rill_protocol/
config.rs

1use anyhow::Error;
2use once_cell::sync::OnceCell;
3use std::convert::identity;
4use std::env;
5use std::fmt;
6use std::str::FromStr;
7
8/// Configuration parameter that can be overriden by an environment variable
9/// or explicitly by setting default value.
10#[derive(Debug)]
11pub struct ConfigPatch<T> {
12    /// High-priority value
13    pre: &'static str,
14    /// Low-priority value
15    post: OnceCell<T>,
16}
17
18impl<T> ConfigPatch<T> {
19    pub const fn new(pre: &'static str) -> Self {
20        Self {
21            pre,
22            post: OnceCell::new(),
23        }
24    }
25
26    pub const fn var(&self) -> &'static str {
27        self.pre
28    }
29
30    pub fn env_var(&self) -> Result<Option<T>, Error>
31    where
32        T: FromStr,
33    {
34        if let Ok(s) = env::var(self.pre) {
35            let value = s.parse().map_err(|_err| {
36                Error::msg(format!("Can't parse {} variable from '{}'.", self.pre, s))
37            })?;
38            Ok(Some(value))
39        } else {
40            Ok(None)
41        }
42    }
43
44    /// Offers an alternative default if no other value provided.
45    pub fn offer(&self, value: T) {
46        if let Err(_err) = self.post.set(value) {
47            log::error!("Config value {} already overriden.", self.pre);
48        }
49    }
50
51    pub fn get<F, D>(&self, value: F, default: D) -> T
52    where
53        T: fmt::Debug + FromStr + Clone,
54        F: Fn() -> Option<T>,
55        D: Fn() -> T,
56    {
57        let value = self
58            .env_var()
59            .map_err(|err| {
60                log::error!("Default value for {} will be used: {}", self.pre, err);
61            })
62            .ok()
63            .and_then(identity)
64            .or_else(value)
65            .or_else(|| self.post.get().cloned())
66            .unwrap_or_else(default);
67        log::debug!("{} = {:?}", self.pre, value);
68        value
69    }
70}
rill_protocol/config.rs

rill_protocol/
config.rs
