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resource.go
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resource.go
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package template
import (
"crypto/sha256"
"encoding/hex"
"fmt"
"io/ioutil"
"github.com/hashicorp/terraform/config"
"github.com/hashicorp/terraform/config/lang"
"github.com/hashicorp/terraform/config/lang/ast"
"github.com/hashicorp/terraform/helper/schema"
"github.com/mitchellh/go-homedir"
)
func resource() *schema.Resource {
return &schema.Resource{
Create: Create,
Delete: Delete,
Exists: Exists,
Read: Read,
Schema: map[string]*schema.Schema{
"filename": &schema.Schema{
Type: schema.TypeString,
Required: true,
Description: "file to read template from",
ForceNew: true,
},
"vars": &schema.Schema{
Type: schema.TypeMap,
Optional: true,
Default: make(map[string]interface{}),
Description: "variables to substitute",
ForceNew: true,
},
"rendered": &schema.Schema{
Type: schema.TypeString,
Computed: true,
Description: "rendered template",
},
},
}
}
func Create(d *schema.ResourceData, meta interface{}) error {
rendered, err := render(d)
if err != nil {
return err
}
d.Set("rendered", rendered)
d.SetId(hash(rendered))
return nil
}
func Delete(d *schema.ResourceData, meta interface{}) error {
d.SetId("")
return nil
}
func Exists(d *schema.ResourceData, meta interface{}) (bool, error) {
rendered, err := render(d)
if err != nil {
return false, err
}
return hash(rendered) == d.Id(), nil
}
func Read(d *schema.ResourceData, meta interface{}) error {
// Logic is handled in Exists, which only returns true if the rendered
// contents haven't changed. That means if we get here there's nothing to
// do.
return nil
}
var readfile func(string) ([]byte, error) = ioutil.ReadFile // testing hook
func render(d *schema.ResourceData) (string, error) {
filename := d.Get("filename").(string)
vars := d.Get("vars").(map[string]interface{})
path, err := homedir.Expand(filename)
if err != nil {
return "", err
}
buf, err := readfile(path)
if err != nil {
return "", err
}
rendered, err := execute(string(buf), vars)
if err != nil {
return "", fmt.Errorf("failed to render %v: %v", filename, err)
}
return rendered, nil
}
// execute parses and executes a template using vars.
func execute(s string, vars map[string]interface{}) (string, error) {
root, err := lang.Parse(s)
if err != nil {
return "", err
}
varmap := make(map[string]ast.Variable)
for k, v := range vars {
// As far as I can tell, v is always a string.
// If it's not, tell the user gracefully.
s, ok := v.(string)
if !ok {
return "", fmt.Errorf("unexpected type for variable %q: %T", k, v)
}
varmap[k] = ast.Variable{
Value: s,
Type: ast.TypeString,
}
}
cfg := lang.EvalConfig{
GlobalScope: &ast.BasicScope{
VarMap: varmap,
FuncMap: config.Funcs,
},
}
out, typ, err := lang.Eval(root, &cfg)
if err != nil {
return "", err
}
if typ != ast.TypeString {
return "", fmt.Errorf("unexpected output ast.Type: %v", typ)
}
return out.(string), nil
}
func hash(s string) string {
sha := sha256.Sum256([]byte(s))
return hex.EncodeToString(sha[:])
}