! http: introduce a distinction between "?key=" and "?key" in queries, …

…fixes #460

The breaking change is that a parse/render round-trip will reproduce a
trailing '=' if the value is empty as well as no trailing '=' if it was
originally missing.

Also, the default behavior was changed so that '=' is always rendered even
for empty values unless you use the special value `Query.EmptyValue`.

spray-http/src/main/scala/spray/http/Uri.scala

@@ -438,7 +438,8 @@ object Uri {
           case Query.Cons(key, value, tail) ⇒
             if (q ne this) r ~~ '&'
             enc(key)
-            if (!value.isEmpty) { r ~~ '='; enc(value) }
+            if (value ne Query.EmptyValue) r ~~ '='
+            enc(value)
             append(tail)
           case Query.Raw(value) ⇒ r ~~ value
         }
@@ -447,6 +448,9 @@ object Uri {
     override def newBuilder: mutable.Builder[(String, String), Query] = Query.newBuilder
   }
   object Query {
+    /** A special empty String value which will be rendered without a '=' after the key. */
+    val EmptyValue: String = new String(Array.empty[Char])
+
     /**
      * Parses the given String into a Query instance.
      * Note that this method will never return Query.Empty, even for the empty String.

spray-http/src/main/scala/spray/http/parser/UriParser.scala

@@ -302,7 +302,7 @@ private[http] class UriParser(input: ParserInput, charset: Charset, mode: Uri.Pa
     // putting some pressure onto the JVM stack
     def readKVP(): Query = {
       val key = part
-      val value = if (ch('=')) part else ""
+      val value = if (ch('=')) part else Query.EmptyValue
       val tail = if (ch('&')) readKVP() else Query.Empty
       Query.Cons(key, value, tail)
     }

spray-http/src/test/scala/spray/http/UriSpec.scala

@@ -361,8 +361,8 @@ class UriSpec extends Specification {
       // queries
       normalize("?") === "?"
       normalize("?key") === "?key"
-      normalize("?key=") === "?key" // our query model cannot discriminate between these two inputs
-      normalize("?key=&a=b") === "?key&a=b" // our query model cannot discriminate between these two inputs
+      normalize("?key=") === "?key="
+      normalize("?key=&a=b") === "?key=&a=b"
       normalize("?key={}&a=[]") === "?key=%7B%7D&a=%5B%5D"
       normalize("?key={}&a=[]", mode = Uri.ParsingMode.Strict) must throwAn[IllegalUriException]
       normalize("?=value") === "?=value"

spray-httpx/src/test/scala/spray/httpx/marshalling/BasicMarshallersSpec.scala

@@ -45,8 +45,8 @@ class BasicMarshallersSpec extends Specification {
   "The FormDataMarshaller" should {
     "properly marshal FormData instances to application/x-www-form-urlencoded entity bodies" in {
       marshal(FormData(Map("name" -> "Bob", "pass" -> "hällo", "admin" -> ""))) ===
-        Right(HttpEntity(ContentType(`application/x-www-form-urlencoded`, `UTF-8`), "name=Bob&pass=h%E4llo&admin"))
+        Right(HttpEntity(ContentType(`application/x-www-form-urlencoded`, `UTF-8`), "name=Bob&pass=h%E4llo&admin="))
     }
   }
 
-}
+}