Segfault in unsafe operation within `set_message_callback`

[raphaellaude]

Hello! Thank you for putting this cool crate together. I'm hitting a segfault when trying to append to my trainer. Not sure if this is a bug in the crate or my code. Here's the error:

(lldb) process launch -- train
Process 37281 launched: '/Users/raphaellaude/Documents/GitHub/rust_addr_clean/target/debug/us_addrs' (arm64)
Address: ["431", "Marietta", "St", "NW", "Fl.", "3"]
Tags: ["AddressNumber", "StreetName", "StreetNamePostType", "StreetNamePostDirectional", "OccupancyType", "OccupancyIdentifier"]
Process 37281 stopped
* thread #1, name = 'main', queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x28)
    frame #0: 0x000000010006d5e0 us_addrs`crfsuite::Trainer::set_message_callback::he14ba900e348f69f(self=0x000000016fdfddb8) at lib.rs:582:13
   579 	    // XXX: make it a public API?
   580 	    fn set_message_callback(&mut self) {
   581 	        unsafe {
-> 582 	            (*self.trainer)
   583 	                .set_message_callback
   584 	                .map(|f| f(self.trainer, mem::transmute(self), Some(logging_callback)))
   585 	                .unwrap();
Target 0: (us_addrs) stopped.

And my code:

use std::fs::File;
use std::io::BufReader;

use crfsuite::{Algorithm, GraphicalModel, Trainer};
use xml::reader::{EventReader, XmlEvent};

use crate::{get_address_features, tokenize};

pub fn train_model() -> std::io::Result<()> {
    let file = File::open("training/labeled.xml")?;
    let file = BufReader::new(file);

    let parser = EventReader::new(file);

    let mut trainer = Trainer::new(false);

    let mut address: Vec<String> = Vec::new();
    let mut yseq: Vec<String> = Vec::new(); // make Vec<AddressComponent>
                                            // let mut yseq: &[String];

    for e in parser {
        match e {
            Ok(XmlEvent::StartElement { name, .. }) => {
                if name.local_name == "AddressString" {
                    address.clear();
                    yseq.clear();
                } else {
                    yseq.push(name.local_name.to_string());
                }
            }
            Ok(XmlEvent::Characters(s)) => {
                address.push(s);
            }
            Ok(XmlEvent::EndElement { name }) => {
                if name.local_name == "AddressString" {
                    println!("Address: {:?}", address);
                    let tokens = tokenize(&address.join(" "));
                    let xseq = get_address_features(&tokens);
                    println!("Tags: {:?}", yseq);

                    match trainer.append(&xseq, &yseq, 0) {
                        Ok(()) => println!("Appended data"),
                        Err(e) => {
                            eprintln!("Error appending data: {}", e);
                            break;
                        }
                    }
                }
            }
            Err(e) => {
                eprintln!("Error: {e}");
                break;
            }
            _ => {}
        }
    }

    match trainer.select(Algorithm::LBFGS, GraphicalModel::CRF1D) {
        Ok(()) => println!("Selected algorithm"),
        Err(e) => println!("Error selecting algorithm: {}", e),
    }

    match trainer.train("usaddr.crfsuite", -1) {
        Ok(()) => println!("Trained model"),
        Err(e) => println!("Error training model: {}", e),
    }

    Ok(())
}

Any examples or help greatly appreciated! Thank you!

[raphaellaude]

I figured out that this is because trainer.select() needs to be called before any data can be appended. I think this could be addressed in the documentation. Will try to submit a small PR documenting this sometime soon...