[DRAFT] Set StreamReadConstraints.maxStringLength for IR parsing only

How on earth do we get the type checking right!!

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

@@ -27,7 +27,6 @@ import scala.reflect.ClassTag
 import java.io._
 import java.nio.charset.StandardCharsets
 
-import com.fasterxml.jackson.core.StreamReadConstraints
 import org.json4s._
 import org.json4s.jackson.{JsonMethods, Serialization}
 
@@ -55,18 +54,6 @@ trait BackendContext {
 }
 
 abstract class Backend {
-  // From https://github.com/hail-is/hail/issues/14580 :
-  //   IR can get quite big, especially as it can contain an arbitrary
-  //   amount of encoded literals from the user's python session. This
-  //   was a (controversial) restriction imposed by Jackson and should be lifted.
-  //
-  // We remove this restriction for all backends, and we do so here, in the
-  // constructor since constructing a backend is one of the first things that
-  // happens and this constraint should be overrided as early as possible.
-  StreamReadConstraints.overrideDefaultStreamReadConstraints(
-    StreamReadConstraints.builder().maxStringLength(Integer.MAX_VALUE).build()
-  )
-
   val persistedIR: mutable.Map[Int, BaseIR] = mutable.Map()
 
   protected[this] def addJavaIR(ir: BaseIR): Int = {

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

@@ -31,10 +31,11 @@ import java.io._
 import java.nio.charset.StandardCharsets
 import java.util.concurrent._
 
+import com.fasterxml.jackson.databind.DeserializationFeature.USE_BIG_INTEGER_FOR_INTS
+
 import org.apache.log4j.Logger
 import org.json4s.{DefaultFormats, Formats}
 import org.json4s.JsonAST._
-import org.json4s.jackson.JsonMethods
 
 class ServiceBackendContext(
   val billingProject: String,
@@ -464,7 +465,17 @@ object ServiceBackendAPI {
 
     implicit val formats: Formats = DefaultFormats
 
-    val input = using(fs.openNoCompression(inputURL))(JsonMethods.parse(_))
+    val JsonFactory factory = JsonFactory.builder()
+      .streamReadConstraints(StreamReadConstraints.builder().maxStringLength(Integer.MAX_VALUE).build())
+      .build();
+
+    val mapper = new ObjectMapper(factory)
+    mapper.registerModule(new Json4sScalaModule)
+    mapper.configure(USE_BIG_INTEGER_FOR_INTS, true)
+
+    val reader = mapper.readerFor(classOf[JValue])
+    val input = using(fs.openNoCompression(inputURL))(reader.readValue[JValue](_))
+
     val rpcConfig = (input \ "config").extract[ServiceBackendRPCPayload]
 
     // FIXME: when can the classloader be shared? (optimizer benefits!)