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capnproto / capnproto-rust

Cap'n Proto for Rust
MIT License
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`set_root_canonical` errors on assertion #424

Closed NicholasLYang closed 1 year ago

NicholasLYang commented 1 year ago

Hi,

We've started getting errors because this assertion in set_root_canonical is false:

We're calling it to canonicalize a message, specifically right here. Is there a specific reason why the assertion is false? Do we need to do something else before calling this function?

dwrensha commented 1 year ago

The Allocator needs to have enough space in its first segment for the entire message. When you do Builder::new(HeapAllocator::default()), your allocator has a first segment size of 1024 words: https://github.com/capnproto/capnproto-rust/blob/dd9c072ce48c8e5377b3844ecaca832749eece08/capnp/src/message.rs#L661

Here's how the canoncalize() function makes sure there is enough space: https://github.com/capnproto/capnproto-rust/blob/dd9c072ce48c8e5377b3844ecaca832749eece08/capnp/src/message.rs#L288-L290

(Hm... looking at that now, I'm not sure about that + 1 there. Maybe target_size() is enough in itself and that's a (relatively harmless) bug.)

NicholasLYang commented 1 year ago

Ah gotcha. Thanks!