quicktemplate

Fast, powerful, yet easy to use template engine for Go. Inspired by mako templates philosophy.

Features

• Extremely fast. Templates are converted into Go code and then compiled.
• Almost all the bugs are caught during template compilation, so production suffers less from template-related bugs.
• Easy to use. See quickstart and examples for details.
• Powerful. Arbitrary Go code may be embedded into and mixed with templates. Be careful with this power - do not query db and/or external resources from templates unless you miss php way in Go :) This power is mostly for arbitrary data transformations.
• Easy to understand template inheritance powered by Go interfaces. See this example for details.
• Templates are compiled into a single binary, so there is no need in copying template files to the server.

Drawbacks

• Templates cannot be updated on the fly on the server, since they are compiled into a single binary. Take a look at fasttemplate if you need fast template engine for simple dynamically updated templates.

Performance comparison with html/template

Quicktemplate is more than 20x faster than html/template. The following simple template is used in the benchmark:

• html/template version
• quicktemplate version

Benchmark results:

$ go test -bench=Template -benchmem github.com/valyala/quicktemplate/tests
BenchmarkQuickTemplate1-4                 	10000000	       120 ns/op	       0 B/op	       0 allocs/op
BenchmarkQuickTemplate10-4                	 3000000	       441 ns/op	       0 B/op	       0 allocs/op
BenchmarkQuickTemplate100-4               	  300000	      3945 ns/op	       0 B/op	       0 allocs/op
BenchmarkHTMLTemplate1-4                  	  500000	      2501 ns/op	     752 B/op	      23 allocs/op
BenchmarkHTMLTemplate10-4                 	  100000	     12442 ns/op	    3521 B/op	     117 allocs/op
BenchmarkHTMLTemplate100-4                	   10000	    123392 ns/op	   34498 B/op	    1152 allocs/op

goTemplateBenchmark compares QuickTemplate with numerous go templating packages. QuickTemplate performs favorably.

Security

• All the template placeholders are html-escaped by default.
• Template placeholders for JSON strings prevents from </script>-based XSS attacks:

{% func FailedXSS() %}
<script>
    var s = {%q= "</script><script>alert('you pwned!')" %};
</script>
{% endfunc %}

Examples

See examples.

Quick start

Let's start with a minimal template example:

All the text outside function templates is treated as comments,
i.e. it is just ignored by quicktemplate compiler (qtc). It is for humans.

Hello is a simple template function.
{% func Hello(name string) %}
	Hello, {%s name %}!
{% endfunc %}

Save this file into templates folder under the name hello.qtpl and run qtc inside this folder. qtc may be installed by issuing:

go get -u github.com/valyala/quicktemplate/qtc

If all went ok, hello.qtpl.go file must appear in the templates folder. This file contains Go code for hello.qtpl. Let's use it!

Create a file main.go outside templates folder and put the following code there:

package main

import (
	"fmt"

	"./templates"
)

func main() {
	fmt.Printf("%s\n", templates.Hello("Foo"))
	fmt.Printf("%s\n", templates.Hello("Bar"))
}

Then run go run. If all went ok, you'll see something like this:

	Hello, Foo!


	Hello, Bar!

Let's create more complex template, which calls other template functions, contains loops, conditions, breaks, continue and returns. Put the following template into templates/greetings.qtpl:

Greetings greets up to 42 names.
It also greets John differently comparing to others.
{% func Greetings(names []string) %}
	{% if len(names) == 0 %}
		Nobody to greet :(
		{% return %}
	{% endif %}

	{% for i, name := range names %}
		{% if i == 42 %}
			I'm tired to greet so many people...
			{% break %}
		{% elseif name == "John" %}
			{%= sayHi("Mr. " + name) %}
			{% continue %}
		{% else%}
			{%= Hello(name) %}
		{% endif %}
	{% endfor %}
{% endfunc %}

sayHi is unexported, since it starts with lowercase letter.
{% func sayHi(name string) %}
	Hi, {%s name %}
{% endfunc %}

Note that every template file may contain arbitrary number
of template functions. For instance, this file contains Greetings and sayHi
functions.

Run qtc inside templates folder. Now the folder should contain two files with Go code: hello.qtpl.go and greetings.qtpl.go. These files form a single templates Go package. Template functions and other template stuff is shared between template files located in the same folder. So Hello template function may be used inside greetings.qtpl while it is defined in hello.qtpl. Moreover, the folder may contain ordinary Go files and its' contents may be used inside templates.

Now put the following code into main.go:

package main

import (
	"bytes"
	"fmt"

	"./templates"
)

func main() {
	names := []string{"Kate", "Go", "John", "Brad"}

	// qtc creates Write* function for each template function.
	// Such functions accept io.Writer as first parameter:
	var buf bytes.Buffer
	templates.WriteGreetings(&buf, names)

	fmt.Printf("buf=\n%s", buf.Bytes())
}

Careful readers may notice different output tags were used in these templates: {%s name %} and {%= Hello(name) %}. What's the difference? The {%s x %} is used for printing html-safe strings, while {%= F() %} is used for embedding template function calls. Quicktemplate supports also other output tags:

• {%d num %} for integers.
• {%f float %} for float64. Floating point precision may be set via {%f.precision float %}. For example, {%f.2 1.2345 %} outputs 1.23.
• {%z bytes %} for byte slices.
• {%q str %} and {%qz bytes %} for json-compatible quoted strings.
• {%j str %} and {%jz bytes %} for embedding str into json string. Unlike {%q str %} it doesn't quote the string.
• {%u str %} and {%uz bytes %} for URL encoding the given str.
• {%v anything %} is equivalent to %v in printf-like functions.

All these output tags produce html-safe output, i.e. they escape < to <, > to >, etc. If you don't want html-safe output, then just put = after the tag. For example: {%s= "<h1>This h1 won't be escaped</h1>" %}.

As you may notice {%= F() %} and {%s= F() %} produce the same output for {% func F() %}. But the first one is optimized for speed - it avoids memory allocations and copy. So stick to it when embedding template function calls.

All the ouptut tags except of {%= F() %} may contain arbitrary valid Go expression instead of just identifier. For example:

Import fmt for fmt.Sprintf()
{% import "fmt" %}

FmtFunc uses fmt.Sprintf() inside output tag
{% func FmtFunc(s string) %}
	{%s fmt.Sprintf("FmtFunc accepted %q string", s) %}
{% endfunc %}

There are other useful tags supported by quicktemplate:

• {% comment %}

  {% comment %}
      This is a comment. It won't trap into the output.
      It may contain {% arbitrary tags %}. They are just ignored.
  {% endcomment %}
  

• {% plain %}

    {% plain %}
        Tags will {% trap into %} the output {% unmodified %}.
        Plain block may contain invalid and {% incomplete tags.
    {% endplain %}
  ```

* `{% collapsespace %}`

  ```qtpl
  {% collapsespace %}
      <div>
          <div>space between lines</div>
             and {%s " tags" %}
           <div>is collapsed into a single space
           unless{% newline %}or{% space %}is used</div>
      </div>
  {% endcollapsespace %}
  ```

  Is converted into

  ```
  <div> <div>space between lines</div> and tags <div>is collapsed into a single space unless
  or is used</div> </div>
  ```

* `{% stripspace %}`

  ```qtpl
  {% stripspace %}
       <div>
           <div>space between lines</div>
              and {%s " tags" %}
           <div>is removed unless{% newline %}or{% space %}is used</div>
       </div>
  {% endstripspace %}
  ```

  Is converted into

  ```
  <div><div>space between lines</div>and tags<div>is removed unless
  or is used</div></div>
  ```

* `{% switch %}`, `{% case %}` and `{% default %}`:


  ```qtpl
  1 + 1 =
  {% switch 1+1 %}
  {% case 2 %}
  2?
  {% case 42 %}
  42!
  {% default %}
      I don't know :(
  {% endswitch %}
  ```

* `{% code %}`:

  ```qtpl
  {% code
  // arbitrary Go code may be embedded here!
  type FooArg struct {
      Name string
      Age int
  }
  %}
  ```

* `{% import %}`:

  ```qtpl
  Import external packages.
  {% import "foo/bar" %}
  {% import (
      "foo"
      bar "baz/baa"
  ) %}
  ```

* `{% interface %}`:

  ```qtpl
  Interfaces allow powerful templates' inheritance
  {%
  interface Page {
      Title()
      Body(s string, n int)
      Footer()
  }
  %}

  PrintPage prints Page
  {% func PrintPage(p Page) %}
      <html>
          <head><title>{%= p.Title() %}</title></head>
          <body>
              <div>{%= p.Body("foo", 42) %}</div>
              <div>{%= p.Footer() %}</div>
          </body>
      </html>
  {% endfunc %}

  Base page implementation
  {% code
  type BasePage struct {
      TitleStr string
      FooterStr string
  }
  %}
  {% func (bp *BasePage) Title() %}{%s bp.TitleStr %}{% endfunc %}
  {% func (bp *BasePage) Body(s string, n int) %}
      <b>s={%q s %}, n={%d n %}</b>
  {% endfunc %}
  {% func (bp *BasePage) Footer() %}{%s bp.FooterStr %}{% endfunc %}

  Main page implementation
  {% code
  type MainPage struct {
      // inherit from BasePage
      BasePage

      // real body for main page
      BodyStr string
  }
  %}

  Override only Body
  Title and Footer are used from BasePage.
  {% func (mp *MainPage) Body(s string, n int) %}
      <div>
          main body: {%s mp.BodyStr %}
      </div>
      <div>
          base body: {%= mp.BasePage.Body(s, n) %}
      </div>
  {% endfunc %}
  ```

  See [basicserver example](https://github.com/valyala/quicktemplate/tree/master/examples/basicserver)
  for more details.


# Performance optimization tips

* Prefer calling `WriteFoo` instead of `Foo` when generating template output
  for `{% func Foo() %}`. This avoids unnesessary memory allocation and a copy
  for a `string` returned from `Foo()`.

* Prefer `{%= Foo() %}` instead of `{%s= Foo() %}` when embedding
  a function template `{% func Foo() %}`. Though both approaches generate
  identical output, the first approach is optimized for speed.

* Prefer using existing output tags instead of passing `fmt.Sprintf`
  to `{%s %}`. For instance, use `{%d num %}` instead
  of `{%s fmt.Sprintf("%d", num) %}`, because the first approach is optimized
  for speed.

* Prefer using specific output tags instead of generic output tag
  `{%v %}`. For instance, use `{%s str %}` instead of `{%v str %}`, since
  specific output tags are optimized for speed.

* Prefer creating custom function templates instead of composing complex
  strings by hands before passing them to `{%s %}`.
  For instance, the first approach is slower than the second one:

  ```qtpl
  {% func Foo(n int) %}
      {% code
      // construct complex string
      complexStr := ""
      for i := 0; i < n; i++ {
          complexStr += fmt.Sprintf("num %d,", i)
      }
      %}
      complex string = {%s= complexStr %}
  {% endfunc %}
  ```

  ```qtpl
  {% func Foo(n int) %}
      complex string = {%= complexStr(n) %}
  {% endfunc %}

  // Wrap complexStr func into stripspace for stripping unnesessary space
  // between tags and lines.
  {% stripspace %}
  {% func complexStr(n int) %}
      {% for i := 0; i < n; i++ %}
          num{% space %}{%d i %}{% newline %}
      {% endfor %}
  {% endfunc %}
  {% endstripspace %}
  ```

* Make sure that the `io.Writer` passed to `Write*` functions
  is [buffered](https://golang.org/pkg/bufio/#Writer).
  This will minimize the number of `write`
  [syscalls](https://en.wikipedia.org/wiki/System_call),
  which may be quite expensive.

  Note: There is no need in wrapping [fasthttp.RequestCtx](https://godoc.org/github.com/valyala/fasthttp#RequestCtx)
  into [bufio.Writer](https://golang.org/pkg/bufio/#Writer), since it is already buffered.

* [Profile](http://blog.golang.org/profiling-go-programs) your programs
  for memory allocations and fix top functions from
  `go tool pprof --alloc_objects` output.


# Use cases

While the main quicktemplate purpose is generating html, it may be used
for generating other data too. For example, JSON and XML marshaling may
be easily implemented with quicktemplate:

```qtpl
{% code
type MarshalRow struct {
  Msg string
  N int
}

type MarshalData struct {
  Foo int
  Bar string
  Rows []MarshalRow
}
%}

// JSON marshaling
{% stripspace %}
{% func (d *MarshalData) JSON() %}
{
  "Foo": {%d d.Foo %},
  "Bar": {%q= d.Bar %},
  "Rows":[
  	{% for i, r := range d.Rows %}
  		{
  			"Msg": {%q= r.Msg %},
  			"N": {%d r.N %}
  		}
  		{% if i + 1 < len(d.Rows) %},{% endif %}
  	{% endfor %}
  ]
}
{% endfunc %}
{% endstripspace %}

// XML marshaling
{% stripspace %}
{% func (d *MarshalData) XML() %}
<MarshalData>
  <Foo>{%d d.Foo %}</Foo>
  <Bar>{%s d.Bar %}</Bar>
  <Rows>
  {% for _, r := range d.Rows %}
  	<Row>
  		<Msg>{%s r.Msg %}</Msg>
  		<N>{%d r.N %}</N>
  	</Row>
  {% endfor %}
  </Rows>
</MarshalData>
{% endfunc %}
{% endstripspace %}

Usually marshaling built with quicktemplate works faster than the marshaling implemented via standard encoding/json and encoding/xml. The corresponding benchmark results:

go test -bench=Marshal -benchmem github.com/valyala/quicktemplate/tests
BenchmarkMarshalJSONStd1-4                	 3000000	       480 ns/op	       8 B/op	       1 allocs/op
BenchmarkMarshalJSONStd10-4               	 1000000	      1842 ns/op	       8 B/op	       1 allocs/op
BenchmarkMarshalJSONStd100-4              	  100000	     15820 ns/op	       8 B/op	       1 allocs/op
BenchmarkMarshalJSONStd1000-4             	   10000	    159327 ns/op	      59 B/op	       1 allocs/op
BenchmarkMarshalJSONQuickTemplate1-4      	10000000	       162 ns/op	       0 B/op	       0 allocs/op
BenchmarkMarshalJSONQuickTemplate10-4     	 2000000	       748 ns/op	       0 B/op	       0 allocs/op
BenchmarkMarshalJSONQuickTemplate100-4    	  200000	      6572 ns/op	       0 B/op	       0 allocs/op
BenchmarkMarshalJSONQuickTemplate1000-4   	   20000	     66784 ns/op	      29 B/op	       0 allocs/op
BenchmarkMarshalXMLStd1-4                 	 1000000	      1652 ns/op	       2 B/op	       2 allocs/op
BenchmarkMarshalXMLStd10-4                	  200000	      7533 ns/op	      11 B/op	      11 allocs/op
BenchmarkMarshalXMLStd100-4               	   20000	     65763 ns/op	     195 B/op	     101 allocs/op
BenchmarkMarshalXMLStd1000-4              	    2000	    663373 ns/op	    3522 B/op	    1002 allocs/op
BenchmarkMarshalXMLQuickTemplate1-4       	10000000	       145 ns/op	       0 B/op	       0 allocs/op
BenchmarkMarshalXMLQuickTemplate10-4      	 3000000	       597 ns/op	       0 B/op	       0 allocs/op
BenchmarkMarshalXMLQuickTemplate100-4     	  300000	      5833 ns/op	       0 B/op	       0 allocs/op
BenchmarkMarshalXMLQuickTemplate1000-4    	   30000	     53000 ns/op	      32 B/op	       0 allocs/op

FAQ

• Why quicktemplate syntax is incompatible with html/template?

  Because html/template syntax isn't expressive enough for quicktemplate.

• What's the difference between quicktemplate and ego?

  Ego is similar to quicktemplate in the sense it converts templates into Go code. But it misses the following stuff, which makes quicktemplate so powerful and easy to use:

  • Defining multiple function templates in a single template file.
  • Embedding function templates inside other function templates.
  • Template interfaces, inheritance and overriding. See this example for details.
  • Top-level comments outside function templates.
  • Template packages.
  • Combining arbitrary Go files with template files in template packages.
  • Performance optimizations.

• What's the difference between quicktemplate and gorazor?

  Gorazor is similar to quicktemplate in the sense it converts templates into Go code. But it misses the following useful features:

  • Clear syntax insead of hard-to-understand magic stuff related to template arguments, template inheritance and embedding function templates into other templates.
  • Performance optimizations.

• I didn't find an answer for my question here

  Try exploring these questions.