feat(config): load client settings from config file

AGENTS.md

@@ -31,7 +31,7 @@ tunnel/stream.go        — Stream interface (io.ReadWriteCloser + Source/Target
 server/reconstructed_conn.go — Replays re-serialized headers + buffered body + raw conn after hijack
 store/store.go          — In-memory request/response recorder with pub/sub (SSE)
 web/web.go              — Local tunnel monitor (port 8181), SSE endpoint
-config/config.go        — Reflection-based config from struct tags → flags + env vars
+config/config.go        — Reflection-based config from struct tags → flags + env vars + client config file
 pkg/maps/map.go         — Generic sync.RWMutex-guarded map
 ```
 
@@ -39,7 +39,7 @@ pkg/maps/map.go         — Generic sync.RWMutex-guarded map
 
 - **Go style**: standard `gofmt`, golangci-lint with `.golangci.toml`
 - **Comment style**: Title Case heading above logical blocks (see root `AGENTS.md`)
-- **Config**: add struct tags (`json`, `default`, `description`) to `ServerConfig` or `ClientConfig` — flags and env vars are auto-derived
+- **Config**: add struct tags (`json`, `default`, `description`) to `ServerConfig` or `ClientConfig` — flags and env vars are auto-derived. Client config may also come from `./conduit.json` or `~/.config/conduit/config.json` for `server`, `api_key`, `log_level`, and `log_format` only.
 - **Logging**: use `logrus` (`log` alias); structured fields preferred
 - **Concurrency**: use `pkg/maps.Map` for shared maps; protect other shared state with `sync.Mutex`
 - **Error handling**: return errors up; log at command/entry-point level. Use `fmt.Errorf` with `%w` for wrapping

config/config.go

@@ -1,10 +1,12 @@
 package config
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"net/url"
 	"os"
+	"path/filepath"
 	"reflect"
 	"strings"
 
@@ -69,7 +71,7 @@ func GetServerConfig(cmdFlags *pflag.FlagSet) (*ServerConfig, error) {
 
 	cfgValues := make(map[string]string)
 	for _, def := range defs {
-		cfgValues[def.Key] = getConfigValue(cmdFlags, def)
+		cfgValues[def.Key] = getConfigValue(cmdFlags, nil, def)
 	}
 
 	cfg := &ServerConfig{
@@ -86,9 +88,15 @@ func GetServerConfig(cmdFlags *pflag.FlagSet) (*ServerConfig, error) {
 func GetClientConfig(cmdFlags *pflag.FlagSet) (*ClientConfig, error) {
 	defs := GetConfigDefs[ClientConfig]()
 
+	// Load Client Config File
+	fileValues, err := getClientConfigFileValues()
+	if err != nil {
+		return nil, err
+	}
+
 	cfgValues := make(map[string]string)
 	for _, def := range defs {
-		cfgValues[def.Key] = getConfigValue(cmdFlags, def)
+		cfgValues[def.Key] = getConfigValue(cmdFlags, fileValues, def)
 	}
 
 	cfg := &ClientConfig{
@@ -122,7 +130,33 @@ func getBaseConfig(cfgValues map[string]string) BaseConfig {
 	}
 }
 
-func getConfigValue(cmdFlags *pflag.FlagSet, def ConfigDef) string {
+func getClientConfigFileValues() (map[string]string, error) {
+	path, err := findConfigFile()
+	if err != nil {
+		return nil, err
+	}
+	if path == "" {
+		return nil, nil
+	}
+
+	// Load Config File
+	values, err := loadConfigFile(path)
+	if err != nil {
+		return nil, err
+	}
+
+	// Keep Client File Settings Explicit - Tunnel name and target are intentionally
+	// not read from the config file because they should be provided per invocation.
+	clientValues := make(map[string]string)
+	for key, value := range values {
+		if isClientFileConfigKey(key) {
+			clientValues[key] = value
+		}
+	}
+	return clientValues, nil
+}
+
+func getConfigValue(cmdFlags *pflag.FlagSet, fileValues map[string]string, def ConfigDef) string {
 	// 1. Get Flags First
 	if cmdFlags != nil {
 		if val, err := cmdFlags.GetString(def.Key); err == nil && val != "" && val != def.Default {
@@ -135,10 +169,65 @@ func getConfigValue(cmdFlags *pflag.FlagSet, def ConfigDef) string {
 		return envVal
 	}
 
-	// 3. Defaults Last
+	// 3. Config File Next
+	if fileValues != nil {
+		if val := fileValues[def.Key]; val != "" {
+			return val
+		}
+	}
+
+	// 4. Defaults Last
 	return def.Default
 }
 
+func findConfigFile() (string, error) {
+	// Check Project Config
+	localPath := "conduit.json"
+	if _, err := os.Stat(localPath); err == nil {
+		return localPath, nil
+	} else if !errors.Is(err, os.ErrNotExist) {
+		return "", err
+	}
+
+	// Check User Config
+	configDir, err := os.UserConfigDir()
+	if err != nil {
+		return "", nil
+	}
+	userPath := filepath.Join(configDir, "conduit", "config.json")
+	if _, err := os.Stat(userPath); err == nil {
+		return userPath, nil
+	} else if !errors.Is(err, os.ErrNotExist) {
+		return "", err
+	}
+
+	return "", nil
+}
+
+func loadConfigFile(path string) (map[string]string, error) {
+	// Read Config File
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+
+	// Decode Config File
+	values := make(map[string]string)
+	if err := json.Unmarshal(data, &values); err != nil {
+		return nil, fmt.Errorf("failed to parse config file %s: %w", path, err)
+	}
+	return values, nil
+}
+
+func isClientFileConfigKey(key string) bool {
+	switch key {
+	case "server", "api_key", "log_level", "log_format":
+		return true
+	default:
+		return false
+	}
+}
+
 func processFields(t reflect.Type, defs *[]ConfigDef) {
 	for i := 0; i < t.NumField(); i++ {
 		field := t.Field(i)

config/config_test.go

@@ -0,0 +1,144 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/spf13/pflag"
+)
+
+func TestLoadConfigFile(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"server":"https://example.com","api_key":"secret"}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	// Load Config File
+	values, err := loadConfigFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Verify Values
+	if values["server"] != "https://example.com" {
+		t.Fatalf("expected server from config file, got %q", values["server"])
+	}
+	if values["api_key"] != "secret" {
+		t.Fatalf("expected api_key from config file, got %q", values["api_key"])
+	}
+}
+
+func TestFindConfigFile(t *testing.T) {
+	workDir := t.TempDir()
+	configDir := t.TempDir()
+	oldDir, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		if err := os.Chdir(oldDir); err != nil {
+			t.Fatal(err)
+		}
+	}()
+	if err := os.Chdir(workDir); err != nil {
+		t.Fatal(err)
+	}
+	t.Setenv("XDG_CONFIG_HOME", configDir)
+
+	// Missing Config File
+	path, err := findConfigFile()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if path != "" {
+		t.Fatalf("expected no config file, got %q", path)
+	}
+
+	// User Config File
+	userPath := filepath.Join(configDir, "conduit", "config.json")
+	if err := os.MkdirAll(filepath.Dir(userPath), 0o700); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(userPath, []byte(`{}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	path, err = findConfigFile()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if path != userPath {
+		t.Fatalf("expected user config file %q, got %q", userPath, path)
+	}
+
+	// Local Config File Precedence
+	localPath := "conduit.json"
+	if err := os.WriteFile(localPath, []byte(`{}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	path, err = findConfigFile()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if path != localPath {
+		t.Fatalf("expected local config file %q, got %q", localPath, path)
+	}
+}
+
+func TestGetConfigValuePriority(t *testing.T) {
+	def := ConfigDef{Key: "server", Env: "CONDUIT_SERVER", Default: "default"}
+	fileValues := map[string]string{"server": "file"}
+
+	// Config File Beats Default
+	if value := getConfigValue(nil, fileValues, def); value != "file" {
+		t.Fatalf("expected file value, got %q", value)
+	}
+
+	// Environment Beats Config File
+	t.Setenv("CONDUIT_SERVER", "env")
+	if value := getConfigValue(nil, fileValues, def); value != "env" {
+		t.Fatalf("expected env value, got %q", value)
+	}
+
+	// Flags Beat Environment
+	flags := pflag.NewFlagSet("test", pflag.ContinueOnError)
+	flags.String("server", "default", "server")
+	if err := flags.Set("server", "flag"); err != nil {
+		t.Fatal(err)
+	}
+	if value := getConfigValue(flags, fileValues, def); value != "flag" {
+		t.Fatalf("expected flag value, got %q", value)
+	}
+}
+
+func TestGetClientConfigFileValuesIgnoresTunnelSettings(t *testing.T) {
+	workDir := t.TempDir()
+	oldDir, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		if err := os.Chdir(oldDir); err != nil {
+			t.Fatal(err)
+		}
+	}()
+	if err := os.Chdir(workDir); err != nil {
+		t.Fatal(err)
+	}
+
+	// Write Local Config File
+	if err := os.WriteFile("conduit.json", []byte(`{"server":"https://example.com","api_key":"secret","name":"saved","target":"localhost:3000"}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	values, err := getClientConfigFileValues()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if values["server"] != "https://example.com" {
+		t.Fatalf("expected server from config file, got %q", values["server"])
+	}
+	if values["name"] != "" || values["target"] != "" {
+		t.Fatalf("expected tunnel settings to be ignored, got name=%q target=%q", values["name"], values["target"])
+	}
+}