refactor: move inner classes to top level (#2846)

* refactor: move inner classes to top level

Move the gRPC-related inner classes from AbstractResultSet to
top-level classes, so they are easier to modify and maintain.

This change only contains modifications that are needed to move
these inner classes. There are no functional changes.

* feat: support lazy decoding of query results (#2847)

* feat: support lazy decoding of query results

Adds an option for lazy decoding of query results. Currently, all values
in a query result row are decoded from protobuf values to plain Java
objects at the moment that the result set is advanced to the next row.
This means that all values are decoded, regardless whether the
application actually fetches these or not.

Lazy decoding also enables the possibility for (internal) consumers
of a result set to access the protobuf value before it is converted
to a plain Java object. This for example allows ChecksumResultSet to
calculate the checksum based on the protobuf value, instead of a
Java object, which can be more efficient.

* fix: add null check

* perf: calculate checksum using protobuf values (#2848)

* perf: calculate checksum using protobuf values

* chore: cleanup

* test: remove unrelated test

* fix: undo change to public API

* chore: cleanup|

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

README.md

@@ -57,13 +57,13 @@ implementation 'com.google.cloud:google-cloud-spanner'
 If you are using Gradle without BOM, add this to your dependencies:
 
 ```Groovy
-implementation 'com.google.cloud:google-cloud-spanner:6.57.0'
+implementation 'com.google.cloud:google-cloud-spanner:6.58.0'
 ```
 
 If you are using SBT, add this to your dependencies:
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "6.57.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "6.58.0"
 ```
 <!-- {x-version-update-end} -->
 
@@ -444,7 +444,7 @@ Java is a registered trademark of Oracle and/or its affiliates.
 [kokoro-badge-link-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-spanner/java11.html
 [stability-image]: https://img.shields.io/badge/stability-stable-green
 [maven-version-image]: https://img.shields.io/maven-central/v/com.google.cloud/google-cloud-spanner.svg
-[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-spanner/6.57.0
+[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-spanner/6.58.0
 [authentication]: https://github.com/googleapis/google-cloud-java#authentication
 [auth-scopes]: https://developers.google.com/identity/protocols/oauth2/scopes
 [predefined-iam-roles]: https://cloud.google.com/iam/docs/understanding-roles#predefined_roles

google-cloud-spanner/src/main/java/com/google/cloud/spanner/AbstractReadContext.java

@@ -28,9 +28,6 @@
 import com.google.api.gax.core.ExecutorProvider;
 import com.google.cloud.Timestamp;
 import com.google.cloud.spanner.AbstractResultSet.CloseableIterator;
-import com.google.cloud.spanner.AbstractResultSet.GrpcResultSet;
-import com.google.cloud.spanner.AbstractResultSet.GrpcStreamIterator;
-import com.google.cloud.spanner.AbstractResultSet.ResumableStreamIterator;
 import com.google.cloud.spanner.AsyncResultSet.CallbackResponse;
 import com.google.cloud.spanner.AsyncResultSet.ReadyCallback;
 import com.google.cloud.spanner.Options.QueryOption;
@@ -73,6 +70,7 @@ abstract static class Builder<B extends Builder<?, T>, T extends AbstractReadCon
     private TraceWrapper tracer;
     private int defaultPrefetchChunks = SpannerOptions.Builder.DEFAULT_PREFETCH_CHUNKS;
     private QueryOptions defaultQueryOptions = SpannerOptions.Builder.DEFAULT_QUERY_OPTIONS;
+    private DecodeMode defaultDecodeMode = SpannerOptions.Builder.DEFAULT_DECODE_MODE;
     private DirectedReadOptions defaultDirectedReadOption;
     private ExecutorProvider executorProvider;
     private Clock clock = new Clock();
@@ -114,6 +112,11 @@ B setDefaultQueryOptions(QueryOptions defaultQueryOptions) {
       return self();
     }
 
+    B setDefaultDecodeMode(DecodeMode defaultDecodeMode) {
+      this.defaultDecodeMode = defaultDecodeMode;
+      return self();
+    }
+
     B setExecutorProvider(ExecutorProvider executorProvider) {
       this.executorProvider = executorProvider;
       return self();
@@ -414,8 +417,8 @@ void initTransaction() {
   TraceWrapper tracer;
   private final int defaultPrefetchChunks;
   private final QueryOptions defaultQueryOptions;
-
   private final DirectedReadOptions defaultDirectedReadOptions;
+  private final DecodeMode defaultDecodeMode;
   private final Clock clock;
 
   @GuardedBy("lock")
@@ -441,6 +444,7 @@ void initTransaction() {
     this.defaultPrefetchChunks = builder.defaultPrefetchChunks;
     this.defaultQueryOptions = builder.defaultQueryOptions;
     this.defaultDirectedReadOptions = builder.defaultDirectedReadOption;
+    this.defaultDecodeMode = builder.defaultDecodeMode;
     this.span = builder.span;
     this.executorProvider = builder.executorProvider;
     this.clock = builder.clock;
@@ -730,7 +734,8 @@ CloseableIterator<PartialResultSet> startStream(@Nullable ByteString resumeToken
             return stream;
           }
         };
-    return new GrpcResultSet(stream, this);
+    return new GrpcResultSet(
+        stream, this, options.hasDecodeMode() ? options.decodeMode() : defaultDecodeMode);
   }
 
   /**
@@ -874,7 +879,8 @@ CloseableIterator<PartialResultSet> startStream(@Nullable ByteString resumeToken
             return stream;
           }
         };
-    return new GrpcResultSet(stream, this);
+    return new GrpcResultSet(
+        stream, this, readOptions.hasDecodeMode() ? readOptions.decodeMode() : defaultDecodeMode);
   }
 
   private Struct consumeSingleRow(ResultSet resultSet) {