Support config overrides using env variables

Override configuration values by setting PAT_* environment variables.
This is handy when deploying a containerized/scripted setup.

Syntax examples:
* PAT_MYCALL=LA5NTA
* PAT_ARDOP_ADDR="host:port"

config.go

@@ -11,15 +11,26 @@ import (
 	"path"
 	"strings"
 
+	"github.com/kelseyhightower/envconfig"
 	"github.com/la5nta/pat/cfg"
+	"github.com/la5nta/pat/internal/buildinfo"
 	"github.com/la5nta/pat/internal/debug"
 )
 
 func LoadConfig(cfgPath string, fallback cfg.Config) (config cfg.Config, err error) {
 	config, err = ReadConfig(cfgPath)
-	if os.IsNotExist(err) {
-		return fallback, WriteConfig(fallback, cfgPath)
-	} else if err != nil {
+	switch {
+	case os.IsNotExist(err):
+		config = fallback
+		if err := WriteConfig(config, cfgPath); err != nil {
+			return config, err
+		}
+	case err != nil:
+		return config, err
+	}
+
+	// Environment variables overrides values from the config file
+	if err := envconfig.Process(buildinfo.AppName, &config); err != nil {
 		return config, err
 	}
 

go.mod

@@ -12,6 +12,7 @@ require (
 	github.com/gorilla/websocket v1.4.2
 	github.com/harenber/ptc-go/v2 v2.2.3
 	github.com/howeyc/gopass v0.0.0-20190910152052-7cb4b85ec19c
+	github.com/kelseyhightower/envconfig v1.4.0
 	github.com/la5nta/wl2k-go v0.11.8
 	github.com/microcosm-cc/bluemonday v1.0.16
 	github.com/n8jja/Pat-Vara v1.1.4

go.sum

@@ -34,6 +34,8 @@ github.com/howeyc/crc16 v0.0.0-20171223171357-2b2a61e366a6 h1:IIVxLyDUYErC950b8k
 github.com/howeyc/crc16 v0.0.0-20171223171357-2b2a61e366a6/go.mod h1:JslaLRrzGsOKJgFEPBP65Whn+rdwDQSk0I0MCRFe2Zw=
 github.com/howeyc/gopass v0.0.0-20190910152052-7cb4b85ec19c h1:aY2hhxLhjEAbfXOx2nRJxCXezC6CO2V/yN+OCr1srtk=
 github.com/howeyc/gopass v0.0.0-20190910152052-7cb4b85ec19c/go.mod h1:lADxMC39cJJqL93Duh1xhAs4I2Zs8mKS89XWXFGp9cs=
+github.com/kelseyhightower/envconfig v1.4.0 h1:Im6hONhd3pLkfDFsbRgu68RDNkGF1r3dvMUtDTo2cv8=
+github.com/kelseyhightower/envconfig v1.4.0/go.mod h1:cccZRl6mQpaq41TPp5QxidR+Sa3axMbJDNb//FQX6Gg=
 github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=