tinytemplate/
lib.rs

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1//! ## TinyTemplate
2//!
3//! TinyTemplate is a minimal templating library originally designed for use in [Criterion.rs].
4//! It deliberately does not provide all of the features of a full-power template engine, but in
5//! return it provides a simple API, clear templating syntax, decent performance and very few
6//! dependencies.
7//!
8//! ## Features
9//!
10//! The most important features are as follows (see the [syntax](syntax/index.html) module for full
11//! details on the template syntax):
12//!
13//! * Rendering values - `{ myvalue }`
14//! * Conditionals - `{{ if foo }}Foo is true{{ else }}Foo is false{{ endif }}`
15//! * Loops - `{{ for value in row }}{value}{{ endfor }}`
16//! * Customizable value formatters `{ value | my_formatter }`
17//! * Macros `{{ call my_template with foo }}`
18//!
19//! ## Restrictions
20//!
21//! TinyTemplate was designed with the assumption that the templates are available as static strings,
22//! either using string literals or the `include_str!` macro. Thus, it borrows `&str` slices from the
23//! template text itself and uses them during the rendering process. Although it is possible to use
24//! TinyTemplate with template strings loaded at runtime, this is not recommended.
25//!
26//! Additionally, TinyTemplate can only render templates into Strings. If you need to render a
27//! template directly to a socket or file, TinyTemplate may not be right for you.
28//!
29//! ## Example
30//!
31//! ```
32//! #[macro_use]
33//! extern crate serde_derive;
34//! extern crate tinytemplate;
35//!
36//! use tinytemplate::TinyTemplate;
37//! use std::error::Error;
38//!
39//! #[derive(Serialize)]
40//! struct Context {
41//!     name: String,
42//! }
43//!
44//! static TEMPLATE : &'static str = "Hello {name}!";
45//!
46//! pub fn main() -> Result<(), Box<Error>> {
47//!     let mut tt = TinyTemplate::new();
48//!     tt.add_template("hello", TEMPLATE)?;
49//!
50//!     let context = Context {
51//!         name: "World".to_string(),
52//!     };
53//!
54//!     let rendered = tt.render("hello", &context)?;
55//! #   assert_eq!("Hello World!", &rendered);
56//!     println!("{}", rendered);
57//!
58//!     Ok(())
59//! }
60//! ```
61//!
62//! [Criterion.rs]: https://github.com/bheisler/criterion.rs
63//!
64
65extern crate serde;
66extern crate serde_json;
67
68#[cfg(test)]
69#[cfg_attr(test, macro_use)]
70extern crate serde_derive;
71
72mod compiler;
73pub mod error;
74mod instruction;
75pub mod syntax;
76mod template;
77
78use error::*;
79use serde::Serialize;
80use serde_json::Value;
81use std::collections::HashMap;
82use std::fmt::Write;
83use template::Template;
84
85/// Type alias for closures which can be used as value formatters.
86pub type ValueFormatter = dyn Fn(&Value, &mut String) -> Result<()>;
87
88/// Appends `value` to `output`, performing HTML-escaping in the process.
89pub fn escape(value: &str, output: &mut String) {
90    // Algorithm taken from the rustdoc source code.
91    let value_str = value;
92    let mut last_emitted = 0;
93    for (i, ch) in value.bytes().enumerate() {
94        match ch as char {
95            '<' | '>' | '&' | '\'' | '"' => {
96                output.push_str(&value_str[last_emitted..i]);
97                let s = match ch as char {
98                    '>' => "&gt;",
99                    '<' => "&lt;",
100                    '&' => "&amp;",
101                    '\'' => "&#39;",
102                    '"' => "&quot;",
103                    _ => unreachable!(),
104                };
105                output.push_str(s);
106                last_emitted = i + 1;
107            }
108            _ => {}
109        }
110    }
111
112    if last_emitted < value_str.len() {
113        output.push_str(&value_str[last_emitted..]);
114    }
115}
116
117/// The format function is used as the default value formatter for all values unless the user
118/// specifies another. It is provided publicly so that it can be called as part of custom formatters.
119/// Values are formatted as follows:
120///
121/// * `Value::Null` => the empty string
122/// * `Value::Bool` => true|false
123/// * `Value::Number` => the number, as formatted by `serde_json`.
124/// * `Value::String` => the string, HTML-escaped
125///
126/// Arrays and objects are not formatted, and attempting to do so will result in a rendering error.
127pub fn format(value: &Value, output: &mut String) -> Result<()> {
128    match value {
129        Value::Null => Ok(()),
130        Value::Bool(b) => {
131            write!(output, "{}", b)?;
132            Ok(())
133        }
134        Value::Number(n) => {
135            write!(output, "{}", n)?;
136            Ok(())
137        }
138        Value::String(s) => {
139            escape(s, output);
140            Ok(())
141        }
142        _ => Err(unprintable_error()),
143    }
144}
145
146/// Identical to [`format`](fn.format.html) except that this does not perform HTML escaping.
147pub fn format_unescaped(value: &Value, output: &mut String) -> Result<()> {
148    match value {
149        Value::Null => Ok(()),
150        Value::Bool(b) => {
151            write!(output, "{}", b)?;
152            Ok(())
153        }
154        Value::Number(n) => {
155            write!(output, "{}", n)?;
156            Ok(())
157        }
158        Value::String(s) => {
159            output.push_str(s);
160            Ok(())
161        }
162        _ => Err(unprintable_error()),
163    }
164}
165
166/// The TinyTemplate struct is the entry point for the TinyTemplate library. It contains the
167/// template and formatter registries and provides functions to render templates as well as to
168/// register templates and formatters.
169pub struct TinyTemplate<'template> {
170    templates: HashMap<&'template str, Template<'template>>,
171    formatters: HashMap<&'template str, Box<ValueFormatter>>,
172    default_formatter: &'template ValueFormatter,
173}
174impl<'template> TinyTemplate<'template> {
175    /// Create a new TinyTemplate registry. The returned registry contains no templates, and has
176    /// [`format_unescaped`](fn.format_unescaped.html) registered as a formatter named "unescaped".
177    pub fn new() -> TinyTemplate<'template> {
178        let mut tt = TinyTemplate {
179            templates: HashMap::default(),
180            formatters: HashMap::default(),
181            default_formatter: &format,
182        };
183        tt.add_formatter("unescaped", format_unescaped);
184        tt
185    }
186
187    /// Parse and compile the given template, then register it under the given name.
188    pub fn add_template(&mut self, name: &'template str, text: &'template str) -> Result<()> {
189        let template = Template::compile(text)?;
190        self.templates.insert(name, template);
191        Ok(())
192    }
193
194    /// Changes the default formatter from [`format`](fn.format.html) to `formatter`. Usefull in combination with [`format_unescaped`](fn.format_unescaped.html) to deactivate HTML-escaping
195    pub fn set_default_formatter<F>(&mut self, formatter: &'template F)
196    where
197        F: 'static + Fn(&Value, &mut String) -> Result<()>,
198    {
199        self.default_formatter = formatter;
200    }
201
202    /// Register the given formatter function under the given name.
203    pub fn add_formatter<F>(&mut self, name: &'template str, formatter: F)
204    where
205        F: 'static + Fn(&Value, &mut String) -> Result<()>,
206    {
207        self.formatters.insert(name, Box::new(formatter));
208    }
209
210    /// Render the template with the given name using the given context object. The context
211    /// object must implement `serde::Serialize` as it will be converted to `serde_json::Value`.
212    pub fn render<C>(&self, template: &str, context: &C) -> Result<String>
213    where
214        C: Serialize,
215    {
216        let value = serde_json::to_value(context)?;
217        match self.templates.get(template) {
218            Some(tmpl) => tmpl.render(
219                &value,
220                &self.templates,
221                &self.formatters,
222                self.default_formatter,
223            ),
224            None => Err(Error::GenericError {
225                msg: format!("Unknown template '{}'", template),
226            }),
227        }
228    }
229}
230impl<'template> Default for TinyTemplate<'template> {
231    fn default() -> TinyTemplate<'template> {
232        TinyTemplate::new()
233    }
234}
235
236#[cfg(test)]
237mod test {
238    use super::*;
239
240    #[derive(Serialize)]
241    struct Context {
242        name: String,
243    }
244
245    static TEMPLATE: &'static str = "Hello {name}!";
246
247    #[test]
248    pub fn test_set_default_formatter() {
249        let mut tt = TinyTemplate::new();
250        tt.add_template("hello", TEMPLATE).unwrap();
251        tt.set_default_formatter(&format_unescaped);
252
253        let context = Context {
254            name: "<World>".to_string(),
255        };
256
257        let rendered = tt.render("hello", &context).unwrap();
258        assert_eq!(rendered, "Hello <World>!")
259    }
260}
tinytemplate/lib.rs

tinytemplate/
lib.rs
