Module writer 

Model-to-XML-to-ZIP serialization pipeline for writing 3MF files.

This module provides the inverse of the parser: it converts an in-memory Model structure back into a valid 3MF archive (ZIP container with XML and attachments).

Architecture

The writer mirrors the parser module structure but in reverse:

Model → XML Writer → OPC Writer → Package Writer → ZIP Archive

1. Model writer (model_writer): Serializes the Model to XML
2. Mesh writer (mesh_writer): Writes <mesh> elements with vertices and triangles
3. OPC writer (opc_writer): Generates _rels/.rels and [Content_Types].xml
4. Package writer (package_writer): Orchestrates full 3MF package creation
5. ZIP archive: Compresses and writes the final .3mf file

Usage

The primary entry point is the write method on Model:

use lib3mf_core::Model;
use std::fs::File;

// Create or load a model
let model = Model::default();

// Write to a 3MF file
let output = File::create("output.3mf")?;
model.write(output)?;

println!("Model written to output.3mf");

Writer Modules

Core Writers

• model_writer: Writes the <model> root element and resources
• mesh_writer: Writes <mesh> geometry (vertices, triangles, properties)
• opc_writer: Writes OPC metadata (_rels/.rels, [Content_Types].xml)
• package_writer: Orchestrates writing of complete 3MF package
• xml_writer: Low-level XML writing utilities

Extension Writers

• displacement_writer: Writes Displacement Extension data
• Beam Lattice: Not yet implemented (partial support)
• Slice: Partial support (slicestackid attribute only)
• Boolean Operations: Fully supported in model_writer
• Volumetric: Fully supported in model_writer

Known Limitations

The writer has some gaps compared to the parser:

• Beam lattice writer: Not implemented. Models with beam lattices can be read but not written back.
• Slice writer: Only writes slicestackid attribute, doesn’t serialize full slice geometry.
• Namespace optimization: Always emits all namespace declarations rather than only needed ones.

These limitations don’t affect core 3MF functionality but prevent full roundtrip testing for these extensions.

Roundtrip Testing

For supported features, the writer produces output that can be parsed back to an equivalent model:

use lib3mf_core::Model;
use std::io::Cursor;

let original_model = Model::default();

// Write to memory
let mut buffer = Cursor::new(Vec::new());
original_model.write(&mut buffer)?;

// Read back (would need to extract XML from ZIP in practice)
// let parsed_model = parse_model(buffer)?;
// assert_eq!(original_model, parsed_model);

Error Handling

All writing functions return Result<(), Lib3mfError>:

• Io: File system errors, ZIP writing errors, out of disk space
• InvalidStructure: Model contains invalid data that can’t be serialized

The writer never panics on invalid input, though it may produce a 3MF file that fails validation.

Modules

displacement_writer

mesh_writer

model_write_zip

model_writer

opc_writer

package_writer

xml_writer