Enable session cache by default

A session cache can reduce the number of Fleet API calls made by
clients, but needed to be explicitly enabled by the user. With this
change, the cache will be enabled by default and saved to
~/.tesla-cache.json. This path can be overridden using the
`-session-cache` command-line flag or by setting TESLA_CACHE_FILE, as
before.

Users can add the `-disable-session-cache` command-line flag to disable
the feature.

pkg/cli/config.go

@@ -54,6 +54,7 @@ import (
 	"fmt"
 	"io/fs"
 	"os"
+	"path/filepath"
 	"sort"
 	"strings"
 
@@ -146,6 +147,7 @@ type Config struct {
 	TokenFilename    string
 	KeyFilename      string
 	CacheFilename    string
+	DisableCache     bool
 	Backend          keyring.Config
 	BackendType      backendType
 	Debug            bool // Enable keyring debug messages
@@ -185,7 +187,8 @@ func (c *Config) RegisterCommandLineFlags() {
 		if !c.Flags.isSet(FlagVIN) {
 			log.Debug("FlagPrivateKey is set but FlagVIN is not. A VIN is required to send vehicle commands.")
 		}
-		flag.StringVar(&c.CacheFilename, "session-cache", "", "Load session info cache from `file`. Defaults to $TESLA_CACHE_FILE.")
+		flag.StringVar(&c.CacheFilename, "session-cache", "", "Load session info cache from `file`. Defaults to $TESLA_CACHE_FILE then ~/.tesla-cache.json.")
+		flag.BoolVar(&c.DisableCache, "disable-session-cache", false, "Disable the session info cache.")
 		flag.StringVar(&c.KeyringKeyName, "key-name", "", "System keyring `name` for private key. Defaults to $TESLA_KEY_NAME.")
 		flag.StringVar(&c.KeyFilename, "key-file", "", "A `file` containing private key. Defaults to $TESLA_KEY_FILE.")
 		flag.Var(&c.Domains, "domain", "Domains to connect to (can be repeated; omit for all)")
@@ -236,8 +239,13 @@ func (c *Config) ReadFromEnvironment() {
 		}
 	}
 	if c.Flags.isSet(FlagPrivateKey) {
-		if c.CacheFilename == "" {
+		if !c.DisableCache && c.CacheFilename == "" {
 			c.CacheFilename = os.Getenv(EnvTeslaCacheFile)
+			if c.CacheFilename == "" {
+				if homeDir := os.Getenv("HOME"); homeDir != "" {
+					c.CacheFilename = filepath.Join(homeDir, ".tesla-cache.json")
+				}
+			}
 			log.Debug("Set session cache file to '%s'", c.CacheFilename)
 		}
 		if c.KeyringKeyName == "" && c.KeyFilename == "" {
@@ -286,11 +294,12 @@ func (c *Config) ReadFromEnvironment() {
 // If c.CacheFilename is not set or no vehicle handshake has occurred, then this method does
 // nothing.
 func (c *Config) UpdateCachedSessions(v *vehicle.Vehicle) {
-	if c.CacheFilename != "" && c.sessions != nil {
-		v.UpdateCachedSessions(c.sessions)
-		if err := c.sessions.ExportToFile(c.CacheFilename); err != nil {
-			log.Error("Error updating cache: %s", err)
-		}
+	if c.CacheFilename == "" || c.sessions == nil {
+		return
+	}
+	v.UpdateCachedSessions(c.sessions)
+	if err := c.sessions.ExportToFile(c.CacheFilename); err != nil {
+		log.Error("Error updating cache: %s", err)
 	}
 }