RFR: 8275138: WebView: UserAgent string is empty for first request

[Ambarish Rapte]

On Thu, 14 Oct 2021 12:32:24 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

> The failure was caused by a change that was done in connection with the WebKit 610.2 update, [JDK-8259635](https://bugs.openjdk.java.net/browse/JDK-8259635). The `FrameLoaderClient::userAgent` function was changed in WebKit itself to be a const method in WebKit 610.2. We override that method in `FrameLoaderClientJava` to return the user agent string, which is done by reading the user agent from an instance of the `Page` class.  `FrameLoaderClientJava` has a `m_page` field that is lazily initialized whenever it is needed. This lazy initialization can no longer be done from the `userAgent` method, since it is `const`, as can be seen from this change that was done as part of WebKit 610.2:
> 
> 
> --- a/modules/javafx.web/src/main/native/Source/WebKitLegacy/java/WebCoreSupport/FrameLoaderClientJava.cpp
> +++ b/modules/javafx.web/src/main/native/Source/WebKitLegacy/java/WebCoreSupport/FrameLoaderClientJava.cpp
> -String FrameLoaderClientJava::userAgent(const URL&)
> +String FrameLoaderClientJava::userAgent(const URL&) const
>  {
> -    return page()->settings().userAgent();
> +    if (!m_page)
> +        return emptyString();
> +    return m_page->settings().userAgent();
>  }
> 
> 
> Formerly, if the `m_page` field was uninitialized, FrameLoaderClient::userAgent would have initialized it by the call to the `page()` function, but since it is now `const` we can't do that. This means that the user agent string will be empty until some other method is called that initializes the `m_page` field.
> 
> The fix is to initialize that field when the `WebPage` is created. We can't do it in the constructor, since the needed reference to the `Page` class isn't yet available, so I added an `init` method that is called from `WebPage::twkInit`.
> 
> I added a new unit test that fails without the fix and passes with the fix.

looks good to me too.

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Marked as reviewed by arapte (Reviewer).

PR: https://git.openjdk.java.net/jfx/pull/643