renderTemplate — write to a buffer first — http://elithrar.github.io/article/custom-handlers-avoiding-globals/

templates.go

import (
    "fmt"
    "html/template"
    "net/http"

    "github.com/oxtoacart/bpool"
)

var bufpool *bpool.BufferPool

// renderTemplate is a wrapper around template.ExecuteTemplate.
// It writes into a bytes.Buffer before writing to the http.ResponseWriter to catch
// any errors resulting from populating the template.
func (c *appContext) renderTemplate(w http.ResponseWriter, name string, data map[string]interface{}) error {
    // Ensure the template exists in the map.
    tmpl, ok := c.templates[name]
    if !ok {
        return fmt.Errorf("The template %s does not exist.", name)
    }

    // Create a buffer to temporarily write to and check if any errors were encountered.
    buf := c.bufpool.Get()
    err := tmpl.ExecuteTemplate(&buf, "base", data)
    if err != nil {
        c.bufpool.Put(buf)
        return err
    }

    // Set the header and write the buffer to the http.ResponseWriter
    w.Header().Set("Content-Type", "text/html; charset=utf-8")
    buf.WriteTo(w)
    c.bufpool.Put(buf)
    return nil
}