RFR: 8288717: Add a means to close idle connections in HTTP/2 connection pool

[Jaikiran Pai]

On Tue, 6 Sep 2022 13:56:15 GMT, Conor Cleary <ccleary at openjdk.org> wrote:

> **Issue**
> When using HTTP/2 with the HttpClient, it can often be necessary to close an idle Http2 Connection before a server sends a GOAWAY frame. For example, a server or cloud based tool could close a TCP connection silently when it is idle for too long resulting in ConnectionResetException being thrown by the HttpClient.
> 
> **Proposed Solution**
> A new system property, `jdk.httpclient.idleConnectionTimeout`, was added and is used to specify in Milliseconds how long an idle connection (idle connections are those which have no currently active streams) for the HttpClient before the connection is closed.

src/java.net.http/share/classes/jdk/internal/net/http/HttpClientImpl.java line 1525:

> 1523:     }
> 1524: 
> 1525:     public Optional<Duration> idleConnectionTimeout() {

Perhaps change this to a package private method instead of a public one?

src/java.net.http/share/classes/jdk/internal/net/http/HttpClientImpl.java line 1695:

> 1693:     private Duration getIdleConnectionTimeoutProp() {
> 1694:         // Http 2 in prop name somewhere
> 1695:         String s = Utils.getNetProperty("jdk.httpclient.idleConnectionTimeout");

Is this new system property expected/allowed to be configured even in `net.properties` file? The implementation of `Utils.getNetProperty` will check even the `net.properties` file for this value, so just checking if that's what we want. If we do want this to be configurable in `net.properties`, should we updated that file to have a commented section which this property and some documentation about it?

Furthermore, I think we should read this value just once and cache the `Duration` as a static member of this class instead of reading this more than once.

src/java.net.http/share/classes/jdk/internal/net/http/HttpClientImpl.java line 1697:

> 1695:         String s = Utils.getNetProperty("jdk.httpclient.idleConnectionTimeout");
> 1696:         if (s != null)
> 1697:             return Duration.ofMillis(Long.parseLong(s));

Should we catch any `NumberFormatException` here and just default to `null` duration (i.e. no idle timeout)? Same for negative and `0` value(s)?

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PR: https://git.openjdk.org/jdk/pull/10183