[Filebeat] httpjson input set Content-Type correctly

CHANGELOG.next.asciidoc

@@ -392,6 +392,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Zoom module pipeline failed to ingest some chat_channel events. {pull}23904[23904]
 - Fix Netflow module issue with missing `internal_networks` config parameter. {issue}24094[24094] {pull}24110[24110]
 - Fix aws/vpcflow generating errors for empty logs or unidentified formats. {pull}24167[24167]
+- in httpjson input using encode_as "application/x-www-form-urlencoded" now sets Content-Type correctly {issue}24331[24331] {pull}24336[24336]
 
 *Heartbeat*
 

x-pack/filebeat/docs/inputs/input-httpjson.asciidoc

@@ -349,7 +349,7 @@ HTTP method to use when making requests. `GET` or `POST` are the options. Defaul
 [float]
 ==== `request.encode_as`
 
-ContentType used for encoding the request body. If set it will force the encoding in the specified format regardless of the `Content-Type` header value, otherwise it will honor it if possible or fallback to `application/json`. By default the requests are sent with `Content-Type: application/json`. Supported values: `application/json` and `application\x-www-form-urlencoded`. `application/x-www-form-encoded` will url encode the `url.params` and set them as the body. It is not set by default.
+ContentType used for encoding the request body. If set it will force the encoding in the specified format regardless of the `Content-Type` header value, otherwise it will honor it if possible or fallback to `application/json`. By default the requests are sent with `Content-Type: application/json`. Supported values: `application/json` and `application/x-www-form-urlencoded`. `application/x-www-form-urlencoded` will url encode the `url.params` and set them as the body. It is not set by default.
 
 [float]
 ==== `request.body`

x-pack/filebeat/input/httpjson/internal/v2/encoding.go

@@ -91,6 +91,9 @@ func encodeAsJSON(trReq transformable) ([]byte, error) {
 	if len(trReq.body()) == 0 {
 		return nil, nil
 	}
+	header := trReq.header()
+	header.Set("Content-Type", "application/json")
+	trReq.setHeader(header)
 	return json.Marshal(trReq.body())
 }
 
@@ -103,6 +106,9 @@ func encodeAsForm(trReq transformable) ([]byte, error) {
 	body := []byte(url.RawQuery)
 	url.RawQuery = ""
 	trReq.setURL(url)
+	header := trReq.header()
+	header.Set("Content-Type", "application/x-www-form-urlencoded")
+	trReq.setHeader(header)
 	return body, nil
 }
 

x-pack/filebeat/input/httpjson/internal/v2/encoding_test.go

@@ -61,5 +61,6 @@ func TestEncodeAsForm(t *testing.T) {
 		trReq.setURL(*u)
 		res, err := encodeAsForm(trReq)
 		assert.Equal(t, test.body, string(res))
+		assert.Equal(t, "application/x-www-form-urlencoded", trReq.header().Get("Content-Type"))
 	}
 }