Allow flag or file based configuration

cmd/flags.go

@@ -23,26 +23,17 @@ import (
 	"bitbucket.org/creachadair/shell"
 )
 
-// ParseFlagFile parses a set of flags from a file at the provided
-// path. Re-calls flag.Parse() after parsing the flags in the file
-// so that flags provided on the command line take precedence over
-// flags provided in the file.
-func ParseFlagFile(path string) error {
-	file, err := ioutil.ReadFile(path)
-	if err != nil {
-		return err
-	}
-
-	// Expand any environment variables in the file
-	flagsString := os.ExpandEnv(string(file))
-
-	args, valid := shell.Split(flagsString)
+func parseFlags(file string) error {
+	args, valid := shell.Split(file)
 	if !valid {
 		return errors.New("flag file contains unclosed quotations")
 	}
+	// Expand any environment variables in the args
+	for i := range args {
+		args[i] = os.ExpandEnv(args[i])
+	}
 
-	err = flag.CommandLine.Parse(args)
-	if err != nil {
+	if err := flag.CommandLine.Parse(args); err != nil {
 		return err
 	}
 
@@ -51,3 +42,15 @@ func ParseFlagFile(path string) error {
 	flag.Parse()
 	return nil
 }
+
+// ParseFlagFile parses a set of flags from a file at the provided
+// path. Re-calls flag.Parse() after parsing the flags in the file
+// so that flags provided on the command line take precedence over
+// flags provided in the file.
+func ParseFlagFile(path string) error {
+	file, err := ioutil.ReadFile(path)
+	if err != nil {
+		return err
+	}
+	return parseFlags(string(file))
+}

cmd/flags_test.go

@@ -0,0 +1,104 @@
+// Copyright 2017 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cmd
+
+import (
+	"flag"
+	"os"
+	"testing"
+)
+
+func TestParseFlags(t *testing.T) {
+	var a, b string
+	flag.StringVar(&a, "a", "", "")
+	flag.StringVar(&b, "b", "", "")
+
+	flag.CommandLine.Init(os.Args[0], flag.ContinueOnError)
+
+	tests := []struct {
+		contents    string
+		env         map[string]string
+		cliArgs     []string
+		expectedErr string
+		expectedA   string
+		expectedB   string
+	}{
+		{
+			contents:  "-a one -b two",
+			expectedA: "one",
+			expectedB: "two",
+		},
+		{
+			contents:  "-a one\n-b two",
+			expectedA: "one",
+			expectedB: "two",
+		},
+		{
+			contents:  "-a one \\\n-b two",
+			expectedA: "one",
+			expectedB: "two",
+		},
+		{
+			contents:  "-a one",
+			cliArgs:   []string{"-b", "two"},
+			expectedA: "one",
+			expectedB: "two",
+		},
+		{
+			contents:  "-a one\n-b two",
+			cliArgs:   []string{"-b", "three"},
+			expectedA: "one",
+			expectedB: "three",
+		},
+		{
+			contents:  "-a one\n-b $TEST_VAR",
+			env:       map[string]string{"TEST_VAR": "from env"},
+			expectedA: "one",
+			expectedB: "from env",
+		},
+		{
+			contents:    "-a one -b two -c three",
+			expectedErr: "flag provided but not defined: -c",
+		},
+	}
+
+	initalArgs := os.Args[:]
+	for _, tc := range tests {
+		a, b = "", ""
+		os.Args = initalArgs[:]
+		if len(tc.cliArgs) > 0 {
+			os.Args = append(os.Args, tc.cliArgs...)
+		}
+		for k, v := range tc.env {
+			if err := os.Setenv(k, v); err != nil {
+				t.Errorf("os.SetEnv failed: %s", err)
+			}
+		}
+		err := parseFlags(tc.contents)
+		if err != nil {
+			if err.Error() == tc.expectedErr {
+				continue
+			}
+			t.Errorf("parseFlags failed: wanted: %q, got: %q", tc.expectedErr, err)
+			continue
+		}
+		if tc.expectedA != a {
+			t.Errorf("flag 'a' not properly set: wanted: %q, got %q", tc.expectedA, a)
+		}
+		if tc.expectedB != b {
+			t.Errorf("flag 'b' not properly set: wanted: %q, got %q", tc.expectedB, b)
+		}
+	}
+}