Nima WebClient headers methods

[romain-grecourt]

In v3 we had this:

WebClientRequestHeaders headers =
        WebClient.builder()
                 .addHeader("h1", "v1") // String, String
                 .addCookie("foo", "bar")
                // default contentType and accepted cannot be set in the builder
                 .build()
                 .get()
                 .addHeader("h2", "v1", "v2") // String, String...
                 .addHeader("h3", List.of("v1", "v2"))  // String, List<String>
                 .headers(h -> {
                     h.add("h4", "v1", "v2"); // String, String...
                     h.add("h5", List.of("v1", "v2")); // String, List<String>
                     return h;
                 })
                 .addHeaders(HashParameters.create(Map.of("h6", List.of("v1", "v2")))) // bulk add
                 .headers(HashHeaders.create(Map.of("h6", List.of("v1", "v2")))) // bulk set
                 .contentType(MediaType.APPLICATION_XML)
                 .accept(MediaType.TEXT_PLAIN, MediaType.APPLICATION_JSON)
                 .headers(); // ClientRequestHeaders getter

As of V4 pre M1 we have this:

Http1Client.builder()
           .header(Header.create(Header.create("h1"), "v1", "v2"))  // HeaderValue
           //.header(HeaderName, String...) is missing
           .header(Header.create("h3"), List.of("v1", "v2")) // HeaderName, List<String>
           .headers(h -> {
               // ClientRequestHeaders
               return h;
           })
           .build()
           .get()
           .header(Header.create(Header.create("h6"), "v1")) // HeaderValue
           .header(Header.create("h7"), "v1") // HeaderName, String          <-- Not 'String...'
           // .header(HeaderName, List<String>) is missing
           .headers(h -> {
               // ClientRequestHeaders, same as above
               return h;
           })
            //.accept(HttpMediaType) is missing
            // contentType(HttpMediaType) is missing 
            // .headers() is missing

---

Header value types

• Add WebClient.Builder.header(HeaderName, String... value)
• Update ClientRequest.header(Http.HeaderName name, String value) to use varag for the value
• Add ClientRequest.header(Http.HeaderName name, List<String> value)

This will make the methods available on WebClient.Builder and ClientRequest symmetrical, (variants for String..., and List<String> for all header)

MediaType

• Add ClientRequest.contentType(Mediatype)
• Update ClientRequestHeaders.accept(HttpMediatype... accepted) to use HttpMediatype instead since the implementation of the method does not require it and HttpMediatype extends MediaType
• Add ClientRequest.accept(Mediatype... acceptedTypes)

Ignoring HttpMediaType variants, see details in #7058

Bulk add

V3 WebClientRequestBuilder had methods to operate on bulk headers

• one that adds bulk headers, see the javadoc
• one that sets (or resets) all headers, see the javadoc

There is no way to easily add bulk headers (E.g. from a server request):

• Add ClientRequest.headers(Headers)

The hard set (or reset) can be achieved with .headers(Function<ClientRequestHeaders, WritableHeaders<?>>)

ClientRequestHeaders getter

The only way to inspect the headers is to use .headers(Function<ClientRequestHeaders, WritableHeaders<?>>)

• Add ClientRequest.headers() : ClientRequestHeaders