Rust

Updated Oct 28, 2026

The Rust crates provide a fast data management framework built on the Fairspec standard and Polars DataFrames. They support a wide range of tabular formats — CSV, TSV, JSON, JSONL, XLSX, ODS, Arrow, Parquet, SQLite — plus inline data. Function names are the Python library's, so a Python example translates call by call.

The pages in this section show how to load, validate, and save tables in each format.

Conventions

The fairspec crate exports the high-level API (load_table, validate_dataset, …) and re-exports the lower crates as modules: fairspec::fairspec_metadata (descriptors and models), fairspec::fairspec_dataset (files and dataset plugins) and fairspec::fairspec_table (Polars tables and format plugins).

Examples in this section are bodies of a function returning Result<(), Box<dyn std::error::Error>>, so ? works on every call. Descriptors are built from JSON with serde_json, using the same camelCase keys as a dataset.json:

use fairspec::fairspec_metadata::Resource;
use fairspec::{ValidateTableOptions, validate_table};
use serde_json::json;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let resource: Resource = serde_json::from_value(json!({
        "data": "data.csv",
        "fileDialect": {"format": "csv", "delimiter": ";"},
    }))?;

    let report = validate_table(&resource, &ValidateTableOptions::default())?;
    println!("{}", report.valid);
    Ok(())
}

Keyword arguments of the Python library are positional Option parameters or an options struct with a Default, so ..Default::default() leaves the rest unset. The API is synchronous.

Remote URLs

Loading functions fetch any http(s) URL they are given: descriptors, schemas and their $refs, data files, and CKAN, Zenodo and GitHub datasets. A service handling untrusted URLs should refuse hosts that resolve to a loopback, private, link-local (cloud metadata at 169.254.169.254 among them) or other non-public address:

use fairspec::fairspec_metadata::{HostPolicy, set_host_policy};

set_host_policy(Some(HostPolicy::Public)); // None falls back to FAIRSPEC_HOST_POLICY

The check runs on the address actually connected to and again on every redirect, and proxy settings are ignored under it. The policy is process-wide. Without a call, the FAIRSPEC_HOST_POLICY environment variable (any or public) decides, and the default is any. The MCP server starts with public.