Varnish Cache is not sending Content-Length header to backend server - varnish

Question

i am trying to cache POST request by using Varnish cache. I am using vcl file as
vcl 4.0;
import std;
import bodyaccess;
backend default {
.host = "**.***.**.***";
.port = "**";
}
sub vcl_recv {
unset req.http.x-cache;
unset req.http.X-Body-Len;
if (req.method == "POST") {
std.log("Will cache POST for: " + req.http.host + req.url);
std.cache_req_body(3000KB);
set req.http.X-Body-Len = bodyaccess.len_req_body();
if (req.http.X-Body-Len == "-1") {
return(synth(400, "The request body size exceeds the limit"));
}
return (hash);
}
}
sub vcl_hash {
# To cache POST and PUT requests
if (req.http.X-Body-Len) {
bodyaccess.hash_req_body();
} else {
hash_data("");
}
}
sub vcl_backend_fetch {
if (bereq.http.X-Body-Len) {
set bereq.method = "POST";
}
}
sub vcl_backend_response {
set beresp.ttl = 86400s;
unset beresp.http.Cache-Control;
set beresp.http.Cache-Control = "public, max-age=86400";
}
sub vcl_hit {
set req.http.x-cache = "hit";
}
sub vcl_miss {
set req.http.x-cache = "miss";
}
sub vcl_pass {
set req.http.x-cache = "pass";
}
sub vcl_pipe {
set req.http.x-cache = "pipe uncacheable";
}
sub vcl_synth {
set resp.http.x-cache = "synth synth";
}
sub vcl_deliver {
if (obj.uncacheable) {
set req.http.x-cache = req.http.x-cache + " uncacheable" ;
} else {
set req.http.x-cache = req.http.x-cache + " cached" ;
}
set resp.http.x-cache = req.http.x-cache;
}
When i am doing post request directly it is working fine but as soon as I go through Cache Server, backend Server is returning "HTTP Error 411. The request must be chunked or have a content length."
On debugging furthet
What I found from varnishlog is
3 BereqMethod b POST
3 BereqURL b /someurl
3 BereqProtocol b HTTP/1.1
3 BereqHeader b Content-Type: application/json
3 BereqHeader b Accept-Language: en-US
3 BereqHeader b User-Agent: PostmanRuntime/7.24.0
3 BereqHeader b Accept: */*
3 BereqHeader b Postman-Token: 6fe71b81-841d-400f-957a-45b6518bfca6
3 BereqHeader b Host: *.*.*.*
3 BereqHeader b X-Forwarded-For: *.*.*.*
3 BereqHeader b X-Body-Len: 161
3 BereqHeader b Accept-Encoding: gzip
3 BereqHeader b x-cache: miss
3 BereqMethod b GET
3 BereqHeader b X-Varnish: 3
Varnish is not sending Content-Length where backend server needs it
How can I set this content-length

Answer 1

You can set it as any other header, i.e. in vcl_recv:
set req.http.Content-Length = "value"