RFR: 8328716: [TestBug] Screen capturing utility for failed tests [v6]

[Andy Goryachev]

On Fri, 4 Apr 2025 21:28:59 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> hmm, not sure if I share the concern (did I understand the concern?)
>> 
>> the idea is to have a low-level method `takeScreenshotBase64(prefix, postfix)` that can be used in non-standard situations, but also provide the convenience method that will be used in the tests, `writeScreenshotBase64()`.
>
>> hmm, not sure if I share the concern (did I understand the concern?)
>> 
>> the idea is to have a low-level method `takeScreenshotBase64(prefix, postfix)` that can be used in non-standard situations, but also provide the convenience method that will be used in the tests, `writeScreenshotBase64()`.
> 
> That part sounds fine. However, even in non-standard situations, the caller of `takeScreenshotBase64` should not be expected to pass `"data:image/png;base64,"` to that method. It is the method itself that knows that the format is PNG, so that method should provide that part of the string when converting it to a base64 screenshot. So, for example:
> 
> 
>     takeScreenshotBase64(null, null);  <-- returns a data URL of a base64-encoded PNG
>     takeScreenshotBase64("{ screenshot:", "}"); <-- return the same with the prefix and postfix
> 
> 
> So what I'm trying to say is that `"data:image/png;base64,"` is an integral part of the base64-encoded image, not an optional prefix that a caller must pass in.

One thing that happened recently (in the past 10 years or so) is that JSON became a frequently used format for logs.  It's not perfect, but it's easy to parse.  With that, json-oriented log viewers came.

We don't have a consistent way to log data (or show data in `.toString()`).  A good log viewer can pretty print an object in the log file, decode a hex- or base-64 encoded string, or even run a query on a log file.

We are not ready for JSON logs, I admit, but this was the rationale behind the design of this class:

- a low-level method that returns byte[]
- a base-64 encoding method that allows for custom prefix/suffix to be able to do a data url or a json
- a convenience method to use in tests

Also, considering what you said about gradle and stderr, perhaps `writeScreenshot()` should always emit to stderr.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1746#discussion_r2029466429