JsonSyntaxException is used to wrap IOExceptions in fromJson instead of using JsonIOException

[GoogleCodeExporter]

What steps will reproduce the problem?
1. call fromJson(JsonReader reader, Type typeOfT) while provoking an IOException

What is the expected output? What do you see instead?
The thrown exception will be a JsonSyntaxException instead of a JsonIOException.


What version of the product are you using? On what operating system?
com.google.code:gson:gson:2.2.2


Please provide any additional information below.
The JsonSyntaxException is clearly the wrong wrapper for an IOException, 
because it makes it really awkward to differentiate network exceptions from 
syntax exceptions. Network exceptions can be recovered from by retrying, while 
syntax exceptions indicate a programming error on the client or server side.

Original issue reported on code.google.com by s.groeb...@googlemail.com on 13 Dec 2013 at 11:05

[GrahamBorland]

Confirmed, this means that calls to Gson.fromJson(JsonReader reader, Type typeOfT) can not simply check for an IOException.

This does not work; the exception goes uncaught and kills the app.

Reader jsonReader = ...;
try {
    return new Gson().fromJson(jsonReader, someType);
} catch (IOException e) {
    // log the failure and try again?
}

[GrahamBorland]

This is the workaround I'm using to extract the underlying IOException.

try {
    return new Gson().fromJson(jsonReader, someType);
} catch (IOException | JsonSyntaxException e) {
    IOException ioException = null;

    if (e instanceof IOException) {
        ioException = (IOException) e;
    } else {
        Throwable cause = e.getCause();
        if (cause instanceof IOException) {
            ioException = (IOException) cause;
        }
    }

    if (ioException != null) {
        onFailure(call, ioException);
    } else {
        throw e;
    }
}

[GrahamBorland]

Here's the culprit:

} catch (IOException e) {
      // TODO(inder): Figure out whether it is indeed right to rethrow this as JsonSyntaxException
      throw new JsonSyntaxException(e);

Typing out that TODO would actually have been more effort than just doing the right thing. :)