# RE: nginx+lua reverse proxy empty body (weird repeatable behavior)

**URL:** <https://www.ruby-forum.com/t/re-nginx-lua-reverse-proxy-empty-body-weird-repeatable-behavior/229226>\
**Category:** NGINX\
**Created:** [November 29, 2012, 10:52am UTC](https://www.ruby-forum.com/t/re-nginx-lua-reverse-proxy-empty-body-weird-repeatable-behavior/229226 "2012-11-29T10:52:06Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Bart\_van\_Deenen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/ea666f/32.png) [@Bart\_van\_Deenen](https://www.ruby-forum.com/u/Bart_van_Deenen)\
**Post date:** [November 29, 2012, 10:52am UTC](https://www.ruby-forum.com/t/re-nginx-lua-reverse-proxy-empty-body-weird-repeatable-behavior/229226/1 "2012-11-29T10:52:06Z")

</div>

Hi all

It seems the body\_filter\_by\_lua section is bypassed somehow, it just  
doesn’t receive the proxied data. I have this simplified testcase which  
at least for my setup is completely repeatable. See below.

In short, I do a curl call to localhost:9001, which gets the proxied  
server www.spelletjes.nl, and I correctly receive the index file  
including the “Speel” string that I’m trying to replace. But the lua  
section only says: “empty string”. Once! So how did the server data get  
through to my curl call? Using openresty 1.2.4.7 (nginx 1.2.4 +  
ngx\_lua-0.7.4 and more). The nginx.conf shown below is all there is, I  
am not using anything else.

I could really use some help here.

Thanks

Bart van Deenen

nginx.conf:

worker\_processes 1;  
error\_log logs/error.log debug;  
events {  
worker\_connections 1024;  
}  
http {  
server {  
client\_body\_in\_single\_buffer on;  
listen 9001;  
location / {  
proxy\_pass [http://www.spelletjes.nl:80](http://www.spelletjes.nl:80);  
proxy\_set\_header X-Real-IP $remote\_addr;  
body\_filter\_by\_lua ’

if ngx.arg[1] ~= “” then  
print ( “The body is " … ngx.arg[1])  
ngx.arg[1] = string.gsub(ngx.arg[1], “Speel”, “NGINX”)  
else  
print(ngx.var.uri … " has empty body” … ngx.arg[1])  
end  
';

```
    }
}

```

}

curl call:

curl -v -o spelletjes.html [http://localhost:9001/](http://localhost:9001/)

- About to connect() to localhost port 9001 (#0)
- Trying 127.0.0.1…  
% Total % Received % Xferd Average Speed Time Time Time  
Current  
Dload Upload Total Spent Left  
Speed  
0 0 0 0 0 0 0 0 --:–:-- --:–:-- --:–:–  
0\* connected
- Connected to localhost (127.0.0.1) port 9001 (#0)

> GET / HTTP/1.1  
> User-Agent: curl/7.27.0  
> Host: localhost:9001  
> Accept: _/_

- additional stuff not fine transfer.c:1037: 0 0
- HTTP 1.1 or later with persistent connection, pipelining supported  
\< HTTP/1.1 200 OK  
\< Server: ngx\_openresty/1.2.4.9  
\< Date: Thu, 29 Nov 2012 09:37:35 GMT  
\< Content-Type: text/html; charset=UTF-8  
\< Content-Length: 149577  
\< Connection: keep-alive  
\< RTSS: 1-1297-2  
\< Vary: Accept-Encoding  
\< Cache-Control: max-age=3600  
\< P3P: CP=“IDC DSP COR CURa ADMa OUR IND PHY ONL COM STA”  
\< P3P: policyref=“[http://www.spelletjes.nl/w3c/p3p.xml](http://www.spelletjes.nl/w3c/p3p.xml)”, CP="DSP IDC CUR  
ADM PSA PSDi OTPi DELi STP NAV COM UNI INT PHY DEM "  
\< X-Id: 066  
\< Expires: Thu, 29 Nov 2012 10:29:59 GMT  
\< Last-Modified: Thu, 29 Nov 2012 09:29:59 GMT  
\<  
{ [data not shown]  
100 146k 100 146k 0 0 3163k 0 --:–:-- --:–:-- --:–:–  
3246k
- Connection #0 to host localhost left intact
- Closing connection #0

error.log:  
1 2012/11/29 10:37:29 [notice] 4013#0: using the “epoll” event method  
2 2012/11/29 10:37:29 [notice] 4013#0: start worker processes  
3 2012/11/29 10:37:29 [notice] 4013#0: start worker process 4218  
4 2012/11/29 10:37:29 [notice] 4013#0: signal 17 (SIGCHLD) received  
5 2012/11/29 10:37:29 [notice] 4013#0: worker process 4215 exited with  
code 0  
6 2012/11/29 10:37:29 [notice] 4013#0: signal 29 (SIGIO) received  
7 2012/11/29 10:37:35 [notice] 4218#0: \*65 [lua] variations.lua:67: /  
has empty body while sending to client, client: 127.0.0.1,  
server: , request: “GET / HTTP/1.1”, upstream:  
“[http://212.72.60.182:80/](http://212.72.60.182:80/)”, host: “localhost: 9001”  
8 2012/11/29 10:37:35 [info] 4218#0: \*65 client 127.0.0.1 closed  
keepalive connection (104: Connection reset by peer)

And the output of the curl call (the local file spelletjes.html) does  
contain the correct html (from the proxied server, including the string  
‘Speel’ that I’m trying to match on).

---

<div class="post-metadata">

**Author:** ![Bart\_van\_Deenen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/ea666f/32.png) [@Bart\_van\_Deenen](https://www.ruby-forum.com/u/Bart_van_Deenen)\
**Post date:** [November 30, 2012, 3:16am UTC](https://www.ruby-forum.com/t/re-nginx-lua-reverse-proxy-empty-body-weird-repeatable-behavior/229226/2 "2012-11-30T03:16:13Z")

</div>

Hello!

On Thu, Nov 29, 2012 at 1:51 AM, Bart van Deenen wrote:

> It seems the body\_filter\_by\_lua section is bypassed somehow, it just doesn’t  
> receive the proxied data. I have this simplified testcase which at least for my  
> setup is completely repeatable. See below.

With your (exact) code sample, I cannot see any issues with  
ngx\_openresty 1.2.4.9 on Linux x86\_64.

For a _single_ request to location / (note: not multiple!), I’m  
getting 26 non-empty data chunks:

```
$ grep 'The body is' logs/error.log | wc -l
26

```

and also one empty data chunk (which is generated by ngx\_proxy to  
solely signal the end of the body):

```
$ grep 'has empty body' logs/error.log | wc -l
1

```

You can try to scan your error.log on your side.

For big enough response bodies, it’s common to see multiple data  
chunks emitted by ngx\_proxy to the output body filter chain. And your  
body\_filter\_by\_lua handler will be called multiple times, one time for  
one data chunk, for a _single_ response.

BTW, please post such questions to the openresty-en mailing list  
([https://groups.google.com/group/openresty-en](https://groups.google.com/group/openresty-en) ) instead so that I can  
see your mails sooner rather than later 🙂

Best regards,  
-agentzh