From 397de41d032e38d43072e1e7c3fe9634d94a0b29 Mon Sep 17 00:00:00 2001
From: Gary Tierney <gary.tierney@fastmail.com>
Date: Fri, 28 Oct 2022 11:27:04 +0100
Subject: [PATCH] Avoid communicating with S3 unless necessary

Previously the S3 source would eagerly connect to S3 retrieve
information about the object being requested when creating a stream.
This change defers retrieval of properties from S3 until needed by the
S3StreamFactory, and allows cached files to be served directly from disk
with no intermediate S3 lookups.
---
 .../cantaloupe/source/S3ObjectInfoSupplier.java       | 11 +++++++++++
 .../illinois/library/cantaloupe/source/S3Source.java  |  8 +++++---
 .../library/cantaloupe/source/S3StreamFactory.java    |  6 ++++--
 .../cantaloupe/source/S3StreamFactoryTest.java        |  2 +-
 4 files changed, 21 insertions(+), 6 deletions(-)
 create mode 100644 src/main/java/edu/illinois/library/cantaloupe/source/S3ObjectInfoSupplier.java

diff --git a/src/main/java/edu/illinois/library/cantaloupe/source/S3ObjectInfoSupplier.java b/src/main/java/edu/illinois/library/cantaloupe/source/S3ObjectInfoSupplier.java
new file mode 100644
index 000000000..f48a9651b
--- /dev/null
+++ b/src/main/java/edu/illinois/library/cantaloupe/source/S3ObjectInfoSupplier.java
@@ -0,0 +1,11 @@
+package edu.illinois.library.cantaloupe.source;
+
+import java.io.IOException;
+
+/**
+ * Deferred accessor to {@link S3ObjectInfo}.
+ */
+@FunctionalInterface
+public interface S3ObjectInfoSupplier {
+    S3ObjectInfo get() throws IOException;
+}
diff --git a/src/main/java/edu/illinois/library/cantaloupe/source/S3Source.java b/src/main/java/edu/illinois/library/cantaloupe/source/S3Source.java
index 93db8621f..67ac60fe3 100644
--- a/src/main/java/edu/illinois/library/cantaloupe/source/S3Source.java
+++ b/src/main/java/edu/illinois/library/cantaloupe/source/S3Source.java
@@ -422,9 +422,11 @@ private S3ObjectInfo getObjectInfoUsingDelegateStrategy()
 
     @Override
     public StreamFactory newStreamFactory() throws IOException {
-        S3ObjectInfo info = getObjectInfo();
-        info.setLength(getObjectAttributes().length);
-        return new S3StreamFactory(info);
+        return new S3StreamFactory(() -> {
+            S3ObjectInfo info = getObjectInfo();
+            info.setLength(getObjectAttributes().length);
+            return info;
+        });
     }
 
     @Override
diff --git a/src/main/java/edu/illinois/library/cantaloupe/source/S3StreamFactory.java b/src/main/java/edu/illinois/library/cantaloupe/source/S3StreamFactory.java
index d08a0af76..d27d92db3 100644
--- a/src/main/java/edu/illinois/library/cantaloupe/source/S3StreamFactory.java
+++ b/src/main/java/edu/illinois/library/cantaloupe/source/S3StreamFactory.java
@@ -24,14 +24,15 @@ class S3StreamFactory implements StreamFactory {
     private static final int DEFAULT_CHUNK_SIZE       = 1024 * 512;
     private static final int DEFAULT_CHUNK_CACHE_SIZE = 1024 * 1024 * 10;
 
-    private S3ObjectInfo objectInfo;
+    private S3ObjectInfoSupplier objectInfo;
 
-    S3StreamFactory(S3ObjectInfo objectInfo) {
+    S3StreamFactory(S3ObjectInfoSupplier objectInfo) {
         this.objectInfo = objectInfo;
     }
 
     @Override
     public InputStream newInputStream() throws IOException {
+        final S3ObjectInfo objectInfo = this.objectInfo.get();
         final InputStream responseStream =
                 S3Source.newObjectInputStream(objectInfo);
 
@@ -100,6 +101,7 @@ public ImageInputStream newSeekableStream() throws IOException {
             LOGGER.debug("newSeekableStream(): using {}-byte chunks",
                     chunkSize);
 
+            final S3ObjectInfo objectInfo = this.objectInfo.get();
             final S3HTTPImageInputStreamClient client =
                     new S3HTTPImageInputStreamClient(objectInfo);
 
diff --git a/src/test/java/edu/illinois/library/cantaloupe/source/S3StreamFactoryTest.java b/src/test/java/edu/illinois/library/cantaloupe/source/S3StreamFactoryTest.java
index c1432a948..3a8082cc3 100644
--- a/src/test/java/edu/illinois/library/cantaloupe/source/S3StreamFactoryTest.java
+++ b/src/test/java/edu/illinois/library/cantaloupe/source/S3StreamFactoryTest.java
@@ -109,7 +109,7 @@ public void setUp() throws Exception {
         info.setKey(FIXTURE_KEY);
         info.setLength(1584);
 
-        instance = new S3StreamFactory(info);
+        instance = new S3StreamFactory(() -> info);
     }
 
     @Test