handlebars-rust

Rust templating with Handlebars templating language.

Getting Started

Quick Start

extern crate handlebars;
#[macro_use]
extern crate serde_json;

use handlebars::Handlebars;

fn main() {
    let mut reg = Handlebars::new();
    // render without register
    println!(
        "{}",
        reg.render_template("Hello {{name}}", &json!({"name": "foo"}))
            .unwrap()
    );

    // register template using given name
    reg.register_template_string("tpl_1", "Good afternoon, {{name}}")
        .unwrap();
    println!("{}", reg.render("tpl_1", &json!({"name": "foo"})).unwrap());
}

Note that I use unwrap here which is not recommended in your real code.

Code Example

If you are not familiar with handlebars language syntax, it is recommended to walk through their introduction first.

Check render example in the source tree. The example shows you how to:

• Create a Handlebars registry and register the template from files;
• Create a custom Helper with closure or struct implementing HelperDef, and register it;
• Define and prepare some data;
• Render it;

Run cargo run --example render to see results. (or RUST_LOG=handlebars=info cargo run --example render for logging output).

Checkout examples/ for more concrete demos of current API.

From 0.26, Serde JSON is the default type system for this library. The data you pass to handlebars template must implements the Serialize trait. Note that we don't actually serialize data to JSON string, we just use the JSON type: number, boolean and etc.

Rustc_serialize is now officially deprecated. If your application is still using it, you need to use handlebars-rust 0.25.*.

Document

Rust doc.

Changelog

Change log is available in the source tree named as CHANGELOG.md.

Contributor Guide

Any contribution to this library is welcomed. To get started into development, I have several Helper Wanted issue, with difficult level labeled. When running into any problem, feel free to contact me on github.

I'm always looking for maintainers to work together on this library, also let me know (via email or anywhere in the issue tracker) if you want to join.

Donation

I'm now accepting donation on liberapay, if you find my work helpful and want to keep it going.

Why (this) Handlebars?

Handlebars is a real-world templating system that you can use to build your application without pain.

Features

Isolation of Rust and HTML

This library doesn't attempt to use some macro magic to allow you to write your template within your rust code. I admit that it's fun to do that but it doesn't fit real-world use case.

Limited but essential control structure built-in

Only essential control directive if and each were built-in. This prevents you to put too much application logic into your template.

Extensible helper system

You can write your own helper with Rust! It can be a block helper or inline helper. Put you logic into the helper and don't repeat yourself.

A helper can be as a simple as a Rust function like:

fn hex_helper (h: &Helper, _: &Handlebars, _: &Context, rc: &mut
    RenderContext, out: &mut Output) -> Result<(), RenderError> {

    // just for example, add error check for unwrap
    let param = h.param(0).unwrap().value();
    let rendered = format!("0x{:x}", param.as_u64().unwrap());

    out.write(rendered.into_bytes().as_ref())
}

/// register the helper
handlebars.register_helper("hex", Box::new(hex_helper));

And using it in your template:

{{hex my_value}}

Template inheritance

Every time I look into a templating system, I will investigate its support for template inheritance.

Template include is not sufficient for template reuse. In most case you will need a skeleton of page as parent (header, footer, etc.), and embed you page into this parent.

You can find a real example for template inheritance in examples/partials.rs, and templates used by this file.

WebAssembly compatible

You can use this handlebars implementation in your rust project that compiles to WebAssembly. Checkout my fork of todomvc demo.

Strict mode

Handlebars, the language designed to work with JavaScript, has no strict restriction on accessing non-existed fields or index. It generates empty string for such case. However, in Rust we want a little bit strict sometime.

By enabling strict_mode on handlebars:

handlebars.set_strict_mode(true);

You will get a RenderError when accessing fields that not exists.

Limitations

• This implementation is not fully compatible with the original javascript version. Specifically, mustache list iteration and null check doesn't work. But you can use #each and #if for same behavior.
• You will need to make your data Serializable on serde. We don't actually serialize data into JSON string or similar. However, we use JSON data type system in template render process.

Handlebars-js features supported in Handlebars-rust

• Expression / Block Helpers
• Built-in helpers
  • each
  • if
  • with
  • lookup
  • log
• Custom helper
• Parameter and hashes for helper, block params
• Partials, include, template inheritance
• Omitting whitespace with ~
• Subexpression {{(foo bar)}}
• Json expression a.b.[0] and a.b.[c]
• RawHelper syntax {{{{raw-helper}}}}...{{{{/raw-helper}}}}
• Decorator, implemented in Rust way

JavaScript implementation features we don't have

• Mustache block (use if/each instead)
• Chained else

Feel free to report an issue if you find something broken. We aren't going to implement all features of handlebars-js, but we should have a workaround for cases we don't support.

Handlebars for Web Frameworks

• Iron: handlebars-iron
• Rocket: rocket/contrib

Using handlebars-rust?

Add your project to our adopters.

License

This library (handlebars-rust) is open sourced under MIT License.