finatra-http: Get rid of MediaType

Problem

MediaType is one of our last guava dependencies, so we'll be able to start
removing guava once we can get rid of it.

Solution

Replace MediaType with a String everywhere the finatra API requires a MediaType,
and rely on method in finagle's MediaType to check equality for media types and
handle utf8 charsets.

JIRA Issues: CSL-5672

Differential Revision: https://phabricator.twitter.biz/D308761

CHANGELOG.rst

@@ -7,6 +7,14 @@ Note that ``PHAB_ID=#`` and ``RB_ID=#`` correspond to associated messages in com
 Unreleased
 ----------
 
+New Features
+~~~~~~~~~~~~
+
+* finagle-http: Add two new methods to `com.twitter.finagle.http.MediaType`,
+  `MediaType#typeEquals` for checking if two media types have the same type and
+  subtype, ignoring their charset, and `MediaType#addUtf8Charset` for easily
+  setting a utf-8 charset.  ``PHAB_ID=D308761``
+
 Runtime Behavior Changes
 ~~~~~~~~~~~~~~~~~~~~~~~~
 

finagle-base-http/src/main/scala/com/twitter/finagle/http/MediaType.scala

@@ -6,19 +6,49 @@ object MediaType {
   val Csv = "application/csv"
   val Gif = "image/gif"
   val Html = "text/html"
+  val HtmlUtf8 = "text/html; charset=utf-8"
   val Iframe = "application/iframe"
   val Javascript = "application/javascript"
   val Jpeg = "image/jpeg"
   val Json = "application/json"
+  val JsonUtf8 = "application/json; charset=utf-8"
   val JsonPatch = "application/json-patch+json"
   val MultipartForm = "multipart/form-data"
   val OctetStream = "application/octet-stream"
   val PlainText = "text/plain"
+  val PlainTextUtf8 = "text/plain; charset=utf-8"
   val Png = "image/png"
   val Rss = "application/rss+xml"
   val Txt = "text/plain"
   val WwwForm = "application/x-www-form-urlencoded"
   val Xls = "application/vnd.ms-excel"
   val Xml = "application/xml"
+  val XmlUtf8 = "application/xml; charset=utf-8"
   val Zip = "application/zip"
+
+  /**
+   * Adds a utf-8 charset parameter to a media type string.
+   *
+   * Note that if a charset is already set that it will add a second one,
+   * it does not inspect the provided media type.
+   */
+  def addUtf8Charset(mediaType: String): String =
+    mediaType + "; charset=utf-8"
+
+  /**
+   * Checks equality for two media types, based on their type and subtype.
+   *
+   * This ignores media type parameters and suffixes.
+   */
+  def typeEquals(left: String, right: String): Boolean = {
+    val leftIndex = {
+      val index = left.indexOf(';')
+      if (index == -1) left.length else index
+    }
+    val rightIndex = {
+      val index = right.indexOf(';')
+      if (index == -1) right.length else index
+    }
+    (leftIndex == rightIndex) && left.regionMatches(0, right, 0, leftIndex)
+  }
 }