1 files changed, 51 insertions, 0 deletions
diff --git a/src/mongo/gotools/common/db/read_preferences.go b/src/mongo/gotools/common/db/read_preferences.go
new file mode 100644
index 00000000000..9dec319ca48
--- /dev/null
+++ b/src/mongo/gotools/common/db/read_preferences.go
@@ -0,0 +1,51 @@
+package db
+
+import (
+	"fmt"
+
+	"github.com/mongodb/mongo-tools/common/json"
+	"gopkg.in/mgo.v2"
+	"gopkg.in/mgo.v2/bson"
+)
+
+type readPrefDoc struct {
+	Mode string
+	Tags bson.D
+}
+
+const (
+	WarningNonPrimaryMongosConnection = "Warning: using a non-primary readPreference with a " +
+		"connection to mongos may produce inconsistent duplicates or miss some documents."
+)
+
+func ParseReadPreference(rp string) (mgo.Mode, bson.D, error) {
+	var mode string
+	var tags bson.D
+	if rp == "" {
+		return mgo.Nearest, nil, nil
+	}
+	if rp[0] != '{' {
+		mode = rp
+	} else {
+		var doc readPrefDoc
+		err := json.Unmarshal([]byte(rp), &doc)
+		if err != nil {
+			return 0, nil, fmt.Errorf("invalid --ReadPreferences json object: %v", err)
+		}
+		tags = doc.Tags
+		mode = doc.Mode
+	}
+	switch mode {
+	case "primary":
+		return mgo.Primary, tags, nil
+	case "primaryPreferred":
+		return mgo.PrimaryPreferred, tags, nil
+	case "secondary":
+		return mgo.Secondary, tags, nil
+	case "secondaryPreferred":
+		return mgo.SecondaryPreferred, tags, nil
+	case "nearest":
+		return mgo.Nearest, tags, nil
+	}
+	return 0, nil, fmt.Errorf("invalid readPreference mode '%v'", mode)
+}