Ensure S3InputStream is lazy

Author: cyberdelia

Diff for: src/main/kotlin/com/lapanthere/signals/S3InputStream.kt

@@ -13,6 +13,7 @@ import software.amazon.awssdk.services.s3.model.GetObjectRequest
 import software.amazon.awssdk.services.s3.model.HeadObjectRequest
 import java.io.InputStream
 import java.io.SequenceInputStream
+import java.time.Instant
 import java.util.Enumeration
 
 internal val AVAILABLE_PROCESSORS = Runtime.getRuntime().availableProcessors()
@@ -35,14 +36,13 @@ public class S3InputStream(
     mutator: (GetObjectRequest.Builder) -> Unit = {}
 ) : InputStream() {
     private val scope = CoroutineScope(Dispatchers.IO)
-    private val parts = byteRange(
-        s3.headObject(
-            HeadObjectRequest.builder()
-                .bucket(bucket)
-                .key(key)
-                .build()
-        ).get().contentLength()
-    )
+    private val s3Object = s3.headObject(
+        HeadObjectRequest.builder()
+            .bucket(bucket)
+            .key(key)
+            .build()
+    ).get()
+    private val parts = byteRange(s3Object.contentLength())
     private val streams = parts.mapIndexed { i, (begin, end) ->
         scope.async(CoroutineName("chunk-${i + 1}"), CoroutineStart.LAZY) {
             s3.getObject(
@@ -56,26 +56,38 @@ public class S3InputStream(
             ).await().asInputStream()
         }
     }.toMutableList()
-    private val buffer = SequenceInputStream(
-        object : Enumeration<InputStream> {
-            private val iterator = streams.iterator()
+    private val buffer: SequenceInputStream by lazy {
+        SequenceInputStream(
+            object : Enumeration<InputStream> {
+                private val iterator = streams.iterator()
 
-            override fun hasMoreElements(): Boolean {
-                // Starts downloading the next chunks ahead.
-                streams.take(parallelism).forEach { it.start() }
-                return iterator.hasNext()
-            }
+                override fun hasMoreElements(): Boolean {
+                    // Starts downloading the next chunks ahead.
+                    streams.take(parallelism).forEach { it.start() }
+                    return iterator.hasNext()
+                }
 
-            override fun nextElement(): InputStream = runBlocking {
-                iterator.use { it.await() }
+                override fun nextElement(): InputStream = runBlocking {
+                    iterator.use { it.await() }
+                }
             }
-        }
-    )
-
-    override fun read(): Int {
-        return buffer.read()
+        )
     }
 
+    public val eTag: String? = s3Object.eTag()
+    public val contentLength: Long? = s3Object.contentLength()
+    public val lastModified: Instant? = s3Object.lastModified()
+    public val metadata: Map<String, String> = s3Object.metadata()
+    public val contentType: String? = s3Object.contentType()
+    public val contentEncoding: String? = s3Object.contentEncoding()
+    public val contentDisposition: String? = s3Object.contentDisposition()
+    public val contentLanguage: String? = s3Object.contentLanguage()
+    public val versionId: String? = s3Object.versionId()
+    public val cacheControl: String? = s3Object.cacheControl()
+    public val expires: Instant? = s3Object.expires()
+
+    override fun read(): Int = buffer.read()
+
     override fun close() {
         buffer.close()
     }

Diff for: src/test/kotlin/com/lapanthere/signals/S3InputStreamTest.kt

@@ -16,7 +16,7 @@ import java.util.concurrent.CompletableFuture
 import kotlin.test.Test
 import kotlin.test.assertFailsWith
 
-class S3InputStreamTest {
+internal class S3InputStreamTest {
     private val bucket = "bucket"
     private val key = "key"
     private val s3: S3AsyncClient = mockk {
@@ -30,6 +30,8 @@ class S3InputStreamTest {
         } returns CompletableFuture.completedFuture(
             HeadObjectResponse.builder()
                 .contentLength(6_291_456)
+                .contentEncoding("application/json")
+                .eTag("d41d8cd98f00b204e9800998ecf8427e-2")
                 .build()
         )
         every {
@@ -59,7 +61,7 @@ class S3InputStreamTest {
     }
 
     @Test
-    fun testDownload() {
+    fun `download a file`() {
         ByteArrayOutputStream().use { target ->
             S3InputStream(bucket = bucket, key = key, s3 = s3).use { stream ->
                 stream.copyTo(target)
@@ -96,7 +98,23 @@ class S3InputStreamTest {
     }
 
     @Test
-    fun testFailure() {
+    fun `downloading starts when reading starts`() {
+        S3InputStream(bucket = bucket, key = key, s3 = s3)
+        verify(exactly = 1) {
+            s3.headObject(
+                HeadObjectRequest.builder()
+                    .bucket(bucket)
+                    .key(key)
+                    .build()
+            )
+        }
+        verify(exactly = 0) {
+            s3.getObject(any<GetObjectRequest>(), any<ByteArrayAsyncResponseTransformer<GetObjectResponse>>())
+        }
+    }
+
+    @Test
+    fun `handle exception on failure`() {
         every {
             s3.getObject(
                 GetObjectRequest.builder()

Diff for: src/test/kotlin/com/lapanthere/signals/S3OutputStreamTest.kt

@@ -22,7 +22,7 @@ import java.util.concurrent.CompletableFuture
 import kotlin.test.Test
 import kotlin.test.assertFailsWith
 
-class S3OutputStreamTest {
+internal class S3OutputStreamTest {
     private val uploadID = "upload-id"
     private val bucket = "bucket"
     private val key = "key"
@@ -96,7 +96,7 @@ class S3OutputStreamTest {
     }
 
     @Test
-    fun testUpload() {
+    fun `uploads a file`() {
         ByteArrayInputStream(ByteArray(32)).use { target ->
             S3OutputStream(bucket = bucket, key = key, s3 = s3).use { stream ->
                 target.copyTo(stream)
@@ -154,7 +154,7 @@ class S3OutputStreamTest {
     }
 
     @Test
-    fun testFailure() {
+    fun `handle exception on failure`() {
         every {
             s3.uploadPart(
                 UploadPartRequest.builder()