com.sun.net.httpserver.Headers issues & optimizations

[Jaikiran Pai]

Hello Robert,

On 07/01/25 12:05 am, robert engels wrote:
 > ...
 >
 > 2. Another proposed change to Headers would be to add a protected 
constructor that allowed you to pass in the Map implementation (or 
null), allowing specialized map data structures that are better suited 
to http headers storage, especially when being converted to/from http2 
headers.
 >
 > Although it is possible to subclass Headers to provide your own map, 
you still pay a penalty because the base class will instantiate a map, 
and the code is quite ugly as you must override every method in the 
Headers class. You can see a sample implementation here 
https://github.com/robaho/httpserver/blob/main/src/main/java/robaho/net/httpserver/OptimizedHeaders.java
 >
 > The subclass does offer the ability to bypass the normalization 
completely with a package level method to be used internally by the 
server when it has already guaranteed the key is normalized.

I don't know if you have noticed, but starting Java 18, the Headers 
class already provides a (public) constructor which allows a Map to be 
passed in to the constructor 
https://docs.oracle.com/en/java/javase/23/docs/api/jdk.httpserver/com/sun/net/httpserver/Headers.html#%3Cinit%3E(java.util.Map). 
The implementation of the constructor however copies over the key/values 
into an internal Map of its own, so the passed Map (implementation) 
plays no further role after that point.

In my opinion, in its current form, the Headers class provides enough 
flexibility to allow for a subclass of Headers to provide a more 
efficient implementation if it wants to. Like you note, such a subclass 
needs to implement all the methods of java.util.Map interface to be able 
to properly provide that support, but it's still doable.

 >
 > 3. The public static of() methods in Headers should be 
changed/removed, as they create a dependency on a sun internal class 
(sun.net.httpserver.UnmodifiableHeaders) from a public “api” class. 
These could be changed to instead wrap the map with an unmodifiable map.
 >

com.sun.net.httpserver.Headers is an API class and the method signature 
of com.sun.net.httpserver.Headers.of() is:

public static com.sun.net.httpserver.Headers of(Map<String,List<String>> 
headers)

The implementation of that method currently returns an instance of 
sun.net.httpserver.UnmodifiableHeaders which is an internal 
implementation class belonging to the same module. I don't follow why 
that's a bad thing - the API itself, through the method signature, 
doesn't expose any internal implementation class.

-Jaikiran