Convert (consume) Builder into TypedReader

[bspeice]

Accidentally PR'd into my forked master, not original repo master.
Addresses #83

[bspeice]

I don't know how we should handle the ReaderOptions - I.e. is it safe to just use the default, or should I expose the ability to pass in an external ReaderOptions?

[dwrensha]

ReaderOptions.traversal_limit_in_words and ReaderOptions.nesting_limit exist to deal with untrusted data. When you have a message::Builder, you must have constructed the data yourself, so it's safe to set both of those options to max_value(). I think that's the right thing to do here.

Note that it also might make sense to convert a message::Builder to a message::Reader without going to a message::TypedReader, and it might make sense to have a message::TypedBuilder in the future. So I think it makes more sense to have separate methods: message::Builder::into_reader() and message::Reader::into_typed(). We may also want to add an message::TypedReader::into_inner() message to allow recovering the reader.

[bspeice]

Idiomatic Rust question then - Should it just be TypedReader From both message::Builder and message::Reader? Saves one extra function call (builder.into_reader().into_typed()) and uses the Rust API's for it.

[dwrensha]

I prefer adding methods with self-explanatory names like into_reader() and into_typed(). We could impl From on top of those methods, if we want that too.

[bspeice]

All the above are done. Let me know if there's anything else, sorry about the wait on this one.

[dwrensha]

Thanks!

[dwrensha]

Hm... it occurs to me that the rest of the codebase uses methods named as_reader() instead of into_reader() for this kind of situation. I wonder if it makes sense to use that naming scheme here also, for the sake of consistency (even if into_*() is more idiomatic in the wider Rust community).

[dwrensha]

into_reader() had an unnecessary type parameter: 5bb2b41

[dwrensha]

After further reflection, I think the into_ prefix is correct here. It signifies that the ownership is being transferred. In constrast, a prefix of as_ usually signifies that something is being borrowed. It's true that many as_reader methods in capnproto-rust (e.g. this one) technically take self by value, but their usual intended use case is more like borrowing, in particular when they are used in conjunction with a borrow() method. (See this blog post for more discussion of these methods.)