templatefile/main.go

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package main
import (
encjson "encoding/json"
"fmt"
"os"
"text/template"
"github.com/hashicorp/hcl/v2"
"github.com/hashicorp/hcl/v2/hclsyntax"
"github.com/zclconf/go-cty/cty"
ctyjson "github.com/zclconf/go-cty/cty/json"
)
func checkErr(e error) {
if e != nil {
panic(e)
}
}
func checkDiags(diag hcl.Diagnostics) {
if diag.HasErrors() {
panic(diag.Error())
}
}
func processGoTemplate(file string, config []byte) {
// The JSON configuration
var confData map[string]interface{}
err := encjson.Unmarshal(config, &confData)
checkErr(err)
// Read the template
data, err := os.ReadFile(file)
checkErr(err)
tpl, err := template.New("conf").Parse(string(data))
checkErr(err)
checkErr(tpl.Execute(os.Stdout, confData))
}
func processHCLTemplate(file string, config []byte) {
fct, err := os.ReadFile(file)
checkErr(err)
expr, diags := hclsyntax.ParseTemplate(fct, file, hcl.Pos{Line: 1, Column: 1})
checkDiags(diags)
// Retrieve values from JSON
var varsVal cty.Value
ctyType, err := ctyjson.ImpliedType(config)
if err != nil {
panic(err)
/* Maybe one day
cexpr, diags := hclsyntax.ParseExpression(config, "", hcl.Pos{Line: 1, Column: 1})
if diags.HasErrors() {
panic(diags.Error())
}
varsVal, diags = cexpr.Value(&hcl.EvalContext{})
fmt.Println(cexpr.Variables())
checkDiags(diags)
*/
} else {
varsVal, err = ctyjson.Unmarshal(config, ctyType)
checkErr(err)
}
ctx := &hcl.EvalContext{
Variables: varsVal.AsValueMap(),
}
for n := range ctx.Variables {
if !hclsyntax.ValidIdentifier(n) {
panic(fmt.Errorf("invalid template variable name %q: must start with a letter, followed by zero or more letters, digits, and underscores", n))
}
}
for _, traversal := range expr.Variables() {
root := traversal.RootName()
if _, ok := ctx.Variables[root]; !ok {
panic(fmt.Errorf("vars map does not contain key %q, referenced at %s", root, traversal[0].SourceRange()))
}
}
val, diags := expr.Value(ctx)
if diags.HasErrors() {
panic(diags.Error())
}
fmt.Printf("%s", val.AsString())
}
func main() {
// The template to process
templateType := os.Args[1]
templateFile := os.Args[2]
config := []byte(os.Args[3])
if templateType == "go" {
processGoTemplate(templateFile, config)
} else if templateType == "hcl" {
processHCLTemplate(templateFile, config)
} else {
panic(fmt.Errorf("Unsupported template type"))
}
}