.google.common.net.HttpHeaders
+import com.google.common.net.MediaType
 import java.io.IOException
 import java.net.http.HttpResponse
+import java.nio.charset.Charset
 
 private val DEFAULT_EXPECTED_STATUS_CODES = setOf(200)
 
@@ -11,3 +14,12 @@ public fun <T> HttpResponse<T>.checkStatusCode(expectedStatusCodes: Set<Int> = D
         throw IOException("Unexpected status code: $status")
     }
 }
+
+public val <T> HttpResponse<T>.contentType: MediaType?
+    get() = headers().firstValue(HttpHeaders.CONTENT_TYPE).map(MediaType::parse).orElse(null)
+
+public val <T> HttpResponse<T>.charset: Charset?
+    get() {
+        val contentType = contentType ?: return null
+        return contentType.charset().orNull()
+    }