large request body in njs

Dmitry Volyntsev xeioex at
Tue Oct 30 09:13:58 UTC 2018

> On 29 Oct 2018, at 23:44, Jonathan Esterhazy <jonathan.esterhazy at> wrote:
> Hello!
> I am trying to use njs (ngx_http_js_module) to modify POSTed request data before sending to an upstream api. Using the req.requestBody function works fine for small requests, but for larger ones causes this error:
> [error] 14#14: *18 js exception: Error: request body is in a file
> If I was using the Lua module, I could use ngx.req.get-body_file function to get this data, but there doesn't seem to be any way to do that in njs. Did I miss something? Is there a way to access the data or find out the filename?

Hi Jonathan!

You have two options here:

1) you can increase the client buffers

According to the documentation: <>

returns the client request body if it has not been written to a temporary file. To ensure that the client request body is in memory, its size should be limited by client_max_body_size, and a sufficient buffer size should be set using client_body_buffer_size.

2) you can open the file with the client’s request using request_body_file variable (

var fs = require(‘fs’);
var large_body = fs.readFileSync(r.variables.request_body_file)

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