feat(envvars): substitute envvars similar to decK

filebasics/filebasics.go

@@ -41,7 +41,13 @@ func ReadFile(filename string) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	return body, nil
+
+	renderedContent, err := renderTemplate(string(body), false)
+	if err != nil {
+		return nil, fmt.Errorf("parsing file: %w", err)
+	}
+
+	return []byte(renderedContent), nil
 }
 
 // MustReadFile reads file contents. Will panic if reading fails.

filebasics/template.go

@@ -0,0 +1,111 @@
+package filebasics
+
+// This file is a copy of: https://github.com/Kong/go-database-reconciler/blob/main/pkg/file/template.go
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"text/template"
+)
+
+// default env var prefix, can be set using SetEnvVarPrefix
+var envVarPrefix = "DECK_"
+
+// SetEnvVarPrefix sets the prefix for environment variables used in the state file.
+// The default prefix is "DECK_". This sets a library global(!!) value.
+func SetEnvVarPrefix(prefix string) {
+	envVarPrefix = prefix
+}
+
+func getPrefixedEnvVar(key string) (string, error) {
+	if !strings.HasPrefix(key, envVarPrefix) {
+		return "", fmt.Errorf("environment variables in the state file must "+
+			"be prefixed with '%s', found: '%s'", envVarPrefix, key)
+	}
+	value, exists := os.LookupEnv(key)
+	if !exists {
+		return "", fmt.Errorf("environment variable '%s' present in state file but not set", key)
+	}
+	return value, nil
+}
+
+// getPrefixedEnvVarMocked is used when we mock the env variables while rendering a template.
+// It will always return the name of the environment variable in this case.
+func getPrefixedEnvVarMocked(key string) (string, error) {
+	if !strings.HasPrefix(key, envVarPrefix) {
+		return "", fmt.Errorf("environment variables in the state file must "+
+			"be prefixed with '%s', found: '%s'", envVarPrefix, key)
+	}
+	return key, nil
+}
+
+func toBool(key string) (bool, error) {
+	return strconv.ParseBool(key)
+}
+
+// toBoolMocked is used when we mock the env variables while rendering a template.
+// It will always return false in this case.
+func toBoolMocked(_ string) (bool, error) {
+	return false, nil
+}
+
+func toInt(key string) (int, error) {
+	return strconv.Atoi(key)
+}
+
+// toIntMocked is used when we mock the env variables while rendering a template.
+// It will always return 42 in this case.
+func toIntMocked(_ string) (int, error) {
+	return 42, nil
+}
+
+func toFloat(key string) (float64, error) {
+	return strconv.ParseFloat(key, 64)
+}
+
+// toFloatMocked is used when we mock the env variables while rendering a template.
+// It will always return 42 in this case.
+func toFloatMocked(_ string) (float64, error) {
+	return 42, nil
+}
+
+func indent(spaces int, v string) string {
+	pad := strings.Repeat(" ", spaces)
+	return strings.Replace(v, "\n", "\n"+pad, -1)
+}
+
+func renderTemplate(content string, mockEnvVars bool) (string, error) {
+	var templateFuncs template.FuncMap
+	if mockEnvVars {
+		templateFuncs = template.FuncMap{
+			"env":     getPrefixedEnvVarMocked,
+			"toBool":  toBoolMocked,
+			"toInt":   toIntMocked,
+			"toFloat": toFloatMocked,
+			"indent":  indent,
+		}
+	} else {
+		templateFuncs = template.FuncMap{
+			"env":     getPrefixedEnvVar,
+			"toBool":  toBool,
+			"toInt":   toInt,
+			"toFloat": toFloat,
+			"indent":  indent,
+		}
+	}
+	t := template.New("state").Funcs(templateFuncs).Delims("${{", "}}")
+
+	t, err := t.Parse(content)
+	if err != nil {
+		return "", err
+	}
+	var buffer bytes.Buffer
+	err = t.Execute(&buffer, nil)
+	if err != nil {
+		return "", err
+	}
+	return buffer.String(), nil
+}