Module zng::env

Process events, external directories and metadata.

This module contains functions and macros that operate on the executable level, not the app level. Zng apps can have multiple process instances, most common a view-process and app-process pair, plus the crash handler.

The app-process is the normal execution, the other processes use on_process_start! to takeover the process if specific environment variables are set. The process start handlers are called on init!, if a process takeover it exits without returning, so only the normal app-process code executes after init!().

fn main() {
   println!("print in all processes");
   zng::env::init!();
   println!("print only in the app-process");

   // get a path in the app config dir, the config dir is created if needed.    
   let my_config = zng::env::config("my-config.txt");

   // read a config file, or create it
   if let Ok(c) = std::fs::read_to_string(&my_config) {
      println!("{c}");
   } else {
      std::fs::write(zng::env::config("my-config.txt"), b"Hello!").unwrap();
   }
}

Note that init must be called in main, it must be called in main to define the lifetime of the processes, this is needed to properly call on_process_exit handlers.

Also see init! docs for details init in "wasm32" and "android" target builds.

Full API

See zng_env for the full API.

Macros

• init
  Inits process metadata, calls process start handlers and defines the process lifetime in main.
• on_process_start
  Register a FnOnce(&ProcessStartArgs) closure to be called on init!.

Structs

• About
  Metadata about the app and main crate.
• ProcessExitArgs
  Arguments for on_process_exit handlers.
• ProcessStartArgs
  Arguments for on_process_start handlers.

Functions

• about
  Gets metadata about the application.
• bin
  Gets a path relative to the package binaries.
• cache
  Gets a path relative to the cache directory for the app.
• clear_cache
  Removes all cache files possible.
• config
  Gets a path relative to the user config directory for the app.
• exit
  Terminates the current process with the specified exit code.
• init_built_res
  Sets a custom path for the “built resources” override checked by res in debug builds.
• init_cache
  Sets a custom cache path.
• init_config
  Sets a custom original_config path.
• init_res
  Sets a custom res path.
• migrate_cache
  Save new_path as the new cache path and make a best effort to move existing cache files.
• migrate_config
  Copied all config to new_path and saves it as the config path.
• on_process_exit
  Register a handler to run once when the current process exits.
• res
  Gets a path relative to the package resources.