Crate hocon 

hocon

Full Lightbend HOCON specification-compliant parser for Rust.

Quick Example

let config = hocon::parse(r#"
    server {
        host = "localhost"
        port = 8080
    }
"#)?;

assert_eq!(config.get_string("server.host")?, "localhost");
assert_eq!(config.get_i64("server.port")?, 8080);

Parsing

• parse – parse a HOCON string into a Config.
• parse_file – parse a HOCON file. Include directives are resolved relative to the file’s directory.
• parse_with_env / parse_file_with_env – parse with a custom environment variable map instead of inheriting the process environment.

Accessing Values

Config provides typed getters that accept dot-separated paths:

Method	Return type
Config::get_string	Result<String, ConfigError>
Config::get_i64	Result<i64, ConfigError>
Config::get_f64	Result<f64, ConfigError>
Config::get_bool	Result<bool, ConfigError>
Config::get_config	Result<Config, ConfigError>
Config::get_list	Result<Vec<HoconValue>, ConfigError>
Config::get_duration	Result<Duration, ConfigError>
Config::get_bytes	Result<i64, ConfigError>

Each typed getter has an _option variant (e.g., Config::get_string_option) that returns Option<T> instead.

Duration and Byte-Size Values

let config = hocon::parse(r#"
    timeout = 30 seconds
    max-upload = 512 MB
"#)?;

let timeout = config.get_duration("timeout")?;
let max_upload = config.get_bytes("max-upload")?;

Duration units: ns, us, ms, s/seconds, m/minutes, h/hours, d/days.

Byte-size units: B, KB, KiB, MB, MiB, GB, GiB, TB, TiB (and their long forms like megabytes, mebibytes).

Serde Deserialization

With the serde feature enabled, deserialize a Config (or sub-config) into any type implementing serde::Deserialize:

use serde::Deserialize;

#[derive(Deserialize)]
struct Server {
    host: String,
    port: u16,
}

let server: Server = config.get_config("server")?.deserialize()?;

Include Files

HOCON supports include directives to compose configuration from multiple files:

include "defaults.conf"

server.port = 9090  # override a value from defaults

When parsing with parse_file, include paths are resolved relative to the file being parsed.

Error Types

• HoconError – unified error returned by parse functions. Wraps:
  • ParseError – syntax errors during lexing or parsing (includes line/column).
  • ResolveError – substitution resolution failures, cycle detection.
  • std::io::Error – file I/O errors (top-level file read; include file errors appear as ResolveError).
• ConfigError – missing keys or type mismatches when accessing values.

HOCON Specification

For the full specification, see the Lightbend HOCON spec.

Re-exports

pub use config::Config;

pub use error::ConfigError;

pub use error::HoconError;

pub use error::ParseError;

pub use error::ResolveError;

pub use value::HoconValue;

pub use value::ScalarType;

pub use value::ScalarValue;

Modules

config

error

value

Functions

parse

Parse a HOCON string into a Config.

parse_file

Parse a HOCON file into a Config.

parse_file_with_env

Parse a HOCON file with a custom environment variable map.

parse_with_env

Parse a HOCON string with a custom environment variable map.