portal/src/chain.rs

//! SHA-256 hashed answer chain. `parent_hashes` is DAG-shaped, but
//! nothing produces more than one parent yet - the shape is reserved
//! for follow-up questions posted back into a visitor's chain.
#![cfg(feature = "ssr")]

use sha2::{Digest, Sha256};

/// Hashes one chain node from its question, its parent hash(es), the
/// submitted responses, and a timestamp. Parents are sorted first so the
/// hash doesn't depend on the order multiple parents happened to arrive
/// in.
pub fn hash_node(
    question_id: &str,
    parent_hashes: &[String],
    responses: &serde_json::Value,
    timestamp_ms: i64,
) -> String {
    let mut parents = parent_hashes.to_vec();
    parents.sort();
    let payload = serde_json::json!({
        "questionId": question_id,
        "parentHashes": parents,
        "responses": responses,
        "timestamp": timestamp_ms,
    });
    let data = serde_json::to_vec(&payload).expect("json values always serialize");
    let mut hasher = Sha256::new();
    hasher.update(&data);
    format!("{:x}", hasher.finalize())
}