Move function definition to inside the socket listen argument list. This is harder to follow, but allows the coroutine to be unique since it is now part of the closure. Multiple files can be served simultaneously this way.

httpserver.lua

@@ -54,12 +54,20 @@ local function parseUri(uri)
    return r
 end
 
--- This variable holds the thread used for sending data back to the user.
--- We do it in a separate thread because we need to yield when sending lots
--- of data in order to avoid overflowing the mcu's buffer.
-local connectionThread
+-- Starts web server in the specified port.
+return function (port)
 
-local function onGet(connection, uri)
+   local s = net.createServer(net.TCP, 10) -- 10 seconds client timeout
+   s:listen(
+      port,
+      function (connection)
+
+         -- This variable holds the thread used for sending data back to the user.
+         -- We do it in a separate thread because we need to yield when sending lots
+         -- of data in order to avoid overflowing the mcu's buffer.
+         local connectionThread
+
+         local function onGet(connection, uri)
             local uri = parseUri(uri)
             local fileExists = file.open(uri.file, "r")
             file.close()
@@ -76,10 +84,11 @@ local function onGet(connection, uri)
                fileServeFunction = dofile("httpserver-static.lc")
             end
             connectionThread = coroutine.create(fileServeFunction)
+            --print("Thread created", connectionThread)
             coroutine.resume(connectionThread, connection, uri.args)
-end
+         end
 
-local function onReceive(connection, payload)
+         local function onReceive(connection, payload)
             --print(payload) -- for debugging
             -- parse payload and decide what to serve.
             local req = parseRequest(payload)
@@ -88,31 +97,32 @@ local function onReceive(connection, payload)
             if req.method == "GET" then onGet(connection, req.uri)
             elseif req.method == nil then dofile("httpserver-static.lc")(conection, {code=400})
             else dofile("httpserver-static.lc")(conection, {code=501}) end
-end
+         end
 
-local function onSent(connection, payload)
-   if coroutine.status(connectionThread) == "dead" then
+         local function onSent(connection, payload)
+            local connectionThreadStatus = coroutine.status(connectionThread)
+            --print (connectionThread, "status is", connectionThreadStatus)
+            if connectionThreadStatus == "dead" then
                -- We're done sending file.
+               --print("Done sending file", connectionThread)
                connection:close()
                connectionThread = nil
-   elseif coroutine.status(connectionThread) == "suspended" then
+            elseif connectionThreadStatus == "suspended" then
                -- Not finished sending file, resume.
+               --print("Resume thread", connectionThread)
                coroutine.resume(connectionThread)
             else
                print ("Fatal error! I did not expect to hit this codepath")
                connection:close()
             end
-end
+         end
 
-local function handleRequest(connection)
          connection:on("receive", onReceive)
          connection:on("sent", onSent)
-end
 
--- Starts web server in the specified port.
-return function (port)
-   local s = net.createServer(net.TCP, 10) -- 10 seconds client timeout
-   s:listen(port, handleRequest)
+      end
+   )
    print("nodemcu-httpserver running at http://" .. wifi.sta.getip() .. ":" ..  port)
    return s
+
 end