fix arguments scope bug in fetch header injection callback#28
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In the string URL branch of the window.fetch override, the callback passed to setAdditionalHeaders used `arguments[1]` to update the fetch options headers. But inside a regular function() `arguments` is rebound to the callback's own argument list, which only receives `extraHeaders` as arguments[0], making arguments[1] always undefined. This caused a "TypeError: Cannot set properties of undefined (setting 'headers')". The error was caught silently by the try/catch in setAdditionalHeaders but a warning was logged. It only appeared for specific requests because only fetch calls using the Request object form (else branch) guard header injection inside a for...in loop, so they only error when extra headers are actually returned. Now we capture `arguments[1]` into a `fetchOptions` variable in the outer window.fetch scope before the callback and reference that variable inside the callback instead.
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In the string URL branch of the window.fetch override, the callback passed to setAdditionalHeaders used
arguments[1]to update the fetch options headers. But inside a regular function()argumentsis rebound to the callback's own argument list, which only receivesextraHeadersas arguments[0], making arguments[1] always undefined.This caused a "TypeError: Cannot set properties of undefined (setting 'headers')". The error was caught silently by the try/catch in setAdditionalHeaders but a warning was logged. It only appeared for specific requests because only fetch calls using the Request object form (else branch) guard header injection inside a for...in loop, so they only error when extra headers are actually returned.
Now we capture
arguments[1]into afetchOptionsvariable in the outer window.fetch scope before the callback and reference that variable inside the callback instead. We also normalize the headers first, since there are three different header objects possible: Headers instance, an array of tuples and a plain object.