Disable Expect 100-Continue by default in Apache 5 HTTP client (#6828)

* Disable Expect 100-Continue by default in Apache 5 HTTP client

* Fix docs

* Update changelog catagory

Author: alextwoods

.changes/next-release/feature-AWSSDKforJavav2-b18ecdd.json

@@ -0,0 +1,6 @@
+{
+    "type": "feature",
+    "category": "Apache 5 HTTP Client",
+    "contributor": "",
+    "description": "Disable Expect 100-Continue by default in the Apache5 HTTP Client."
+}

http-clients/apache5-client/src/main/java/software/amazon/awssdk/http/apache5/Apache5HttpClient.java

@@ -454,7 +454,8 @@ public interface Builder extends SdkHttpClient.Builder<Apache5HttpClient.Builder
         Builder localAddress(InetAddress localAddress);
 
         /**
-         * Configure whether the client should send an HTTP expect-continue handshake before each request.
+         * Configure whether the client should send an HTTP expect-continue handshake before each request. By default
+         * this is disabled.
          */
         Builder expectContinueEnabled(Boolean expectContinueEnabled);
 

http-clients/apache5-client/src/main/java/software/amazon/awssdk/http/apache5/internal/DefaultConfiguration.java

@@ -22,7 +22,7 @@
  */
 @SdkInternalApi
 public final class DefaultConfiguration {
-    public static final Boolean EXPECT_CONTINUE_ENABLED = Boolean.TRUE;
+    public static final Boolean EXPECT_CONTINUE_ENABLED = Boolean.FALSE;
 
     private DefaultConfiguration() {
     }

services/s3/src/main/java/software/amazon/awssdk/services/s3/S3Configuration.java

@@ -234,10 +234,11 @@ public boolean chunkedEncodingEnabled() {
      * By default, the SDK sends the {@code Expect: 100-continue} header for these operations, allowing the server to
      * reject the request before the client sends the full payload. Setting this to {@code false} disables this behavior.
      * <p>
-     * <b>Note:</b> When using the Apache HTTP client, the Apache client also independently adds the
+     * <b>Note:</b> When using the {@code ApacheHttpClient} (Apache 4), the Apache 4 client also independently adds the
      * {@code Expect: 100-continue} header by default via its own {@code expectContinueEnabled} setting. To fully
-     * suppress the header on the wire, you must also disable it on the Apache HTTP client builder using
-     * {@code ApacheHttpClient.builder().expectContinueEnabled(false)}.
+     * suppress the header on the wire, you must also disable it on the Apache4 HTTP client builder using
+     * {@code ApacheHttpClient.builder().expectContinueEnabled(false)}. This does NOT apply to the {@code Apache5HttpClient}
+     * which defaults {@code expectContinueEnabled} to false.
      *
      * @return True if the Expect: 100-continue header is enabled.
      * @see S3Configuration.Builder#expectContinueEnabled(Boolean)