Add environment variable override for cookie configuration (#195)

* Add environment variable override for cookie configuration

Cookies can now be overridden using LEETCODE_CSRF, LEETCODE_SESSION,
and LEETCODE_SITE environment variables when loading configuration.

* Update README.md: add document for overriding cookies with environment
variables.

Author: yousiki

README.md

@@ -321,6 +321,27 @@ csrf = '<your-leetcode-csrf-token>'
 session = '<your-leetcode-session-key>'
 ```
 
+#### Environment variables
+
+The cookies can also be overridden by environment variables, which might be useful to exclude the sensitive information from the configuration file `leetcode.toml`. To do this, you can leave the `csrf` and `session` fields empty in the configuration file and override cookies settings via the environment variables `LEETCODE_CSRF`, `LEETCODE_SESSION`, and `LEETCODE_SITE`:
+
+```toml
+[cookies]
+csrf = ''
+session = ''
+site = 'leetcode.com'
+```
+
+Then set the environment variables:
+
+```bash
+export LEETCODE_CSRF='<your-leetcode-csrf-token>'
+export LEETCODE_SESSION='<your-leetcode-session-key>'
+export LEETCODE_SITE='leetcode.cn' # or 'leetcode.com'
+```
+
+Note that `cookies.site` in still required in the `leetcode.toml` to avoid exception during configuration file parsing, but can be overridden using environment variables.
+
 ## Programmable
 
 If you want to filter LeetCode questions using custom Python scripts, add the following to your the configuration file:

src/config/cookies.rs

@@ -62,3 +62,27 @@ impl Display for Cookies {
         )
     }
 }
+
+/// Override cookies from environment variables
+pub const LEETCODE_CSRF_ENV: &str = "LEETCODE_CSRF";
+pub const LEETCODE_SESSION_ENV: &str = "LEETCODE_SESSION";
+pub const LEETCODE_SITE_ENV: &str = "LEETCODE_SITE";
+
+impl Cookies {
+    /// Load cookies from environment variables, overriding any existing values
+    /// if the environment variables are set.
+    pub fn with_env_override(mut self) -> Self {
+        if let Ok(csrf) = std::env::var(LEETCODE_CSRF_ENV) {
+            self.csrf = csrf;
+        }
+        if let Ok(session) = std::env::var(LEETCODE_SESSION_ENV) {
+            self.session = session;
+        }
+        if let Ok(site) = std::env::var(LEETCODE_SITE_ENV) {
+            if let Ok(leetcode_site) = LeetcodeSite::from_str(&site) {
+                self.site = leetcode_site;
+            }
+        }
+        self
+    }
+}

src/config/mod.rs

@@ -46,14 +46,19 @@ impl Config {
 
         let s = fs::read_to_string(&conf)?;
         match toml::from_str::<Config>(&s) {
-            Ok(config) => match config.cookies.site {
-                cookies::LeetcodeSite::LeetcodeCom => Ok(config),
-                cookies::LeetcodeSite::LeetcodeCn => {
-                    let mut config = config;
-                    config.sys.urls = sys::Urls::new_with_leetcode_cn();
-                    Ok(config)
+            Ok(mut config) => {
+                // Override config.cookies with environment variables
+                config.cookies = config.cookies.with_env_override();
+
+                match config.cookies.site {
+                    cookies::LeetcodeSite::LeetcodeCom => Ok(config),
+                    cookies::LeetcodeSite::LeetcodeCn => {
+                        let mut config = config;
+                        config.sys.urls = sys::Urls::new_with_leetcode_cn();
+                        Ok(config)
+                    }
                 }
-            },
+            }
             Err(e) => {
                 let tmp = Self::root()?.join("leetcode.tmp.toml");
                 Self::write_default(tmp)?;