Support defining hamlib_rigs through env variables

The envconfig package introduced in 77cc83b does not handle map of
structs, so we have to handle hamlib_rigs manually.

This also defaults the "network" attribute to "tcp", which is what most
users want (for rigctld).

cfg/config.go

@@ -124,7 +124,7 @@ type Config struct {
 }
 
 type HamlibConfig struct {
-	// The network type ("serial" or "tcp"). Use 'tcp' for rigctld.
+	// The network type ("serial" or "tcp"). Use 'tcp' for rigctld (default).
 	//
 	// (For serial support: build with "-tags libhamlib".)
 	Network string `json:"network,omitempty"`

config.go

@@ -6,6 +6,7 @@ package main
 
 import (
 	"encoding/json"
+	"fmt"
 	"log"
 	"os"
 	"path"
@@ -33,6 +34,10 @@ func LoadConfig(cfgPath string, fallback cfg.Config) (config cfg.Config, err err
 	if err := envconfig.Process(buildinfo.AppName, &config); err != nil {
 		return config, err
 	}
+	// Environment variables for hamlib rigs (custom syntax not handled by envconfig)
+	if err := readRigsFromEnv(&config.HamlibRigs); err != nil {
+		return config, err
+	}
 
 	// Ensure the alias "telnet" exists
 	if config.ConnectAliases == nil {
@@ -121,6 +126,42 @@ func LoadConfig(cfgPath string, fallback cfg.Config) (config cfg.Config, err err
 	return config, nil
 }
 
+// readRigsFromEnv reads hamlib rigs config from environment.
+// Syntax: PAT_HAMLIB_RIGS_{rig name}_{ATTRIBUTE}
+// _{ATTRIBUTE} is optional (defaults to _ADDRESS).
+// Examples:
+//   - PAT_HAMLIB_RIGS_rig1_NETWORK=tcp
+//   - PAT_HAMLIB_RIGS_rig1_ADDRESS=localhost:8080
+//   - PAT_HAMLIB_RIGS_rig1_VFO=A
+//   - PAT_HAMLIB_RIGS_rig2=localhost:8080
+func readRigsFromEnv(rigs *map[string]cfg.HamlibConfig) error {
+	prefix := strings.ToUpper(buildinfo.AppName) + "_HAMLIB_RIGS_"
+	for _, env := range os.Environ() {
+		attribute, value, _ := strings.Cut(env, "=")
+		if !strings.HasPrefix(attribute, prefix) {
+			continue
+		}
+		attribute = strings.TrimPrefix(attribute, prefix)
+		name, attribute, _ := strings.Cut(attribute, "_")
+		if *rigs == nil {
+			*rigs = make(map[string]cfg.HamlibConfig)
+		}
+		rig := (*rigs)[name]
+		switch attribute {
+		case "ADDRESS", "":
+			rig.Address = value
+		case "NETWORK":
+			rig.Network = value
+		case "VFO":
+			rig.VFO = value
+		default:
+			return fmt.Errorf("invalid attribute '%s' for rig '%s'", attribute, name)
+		}
+		(*rigs)[name] = rig
+	}
+	return nil
+}
+
 func ReadConfig(path string) (config cfg.Config, err error) {
 	data, err := os.ReadFile(path)
 	if err != nil {

config_test.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/la5nta/pat/cfg"
+)
+
+func TestReadRigsFromEnv(t *testing.T) {
+	const prefix = "PAT_HAMLIB_RIGS"
+	unset := func() {
+		for _, env := range os.Environ() {
+			key, _, _ := strings.Cut(env, "=")
+			if strings.HasPrefix(key, prefix) {
+				os.Unsetenv(key)
+			}
+		}
+	}
+	t.Run("simple", func(t *testing.T) {
+		defer unset()
+		var rigs map[string]cfg.HamlibConfig
+		os.Setenv(prefix+"_rig", "localhost:4532")
+		if err := readRigsFromEnv(&rigs); err != nil {
+			t.Fatal(err)
+		}
+		if got := rigs["rig"]; (got != cfg.HamlibConfig{Address: "localhost:4532"}) {
+			t.Fatalf("Got unexpected config: %#v", got)
+		}
+	})
+	t.Run("with VFO", func(t *testing.T) {
+		defer unset()
+		var rigs map[string]cfg.HamlibConfig
+		os.Setenv(prefix+"_rig", "localhost:4532")
+		os.Setenv(prefix+"_rig_VFO", "A")
+		if err := readRigsFromEnv(&rigs); err != nil {
+			t.Fatal(err)
+		}
+		if got := rigs["rig"]; (got != cfg.HamlibConfig{Address: "localhost:4532", VFO: "A"}) {
+			t.Fatalf("Got unexpected config: %#v", got)
+		}
+	})
+	t.Run("full", func(t *testing.T) {
+		defer unset()
+		var rigs map[string]cfg.HamlibConfig
+		os.Setenv(prefix+"_rig_ADDRESS", "/dev/ttyS0")
+		os.Setenv(prefix+"_rig_NETWORK", "serial")
+		os.Setenv(prefix+"_rig_VFO", "B")
+		if err := readRigsFromEnv(&rigs); err != nil {
+			t.Fatal(err)
+		}
+		expect := cfg.HamlibConfig{
+			Address: "/dev/ttyS0",
+			Network: "serial",
+			VFO:     "B",
+		}
+		if got := rigs["rig"]; got != expect {
+			t.Fatalf("Got unexpected config: %#v", got)
+		}
+	})
+}

main.go

@@ -534,6 +534,9 @@ func loadHamlibRigs() map[string]hamlib.VFO {
 			log.Printf("Missing address-field for rig '%s', skipping.", name)
 			continue
 		}
+		if conf.Network == "" {
+			conf.Network = "tcp"
+		}
 
 		rig, err := hamlib.Open(conf.Network, conf.Address)
 		if err != nil {