[Webkit-unassigned] [Bug 273818] New: PerformanceNavigationTiming decodedBodySize larger than encodedBodySize if resource is not encoded

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=273818

            Bug ID: 273818
           Summary: PerformanceNavigationTiming decodedBodySize larger
                    than encodedBodySize if resource is not encoded
           Product: WebKit
           Version: Safari 17
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: New Bugs
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: gernot.raudner at dynatrace.com

On a resource that has no encoding headers specified (e.g. no gzip, example website: https://gernotraudner.at), Safari 17.4.1 reports the `decodedBodySize` smaller than the `encodedBodySize`. In this specific example, the `decodedBodySize` is 294, while the `encodedBodySize` is 303. I can guarantee the server does no encoding, and it doesn't respond with any encoding headers. This seems to work fine with encoded resources though (`encodedBodySize` being smaller than `decodedBodySize`, as expected). So, to reproduce, simply

1. Open the network tab in devtools
2. Go to https://gernotraudner.at
3. enter `const navtimings = performance.getEntriesByType("navigation")[0]; console.log("encoded: ", navtimings.encodedBodySize, ", decoded: ", navtimings.decodedBodySize);` in the console
4. check the network tab and select the resource, check the sizes

In #3 you can see that the `encodedBodySize` is larger than the `decodedBodySize`, which cannot be the case.
Additionally, in #4 you can see that the "Bytes Received" of the body are 303B, while the resource size is 0.29KB. The tab also shows that compression is 0.97x (making it actually larger?).

I'm not 100% certain, but I think this used to work in Safari 16.

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