Function load_model_async 

pub async fn load_model_async<P: AsRef<Path>>(path: P) -> Result<Model>

Asynchronously loads a 3MF model from a file path.

This is the primary entry point for async 3MF loading. It handles all aspects of loading: file I/O, ZIP archive access, OPC relationship parsing, and XML model parsing.

Arguments

• path - Path to the 3MF file (any type implementing AsRef<Path>)

Returns

A fully parsed Model containing all resources, build items, and metadata.

Errors

Returns Lib3mfError::Io if:

• File cannot be opened
• ZIP archive cannot be read
• Archive entries cannot be read

Returns Lib3mfError::InvalidStructure if:

• _rels/.rels file is missing or malformed
• No 3D model relationship is found (must have type http://schemas.microsoft.com/3dmanufacturing/2013/01/3dmodel)
• Model part path is invalid

Returns parsing errors from parse_model if the model XML is malformed.

Implementation Details

Async vs Blocking

• Async operations: File open, ZIP directory reading, entry reading
• Blocking operations: XML parsing (offloaded to tokio::task::spawn_blocking)

The function uses spawn_blocking for XML parsing because it’s CPU-bound work that would otherwise block the tokio executor. This allows other async tasks to progress while parsing happens on a dedicated thread pool.

OPC Discovery

The function follows the Open Packaging Conventions (OPC) standard to discover the main model part:

1. Reads _rels/.rels (package-level relationships)
2. Finds relationship with type ending in /3dmodel
3. Reads the target model part (typically /3D/3dmodel.model)

Examples

use lib3mf_async::loader::load_model_async;
use lib3mf_core::validation::ValidationLevel;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Load a 3MF file
    let model = load_model_async("complex_model.3mf").await?;

    // Validate the loaded model
    let report = model.validate(ValidationLevel::Standard);
    if report.has_errors() {
        eprintln!("Model has validation errors:");
        for item in &report.items {
            eprintln!("  - {}", item.message);
        }
    }

    // Process the model
    println!("Objects: {}", model.resources.iter_objects().count());
    println!("Build items: {}", model.build.items.len());

    Ok(())
}