From 232f6db2f7db5d854e78af452970eed14d3296ae Mon Sep 17 00:00:00 2001
From: urso <steffen.siering@elastic.co>
Date: Mon, 12 Feb 2018 19:21:52 +0100
Subject: [PATCH] document id must be a string

---
 filebeat/input/log/harvester.go |  2 +-
 libbeat/reader/readjson/json.go | 10 ++++++----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/filebeat/input/log/harvester.go b/filebeat/input/log/harvester.go
index f2bed44c6deb..fd5c8c8dd6d0 100644
--- a/filebeat/input/log/harvester.go
+++ b/filebeat/input/log/harvester.go
@@ -370,7 +370,7 @@ func (h *Harvester) onMessage(
 			timestamp = ts
 		}
 
-		if id != nil {
+		if id != "" {
 			meta = common.MapStr{
 				"id": id,
 			}
diff --git a/libbeat/reader/readjson/json.go b/libbeat/reader/readjson/json.go
index e6e055417e8b..a669b3f49ae0 100644
--- a/libbeat/reader/readjson/json.go
+++ b/libbeat/reader/readjson/json.go
@@ -114,7 +114,7 @@ func createJSONError(message string) common.MapStr {
 // respecting the KeysUnderRoot and OverwriteKeys configuration options.
 // If MessageKey is defined, the Text value from the event always
 // takes precedence.
-func MergeJSONFields(data common.MapStr, jsonFields common.MapStr, text *string, config Config) (interface{}, time.Time) {
+func MergeJSONFields(data common.MapStr, jsonFields common.MapStr, text *string, config Config) (string, time.Time) {
 	// The message key might have been modified by multiline
 	if len(config.MessageKey) > 0 && text != nil {
 		jsonFields[config.MessageKey] = *text
@@ -127,12 +127,14 @@ func MergeJSONFields(data common.MapStr, jsonFields common.MapStr, text *string,
 		data["message"] = *text
 	}
 
-	var id interface{}
+	var id string
 	if key := config.DocumentID; key != "" {
 		if tmp, err := jsonFields.GetValue(key); err == nil {
-			id = tmp
+			if v, ok := tmp.(string); ok {
+				id = v
+				jsonFields.Delete(key)
+			}
 		}
-		jsonFields.Delete(key)
 	}
 
 	if config.KeysUnderRoot {