fix jackson max string length in backend http handler

hail/src/main/scala/is/hail/backend/BackendServer.scala

@@ -82,7 +82,7 @@ class BackendHttpHandler(backend: Backend) extends HttpHandler {
     implicit val formats: Formats = DefaultFormats
 
     try {
-      val body = using(exchange.getRequestBody)(JsonMethods.parse(_))
+      val body = using(exchange.getRequestBody)(parseJSON(_))
       if (exchange.getRequestURI.getPath == "/execute") {
         val config = body.extract[ExecutePayload]
         backend.execute(config.ir, config.timed) { (ctx, res, timings) =>

hail/src/main/scala/is/hail/backend/service/ServiceBackend.scala

@@ -465,10 +465,7 @@ object ServiceBackendAPI {
 
     implicit val formats: Formats = DefaultFormats
 
-    StreamReadConstraints.overrideDefaultStreamReadConstraints(
-      StreamReadConstraints.builder().maxStringLength(Integer.MAX_VALUE).build()
-    );
-    val input = using(fs.openNoCompression(inputURL))(JsonMethods.parse(_))
+    val input = using(fs.openNoCompression(inputURL))(parseJSON(_))
     val rpcConfig = (input \ "config").extract[ServiceBackendRPCPayload]
 
     // FIXME: when can the classloader be shared? (optimizer benefits!)

hail/src/main/scala/is/hail/utils/package.scala

@@ -1,18 +1,18 @@
 package is.hail
 
+import com.fasterxml.jackson.core.StreamReadConstraints
 import is.hail.annotations.ExtendedOrdering
 import is.hail.check.Gen
 import is.hail.expr.ir.ByteArrayBuilder
 import is.hail.io.fs.{FS, FileListEntry}
 
-import scala.collection.{mutable, GenTraversableOnce, TraversableOnce}
+import scala.collection.{GenTraversableOnce, TraversableOnce, mutable}
 import scala.collection.generic.CanBuildFrom
 import scala.collection.mutable.ArrayBuffer
 import scala.concurrent.ExecutionException
 import scala.language.higherKinds
 import scala.reflect.ClassTag
 import scala.util.control.NonFatal
-
 import java.io._
 import java.lang.reflect.Method
 import java.net.{URI, URLClassLoader}
@@ -25,7 +25,6 @@ import java.util.concurrent.{
   ExecutorService, RunnableFuture, TimeUnit,
 }
 import java.util.concurrent.atomic.AtomicBoolean
-
 import com.google.common.util.concurrent.AbstractFuture
 import org.apache.commons.io.output.TeeOutputStream
 import org.apache.commons.lang3.StringUtils
@@ -35,9 +34,9 @@ import org.apache.hadoop.mapreduce.lib.input.{FileSplit => NewFileSplit}
 import org.apache.log4j.Level
 import org.apache.spark.{Partition, TaskContext}
 import org.apache.spark.sql.Row
-import org.json4s.{Extraction, Formats, JObject, NoTypeHints, Serializer}
+import org.json4s.{Extraction, Formats, JObject, JValue, JsonInput, NoTypeHints, Serializer}
 import org.json4s.JsonAST.{JArray, JString}
-import org.json4s.jackson.Serialization
+import org.json4s.jackson.{JsonMethods, Serialization}
 import org.json4s.reflect.TypeInfo
 
 package utils {
@@ -527,6 +526,13 @@ package object utils
 
   val defaultJSONFormats: Formats = Serialization.formats(NoTypeHints) + GenericIndexedSeqSerializer
 
+  def parseJSON(in: JsonInput): JValue = {
+    StreamReadConstraints.overrideDefaultStreamReadConstraints(
+      StreamReadConstraints.builder().maxStringLength(Integer.MAX_VALUE).build()
+    )
+    JsonMethods.parse(in)
+  }
+
   def box(i: Int): java.lang.Integer = i
 
   def box(l: Long): java.lang.Long = l