fix: catch CompletionException instead when instruction file is not found (#379)

Author: kessplas

src/main/java/software/amazon/encryption/s3/internal/ContentMetadataDecodingStrategy.java

@@ -10,7 +10,6 @@
 import software.amazon.awssdk.services.s3.S3AsyncClient;
 import software.amazon.awssdk.services.s3.model.GetObjectRequest;
 import software.amazon.awssdk.services.s3.model.GetObjectResponse;
-import software.amazon.awssdk.services.s3.model.NoSuchKeyException;
 import software.amazon.encryption.s3.S3EncryptionClientException;
 import software.amazon.encryption.s3.algorithms.AlgorithmSuite;
 import software.amazon.encryption.s3.materials.EncryptedDataKey;
@@ -24,6 +23,7 @@
 import java.util.Base64;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.CompletionException;
 
 import static software.amazon.encryption.s3.S3EncryptionClientUtilities.INSTRUCTION_FILE_SUFFIX;
 
@@ -233,7 +233,8 @@ private ContentMetadata decodeFromInstructionFile(GetObjectRequest request, GetO
         ResponseInputStream<GetObjectResponse> instruction;
         try {
             instruction = wrappedAsyncClient_.getObject(instructionGetObjectRequest, AsyncResponseTransformer.toBlockingInputStream()).join();
-        } catch (NoSuchKeyException exception) {
+        }
+        catch (CompletionException exception) {
             // Most likely, the customer is attempting to decrypt an object
             // which is not encrypted with the S3 EC.
             throw new S3EncryptionClientException("Instruction file not found! Please ensure the object you are" +

src/test/java/software/amazon/encryption/s3/S3EncryptionClientTest.java

@@ -617,10 +617,15 @@ public void attemptToDecryptPlaintext() {
                 .key(objectKey)
                 .build(), RequestBody.fromString(input));
 
-        // Attempt to get (and decrypt) the (plaintext) object from S3
-        assertThrows(S3EncryptionClientException.class, () -> v3Client.getObject(builder -> builder
-                .bucket(BUCKET)
-                .key(objectKey)));
+        try {
+            v3Client.getObject(builder -> builder
+                    .bucket(BUCKET)
+                    .key(objectKey));
+            fail("expected exception");
+        } catch (S3EncryptionClientException ex) {
+            assertTrue(ex.getMessage().contains("Instruction file not found!"));
+            assertEquals(ex.getCause().getClass(), S3EncryptionClientException.class);
+        }
 
         // Cleanup
         deleteObject(BUCKET, objectKey, v3Client);