[swift-users] NSJSONSerialization barfs writing a Dictionary parsed from JSON: "Invalid type in JSON write (_SwiftValue)"

[Dan Loewenherz]

I've encountered a similar bug and filed a radar a few months ago. My
report was marked as a duplicate but besides that I haven't received any
follow-up. It does appear to have been fixed in Xcode 8.1 / Swift 3.0.1.
http://www.openradar.me/28365419

Essentially, NSJSONSerialization would (does?) crash if you ask it to
encode an array/dictionary of Anys containing an optional value containing
a bridged Foundation type. The below snippet was the easiest demonstration
of the runtime exception.

    let name: String? = "Spike"
    let dogNames: [Any] = [name]

    do {
        try JSONSerialization.data(withJSONObject: dogNames, options:
.prettyPrinted)
    } catch {
        print("HI")
    }


What version of Swift is the user of your framework using?

Dan

On Fri, Nov 18, 2016 at 1:37 PM, Jens Alfke via swift-users <
swift-users at swift.org> wrote:

> A developer using the framework I work on just reported
> <https://forums.couchbase.com/t/exception-caught-in-map-block-of-view-invalid-type-in-json-write--swiftvalue/10808> an
> exception which is triggered by NSJSONSerialization (see backtrace below.)
> Basically an NSDictionary gets parsed from JSON data (in Obj-C), passed to
> a Swift function, which then calls another function (written in Obj-C) that
> serializes it back to JSON data. That last step is crashing due to some
> problem with bridging.
>
> The events leading up to this are:
>
> 1. The framework (written in Obj-C) parses some JSON data using
> NSJSONSerialization, resulting in an NSDictionary.
> 2. The NSDictionary is passed as a parameter to a block; the parameter is
> typed as `NSDictionary*`.
> 3. The block is part of the application, which is written in Swift.
> 4. The block in turn passes that NSDictionary to a function in the
> framework (through a parameter is typed as `id`)
> 5. The framework uses NSJSONSerialization to convert that id to data.
>
> Step 5 is triggering an assertion failure in Foundation. Apparently it
> failed to un-bridge a Swift value in an array back into an NSObject. (From
> the contents of the dictionary I know that the single-object array in
> question contains a string.)
>
> Any idea what’s going on here? I’ve never seen this happen before, and
> this part of our framework has been around for 2 ½ years. People have
> successfully built Swift apps using the framework. (This app was built with
> Xcode 8.0; don’t know what the OS is, though.)
>
> Invalid type in JSON write (_SwiftValue)
> 3   Foundation                          0x0000000111263284 _writeJSONValue
> + 668
> 4   Foundation                          0x00000001112636d9
> ___writeJSONArray_block_invoke + 132
> 5   CoreFoundation                      0x0000000118e1ce2a
> -[__NSSingleObjectArrayI enumerateObjectsWithOptions:usingBlock:] + 58
> 6   Foundation                          0x00000001112633df _writeJSONArray
> + 330
> 7   Foundation                          0x0000000111263204 _writeJSONValue
> + 540
> 8   Foundation                          0x0000000111262f94 -[_NSJSONWriter
> dataWithRootObject:options:error:] + 124
> 9   Foundation                          0x0000000111262e74
> +[NSJSONSerialization dataWithJSONObject:options:error:] + 333
> ...
>
> —Jens
>
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