render

Render

Render is a package that provides functionality for easily rendering JSON, XML, text, binary data, and HTML templates.

Usage

Render can be used with pretty much any web framework providing you can access the http.ResponseWriter from your handler. The rendering functions simply wraps Go's existing functionality for marshaling and rendering data.

• HTML: Uses the html/template package to render HTML templates.
• JSON: Uses the encoding/json package to marshal data into a JSON-encoded response.
• XML: Uses the encoding/xml package to marshal data into an XML-encoded response.
• Binary data: Passes the incoming data straight through to the http.ResponseWriter.
• Text: Passes the incoming string straight through to the http.ResponseWriter.

// main.go
package main

import (
    "encoding/xml"
    "net/http"

    "github.com/unrolled/render"
)

type ExampleXml struct {
    XMLName xml.Name `xml:"example"`
    One     string   `xml:"one,attr"`
    Two     string   `xml:"two,attr"`
}

func main() {
    r := render.New()
    mux := http.NewServeMux()

    mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
        w.Write([]byte("Welcome, visit sub pages now."))
    })

    mux.HandleFunc("/data", func(w http.ResponseWriter, req *http.Request) {
        r.Data(w, http.StatusOK, []byte("Some binary data here."))
    })

    mux.HandleFunc("/text", func(w http.ResponseWriter, req *http.Request) {
        r.Text(w, http.StatusOK, "Plain text here")
    })

    mux.HandleFunc("/json", func(w http.ResponseWriter, req *http.Request) {
        r.JSON(w, http.StatusOK, map[string]string{"hello": "json"})
    })

    mux.HandleFunc("/jsonp", func(w http.ResponseWriter, req *http.Request) {
        r.JSONP(w, http.StatusOK, "callbackName", map[string]string{"hello": "jsonp"})
    })

    mux.HandleFunc("/xml", func(w http.ResponseWriter, req *http.Request) {
        r.XML(w, http.StatusOK, ExampleXml{One: "hello", Two: "xml"})
    })

    mux.HandleFunc("/html", func(w http.ResponseWriter, req *http.Request) {
        // Assumes you have a template in ./templates called "example.tmpl"
        // $ mkdir -p templates && echo "<h1>Hello {{.}}.</h1>" > templates/example.tmpl
        r.HTML(w, http.StatusOK, "example", "World")
    })

    http.ListenAndServe("127.0.0.1:3000", mux)
}

<!-- templates/example.tmpl -->
<h1>Hello {{.}}.</h1>

Available Options

Render comes with a variety of configuration options (Note: these are not the default option values. See the defaults below.):

// ...
r := render.New(render.Options{
    Directory: "templates", // Specify what path to load the templates from.
    FileSystem: &LocalFileSystem{}, // Specify filesystem from where files are loaded.
    Asset: func(name string) ([]byte, error) { // Load from an Asset function instead of file.
      return []byte("template content"), nil
    },
    AssetNames: func() []string { // Return a list of asset names for the Asset function
      return []string{"filename.tmpl"}
    },
    Layout: "layout", // Specify a layout template. Layouts can call {{ yield }} to render the current template or {{ partial "css" }} to render a partial from the current template.
    Extensions: []string{".tmpl", ".html"}, // Specify extensions to load for templates.
    Funcs: []template.FuncMap{AppHelpers}, // Specify helper function maps for templates to access.
    Delims: render.Delims{"{[{", "}]}"}, // Sets delimiters to the specified strings.
    Charset: "UTF-8", // Sets encoding for content-types. Default is "UTF-8".
    DisableCharset: true, // Prevents the charset from being appended to the content type header.
    IndentJSON: true, // Output human readable JSON.
    IndentXML: true, // Output human readable XML.
    PrefixJSON: []byte(")]}',\n"), // Prefixes JSON responses with the given bytes.
    PrefixXML: []byte("<?xml version='1.0' encoding='UTF-8'?>"), // Prefixes XML responses with the given bytes.
    HTMLContentType: "application/xhtml+xml", // Output XHTML content type instead of default "text/html".
    IsDevelopment: true, // Render will now recompile the templates on every HTML response.
    UseMutexLock: true, // Overrides the default no lock implementation and uses the standard `sync.RWMutex` lock.
    UnEscapeHTML: true, // Replace ensure '&<>' are output correctly (JSON only).
    StreamingJSON: true, // Streams the JSON response via json.Encoder.
    HTMLTemplateOption: "missingkey=error", // Sets the option value for HTML templates. See https://pkg.go.dev/html/template#Template.Option for a list of known options.
    RequirePartials: true, // Return an error if a template is missing a partial used in a layout.
    DisableHTTPErrorRendering: true, // Disables automatic rendering of http.StatusInternalServerError when an error occurs.
})
// ...

Default Options

These are the preset options for Render:

r := render.New()

// Is the same as the default configuration options:

r := render.New(render.Options{
    Directory: "templates",
    FileSystem: &LocalFileSystem{},
    Asset: nil,
    AssetNames: nil,
    Layout: "",
    Extensions: []string{".tmpl"},
    Funcs: []template.FuncMap{},
    Delims: render.Delims{"{{", "}}"},
    Charset: "UTF-8",
    DisableCharset: false,
    IndentJSON: false,
    IndentXML: false,
    PrefixJSON: []byte(""),
    PrefixXML: []byte(""),
    BinaryContentType: "application/octet-stream",
    HTMLContentType: "text/html",
    JSONContentType: "application/json",
    JSONPContentType: "application/javascript",
    TextContentType: "text/plain",
    XMLContentType: "application/xhtml+xml",
    IsDevelopment: false,
    UseMutexLock: false,
    UnEscapeHTML: false,
    HTMLTemplateOption: "",
    StreamingJSON: false,
    RequirePartials: false,
    DisableHTTPErrorRendering: false,
    RenderPartialsWithoutPrefix: false,
    BufferPool: GenericBufferPool,
})

JSON vs Streaming JSON

By default, Render does not stream JSON to the http.ResponseWriter. It instead marshalls your object into a byte array, and if no errors occurred, writes that byte array to the http.ResponseWriter. If you would like to use the built it in streaming functionality (json.Encoder), you can set the StreamingJSON setting to true. This will stream the output directly to the http.ResponseWriter. Also note that streaming is only implemented in render.JSON and not render.JSONP.

Loading Templates

By default Render will attempt to load templates with a '.tmpl' extension from the "templates" directory. Templates are found by traversing the templates directory and are named by path and basename. For instance, the following directory structure:

templates/
  |
  |__ admin/
  |      |
  |      |__ index.tmpl
  |      |
  |      |__ edit.tmpl
  |
  |__ home.tmpl

Will provide the following templates:

admin/index
admin/edit
home

Templates can be loaded from an embed.FS.

// ...

//go:embed templates/*.html templates/*.tmpl
var embeddedTemplates embed.FS

// ...

r := render.New(render.Options{
    Directory: "templates",
    FileSystem: &render.EmbedFileSystem{
        FS: embeddedTemplates,
    },
    Extensions: []string{".html", ".tmpl"},
})
// ...

You can also load templates from memory by providing the Asset and AssetNames options, e.g. when generating an asset file using go-bindata.

Layouts

Render provides yield and partial functions for layouts to access:

// ...
r := render.New(render.Options{
    Layout: "layout",
})
// ...

<!-- templates/layout.tmpl -->
<html>
  <head>
    <title>My Layout</title>
    <!-- Render the partial template called `css-$current_template` here -->
    {{ partial "css" }}
  </head>
  <body>
    <!-- render the partial template called `header-$current_template` here -->
    {{ partial "header" }}
    <!-- Render the current template here -->
    {{ yield }}
    <!-- render the partial template called `footer-$current_template` here -->
    {{ partial "footer" }}
  </body>
</html>

current can also be called to get the current template being rendered.

<!-- templates/layout.tmpl -->
<html>
  <head>
    <title>My Layout</title>
  </head>
  <body>
    This is the {{ current }} page.
  </body>
</html>

Partials are defined by individual templates as seen below. The partial template's name needs to be defined as "{partial name}-{template name}".

<!-- templates/home.tmpl -->
{{ define "header-home" }}
<h1>Home</h1>
{{ end }}

{{ define "footer-home"}}
<p>The End</p>
{{ end }}

By default, the template is not required to define all partials referenced in the layout. If you want an error to be returned when a template does not define a partial, set Options.RequirePartials = true.

Character Encodings

Render will automatically set the proper Content-Type header based on which function you call. See below for an example of what the default settings would output (note that UTF-8 is the default, and binary data does not output the charset):

// main.go
package main

import (
    "encoding/xml"
    "net/http"

    "github.com/unrolled/render"
)

type ExampleXml struct {
    XMLName xml.Name `xml:"example"`
    One     string   `xml:"one,attr"`
    Two     string   `xml:"two,attr"`
}

func main() {
    r := render.New(render.Options{})
    mux := http.NewServeMux()

    // This will set the Content-Type header to "application/octet-stream".
    // Note that this does not receive a charset value.
    mux.HandleFunc("/data", func(w http.ResponseWriter, req *http.Request) {
        r.Data(w, http.StatusOK, []byte("Some binary data here."))
    })

    // This will set the Content-Type header to "application/json; charset=UTF-8".
    mux.HandleFunc("/json", func(w http.ResponseWriter, req *http.Request) {
        r.JSON(w, http.StatusOK, map[string]string{"hello": "json"})
    })

    // This will set the Content-Type header to "text/xml; charset=UTF-8".
    mux.HandleFunc("/xml", func(w http.ResponseWriter, req *http.Request) {
        r.XML(w, http.StatusOK, ExampleXml{One: "hello", Two: "xml"})
    })

    // This will set the Content-Type header to "text/plain; charset=UTF-8".
    mux.HandleFunc("/text", func(w http.ResponseWriter, req *http.Request) {
        r.Text(w, http.StatusOK, "Plain text here")
    })

    // This will set the Content-Type header to "text/html; charset=UTF-8".
    mux.HandleFunc("/html", func(w http.ResponseWriter, req *http.Request) {
        // Assumes you have a template in ./templates called "example.tmpl"
        // $ mkdir -p templates && echo "<h1>Hello {{.}}.</h1>" > templates/example.tmpl
        r.HTML(w, http.StatusOK, "example", "World")
    })

    http.ListenAndServe("127.0.0.1:3000", mux)
}

In order to change the charset, you can set the Charset within the render.Options to your encoding value:

// main.go
package main

import (
    "encoding/xml"
    "net/http"

    "github.com/unrolled/render"
)

type ExampleXml struct {
    XMLName xml.Name `xml:"example"`
    One     string   `xml:"one,attr"`
    Two     string   `xml:"two,attr"`
}

func main() {
    r := render.New(render.Options{
        Charset: "ISO-8859-1",
    })
    mux := http.NewServeMux()

    // This will set the Content-Type header to "application/octet-stream".
    // Note that this does not receive a charset value.
    mux.HandleFunc("/data", func(w http.ResponseWriter, req *http.Request) {
        r.Data(w, http.StatusOK, []byte("Some binary data here."))
    })

    // This will set the Content-Type header to "application/json; charset=ISO-8859-1".
    mux.HandleFunc("/json", func(w http.ResponseWriter, req *http.Request) {
        r.JSON(w, http.StatusOK, map[string]string{"hello": "json"})
    })

    // This will set the Content-Type header to "text/xml; charset=ISO-8859-1".
    mux.HandleFunc("/xml", func(w http.ResponseWriter, req *http.Request) {
        r.XML(w, http.StatusOK, ExampleXml{One: "hello", Two: "xml"})
    })

    // This will set the Content-Type header to "text/plain; charset=ISO-8859-1".
    mux.HandleFunc("/text", func(w http.ResponseWriter, req *http.Request) {
        r.Text(w, http.StatusOK, "Plain text here")
    })

    // This will set the Content-Type header to "text/html; charset=ISO-8859-1".
    mux.HandleFunc("/html", func(w http.ResponseWriter, req *http.Request) {
        // Assumes you have a template in ./templates called "example.tmpl"
        // $ mkdir -p templates && echo "<h1>Hello {{.}}.</h1>" > templates/example.tmpl
        r.HTML(w, http.StatusOK, "example", "World")
    })

    http.ListenAndServe("127.0.0.1:3000", mux)
}

Error Handling

The rendering functions return any errors from the rendering engine. By default, they will also write the error to the HTTP response and set the status code to 500. You can disable this behavior so that you can handle errors yourself by setting Options.DisableHTTPErrorRendering: true.

r := render.New(render.Options{
  DisableHTTPErrorRendering: true,
})

//...

err := r.HTML(w, http.StatusOK, "example", "World")
if err != nil{
  http.Redirect(w, r, "/my-custom-500", http.StatusFound)
}

Integration Examples

Echo

// main.go
package main

import (
    "io"
    "net/http"

    "github.com/labstack/echo"
    "github.com/unrolled/render"
)

type RenderWrapper struct { // We need to wrap the renderer because we need a different signature for echo.
    rnd *render.Render
}

func (r *RenderWrapper) Render(w io.Writer, name string, data interface{},c echo.Context) error {
    return r.rnd.HTML(w, 0, name, data) // The zero status code is overwritten by echo.
}

func main() {
    r := &RenderWrapper{render.New()}

    e := echo.New()

    e.Renderer = r

    e.GET("/", func(c echo.Context) error {
        return c.Render(http.StatusOK, "TemplateName", "TemplateData")
    })

    e.Logger.Fatal(e.Start("127.0.0.1:8080"))
}

Gin

// main.go
package main

import (
    "net/http"

    "github.com/gin-gonic/gin"
    "github.com/unrolled/render"
)

func main() {
    r := render.New(render.Options{
        IndentJSON: true,
    })

    router := gin.Default()

    router.GET("/", func(c *gin.Context) {
        r.JSON(c.Writer, http.StatusOK, map[string]string{"welcome": "This is rendered JSON!"})
    })

    router.Run("127.0.0.1:8080")
}

Goji

// main.go
package main

import (
    "net/http"

    "github.com/zenazn/goji"
    "github.com/zenazn/goji/web"
    "github.com/unrolled/render"
)

func main() {
    r := render.New(render.Options{
        IndentJSON: true,
    })

    goji.Get("/", func(c web.C, w http.ResponseWriter, req *http.Request) {
        r.JSON(w, http.StatusOK, map[string]string{"welcome": "This is rendered JSON!"})
    })
    goji.Serve()  // Defaults to ":8000".
}

Negroni

// main.go
package main

import (
    "net/http"

    "github.com/urfave/negroni"
    "github.com/unrolled/render"
)

func main() {
    r := render.New(render.Options{
        IndentJSON: true,
    })
    mux := http.NewServeMux()

    mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
        r.JSON(w, http.StatusOK, map[string]string{"welcome": "This is rendered JSON!"})
    })

    n := negroni.Classic()
    n.UseHandler(mux)
    n.Run("127.0.0.1:8080")
}

Traffic

// main.go
package main

import (
    "net/http"

    "github.com/pilu/traffic"
    "github.com/unrolled/render"
)

func main() {
    r := render.New(render.Options{
        IndentJSON: true,
    })

    router := traffic.New()
    router.Get("/", func(w traffic.ResponseWriter, req *traffic.Request) {
        r.JSON(w, http.StatusOK, map[string]string{"welcome": "This is rendered JSON!"})
    })

    router.Run()  // Defaults to "127.0.0.1:3000".
}