fix: rearrange, cleanup, deprecation and fixes in ServerSideEncryption

[balamurugana]

1. Cleanup formatting issues.
2. Arrange code usage together.
3. Deprecate getType() and marshal(), ServerSideEncryptionCopyWithCustomerKey and
   copyWithCustomerKey(). Use type(), headers(), copySourceHeaders() and withCustomerKey().

[aead]

Java uses getter / setter for properties. Renaming is not idiomatic here.

[balamurugana]

It is old style and minio-java follows this style inspired from okhttp.

[aead]

Okay, can/have we document that? Because a lot of Java code follows the "style" I mentioned...

[balamurugana]

There is no coding standard document we have. Modern style is followed from the beginning of minio-java. There is little different with getter style where getters may return reference of an class member but this style returns copy of a value.

[aead]

Okay

[aead]

Why do we return a new HashMap instead of adding the headers to an existing one? The typical use case is to add the SSE-C headers to the HTTP header map. What do we gain here?

[balamurugana]

Returning Map gives full control to users how they will be manipulated, marshal(Map) mutates passed values which we need to avoid for future failures.

[aead]

Not sure I understand what you mean. How is

Map<String, String> headers = new Map<>();
sse.marshal(headers);

different from:

Map<String, String> headers = sse.headers();

apart from the situation that the the former case avoids a new map allocation when we serialize the SSE object into the HTTP headers - which is the entire purpose of this function. In the later case you crate a new map and "force" an explicit copy. So, in general both options are equally powerful just that we usually want to serialize to the HTTP header map of the request and not create a new map which we have to copy explicitly - or am I missing something.

Anyway minor.

[balamurugana]

There is a little difference. marshal() mutates header map passed, there could be a possible value loss if header map contains any such header. Whereas headers() returns a new copy of SSE headers every time and caller has a control when/how to use returned headers. As this is public class/method, it is not a good idea to mutate a passed header map.

[aead]

There is a little difference. marshal() mutates header map passed, there could be a possible value loss if header map contains any such header.

That I got. I still don't see how this is different from headers. Sure, you make a copy but callers can do that explicitly by passing a new map when they want to avoid overwriting with marshal. So getting the same behavior as headers like shown above. Anyway, the only purpose of this function is to serialize the object to the HTTP request. So you have a S3 API call:

putObject(...) {
   req = new Request();
   req.getHeaders().add("Content-MD5", ...);
   //...   
  sse.marshal(req.getHeaders()); // With new method: req.getHeaders().addAll(sse.headers)
}

As this is public class/method, it is not a good idea to mutate a passed header map.

[aead]

Same

[aead]

Same

[aead]

Anyway, approved

[balamurugana]

Depends on #775 #776 #777

[kannappanr]

ping @aead @sinhaashish

[sinhaashish]

LGTM