Read/Create config file from/in XDG directory

Cargo.lock

  "reqwest 0.8.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo-glutin 0.13.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "toml 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "xdg 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
  "pkg-config 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "xdg"
+version = "2.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "xml-rs"
 version = "0.7.0"
 "checksum winapi-x86_64-pc-windows-gnu 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "98f12c52b2630cd05d2c3ffd8e008f7f48252c042b4871c72aed9dc733b96668"
 "checksum ws2_32-sys 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d59cefebd0c892fa2dd6de581e937301d8552cb44489cdff035c6187cb63fa5e"
 "checksum x11-dl 2.17.2 (registry+https://github.com/rust-lang/crates.io-index)" = "28ec50063128cfdbdfe683b0504a3740e07b779c7c75fa26e941218b5f95e098"
+"checksum xdg 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a66b7c2281ebde13cf4391d70d4c7e5946c3c25e72a7b859ca8f677dcd0b0c61"
 "checksum xml-rs 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "3c1cb601d29fe2c2ac60a2b2e5e293994d87a1f6fa9687a31a15270f909be9c2"

Cargo.toml

 reqwest = "0.8"
 servo-glutin = "0.13"
 toml = "0.4"
+xdg = "2.1"
 
 [build-dependencies]
 gl_generator = "0.8"

src/config.rs

 use std::error::Error;
 use std::fs::File;
-use std::io::Read;
+use std::io::{Read, Write};
 use std::path::{Path, PathBuf};
 use tile_source::TileSource;
 use toml::Value;
+use xdg;
+
+static DEFAULT_CONFIG: &'static str = include_str!("../default_config.toml");
 
 
 pub struct Config {
 }
 
 impl Config {
-    pub fn from_toml<P: AsRef<Path>>(path: P) -> Result<Config, String> {
-        let mut file = File::open(path).map_err(|e| e.description().to_string())?;
+    pub fn load() -> Result<Config, String> {
+        if let Ok(xdg_dirs) = xdg::BaseDirectories::with_prefix("deltamap") {
+            if let Some(config_path) = xdg_dirs.find_config_file("config.toml") {
+                println!("Load config from path {:?}", config_path);
 
-        let mut content = String::new();
-        file.read_to_string(&mut content).map_err(|e| e.description().to_string())?;
+                Config::from_toml_file(config_path)
+            } else {
+                if let Ok(path) = xdg_dirs.place_config_file("config.toml") {
+                    if let Ok(mut file) = File::create(&path) {
+                        println!("write default config {:?}", &path);
+                        file.write_all(DEFAULT_CONFIG.as_bytes());
+                    }
+                }
+
+                Config::from_toml_str(DEFAULT_CONFIG)
+            }
+        } else {
+            Config::from_toml_str(DEFAULT_CONFIG)
+        }
+    }
 
-        match content.parse::<Value>() {
+    pub fn from_toml_str(toml_str: &str) -> Result<Config, String> {
+        match toml_str.parse::<Value>() {
             Ok(Value::Table(ref table)) => {
                 let tile_cache_dir = table.get("tile_cache_dir")
                     .ok_or_else(|| "missing \"tile_cache_dir\" entry".to_string())?
                         .ok_or_else(|| "max_zoom has to be an integer".to_string())
                         .and_then(|m| {
                             if m <= 0 || m > 30 {
-                                Err(format!("max_zoom = {} is out of bounds. Has to be in interval [1, 30].", m))
+                                Err(format!("max_zoom = {} is out of bounds, has to be in interval [1, 30]", m))
                             } else {
                                 Ok(m)
                             }
         }
     }
 
+    pub fn from_toml_file<P: AsRef<Path>>(path: P) -> Result<Config, String> {
+        let mut file = File::open(path).map_err(|e| e.description().to_string())?;
+
+        let mut content = String::new();
+        file.read_to_string(&mut content).map_err(|e| e.description().to_string())?;
+
+        Config::from_toml_str(&content)
+    }
+
     pub fn tile_sources(&self) -> &[(String, TileSource)] {
         &self.sources
     }

src/main.rs

 extern crate linked_hash_map;
 extern crate reqwest;
 extern crate toml;
+extern crate xdg;
 
 
 #[macro_use]
 }
 
 fn main() {
-    let config = config::Config::from_toml("deltamap.toml").unwrap();
+    let config = config::Config::load().unwrap();
     let mut sources = TileSources::new(config.tile_sources()).unwrap();
 
     let mut window = glutin::WindowBuilder::new().build().unwrap();