Parsing json with cjson results in nil table

joel.parker.gm · 2017-09-11T21:18:26+00:00

Hello,The API documentation has this, in part, to say about ngx.flush:"When ngx.flush(true) is called immediately after ngx.print or ngx.say, it causes...

Parsing json with cjson results in nil table

joel.parker.gm

I am trying to parse some json and for some reason the table returned from decode is always nil. Maybe something wrong with the json string but it seems correct. Can anyone tell me what I am doing wrong ?

Here is the config for reference:

load_module modules/ndk_http_module.so;
load_module modules/ngx_http_lua_module.so;

# takes advantage of all the cores in a processor
worker_processes auto;

events {
    worker_connections 1024;
}

http {

    include       mime.types;
    default_type application/octet-stream;

    sendfile        on;
    keepalive_timeout 65;
    gzip on;

    server {
        listen 80;
        server_name localhost;
        root /data/www;

        location / {
                content_by_lua '
                        local cjson = require("cjson")
                        json_text = [[ [{ "message": "somewhere over the rainbow", "key": "7F02D18E-88E7-486D-B51F-550118491CB1"}] ]]
                        value = cjson.decode(json_text)

                        say(cjson.encode(value)) -- returns nil ?
                        ngx.say( value["message"] )

                ';

                resolver 8.8.8.8;
        }

arkade

There are a couple of issues with your code. The first is that you're calling say(cjson.encode(value)) instead of ngx.say(cjson.encode(value))

The second is that when you define json_text, you have put the json object inside a json array (the inner most square brackets). That means to reference "message" you actually have to reference the the position in the array (lua starts and 1 not 0) first. Try this:

local cjson = require("cjson")

local json_text = [[ [{ "message": "somewhere over the rainbow", "key": "7F02D18E-88E7-486D-B51F-550118491CB1"}] ]]

local value = cjson.decode(json_text)

ngx.say(cjson.encode(value))

ngx.say(value[1]["message"])

or alternatively:

local cjson = require("cjson")

local json_text = [[ { "message": "somewhere over the rainbow", "key": "7F02D18E-88E7-486D-B51F-550118491CB1"} ]]

local value = cjson.decode(json_text)

ngx.say(cjson.encode(value))

ngx.say(value["message"])

On Monday, 11 September 2017 23:18:26 UTC+10, Joel Parker wrote:

I am trying to parse some json and for some reason the table returned from decode is always nil. Maybe something wrong with the json string but it seems correct. Can anyone tell me what I am doing wrong ?

Here is the config for reference:

load_module modules/ndk_http_module.so;
load_module modules/ngx_http_lua_module.so;

# takes advantage of all the cores in a processor
worker_processes auto;

events {
    worker_connections 1024;
}

http {

    include       mime.types;
    default_type application/octet-stream;

    sendfile        on;
    keepalive_timeout 65;
    gzip on;

    server {
        listen 80;
        server_name localhost;
        root /data/www;

        location / {
                content_by_lua '
                        local cjson = require("cjson")
                        json_text = [[ [{ "message": "somewhere over the rainbow", "key": "7F02D18E-88E7-486D-B51F-550118491CB1"}] ]]
                        value = cjson.decode(json_text)

                        say(cjson.encode(value)) -- returns nil ?
                        ngx.say( value["message"] )

                ';

                resolver 8.8.8.8;
        }