Support environment variables for selected config fields (#40)

* deployment time config using env variables

* check if ethereum is enabled before replacing the config value with env variable

setup/config/config.go

@@ -23,6 +23,7 @@ import (
 	"os"
 	"path/filepath"
 	"regexp"
+	"strconv"
 	"strings"
 
 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
@@ -291,6 +292,9 @@ func LoadMatrixKey(privateKeyPath string, readFile func(string) ([]byte, error))
 // Derive generates data that is derived from various values provided in
 // the config file.
 func (config *Dendrite) Derive() error {
+	// Replace selected config with env variables.
+	config.replaceWithEnvVariables()
+
 	// Determine registrations flows based off config values
 
 	config.Derived.Registration.Params = make(map[string]interface{})
@@ -576,6 +580,58 @@ func (config *Dendrite) SetupTracing(serviceName string) (closer io.Closer, err
 	)
 }
 
+/*
+*
+Replace selected config with environment variables
+*/
+
+func (config *Dendrite) replaceWithEnvVariables() {
+	// Replace selected fields with env variables
+
+	config.Global.ServerName = gomatrixserverlib.ServerName(
+		replaceWithEnvVariables(string(config.Global.ServerName)),
+	)
+	logrus.Infof("Matrix ServerName=%s\n", config.Global.ServerName)
+
+	config.Global.DatabaseOptions.ConnectionString = DataSource(
+		replaceWithEnvVariables(
+			string(config.Global.DatabaseOptions.ConnectionString),
+		),
+	)
+
+	// If env variable is set, convert the deployment chain IDs from the env
+	// variable into []int and replace the ChainIDs field.
+	if config.ClientAPI.PublicKeyAuthentication.Ethereum.Enabled {
+		deploymentChainIDs := replaceWithEnvVariables(config.ClientAPI.PublicKeyAuthentication.Ethereum.DeploymentChainIDs)
+		chainIds := strings.Split(deploymentChainIDs, ",")
+		if len(chainIds) > 0 && chainIds[0] != "" {
+			var ids []int
+			for _, id := range chainIds {
+				id, err := strconv.Atoi(strings.TrimSpace(id))
+				if err == nil {
+					ids = append(ids, id)
+				}
+			}
+			config.ClientAPI.PublicKeyAuthentication.Ethereum.ChainIDs = ids
+		}
+		logrus.Infof("Supported Ethereum chain IDs=%d\n", config.ClientAPI.PublicKeyAuthentication.Ethereum.ChainIDs)
+	}
+}
+
+var regexpEnvVariables = regexp.MustCompile(`\$\{(?P<Var>\w+)\}`)
+var varIndex = regexpEnvVariables.SubexpIndex("Var")
+
+func replaceWithEnvVariables(value string) string {
+	matches := regexpEnvVariables.FindAllStringSubmatch(value, -1)
+	for _, m := range matches {
+		if varIndex < len(m) {
+			envValue := os.Getenv(m[varIndex])
+			value = strings.ReplaceAll(value, fmt.Sprintf("${%s}", m[varIndex]), envValue)
+		}
+	}
+	return value
+}
+
 // logrusLogger is a small wrapper that implements jaeger.Logger using logrus.
 type logrusLogger struct {
 	l *logrus.Logger

setup/config/config_publickey.go

@@ -24,6 +24,7 @@ type EthereumAuthConfig struct {
 	Enabled            bool   `yaml:"enabled"`
 	Version            uint   `yaml:"version"`
 	ChainIDs           []int  `yaml:"chain_ids"`
+	DeploymentChainIDs string `yaml:"deployment_chain_ids"` // For deployment: use env variable strings to override the chain IDs.
 	EnableAuthz        bool   `yaml:"enable_authz"`         // Flag to enable / disable authorization during development
 }