gunnar-core 2.0.0

//! **The server's generic settings** (`refs/gunnar/settings`, owner decision 2026-10-26).
//!
//! Bytes under a NAME the client chooses, and nothing more. The server knows no setting
//! name and gives no value a meaning: a console stores its own switches here
//! (`console.<switch>`: its names, namespaced by it), so a switch an administrator
//! flips is kept on the server, replicated with the rest of the control state, and outlives a
//! console restart, while gunnar-server learns nothing about what the switch does.
//!
//! Bounded, and every refusal names its limit:
//!
//! * a name is 1 to [`MAX_NAME_BYTES`] bytes of `[a-z0-9._-]`, starting with a letter or digit;
//! * a value is at most [`MAX_VALUE_BYTES`] bytes;
//! * at most [`MAX_SETTINGS`] names are held.
//!
//! Who may read or write is the gRPC door's to decide (`Admin.GetSetting`, `Admin.SetSetting`:
//! server Admin); so is the audit line of each write (who, the name, old → new).

use std::sync::Arc;

use crate::control::ControlStore;
use crate::doc::{impl_doc, DocRef, ShardedMap};
use crate::error::{Error, Result};

/// **The name the settings document is stored under** in the control store.
pub const SETTINGS_REF: &str = "refs/gunnar/settings";
/// The longest setting name, in bytes.
pub const MAX_NAME_BYTES: usize = 128;
/// The largest setting value, in bytes.
pub const MAX_VALUE_BYTES: usize = 4096;
/// The most settings one server holds.
pub const MAX_SETTINGS: usize = 256;

#[derive(Default, Clone, serde::Serialize, serde::Deserialize)]
#[serde(deny_unknown_fields)]
struct SettingsDoc {
    /// Name → the value's bytes, hex.
    #[serde(default)]
    values: ShardedMap<String>,
}

impl_doc!(SettingsDoc { values });

/// Read and write the server's generic settings. Cheap to clone; every clone is the same
/// document.
#[derive(Clone, Debug)]
pub struct SettingsStore {
    doc: DocRef<SettingsDoc>,
}

/// Pure: **is `name` a setting name**: `Err` names the rule it breaks.
pub fn check_name(name: &str) -> Result<()> {
    let refuse = |reason: String| Err(Error::InvalidInput { what: "setting name", reason });
    if name.is_empty() {
        return refuse("empty".to_owned());
    }
    if name.len() > MAX_NAME_BYTES {
        return refuse(format!("{} bytes, more than the {MAX_NAME_BYTES} a name may have", name.len()));
    }
    if !name.bytes().all(|b| b.is_ascii_lowercase() || b.is_ascii_digit() || matches!(b, b'.' | b'_' | b'-')) {
        return refuse(format!("{name:?} has a character outside [a-z0-9._-]"));
    }
    if !name.as_bytes()[0].is_ascii_alphanumeric() {
        return refuse(format!("{name:?} does not start with a letter or a digit"));
    }
    Ok(())
}

fn hex(b: &[u8]) -> String {
    b.iter().map(|x| format!("{x:02x}")).collect()
}

fn unhex(s: &str) -> Result<Vec<u8>> {
    let bad = || Error::InvalidInput { what: "stored setting", reason: "not hex: the settings document is damaged".to_owned() };
    if s.len() % 2 != 0 {
        return Err(bad());
    }
    (0..s.len()).step_by(2).map(|i| s.get(i..i + 2).and_then(|p| u8::from_str_radix(p, 16).ok()).ok_or_else(bad)).collect()
}

impl SettingsStore {
    /// Open the settings document held in `store` (the server's control store).
    pub fn new(store: Arc<dyn ControlStore>) -> Result<Self> {
        Ok(SettingsStore { doc: DocRef::new(store, SETTINGS_REF)? })
    }

    /// The value stored under `name`, or `None` where nothing is.
    pub fn get(&self, name: &str) -> Result<Option<Vec<u8>>> {
        check_name(name)?;
        self.doc.load()?.values.get(name)?.map(|v| unhex(&v)).transpose()
    }

    /// Store `value` under `name`, replacing what was there; the value it replaced, `None`
    /// for a new name. Refused by name past a bound.
    pub fn set(&self, name: &str, value: &[u8]) -> Result<Option<Vec<u8>>> {
        check_name(name)?;
        if value.len() > MAX_VALUE_BYTES {
            return Err(Error::InvalidInput { what: "setting value", reason: format!("{} bytes, more than the {MAX_VALUE_BYTES} a value may have", value.len()) });
        }
        let previous = self.doc.update(|doc| {
            if !doc.values.contains_key(name)? && doc.values.len() >= MAX_SETTINGS {
                return Err(Error::InvalidInput { what: "setting", reason: format!("this server holds {MAX_SETTINGS} settings already, the most it keeps") });
            }
            doc.values.insert(name.to_owned(), hex(value))
        })?;
        previous.map(|v| unhex(&v)).transpose()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn store() -> SettingsStore {
        SettingsStore::new(Arc::new(crate::control::RedbControlStore::in_memory().expect("a store"))).expect("the document")
    }

    #[test]
    fn a_setting_is_stored_replaced_and_read_back_and_an_unset_one_is_none() {
        let s = store();
        assert_eq!(s.get("console.a-switch").unwrap(), None);
        assert_eq!(s.set("console.a-switch", b"on").unwrap(), None, "a new name replaced nothing");
        assert_eq!(s.get("console.a-switch").unwrap().as_deref(), Some(&b"on"[..]));
        assert_eq!(s.set("console.a-switch", b"off").unwrap().as_deref(), Some(&b"on"[..]), "the value it replaced");
        assert_eq!(s.get("console.a-switch").unwrap().as_deref(), Some(&b"off"[..]));
        assert_eq!(s.set("x", &[0, 255, 7]).unwrap(), None);
        assert_eq!(s.get("x").unwrap().as_deref(), Some(&[0u8, 255, 7][..]), "any bytes");
    }

    #[test]
    fn every_bound_is_refused_by_name() {
        let s = store();
        let words = |e: Error| e.to_string();
        assert!(words(s.set("", b"").unwrap_err()).contains("empty"));
        assert!(words(s.set(&"a".repeat(MAX_NAME_BYTES + 1), b"").unwrap_err()).contains("128"));
        assert!(s.set(&"a".repeat(MAX_NAME_BYTES), b"").is_ok(), "at the bound it is a name");
        assert!(words(s.set("Console.X", b"").unwrap_err()).contains("[a-z0-9._-]"));
        assert!(words(s.set("a/b", b"").unwrap_err()).contains("[a-z0-9._-]"));
        assert!(words(s.set(".hidden", b"").unwrap_err()).contains("start with"));
        assert!(words(s.set("v", &vec![0; MAX_VALUE_BYTES + 1]).unwrap_err()).contains("4096"));
        assert!(s.set("v", &vec![0; MAX_VALUE_BYTES]).is_ok(), "at the bound it is a value");
        assert!(words(s.get("A").unwrap_err()).contains("[a-z0-9._-]"), "a read names the rule too");
    }

    #[test]
    fn a_full_server_refuses_a_new_name_but_replaces_a_held_one() {
        let s = store();
        for i in 0..MAX_SETTINGS {
            s.set(&format!("n{i}"), b"1").unwrap();
        }
        assert!(s.set("one-more", b"1").unwrap_err().to_string().contains(&MAX_SETTINGS.to_string()));
        assert!(s.set("n0", b"2").is_ok(), "a held name is still replaced");
    }
}