http server with mount, client POST json file, how to read content?

[AlojzyB]

Dear folks,
have use 4.3.3 revision, configured as http server using mount and basic auth. Origin and default target are set to json file.

static const struct lws_http_mount mount_vas = {
	/* .mount_next */				NULL,		/* linked-list "next" */
	/* .mountpoint */				"/vas",	/* mountpoint URL */
	/* .origin */					"dev/shm",
	/* .def */						"test.json",
	/* .protocol */					NULL,
	/* .cgienv */					NULL,
	/* .extra_mimetypes */			NULL,
	/* .interpret */				NULL,
	/* .cgi_timeout */				0,
	/* .cache_max_age */			0,
	/* .auth_mask */				0,
	/* .cache_reusable */			0,
	/* .cache_revalidate */			0,
	/* .cache_intermediaries */		0,
	/* .origin_protocol */			LWSMPRO_FILE, /* dynamic */
	/* .mountpoint_len */			4,		/* char count */
	/* .basic_auth_login_file */	".pass-file",
};

Works fine with POST request from client - test.json file is send correctly:

http --verbose -a admin:admin -f POST localhost:80/vas/ seq=0 VIN=4Y1SL65848Z411439 --json

HTTP/1.1 200 OK
cache-control: no-store
content-length: 51
content-security-policy: default-src 'none'; img-src 'self' data: ; script-src 'self'; font-src 'self'; style-src 'self'; connect-src 'self' ws: wss:; frame-ancestors 'none'; base-uri 'none';form-action 'self';
content-type: application/json
etag: 00000033386D4403
referrer-policy: no-referrer
x-content-type-options: nosniff
x-frame-options: deny
x-xss-protection: 1; mode=block

{
"seq": 0,
"vin": "aslkdhfkdsjhgfjhkjdhfgkjfdg"
}

The problem is that have no idea how to read POST request content (json file as on this example) since there is no LWS_CALLBACK_HTTP_BODY nor LWS_CALLBACK_HTTP_BODY_COMPLETION callbacks.

Have read header tokens WSI_TOKEN_HTTP_CONTENT_TYPE and WSI_TOKEN_HTTP_CONTENT_LENGTH which gives correct data: "application/json" and 40 bytes respectively. So, lws have complete POST frame.
Please advice me how to read POST content.

[ffreality]

I figured it out that if I use lws_callback_http_dummy as return value of protocol callback, LWS_CALLBACK_HTTP_BODY won't trigger. So, I used return 0 and char* body = (char*)in; gives Body. But I for my use case, I am trying to integrate library to unreal engine. So, I need to create a proper response logic.