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Published: Jun 7, 2019 License: Apache-2.0 Imports: 16 Imported by: 104



Hero is a handy, fast and powerful go template engine, which pre-compiles the html templates to go code. It has been used in production environment in bthub.io.

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  • High performance.
  • Easy to use.
  • Powerful. template Extend and Include supported.
  • Auto compiling when files change.


Hero is the fastest and least-memory used among currently known template engines in the benchmark. The data of chart comes from https://github.com/SlinSo/goTemplateBenchmark. You can find more details and benchmarks from that project.


go get github.com/shiyanhui/hero/hero

# Hero needs `goimports` to format the generated codes.
go get golang.org/x/tools/cmd/goimports


hero [options]

  -source string
        the html template file or dir (default "./")
  -dest string
        generated golang files dir, it will be the same with source if not set
  -extensions string
        source file extensions, comma splitted if many (default ".html")
  -pkgname template
        the generated template package name, default is template (default "template")
        whether automatically compile when the source files change

	hero -source="./"
	hero -source="$GOPATH/src/app/template" -dest="./" -extensions=".html,.htm" -pkgname="t" -watch

Quick Start

Assume that we are going to render a user list userlist.html. index.html is the layout, and user.html is an item in the list.

And assumes that they are all under $GOPATH/src/app/template

<!DOCTYPE html>
        <meta charset="utf-8">

        <%@ body { %>
        <% } %>
<%: func UserList(userList []string, buffer *bytes.Buffer) %>

<%~ "index.html" %>

<%@ body { %>
    <% for _, user := range userList { %>
            <%+ "user.html" %>
    <% } %>
<% } %>
    <%= user %>

Then we compile the templates to go code.

hero -source="$GOPATH/src/app/template"

We will get three new .go files under $GOPATH/src/app/template, i.e. index.html.go, user.html.go and userlist.html.go.

Then we write a http server in $GOPATH/src/app/main.go.

package main

import (


func main() {
    http.HandleFunc("/users", func(w http.ResponseWriter, req *http.Request) {
        var userList = []string {

        // Had better use buffer pool. Hero exports `GetBuffer` and `PutBuffer` for this.
        // For convenience, hero also supports `io.Writer`. For example, you can also define
        // the function to `func UserList(userList []string, w io.Writer) (int, error)`,
        // and then:
        //   template.UserList(userList, w)
        buffer := new(bytes.Buffer)
        template.UserList(userList, buffer)

    http.ListenAndServe(":8080", nil)

At last, start the server and visit http://localhost:8080/users in your browser, we will get what we want!

Template syntax

There are only nine necessary kinds of statements, which are:

  • Function Definition <%: func define %>

    • Function definition statement defines the function which represents an html file.
    • The type of the last parameter in the function defined should be *bytes.Buffer for manual buffer management or io.Writer for automatic buffer management ( note: if using io.Writer you may optionally specify return values (int, error) to handle the result of io.Writer.Write). Hero will identify the parameter name automaticly.
    • Example:
      • <%: func UserList(userList []string, buffer *bytes.Buffer) %>
      • <%: func UserList(userList []string, w io.Writer) %>
      • <%: func UserList(userList []string, w io.Writer) (int, error) %>
  • Extend <%~ "parent template" %>

    • Extend statement states the parent template the current template extends.
    • The parent template should be quoted with "".
    • Example: <%~ "index.html" >, which we have mentioned in quick start, too.
  • Include <%+ "sub template" %>

    • Include statement includes a sub-template to the current template. It works like #include in C++.
    • The sub-template should be quoted with "".
    • Example: <%+ "user.html" >, which we also have mentioned in quick start.
  • Import <%! go code %>

    • Import statement imports the packages used in the defined function, and it also contains everything that is outside of the defined function.

    • Import statement will NOT be inherited by child template.

    • Example:

        import (
        var a int
        const b = "hello, world"
        func Add(a, b int) int {
            return a + b
        type S struct {
            Name string
        func (s S) String() string {
            return s.Name
  • Block <%@ blockName { %> <% } %>

    • Block statement represents a block. Child template overwrites blocks to extend parent template.

    • Example:

      <!DOCTYPE html>
              <meta charset="utf-8">
              <%@ body { %>
              <% } %>
  • Code <% go code %>

    • Code statement states all code inside the defined function. It's just go code.

    • Example:

      <% for _, user := range userList { %>
          <% if user != "Alice" { %>
              <%= user %>
          <% } %>
      <% } %>
          a, b := 1, 2
          c := Add(a, b)
  • Raw Value <%==[t] variable %>

    • Raw Value statement will convert the variable to string.

    • t is the type of variable, hero will find suitable converting method by t. Candidates of t are:

      • b: bool
      • i: int, int8, int16, int32, int64
      • u: byte, uint, uint8, uint16, uint32, uint64
      • f: float32, float64
      • s: string
      • bs: []byte
      • v: interface


      • If t is not set, the value of t is s.
      • Had better not use v, cause when t=v, the converting method is fmt.Sprintf("%v", variable) and it is very slow.
    • Example:

      <%== "hello" %>
      <%==i 34  %>
      <%==u Add(a, b) %>
      <%==s user.Name %>
  • Escaped Value <%=[t] variable %>

    • Escaped Value statement is similar with Raw Value statement, but after converting, it will be escaped it with html.EscapesString.

    • t is the same as in Raw Value Statement.

    • Example:

      <%= a %>
      <%=i a + b %>
      <%=u Add(a, b) %>
      <%=bs []byte{1, 2} %>
  • Note <%# note %>

    • Note statement add notes to the template.
    • It will not be added to the generated go source.
    • Example: <# this is just a note example>.


Hero is licensed under the Apache License.




View Source
const (
	TypeBytesBuffer = "bytes.Buffer"
	TypeIOWriter    = "io.Writer"
View Source
const (
	TypeImport = iota
View Source
const (
	Bool      = "b"
	Int       = "i"
	Uint      = "u"
	Float     = "f"
	String    = "s"
	Bytes     = "bs"
	Interface = "v"
View Source
const (
	OpenBrace   = '{'
	CloseBrace  = '}'
	LT          = '<'
	GT          = '>'
	Percent     = '%'
	Exclamation = '!'
	Colon       = ':'
	Tilde       = '~'
	Plus        = '+'
	Equal       = '='
	At          = '@'
	Pound       = '#'
	Space       = ' '
	BreakLine   = '\n'


This section is empty.


func CheckExtension added in v0.0.2

func CheckExtension(path string, extensions []string) bool

func EscapeHTML

func EscapeHTML(html string, buffer *bytes.Buffer)

EscapeHTML escapes the html and then put it to the buffer.

func FormatBool

func FormatBool(b bool, buffer *bytes.Buffer)

FormatBool format bool to string and then put the result to the buffer.

func FormatFloat

func FormatFloat(f float64, buffer *bytes.Buffer)

FormatFloat format float64 to string and then put the result to the buffer.

func FormatInt

func FormatInt(i int64, buffer *bytes.Buffer)

FormatInt format int to string and then put the result to the buffer.

func FormatUint

func FormatUint(u uint64, buffer *bytes.Buffer)

FormatUint formats uint to string and put it to the buffer. It's part of go source: https://github.com/golang/go/blob/master/src/strconv/itoa.go#L60

func Generate

func Generate(source, dest, pkgName string, extensions []string)

Generate generates Go code from source to test. pkgName represents the package name of the generated code.

func GetBuffer

func GetBuffer() *bytes.Buffer

GetBuffer returns a *bytes.Buffer from sync.Pool.

func PutBuffer

func PutBuffer(buffer *bytes.Buffer)

PutBuffer puts a *bytes.Buffer to the sync.Pool.


This section is empty.


Path Synopsis
Code generated by hero.
Code generated by hero.

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