Java http send method

[alex-james-dev]

Hey @brianquinlan,

The tests are passing when I run locally on my machine, but they are failing when run on the GitHub workflow 🤔

Context

This is a PR for the java_http GSoC '23 project 🌞.
Relevant tracking issue: #957.

Purpose

The purpose of this PR is to improve the implementation of the send method of JavaClient (a subclass of package:http BaseClient). This takes us closer to our goal of JavaClient passing all the tests in package:http_client_conformance_tests.

Changes

In this PR we:

• Connect to the URL.

• Set the request headers to those given in BaseRequest.headers.

• Set the request method to the given method in BaseRequest.method.

• Send the request.

• Retrieve the status code, reason phrase, response headers, content length and response body.

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[alex-james-dev]

Hey @brianquinlan, I reverted the commits made to track down the reason the GitHub workflow was failing. It looks like the reason was that the Java client was trying to connect to localhost using IPv4 but the HttpServer was only accepting connections to localhost by IPv6. 🤔

I made a new commit to fix the bug by setting the Java client to prefer IPv6 using the system property:

System.setProperty('java.net.preferIPv6Addresses'.toJString(), 'true'.toJString());

No changes were made to package:http_conformance_tests.
I used jnigen to generate bindings for the System class so that we can call the setProperty method.

The following package:http_conformance_tests are now passing 🎉:

• testResponseBody
• testResponseHeaders
• testRequestHeaders
• testMultipleClients

Thank you for your help!