ESP8266 uart monitor and uploader

monitor.ino

#include <ESP8266WiFi.h>
const char* ssid     = "*********";
const char* password = "*********";

const int bufferLength = 4096;
int bufferIndex = 0;
char buffer[bufferLength];
char bufferTemp[bufferLength];
long lastSend = 0;

void setup() 
{
  Serial.begin(115200);
  delay(100);
  connect();
}

void connect()
{
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED)
    delay(500);

  Serial.println("<wifi connected>");
}

void loop()
{
  long now = millis();
  _yield();
  if (bufferIndex > bufferLength-bufferLength/4 || now-lastSend > 10*1000)
  {
    lastSend = now;
    memcpy(bufferTemp, buffer, bufferLength);
    int nLength = bufferIndex;
    bufferIndex = 0;
    upload(bufferTemp, nLength);
  }
}

void _yield()
{
  yield();
  
  while (Serial.available())
  {
    char c = Serial.read();
    
    if (bufferIndex < bufferLength)
    {
      buffer[bufferIndex++] = c;
    }
  }
}

void upload(char* buffer, int length) 
{
  WiFiClient client;
  if (!client.connect("*********", 80)) {
    Serial.println("<connection failed>");
    return;
  }
  _yield();  
  Serial.print("<sending>");

   client.println("POST /*****/?uartmon HTTP/1.1");
   client.println("Host: *********");
   client.println("Accept: */*");
   client.println("Content-Type: application/x-www-form-urlencoded");
   client.print("Content-Length: ");
   client.println(length);
   client.println();
   client.write((byte*)buffer, length);

   char last[5] = {0, 0, 0, 0, 0};
   bool body = false;
    while (client.connected())
    {
      while (client.available())
      {
        _yield();
        
        char c = (char)client.read();
        if (body)
          Serial.print((char)c);

        last[0]=last[1];
        last[1]=last[2];
        last[2]=last[3];
        last[3]=c;
        body = body | (strcmp(last, "\r\n\r\n")==0);
      }
    }
    client.stop();
  Serial.print("<ok>");    
}

server.php

<?
  header("Access-Control-Allow-Origin: *");   
  header('Access-Control-Allow-Methods: POST, GET, OPTIONS');
  header('Access-Control-Allow-Headers: X-Requested-With, content-type');

  $channel = preg_replace("/[^A-Za-z0-9 ]/", '', $_SERVER["QUERY_STRING"]);
  $content = file_get_contents("php://input");

  file_put_contents("data/last_".$channel, $content);
  if ($content != "" && $content != "\n")
  {
    file_put_contents("data/".$channel."/".getCurrent(), $content, FILE_APPEND);
  }

  function getCurrent()
  {
    return date("Y-m-d").".txt";
  }

  function getTs()
  {
    return date("Y-m-d H:i:s");
  }
?>