Feat(config): support ${var:-word} and ${var:+word} syntax

README.md

@@ -10,9 +10,9 @@ This is a generalized JSON RPC proxy server with features specifically designed
 
 Pull vendors: `git submodule update --init --recursive`
 
-Quick start: `cargo run -- --config config.yml`
+Quick start: `cargo run -- --config configs/config.yml`
 
-This will run a proxy server with [config.yml](config.yml) as the configuration file.
+This will run a proxy server with [config.yml](configs/config.yml) as the configuration file.
 
 Run with `RUSTFLAGS="--cfg tokio_unstable"` to enable [tokio-console](https://github.com/tokio-rs/console)
 
@@ -24,7 +24,11 @@ Run with `RUSTFLAGS="--cfg tokio_unstable"` to enable [tokio-console](https://gi
   - Log format. Default: `full`.
   - Options: `full`, `pretty`, `json`, `compact`
 
-In addition, you can refer env variables in `config.yml` by using `${SOME_ENV}`
+In addition, you can refer env variables in `config.yml` by using following syntax:
+
+- `${variable}`
+- `${variable:-word}` indicates that if variable is set then the result will be that value. If variable is not set then word will be the result.
+- `${variable:+word}` indicates that if variable is set then word will be the result, otherwise the result is the empty string.
 
 ## Features
 

configs/config_with_env.yml

@@ -0,0 +1,56 @@
+extensions:
+  client:
+    endpoints:
+      - wss://acala-rpc.dwellir.com
+      - wss://acala-rpc-0.aca-api.network
+    health_check:
+      interval_sec: 10 # check interval, default is 10s
+      healthy_response_time_ms: 500 # max response time to be considered healthy, default is 500ms
+      health_method: system_health
+      response: # response contains { isSyncing: false }
+        !contains
+          - - isSyncing
+            - !eq false
+  event_bus:
+  substrate_api:
+    stale_timeout_seconds: 180 # rotate endpoint if no new blocks for 3 minutes
+  telemetry:
+    provider: none
+  cache:
+    default_ttl_seconds: 60
+    default_size: 500
+  merge_subscription:
+    keep_alive_seconds: 60
+  server:
+    port: ${SUBWAY_PORT:-9944}
+    listen_address: '0.0.0.0'
+    max_connections: ${SUBWAY_MAX_CONNECTIONS:-2000}
+    http_methods:
+      - path: /health
+        method: system_health
+      - path: /liveness
+        method: chain_getBlockHash
+    cors: all
+  rate_limit: # these are for demo purpose only, please adjust to your needs
+    connection: # 20 RPC requests per second per connection
+      burst: 20
+      period_secs: 1
+    ip: # 500 RPC requests per 10 seconds per ip
+      burst: 500
+      period_secs: 10
+    # use X-Forwarded-For header to get real ip, if available (e.g. behind a load balancer).
+    # WARNING: Use with caution, as this xff header can be forged.
+    use_xff: true # default is false
+
+middlewares:
+  methods:
+    - delay
+    - response
+    - inject_params
+    - cache
+    - upstream
+  subscriptions:
+    - merge_subscription
+    - upstream
+
+rpcs: substrate

src/cli.rs

@@ -0,0 +1,12 @@
+use clap::Parser;
+use std::path::PathBuf;
+#[derive(Parser, Debug)]
+#[command(version, about)]
+pub struct Command {
+    /// The config file to use
+    #[arg(short, long, default_value = ".configs/config.yml")]
+    pub config: PathBuf,
+}
+pub fn parse_args() -> Command {
+    Command::parse()
+}

src/config/mod.rs

@@ -2,8 +2,8 @@ use anyhow::{bail, Context};
 use regex::{Captures, Regex};
 use std::env;
 use std::fs;
+use std::path;
 
-use clap::Parser;
 use serde::Deserialize;
 
 use crate::extensions::ExtensionsConfig;
@@ -14,14 +14,6 @@ mod rpc;
 const SUBSTRATE_CONFIG: &str = include_str!("../../rpc_configs/substrate.yml");
 const ETHEREUM_CONFIG: &str = include_str!("../../rpc_configs/ethereum.yml");
 
-#[derive(Parser, Debug)]
-#[command(version, about)]
-struct Command {
-    /// The config file to use
-    #[arg(short, long, default_value = "./config.yml")]
-    config: String,
-}
-
 #[derive(Deserialize, Debug)]
 pub struct RpcDefinitionsWithBase {
     #[serde(default)]
@@ -150,17 +142,16 @@ impl From<ParseConfig> for Config {
 }
 
 // read config file specified in command line
-pub fn read_config() -> Result<Config, anyhow::Error> {
-    let cmd = Command::parse();
-
+pub fn read_config(path: impl AsRef<path::Path>) -> Result<Config, anyhow::Error> {
+    let path = path.as_ref();
     let templated_config_str =
-        fs::read_to_string(&cmd.config).with_context(|| format!("Unable to read config file: {}", cmd.config))?;
+        fs::read_to_string(path).with_context(|| format!("Unable to read config file: {}", path.display()))?;
 
     let config_str = render_template(&templated_config_str)
-        .with_context(|| format!("Unable to preprocess config file: {}", cmd.config))?;
+        .with_context(|| format!("Unable to preprocess config file: {}", path.display()))?;
 
-    let config: ParseConfig =
-        serde_yaml::from_str(&config_str).with_context(|| format!("Unable to parse config file: {}", cmd.config))?;
+    let config: ParseConfig = serde_yaml::from_str(&config_str)
+        .with_context(|| format!("Unable to parse config file: {}", path.display()))?;
     let config: Config = config.into();
 
     // TODO: shouldn't need to do this here. Creating a server should validates everything
@@ -170,18 +161,37 @@ pub fn read_config() -> Result<Config, anyhow::Error> {
 }
 
 fn render_template(templated_config_str: &str) -> Result<String, anyhow::Error> {
-    // match pattern: ${SOME_VAR}
-    let re = Regex::new(r"\$\{([^\}]+)\}").unwrap();
+    // match pattern with 1 group: {variable_name}
+    // match pattern with 3 groups: {variable:-word} or {variable:+word}
+    // note: incompete syntax like {variable:-} will be matched since group1 is ungreedy match
+    // but typically it will be rejected due to there is not corresponding env vars
+    let re = Regex::new(r"\$\{([^}]+?)(?:(:-|:\+)([^}]+))?\}").unwrap();
 
     let mut config_str = String::with_capacity(templated_config_str.len());
     let mut last_match = 0;
     // replace pattern: with env variables
-    let replacement = |caps: &Captures| -> Result<String, env::VarError> { env::var(&caps[1]) };
+    let replacement = |caps: &Captures| -> Result<String, env::VarError> {
+        match (caps.get(2), caps.get(3)) {
+            (Some(sign), Some(value_default)) => {
+                if sign.as_str() == ":-" {
+                    env::var(&caps[1]).or(Ok(value_default.as_str().to_string()))
+                } else if sign.as_str() == ":+" {
+                    Ok(env::var(&caps[1]).map_or("".to_string(), |_| value_default.as_str().to_string()))
+                } else {
+                    Err(env::VarError::NotPresent)
+                }
+            }
+            (None, None) => env::var(&caps[1]),
+            _ => Err(env::VarError::NotPresent),
+        }
+    };
 
     // replace every matches with early return
     // when encountering error
     for caps in re.captures_iter(templated_config_str) {
-        let m = caps.get(0).expect("Matched pattern should have at least one capture");
+        let m = caps
+            .get(0)
+            .expect("i==0 means implicit unnamed group that includes the entire match, which is infalliable");
         config_str.push_str(&templated_config_str[last_match..m.start()]);
         config_str.push_str(
             &replacement(&caps).with_context(|| format!("Unable to replace environment variable {}", &caps[1]))?,
@@ -231,13 +241,56 @@ mod tests {
     fn render_template_basically_works() {
         env::set_var("KEY", "value");
         env::set_var("ANOTHER_KEY", "another_value");
-        let templated_config_str = "${KEY} ${ANOTHER_KEY}";
+        let templated_config_str = "${KEY} some random_$tring {inside ${ANOTHER_KEY}";
         let config_str = render_template(templated_config_str).unwrap();
-        assert_eq!(config_str, "value another_value");
+        assert_eq!(config_str, "value some random_$tring {inside another_value");
 
         env::remove_var("KEY");
         let config_str = render_template(templated_config_str);
         assert!(config_str.is_err());
         env::remove_var("ANOTHER_KEY");
     }
+
+    #[test]
+    fn render_template_supports_minus_word_syntax() {
+        // ${variable:-word} indicates that if variable is set then the result will be that value. If variable is not set then word will be the result.
+        env::set_var("absent_key", "value_set");
+        let templated_config_str = "${absent_key:-value_default}";
+        let config_str = render_template(templated_config_str).unwrap();
+        assert_eq!(config_str, "value_set");
+        // remove the env
+        env::remove_var("absent_key");
+        let config_str = render_template(templated_config_str).unwrap();
+        assert_eq!(config_str, "value_default")
+    }
+
+    #[test]
+    fn render_template_supports_plus_word_syntax() {
+        // ${variable:+word} indicates that if variable is set then word will be the result, otherwise the result is the empty string.
+        env::set_var("present_key", "any_value");
+        let templated_config_str = "${present_key:+value_default}";
+        let config_str = render_template(templated_config_str).unwrap();
+        assert_eq!(config_str, "value_default");
+        // remove the env
+        env::remove_var("present_key");
+        let config_str = render_template(templated_config_str).unwrap();
+        assert_eq!(config_str, "")
+    }
+
+    #[test]
+    fn render_template_gets_error_when_syntax_is_incomplete() {
+        let templated_config_str = "${variable:-}";
+        let config_str = render_template(templated_config_str);
+        assert!(config_str.is_err());
+        let template_config_str = "${variable:+}";
+        let config_str = render_template(template_config_str);
+        assert!(config_str.is_err());
+    }
+
+    #[test]
+    fn read_config_with_render_template_works() {
+        // It's enough to check the replacement works
+        // if config itself has proper data validation
+        let _config = read_config("configs/config_with_env.yml").unwrap();
+    }
 }

src/lib.rs

@@ -1,3 +1,4 @@
+pub mod cli;
 pub mod config;
 pub mod extensions;
 pub mod logger;

src/main.rs

@@ -1,7 +1,8 @@
 #[tokio::main]
 async fn main() -> anyhow::Result<()> {
     // read config from file
-    let config = subway::config::read_config()?;
+    let cli = subway::cli::parse_args();
+    let config = subway::config::read_config(&cli.config)?;
 
     subway::logger::enable_logger();
     tracing::trace!("{:#?}", config);