Add string slice config support

When overriding a configuration option via the env which is supposed
to be a collection collection (slice) of options, the override is
instead interpretted as a string.  This patch modifies the config
decode hook to handle this special case and appropriately decode the env
override to a []string instead of a plain string.

There is no JIRA issue associated with this, but is being done to
support the Kafka epic effort, visible here:

https://jira.hyperledger.org/browse/FAB-32

Reclaim commit after a little Gerrit accident

Change-Id: Iae800b5237549232b90c7d7cf91590a3d8caf178
Signed-off-by: Jason Yellick <jyellick@us.ibm.com>

orderer/config/config_test.go

@@ -17,8 +17,11 @@ limitations under the License.
 package config
 
 import (
+	"bytes"
 	"fmt"
 	"os"
+	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/spf13/viper"
@@ -50,6 +53,45 @@ func TestBadConfig(t *testing.T) {
 	}
 }
 
+type testSlice struct {
+	Inner struct {
+		Slice []string
+	}
+}
+
+func TestEnvSlice(t *testing.T) {
+	envVar := "ORDERER_INNER_SLICE"
+	envVal := "[a, b, c]"
+	os.Setenv(envVar, envVal)
+	defer os.Unsetenv(envVar)
+	config := viper.New()
+	config.SetEnvPrefix(Prefix)
+	config.AutomaticEnv()
+	replacer := strings.NewReplacer(".", "_")
+	config.SetEnvKeyReplacer(replacer)
+	config.SetConfigType("yaml")
+
+	data := "---\nInner:\n    Slice: [d,e,f]"
+
+	err := config.ReadConfig(bytes.NewReader([]byte(data)))
+
+	if err != nil {
+		t.Fatalf("Error reading %s plugin config: %s", Prefix, err)
+	}
+
+	var uconf testSlice
+
+	err = ExactWithDateUnmarshal(config, &uconf)
+	if err != nil {
+		t.Fatalf("Failed to unmarshal with: %s", err)
+	}
+
+	expected := []string{"a", "b", "c"}
+	if !reflect.DeepEqual(uconf.Inner.Slice, expected) {
+		t.Fatalf("Did not get back the right slice, expeced: %v got %v", expected, uconf.Inner.Slice)
+	}
+}
+
 // TestEnvInnerVar verifies that with the Unmarshal function that
 // the environmental overrides still work on internal vars.  This was
 // a bug in the original viper implementation that is worked around in

orderer/config/config_util.go

@@ -17,6 +17,10 @@ limitations under the License.
 package config
 
 import (
+	"reflect"
+	"strings"
+	"time"
+
 	"github.com/mitchellh/mapstructure"
 	"github.com/spf13/viper"
 )
@@ -45,6 +49,37 @@ func getKeysRecursively(base string, v *viper.Viper, nodeKeys map[string]interfa
 	return result
 }
 
+// customDecodeHook adds the additional functions of parsing durations from strings
+// as well as parsing strings of the format "[thing1, thing2, thing3]" into string slices
+// Note that whitespace around slice elements is removed
+func customDecodeHook() mapstructure.DecodeHookFunc {
+	durationHook := mapstructure.StringToTimeDurationHookFunc()
+	return func(f reflect.Type, t reflect.Type, data interface{}) (interface{}, error) {
+		dur, err := mapstructure.DecodeHookExec(durationHook, f, t, data)
+		if err == nil {
+			if _, ok := dur.(time.Duration); ok {
+				return dur, nil
+			}
+		}
+
+		if f.Kind() != reflect.String {
+			return data, nil
+		}
+
+		raw := data.(string)
+		l := len(raw)
+		if raw[0] == '[' && raw[l-1] == ']' {
+			slice := strings.Split(raw[1:l-1], ",")
+			for i, v := range slice {
+				slice[i] = strings.TrimSpace(v)
+			}
+			return slice, nil
+		}
+
+		return data, nil
+	}
+}
+
 // ExactWithDateUnmarshal is intended to unmarshal a config file into a structure
 // producing error when extraneous variables are introduced and supporting
 // the time.Duration type
@@ -58,7 +93,7 @@ func ExactWithDateUnmarshal(v *viper.Viper, output interface{}) error {
 		Metadata:         nil,
 		Result:           output,
 		WeaklyTypedInput: true,
-		DecodeHook:       mapstructure.StringToTimeDurationHookFunc(),
+		DecodeHook:       customDecodeHook(),
 	}
 
 	decoder, err := mapstructure.NewDecoder(config)