fix content-length header not being sent when messages have empty bodies since streaming mode was used in these cases (#755)

Author: felixdivo

fuel/src/main/kotlin/com/github/kittinunf/fuel/toolbox/HttpClient.kt

@@ -234,7 +234,11 @@ class HttpClient(
 
     private fun setBodyIfDoOutput(connection: HttpURLConnection, request: Request) {
         val body = request.body
-        if (!connection.doOutput || body.isEmpty()) {
+        if (!connection.doOutput) {
+            return
+        }
+        if (body.isEmpty()) {
+            connection.setFixedLengthStreamingMode(0L)
             return
         }
 

fuel/src/test/kotlin/com/github/kittinunf/fuel/toolbox/HttpClientTest.kt

@@ -56,7 +56,19 @@ class HttpClientTest : MockHttpTestCase() {
     }
 
     @Test
-    fun setsContentLengthIfKnown() {
+    fun setsContentLengthIfKnownZero() {
+        val request = reflectedRequest(Method.POST, "content-length-test")
+                .body("")
+
+        val (_, _, result) = request.responseObject(MockReflected.Deserializer())
+        val (data, error) = result
+
+        assertThat("Expected data, actual error $error", data, notNullValue())
+        assertThat(data!![Headers.CONTENT_LENGTH].firstOrNull(), equalTo("0"))
+    }
+
+    @Test
+    fun setsContentLengthIfKnownNonZero() {
         val request = reflectedRequest(Method.POST, "content-length-test")
             .body("my-body")