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use mustache::{Error, Template, compile_path};
use serde::Serialize;
use std::collections::HashMap;
use std::fs::metadata;
use std::io::Write;
use std::path::{Path, PathBuf};
use std::sync::RwLock;
use std::time::{Duration, SystemTime};
struct TemplateEntry {
template: Template, // Compiled template
mtime: SystemTime, // mtime of parsed template file
last_checked: SystemTime, // last time the template file mtime was checked
}
impl TemplateEntry {
// Loads a template from the given filename
fn from_template_file<P: AsRef<Path>>(filename: P) -> Result<TemplateEntry, Error> {
let path = filename.as_ref();
let template = compile_path(path)?;
let attr = metadata(path)?;
Ok(TemplateEntry{template: template, mtime: attr.modified()?, last_checked: SystemTime::now()})
}
// render the tempate with the given data
fn render<W, D>(&self, writer: &mut W, data: &D) -> Result<(), Error>
where W: Write, D: Serialize {
self.template.render(writer, data)
}
}
/// ReloadPolicy controls how often the modification time of template
/// file is checked. Checks take place only when rendering the
/// template.
pub enum ReloadPolicy {
/// Never check for changes. Once loaded, templates will not
/// change unless one of TemplateCache::clear or
/// TemplateCache::reload_template are called, or the server is
/// restarted.
Never,
/// Check after a period of time. For example, with a duration of
/// 30 min, the template will be checked no more than once every
/// 30 min.
Periodic(Duration),
/// Check every time the template is rendered.
Always,
}
/// Cache of compiled mustache templates
pub struct TemplateCache {
cache: RwLock<HashMap<PathBuf, TemplateEntry>>,
reload_policy: ReloadPolicy,
}
impl TemplateCache {
/// Create a TemplateCache with the specified reload policy
pub fn with_policy(policy: ReloadPolicy) -> TemplateCache {
TemplateCache{cache: RwLock::new(HashMap::new()), reload_policy: policy}
}
/// Remove all cache entries
pub fn clear(&self) {
let mut c = self.cache.write().expect("TemplateCache::clear - cache poisoned");
c.clear();
}
/// Force a reload of a template into the cache
pub fn reload_template<P>(&self, path: P) -> Result<(), Error>
where P: AsRef<Path> {
let mut c = self.cache.write().expect("TemplateCache::reload_template - cache poisoned");
let template = TemplateEntry::from_template_file(&path)?;
c.insert(path.as_ref().to_path_buf(), template);
Ok(())
}
// Tries to render the template with the given data. This method
// only needs a read lock. Returns:
//
// * Ok(true) - successfully rendered
//
// * Ok(false) - template needs loading, either it was never
// loaded, or it is outdated
//
// * Err(e) - mustache error
fn try_render_template<P, W, D>(&self, path: P, writer: &mut W, data: &D) -> Result<bool, Error>
where P: AsRef<Path>, W: Write, D: Serialize {
let c = self.cache.read().expect("TemplateCache::try_render_template - cache poisoned");
if let Some(template) = c.get(&path.as_ref().to_path_buf()) {
let check_mtime = match self.reload_policy {
ReloadPolicy::Never => false,
ReloadPolicy::Always => true,
ReloadPolicy::Periodic(period) => {
let now = SystemTime::now();
if let Ok(duration) = now.duration_since(template.last_checked) {
duration > period
} else {
// wierdness, we went back in time, force reload
true
}
}
};
if check_mtime {
let mtime = metadata(path)?.modified()?;
if mtime > template.mtime {
return Ok(false);
}
}
template.render(writer, data)?;
Ok(true)
} else {
Ok(false)
}
}
// Load the template from disk, compile it, store the compiled
// template in cache, and render. This needs a write lock.
fn load_render_template<P, W, D>(&self, path: P, writer: &mut W, data: &D) -> Result<(), Error>
where P: AsRef<Path>, W: Write, D: Serialize {
let mut c = self.cache.write().expect("TemplateCache::load_render_template - cache poisoned");
let template = TemplateEntry::from_template_file(&path)?;
template.render(writer, data)?;
c.insert(path.as_ref().to_path_buf(), template);
Ok(())
}
/// Render the template at `path` to `writer` with
/// `data`. Templates will be reloaded if necessary according to
/// the reload policy.
pub fn render<P, W, D>(&self, path: P, writer: &mut W, data: &D) -> Result<(), Error>
where P: AsRef<Path>, W: Write, D: Serialize {
let rendered = match self.try_render_template(&path, writer, data) {
Ok(r) => r,
Err(e) => {
// Previously compiled template failed to render. Log
// an error and force a reload.
error!("Template render error: {:?}", e);
false
},
};
if !rendered {
self.load_render_template(&path, writer, data)
} else {
Ok(())
}
}
}