Re: Desperate question about nginx and sub requests :)

agentzh · 2014-07-17T04:06:02+00:00

Hi,This is a definitely a timeout error, though the error you're getting is because I failed to test for it (this only applies to pipelined requests). I&...

Re: Desperate question about nginx and sub requests :)

agentzh

Hello!

On Wed, Jul 16, 2014 at 5:29 AM, Marcin Strągowski wrote:
> I am aware that you probably get tons of this kind of email on daily basis

Yes I do :) I have to take quite a few hours to process user emails everyday.

> however i’m writing to you with question about writing http module for nginx

Well, you're strongly recommended to post such questions to the
openresty-en mailing list instead:
https://groups.google.com/group/openresty-en such that other
knowledgeable people can have a chance to help you as well (which
means less work load on my side). Also that way other developers with
similar questions can get the responses in Google as well.

> so the problem is - i’m trying to write a simple module which will handle
> location http request (post) with data - and send this data asynchronously
> to 2 locations (2 sub requests) , it should wait for those 2 subrequest to
> finish and read the data returned by subrequests and by analysing the body
> of those subrequests result module should return as a response one of those
> subrequest bodies.

I think you should read the implementation of the
ngx.location.capture_multi() API function provided by the ngx_lua
module instead:

    https://github.com/openresty/lua-nginx-module#ngxlocationcapture_multi

Also, I think maybe you can directly reuse ngx_lua module for your
tasks instead of the burden of reinventing the wheel.

> but i have no idea and any clue how to wait for subrequest results
> and how to get their data so i could analyse it and how finally pass one of
> their bodies as a primary http response ..
>

Well, for this particular question, you just need a custom output
header/body filter to capture the subrequests' responses and then save
them to the parent request's "ctx". For example, in ngx_lua, we have
the capturing filters here:

    https://github.com/openresty/lua-nginx-module/blob/master/src/ngx_http_lua_capturefilter.c

Best regards,
-agentzh

P.S. I'm cc'ing the openersty-en mailing list.

marcin.stragowski

Hi, thank you for your response .. i tried to implement the feature as you suggested - in lua using your module

but still there is a problem - please take a look at lua code :

(booth data1 and data2 are locations in nginx conf)

location /datacenter {

lua_need_request_body on;

client_max_body_size 20k;

client_body_buffer_size 20k;

content_by_lua '

res1, res2 = ngx.location.capture_multi({{"/data1", { method = ngx.HTTP_POST, body = ngx.var.request_body } }, {"/data2", { method = ngx.HTTP_POST, body = ngx.var.request_body} }})

if (res1.status ~= ngx.HTTP_OK and res2.status ~= ngx.HTTP_OK) then

ngx.exit(204)

elseif res1.status ~= ngx.HTTP_OK then

ngx.print(res2.body)

ngx.exit(ngx.HTTP_OK)

elseif res2.status ~= ngx.HTTP_OK then

ngx.print(res1.body)

ngx.exit(ngx.HTTP_OK)

end

ngx.log(ngx.ERR, res1.body) <------------------- i got empty string here - so i cant parse content , but if i call ngx.print(res1.body) the body prints fine to the result

i, j = string.find(res1.body, "data", 0, 1)

k,r = string.find(res1.body, ":", j - 1, 1)

i = string.find(res1.body, ",", k, 1)

data1 = tonumber(string.sub(res1.body, k + 1, i - 1))

i,j = string.find(res2.body, "data",0,1)

k = string.find(res2.body, ":", j, 1)

i = string.find(res2.body, ",", k, 1)

data2 = tonumber(string.sub(res2.body, k + 1, i - 1))

if data1 > data2 then

ngx.print(res1.body)

else

ngx.print(res2.body)

end

ngx.exit(ngx.HTTP_OK)

}

the subrequests body are available only after calling ngx.print(subrequest.body).. but it's of course printing the body of subrequest to response of request (which i'm trying to avoid because i didn't make decision which subrequest body to send)

can you tell me what am i doing wrong ?

W dniu środa, 16 lipca 2014 22:06:03 UTC+2 użytkownik agentzh napisał:

Hello!

On Wed, Jul 16, 2014 at 5:29 AM, Marcin Strągowski wrote:
> I am aware that you probably get tons of this kind of email on daily basis

Yes I do :) I have to take quite a few hours to process user emails everyday.

> however i’m writing to you with question about writing http module for nginx

Well, you're strongly recommended to post such questions to the
openresty-en mailing list instead:
https://groups.google.com/group/openresty-en such that other
knowledgeable people can have a chance to help you as well (which
means less work load on my side). Also that way other developers with
similar questions can get the responses in Google as well.

> so the problem is - i’m trying to write a simple module which will handle
> location http request (post) with data - and send this data asynchronously
> to 2 locations (2 sub requests) , it should wait for those 2 subrequest to
> finish and read the data returned by subrequests and by analysing the body
> of those subrequests result module should return as a response one of those
> subrequest bodies.

I think you should read the implementation of the
ngx.location.capture_multi() API function provided by the ngx_lua
module instead:

https://github.com/openresty/lua-nginx-module#ngxlocationcapture_multi

Also, I think maybe you can directly reuse ngx_lua module for your
tasks instead of the burden of reinventing the wheel.

> but i have no idea and any clue how to wait for subrequest results
> and how to get their data so i could analyse it and how finally pass one of
> their bodies as a primary http response ..
>

Well, for this particular question, you just need a custom output
header/body filter to capture the subrequests' responses and then save
them to the parent request's "ctx". For example, in ngx_lua, we have
the capturing filters here:

https://github.com/openresty/lua-nginx-module/blob/master/src/ngx_http_lua_capturefilter.c

Best regards,
-agentzh

P.S. I'm cc'ing the openersty-en mailing list.

marcin.stragowski

Hi, thank you for your response .. i tried to implement the feature as you suggested - in lua using your module

but still there is a problem - please take a look at lua code :

(booth data1 and data2 are locations in nginx conf)

location /datacenter {

lua_need_request_body on;

client_max_body_size 20k;

client_body_buffer_size 20k;

content_by_lua '

res1, res2 = ngx.location.capture_multi({{"/data1", { method = ngx.HTTP_POST, body = ngx.var.request_body } }, {"/data2", { method = ngx.HTTP_POST, body = ngx.var.request_body} }})

if (res1.status ~= ngx.HTTP_OK and res2.status ~= ngx.HTTP_OK) then

ngx.exit(204)

elseif res1.status ~= ngx.HTTP_OK then

ngx.print(res2.body)

ngx.exit(ngx.HTTP_OK)

elseif res2.status ~= ngx.HTTP_OK then

ngx.print(res1.body)

ngx.exit(ngx.HTTP_OK)

end

ngx.log(ngx.ERR, res1.body) <------------------- i got empty string here - so i cant parse content , but if i call ngx.print(res1.body) the body prints fine to the result

i, j = string.find(res1.body, "data", 0, 1)

k,r = string.find(res1.body, ":", j - 1, 1)

i = string.find(res1.body, ",", k, 1)

data1 = tonumber(string.sub(res1.body, k + 1, i - 1))

i,j = string.find(res2.body, "data",0,1)

k = string.find(res2.body, ":", j, 1)

i = string.find(res2.body, ",", k, 1)

data2 = tonumber(string.sub(res2.body, k + 1, i - 1))

if data1 > data2 then

ngx.print(res1.body)

else

ngx.print(res2.body)

end

ngx.exit(ngx.HTTP_OK)

}

W dniu środa, 16 lipca 2014 22:06:03 UTC+2 użytkownik agentzh napisał:

Hello!

On Wed, Jul 16, 2014 at 5:29 AM, Marcin Strągowski wrote:
> I am aware that you probably get tons of this kind of email on daily basis

Yes I do :) I have to take quite a few hours to process user emails everyday.

> however i’m writing to you with question about writing http module for nginx

Well, you're strongly recommended to post such questions to the
openresty-en mailing list instead:
https://groups.google.com/group/openresty-en such that other
knowledgeable people can have a chance to help you as well (which
means less work load on my side). Also that way other developers with
similar questions can get the responses in Google as well.

> so the problem is - i’m trying to write a simple module which will handle
> location http request (post) with data - and send this data asynchronously
> to 2 locations (2 sub requests) , it should wait for those 2 subrequest to
> finish and read the data returned by subrequests and by analysing the body
> of those subrequests result module should return as a response one of those
> subrequest bodies.

I think you should read the implementation of the
ngx.location.capture_multi() API function provided by the ngx_lua
module instead:

https://github.com/openresty/lua-nginx-module#ngxlocationcapture_multi

Also, I think maybe you can directly reuse ngx_lua module for your
tasks instead of the burden of reinventing the wheel.

> but i have no idea and any clue how to wait for subrequest results
> and how to get their data so i could analyse it and how finally pass one of
> their bodies as a primary http response ..
>

Well, for this particular question, you just need a custom output
header/body filter to capture the subrequests' responses and then save
them to the parent request's "ctx". For example, in ngx_lua, we have
the capturing filters here:

https://github.com/openresty/lua-nginx-module/blob/master/src/ngx_http_lua_capturefilter.c

Best regards,
-agentzh

P.S. I'm cc'ing the openersty-en mailing list.

agentzh

Hello!

On Mon, Jul 21, 2014 at 8:09 AM,  marcin.stragowski wrote:
> Hi, thank you for your response .. i tried to implement the feature as you
> suggested - in lua using your module
>
> but still there is a problem - please take a look at lua code :
[...]
>                                ngx.log(ngx.ERR, res1.body)
> <------------------- i got empty string here - so i cant parse content , but
> if i call ngx.print(res1.body) the body prints fine to the result
>

I've tried the following standalone example based on your
configuration snippet on my Linux x86_64 with nginx 1.7.2 + ngx_lua
0.9.10 and it works perfectly for me:

    location = /datacenter {
        client_max_body_size 20k;
        client_body_buffer_size 20k;
        lua_need_request_body on;

        content_by_lua '
            local body = ngx.req.get_body_data()  -- FIXME: handle the
case that body is nil.
            local res1, res2 = ngx.location.capture_multi{
                {"/data1", { method = ngx.HTTP_POST,
                             body = body } },
                {"/data2", { method = ngx.HTTP_POST,
                             body = body } }
            }

            ngx.log(ngx.ERR, "res1 body: ", res1.body)
            ngx.print(res1.body)
            ngx.print(res2.body)
        ';
    }

    location = /data1 {
        proxy_set_header Accept-Encoding '';  # to suppress gzip compression
        proxy_pass http://127.0.0.1:$server_port/echoback?a;
    }

    location = /data2 {
        proxy_set_header Accept-Encoding '';  # to suppress gzip compression
        proxy_pass http://127.0.0.1:$server_port/echoback?b;
    }

    # to emulate the backend service:
    location = /echoback {
        client_max_body_size 20k;
        client_body_buffer_size 20k;

        content_by_lua '
            ngx.req.read_body()
            local data = ngx.req.get_body_data()
            ngx.say(ngx.var.args, ": ", data)
        ';
    }

Accessing /datacenter with curl like this:

    $ curl -d 'hello world' localhost:8080/datacenter
    a: hello world
    b: hello world

And then check the nginx error log for our logging message:

    $ grep 'res1 body' logs/error.log
    2014/07/21 13:01:18 [error] 22654#0: *1 [lua] content_by_lua:10:
res1 body: a: hello world

The res1.body is not empty when feeding into ngx.log().

Using my mockeagain to emulate extremely slow network conditions do
not break this test case either:
https://github.com/openresty/mockeagain

I suggest you also provide a standalone minimal test case that can
reliably reproduce the issue on others boxes (in particular, my box)
with precise steps. That will help us debug your issues more
effectively. (Also, you might find your own mistakes (if any) during
your minimization process ;))

Another suggestion is to always provide the detailed information about
the versions of related software you're using. Like the version of
ngx_lua, nginx, and/or openresty (as well as OS) when reporting
problems. It can be very helpful.

Best regards,
-agentzh