Add S3ByteArrayFetching as a guiding alias

aws-s3/aws-sdk-v2/src/main/scala/com/gu/etagcaching/aws/sdkv2/s3/S3ObjectFetching.scala

@@ -1,8 +1,9 @@
 package com.gu.etagcaching.aws.sdkv2.s3
 
 import com.gu.etagcaching.Endo
-import com.gu.etagcaching.aws.s3.ObjectId
+import com.gu.etagcaching.aws.s3.{ObjectId, S3ByteArrayFetching, S3ObjectFetchingUsing}
 import com.gu.etagcaching.aws.sdkv2.s3.response.Transformer
+import com.gu.etagcaching.aws.sdkv2.s3.response.Transformer.Bytes
 import com.gu.etagcaching.fetching.{ETaggedData, Fetching, Missing, MissingOrETagged}
 import software.amazon.awssdk.core.internal.util.ThrowableUtils
 import software.amazon.awssdk.services.s3.S3AsyncClient
@@ -42,3 +43,10 @@ case class S3ObjectFetching[Response](s3Client: S3AsyncClient, transformer: Tran
     }
 }
 
+object S3ObjectFetching extends S3ObjectFetchingUsing[S3AsyncClient] {
+  /**
+   * Convenience method for creating a fetcher that just returns a simple byte array.
+   */
+  def byteArrayWith(s3AsyncClient: S3AsyncClient): S3ByteArrayFetching =
+    S3ObjectFetching(s3AsyncClient, Bytes).mapResponse(_.asByteArray())
+}

aws-s3/base/src/main/scala/com/gu/etagcaching/aws/s3/S3ObjectFetchingUsing.scala

@@ -0,0 +1,5 @@
+package com.gu.etagcaching.aws.s3
+
+trait S3ObjectFetchingUsing[AWSClient] {
+  def byteArrayWith(awsClient: AWSClient): S3ByteArrayFetching
+}

aws-s3/base/src/main/scala/com/gu/etagcaching/aws/s3/package.scala

@@ -0,0 +1,18 @@
+package com.gu.etagcaching.aws
+
+import com.gu.etagcaching.fetching.Fetching
+
+package object s3 {
+  /**
+   * To get an instance of `S3ByteArrayFetching`, add "com.gu.etag-caching" %% "aws-s3-sdk-v2"
+   * as a dependency, then:
+   *
+   * {{{
+   * import com.gu.etagcaching.aws.sdkv2.s3.S3ObjectFetching
+   *
+   * val s3AsyncClient: software.amazon.awssdk.services.s3.S3AsyncClient = ??? // use AWS SDK v2
+   * val s3Fetching: S3ByteArrayFetching = S3ObjectFetching.byteArrayWith(s3AsyncClient)
+   * }}}
+   */
+  type S3ByteArrayFetching = Fetching[ObjectId, Array[Byte]]
+}