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urldata: make magic be the first struct field #6484

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@bagder bagder commented Jan 19, 2021

By making the magic identifier the same size and at the same place
within the structs (easy, multi, share), libcurl will be able to more
reliably detect and safely error out if an application passes in the
wrong handle to APIs. Easier to detect and less likely to cause crashes
if done.

Such mixups can't be detected at compile-time due to them being
typedefed void pointers - unless CURL_STRICTER is defined.

By making the `magic` identifier the same size and at the same place
within the structs (easy, multi, share), libcurl will be able to more
reliably detect and safely error out if an application passes in the
wrong handle to APIs. Easier to detect and less likely to cause crashes
if done.

Such mixups can't be detected at compile-time due to them being
typedefed void pointers - unless `CURL_STRICTER` is defined.
@jay
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@jay jay commented Jan 19, 2021

Not that I'm against this but note I have an example ListEasyHandles.c that uses those internal structs. I guarded it with a version check of course.

@bagder
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@bagder bagder commented Jan 19, 2021

Right, and we do have opaque structs for this very reason: to allow us to modify them without breaking any user applications. At least I don't think we will change the beginning of the structs very often...

@bagder bagder closed this in 942cf12 Jan 20, 2021
@bagder bagder deleted the bagder/handle-diff branch Jan 20, 2021
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