Lua socket error on connection - sockets

Question

I'm trying to make a http get, using Lua Socket:
local client = socket.connect('warm-harbor-2019.herokuapp.com',80)
if client then
client:send("GET /get_tweets HTTP/1.0\r\n\r\n")
s, status, partial = client:receive(1024)
end
end
I expect s to be a tweet, since the get that I'm making returns one.
But I'm getting:
http/1.1 404 object not found

Answer 1

Here is a runnable version of your code example (that exhibit the problem you described):
local socket = require "socket"
local client = socket.connect('warm-harbor-2019.herokuapp.com',80)
if client then
client:send("GET /get_tweets HTTP/1.0\r\n\r\n")
local s, status, partial = client:receive(1024)
print(s)
end
If you read the error page returned, you can see that its title is Heroku | No such app.
The reason for that is that the Heroku router only works when a Host header is provided. The easiest way to do it is to use the actual HTTP module of LuaSocket instead of TCP directly:
local http = require "socket.http"
local s, status, headers = http.request("http://warm-harbor-2019.herokuapp.com/get_tweets")
print(s)
If you cannot use socket.http you can pass the Host header manually:
local socket = require "socket"
local client = socket.connect('warm-harbor-2019.herokuapp.com',80)
client:send("GET /get_tweets HTTP/1.0\r\nHost: warm-harbor-2019.herokuapp.com\r\n\r\n")
local s, status, partial = client:receive(1024)
print(s, status, partial)
With my version of LuaSocket, s will be nil, status will be "closed" and partial will contain the full HTTP response (with headers etc).