xtemplate

xtemplate

xtemplate is a html/template-based hypertext preprocessor and rapid application development web server written in Go. Its good defaults handle typical server activity, enabling authors to focus on building hypermedia-exchange-oriented websites by defining routes and responding to them with template-generated HTML combined with configurable backing data stores.

🎯 Goal

Frustrated with the status-quo of frameworks that add more abstractions than they solve problems, I set out to create something that feels more like wrestling directly with first-class citizens of the web:

• HTTP paths and matching server path patterns
• Responding to an HTTP request with a template-generated HTML
• Access to various backing data sources

🎇 The idea of xtemplate is that all of these can be managed with a directory of Go template files.

✨ Features

Click a feature to expand and show details:

📦 How to run

0. 📦 As a Docker container

...

1. 📦 As a Caddy plugin

The xtemplate/caddy plugin offers all xtemplate features integrated into Caddy, a fast and extensible multi-platform HTTP/1-2-3 web server with automatic HTTPS.

Download Caddy with xtemplate/caddy middleware plugin built-in:

https://caddyserver.com/download?package=github.com%2Finfogulch%2Fxtemplate&package=github.com%2Fncruces%2Fgo-sqlite3

This is the simplest Caddyfile that uses the xtemplate/caddy plugin:

routes {
  xtemplate
}

Alternatively, build with the xcaddy CLI tool.

2. 📦 As the default CLI application

Download from the Releases page or build the binary in ./cmd.

Custom builds can include your chosen db drivers, make Go functions available to the template definitions, and even embed templates for true single binary deployments. The ./cmd package is the reference CLI application, consider starting your customization there.

$ ./xtemplate -h
v0.8.3
Usage: xtemplate [--template-dir TEMPLATE-DIR] [--template-ext TEMPLATE-EXT] [--minify] [--ldelim LDELIM] [--rdelim RDELIM] [--watch WATCH] [--watchtemplates] [--listen LISTEN] [--loglevel LOGLEVEL] [--config CONFIG] [--config-file CONFIG-FILE]

Options:
  --template-dir TEMPLATE-DIR, -t TEMPLATE-DIR [default: templates]
  --template-ext TEMPLATE-EXT [default: .html]
  --minify, -m [default: true]
  --ldelim LDELIM [default: {{]
  --rdelim RDELIM [default: }}]
  --watch WATCH
  --watchtemplates [default: true]
  --listen LISTEN, -l LISTEN [default: 0.0.0.0:8080]
  --loglevel LOGLEVEL [default: -2]
  --config CONFIG, -c CONFIG
  --config-file CONFIG-FILE, -f CONFIG-FILE
  --help, -h             display this help and exit
  --version              display version and exit

Examples:
    Listen on port 80:
    $ ./xtemplate --listen :80

    Specify a context directory and reload when it changes:
    $ ./xtemplate --template-dir public --watch-templates

    Parse template files matching a custom extension and minify them:
    $ ./xtemplate --template-ext ".go.html" --minify

3. 📦 As a Go library

xtemplate's public Go API starts with a xtemplate.Config, from which you can get either an xtemplate.Instance interface or a xtemplate.Server interface, with the methods config.Instance() and config.Server(), respectively.

An xtemplate.Instance is an immutable http.Handler that can handle requests, and exposes some metadata about the files loaded as well as the ServeMux patterns and associated handlers for individual routes. An xtemplate.Server also handles http requests by forwarding requests to an internal Instance, but the Server can be reloaded by calling server.Reload(), which creates a new Instance with the previous config and atomically switches the handler to direct new requests to the new Instance.

Use an Instance if you have no interest in reloading, or if you want to use xtemplate handlers in your own mux. Use a Server if you want an easy way to smoothly reload and replace the xtemplate Instance behind a http.Handler at runtime.

👨‍🏭 How to use

🧰 Template semantics

xtemplate templates are based on Go's html/template package, with some additional features and enhancements. Here are the key things to keep in mind:

• All template files are loaded recursively from the specified root directory, and they are parsed and cached in memory at startup.
• Each template file is associated with a specific route based on its file path. For example, index.html in the root directory will handle requests to the / path, while admin/settings.html will handle requests to /admin/settings.
• You can define custom routes by defining a template with a special name in your template files. For example, {{define "GET /custom-route"}}...{{end}} will create a new route that handles GET requests to /custom-route. Names also support path parameters as defined by http.ServeMux.
• Template files can be invoked from within other templates using either their full path relative to the template root or by using its defined template name.
• Templates are executed with a uniform context object, which provides access to request data, database connections, and other useful dynamic functionality.
• Templates can also call functions set at startup.

[!note]

Custom dot fields and functions are similar in that they both add functionality to the templates, but dot fields are distinguished in that they are initialized on every request with access to request-scoped details including the underlying http.Request and http.ResponseWriter objects, the request-scoped logger, and the server context.

Thus FuncMap functions are recommended for adding simple computational functionality (like parsing, escaping, data structure manipulation, etc), whereas dot fields are recommended for more complicated tasks like accessing network resources, running database queries, accessing the file system, etc.

📝 Context

The dot context {{.}} set on each template invocation provides access to request-specific data and response control methods, and can be modified to add custom fields with your own methods.

✏️ Built-in dot fields

These fields are always present in relevant template invocations:

• Access instance data with the .X field. See DotX
• Access request details with the .Req field. See DotReq
• Control the HTTP response in buffered template handlers with the .Resp field. See DotResp
• Control flushing behavior for flushing template handlers (i.e. SSE) with the .Flush field. See DotFlush

✏️ Optional dot fields

These optional value providers can be configured with any field name, and can be configured multiple times with different configurations.

• Read and list files. See [DotFS]
• Query and execute SQL statements. See DotDB
• Read template-level key-value map. See DotKV

✏️ Custom dot fields

You can create custom dot fields that expose arbitrary Go functionality to your templates. See 👩‍⚕️ Writing a custom DotProvider.

📐 Functions

These are built-in functions that are available to all invocations and don't depend on request context or mutate state. There are three sets by default: functions that come by default in the go template library, functions from the sprig library, and custom functions added by xtemplate.

You can custom FuncMaps by configuring the Config.FuncMaps field.

• 📏 xtemplate includes funcs to render markdown, sanitize html, convert values to human-readable forms, and to try to call a function to handle an error within the template. See the free functions named FuncXYZ(...) in xtemplate's Go docs for details.
• 📏 Sprig publishes a library of useful template funcs that enable templates to manipulate strings, integers, floating point numbers, and dates, as well as perform encoding tasks, manipulate lists and dicts, converting types, and manipulate file paths See Sprig Function Documentation.
• 📏 Go's built in functions add logic and basic printing functionality. See: text/template#Functions.

🏆 Users

• PixyBlue/lazy-lob-web, a fullstack web lob framework.
• infogulch/xrss, an rss feed reader built with htmx and inline css.
• infogulch/todos, a demo todomvc application.

👷‍♀️ Development

🗺️ Repository structure

xtemplate is split into the following packages:

• github.com/infogulch/xtemplate is a library that exports the Instance struct which can load template files and implements http.Handler that routes requests to templates and serves static files, the Server struct which can atomically reload an Instance on demand, and a number of built-in providers.
• ./app is a library that contains an exported Main function which configures and starts xtemplate with CLI args and accepts config override parameters. This Main fucntion can be used as a reference for using the xtemplate API in advanced use-cases.
• ./cmd is a binary that simply imports a database driver and runs xtemplate/app.Main(). The recommended way to begin customizing xtemplate is to copy the ./cmd package to your own repo, then add your own database driver, provide custom config overrides, etc.
• ./caddy is a Caddy module package that uses xtemplate's Go library API to integrate xtemplate into Caddy server.

[!TIP]

To understand how the xtemplate package works, it may be helpful to skim through the files in this order: config.go, server.go instance.go, build.go, handlers.go.

Testing

Tasks are managed with mise. The task definitions live as Nushell scripts under .config/mise/tasks (sharing helpers from .config/mise/lib.nu) and the tool versions (Go, hurl, Nushell, xcaddy) are pinned in .config/mise/config.toml, so local and CI runs use identical versions. List the available tasks with mise tasks. Each task is a standalone Nushell script, so it can also be run directly (e.g. ./.config/mise/tasks/gotest) from anywhere in the repo without going through mise run.

The integration tests run xtemplate configured to use test/templates as the templates dir and test/context as the FS dot provider, then run the hurl files from the test/tests directory against the running server. The same suite is exercised against all three deployment targets:

• mise run test-cli builds and tests the standalone CLI binary.
• mise run test-caddy builds and tests the Caddy module.
• mise run test-docker builds and tests the Docker image.

mise run ci runs the whole pipeline: lint (lint-nu parse-checks the task scripts with nu --ide-check, lint-go runs golangci-lint), go test (gotest), the three integration targets, and then the release dist and Docker image builds.

👩‍⚕️ Writing a custom DotProvider

Implement the xtemplate.DotConfig interface on your type:

type DotConfig interface {
    FieldName() string            // the dot field name, e.g. "Shop" for {{.Shop}}
    Init(context.Context) error   // called once at instance load
    Value(Request) (any, error)   // called per request; its return is assigned to the dot field
}

Register it by passing xtemplate.WithProvider(yourConfig) as an option to config.Server(...), config.Instance(...), or app.Main(...):

app.Main(xtemplate.WithProvider(&ShopConfig{}))

On startup xtemplate creates a struct that includes your value as a field named by FieldName(). For every request your Value method is called with request details and its return value is assigned onto that struct, which is passed to html/template as the dot value {{.}}. Value must return a stable, non-nil concrete type: it is called once with a mock request at load time to infer the field type via reflection.

Optionally implement xtemplate.CleanupDotProvider to run per-request cleanup (e.g. rolling back a transaction), the way the built-in DotDB provider does.

See examples/dotprovider for a complete, runnable example.

✅ Project history and license

The idea for this project started as infogulch/go-htmx (now archived), which included the first implementations of template-name-based routing, exposing sql db functions to templates, and a persistent templates instance shared across requests and reloaded when template files changed.

go-htmx was refactored and rebased on top of the templates module from the Caddy server to create caddy-xtemplate to add some extra features including reading files directly and built-in funcs for markdown conversion, and to get a jump start on supporting the broad array of web server features without having to implement them from scratch.

xtemplate has since been refactored to be usable independently from Caddy, and is published as a subpackage in this module at ./caddy which uses the public xtemplate Go API and to integrate xtemplate into Caddy as an http middleware.

See CHANGELOG.md for a per-release history of notable changes.

xtemplate is licensed under the Apache 2.0 license. See LICENSE