Add more javadoc

core/http-auth-aws/src/main/java/software/amazon/awssdk/http/auth/aws/internal/io/ChecksumInputStream.java

@@ -23,6 +23,9 @@
 import java.util.zip.Checksum;
 import software.amazon.awssdk.annotations.SdkInternalApi;
 
+/**
+ * An input-stream that takes a collection of checksums, and updates each checksum when it reads data.
+ */
 @SdkInternalApi
 public class ChecksumInputStream extends FilterInputStream {
 

core/http-auth-aws/src/main/java/software/amazon/awssdk/http/auth/aws/internal/io/ChecksumSubscriber.java

@@ -25,6 +25,9 @@
 import org.reactivestreams.Subscription;
 import software.amazon.awssdk.annotations.SdkInternalApi;
 
+/**
+ * A subscriber that takes a collection of checksums, and updates each checksum when it receives data.
+ */
 @SdkInternalApi
 public final class ChecksumSubscriber implements Subscriber<ByteBuffer> {
     private final CompletableFuture<Void> checksumming = new CompletableFuture<>();

core/http-auth-aws/src/main/java/software/amazon/awssdk/http/auth/aws/internal/signer/FlexibleChecksummer.java

@@ -35,7 +35,9 @@
 import software.amazon.awssdk.http.auth.aws.signer.Checksummer;
 
 /**
- * A "flexible" implementation of a checksummer.
+ * A "flexible" implementation of a checksummer. It takes a map of checksums and their header names, computes them efficiently
+ * by updating each checksum while reading the payload (once), and adds the computed checksum strings to the request using the
+ * given header names in the map. This should be used in cases where a (flexible) checksum algorithm is present during signing.
  */
 @SdkInternalApi
 public final class FlexibleChecksummer implements Checksummer {

core/http-auth-aws/src/main/java/software/amazon/awssdk/http/auth/aws/internal/signer/PrecomputedChecksummer.java

@@ -28,8 +28,8 @@
 
 /**
  * An implementation of a checksummer that simply passes along a computed value as a checksum. Specifically, this is used in
- * the cases where the checksum is a pre-defined value that dictates specific behavior by the signer (such as aws-chunked
- * payload signing, unsigned streaming with trailers, etc.).
+ * the cases where the checksum is a pre-defined value that dictates specific behavior by the signer, and flexible checksums is
+ * not enabled for the request (such as aws-chunked payload signing without trailers, unsigned streaming without trailers, etc.).
  */
 @SdkInternalApi
 public final class PrecomputedChecksummer implements Checksummer {

core/http-auth-aws/src/main/java/software/amazon/awssdk/http/auth/aws/signer/Checksummer.java

@@ -48,7 +48,7 @@ static Checksummer create() {
     }
 
     /**
-     * Get a flexible checksummer that uses the given checksum-algorithm and the default.
+     * Get a flexible checksummer that performs two checksums: the given checksum-algorithm and the default (sha256).
      */
     static Checksummer create(ChecksumAlgorithm checksumAlgorithm) {
         if (checksumAlgorithm != null) {
@@ -63,14 +63,15 @@ static Checksummer create(ChecksumAlgorithm checksumAlgorithm) {
     }
 
     /**
-     * Get a flexible checksummer that uses the given checksum-algorithm and the default.
+     * Get a precomputed checksummer that results the given checksum string.
      */
     static Checksummer create(String checksum) {
         return new PrecomputedChecksummer(() -> checksum);
     }
 
     /**
-     * Get a flexible checksummer that uses the given checksum-algorithm and the default.
+     * Get a flexible checksummer that performs two checksums: the given checksum-algorithm and a precomputed checksum from the
+     * given checksum string.
      */
     static Checksummer create(String checksum, ChecksumAlgorithm checksumAlgorithm) {
         if (checksumAlgorithm != null) {