cipd2isolate: Initial CLI parsing boilerplate.

cipd/client/cli/main.go

 // Copyright 2014 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package cli
 
 import (
         "crypto/sha1"
         "encoding/hex"
         "encoding/json"
@@ skipping 250 matching lines @@
 
 func (opts *clientOptions) makeCipdClient(ctx context.Context, root string) (cipd.Client, error) {
         authOpts, err := opts.authFlags.Options()
         if err != nil {
                 return nil, err
         }
         client, err := auth.NewAuthenticator(ctx, auth.OptionalLogin, authOpts).Client()
         if err != nil {
                 return nil, err
         }
-        ua := cipd.UserAgent
-        if prefix := cli.LookupEnv(ctx, CIPDHTTPUserAgentPrefix); prefix.Exists {
-                ua = fmt.Sprintf("%s/%s", prefix.Value, ua)
-        }
         cacheDir := opts.cacheDir
         if cacheDir == "" {
-                if cacheDirEnv := cli.LookupEnv(ctx, CIPDCacheDir); cacheDirEnv.Exists {
-                        cacheDir = cacheDirEnv.Value
-                        if cacheDir != "" && !filepath.IsAbs(cacheDir) {
-                                return nil, fmt.Errorf("Bad %s: not an absolute path - %s", CIPDCacheDir, cacheDir)
-                        }
+                cacheDir, err = CacheDir(ctx)
+                if err != nil {
+                        return nil, err
                 }
         }
         return cipd.NewClient(cipd.ClientOptions{
                 ServiceURL:          opts.serviceURL,
                 Root:                root,
-                UserAgent:           ua,
+                UserAgent:           UserAgent(ctx),
                 CacheDir:            cacheDir,
                 AuthenticatedClient: client,
                 AnonymousClient:     http.DefaultClient,
         })
 }
 
+// UserAgent returns a CIPD user agent string, based on a CLI context.
+//
+// It knows how to use CIPDHTTPUserAgentPrefix env var.
+func UserAgent(ctx context.Context) string {
+        if prefix := cli.LookupEnv(ctx, CIPDHTTPUserAgentPrefix); prefix.Exists {
+                return fmt.Sprintf("%s/%s", prefix.Value, cipd.UserAgent)
+        }
+        return cipd.UserAgent
+}
+
+// CacheDir returns a CIPD cache directory path, based on a CLI context.
+//
+// It knows how to use CIPDCacheDir env var. May return empty string if cache
+// directory is not defined.
+func CacheDir(ctx context.Context) (string, error) {
+        if cacheDirEnv := cli.LookupEnv(ctx, CIPDCacheDir); cacheDirEnv.Exists {
+                cacheDir := cacheDirEnv.Value
+                if cacheDir != "" && !filepath.IsAbs(cacheDir) {
+                        return "", fmt.Errorf("bad %s: not an absolute path - %s", CIPDCacheDir, cacheDir)
+                }
+                return cacheDir, nil
+        }
+        return "", nil
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // inputOptions mixin.
 
 // packageVars holds array of '-pkg-var' command line options.
 type packageVars map[string]string
 
 func (vars *packageVars) String() string {
         // String() for empty vars used in -help output.
         if len(*vars) == 0 {
                 return "key:value"
@@ skipping 1925 matching lines @@
 // subcommand invocations look more natural.
 //
 // Compare:
 //   * Default: cipd set-ref -ref=abc -version=def package/name
 //   * Improved: cipd set-ref package/name -ref=abc -version=def
 //
 // Much better.
 func Main(params Parameters, args []string) int {
         return subcommands.Run(GetApplication(params), fixFlagsPosition(args))
 }