gistfile1.txt

//you need to connect to wifi first

void wifisendfile()
{
  String host="xxx.xxx.xxx.xxx";//your host name or ip
//prepare httpclient
  Serial.println("Starting connection to server...");
  Serial.println(host);
  WiFiClient client;

//start http sending
  if (client.connect(host.c_str(), 80)) 
  {
//open file  
  myFile = SD.open("/pic.jpg");//change to your file name
  int filesize=myFile.size();
  Serial.print("filesize=");
  Serial.println(filesize);
  String fileName = myFile.name();
  String fileSize = String(myFile.size());
    
    Serial.println("reading file");
    if (myFile) 
    {
      String boundary = "CustomizBoundarye----";
      String contentType = "image/jpeg";//change to your file type

 // prepare http post data(generally, you dont need to change anything here)
      String postHeader = "POST " + url + " HTTP/1.1\r\n";
      postHeader += "Host: " + host + ":80 \r\n";
      postHeader += "Content-Type: multipart/form-data; boundary=" + boundary + "\r\n";
      postHeader += "Accept-Charset: utf-8;\r\n";
      String keyHeader = "--" + boundary + "\r\n";
      keyHeader += "Content-Disposition: form-data; name=\"key\"\r\n\r\n";
      String requestHead = "--" + boundary + "\r\n";
      requestHead += "Content-Disposition: form-data; name=\"\"; filename=\"" + fileName + "\"\r\n";
      requestHead += "Content-Type: " + contentType + "\r\n\r\n";
	// post tail
     String tail = "\r\n--" + boundary + "--\r\n\r\n";
	// content length
      int contentLength = keyHeader.length() + requestHead.length() + myFile.size() + tail.length();
      postHeader += "Content-Length: " + String(contentLength, DEC) + "\n\n";

// send post header
      char charBuf0[postHeader.length() + 1];
      postHeader.toCharArray(charBuf0, postHeader.length() + 1);
      client.write(charBuf0);
      //Serial.print("send post header=");
      //Serial.println(charBuf0);
    
// send key header
      char charBufKey[keyHeader.length() + 1];
      keyHeader.toCharArray(charBufKey, keyHeader.length() + 1);
      client.write(charBufKey);
      //Serial.print("send key header=");
      //Serial.println(charBufKey);

// send request buffer
      char charBuf1[requestHead.length() + 1];
      requestHead.toCharArray(charBuf1, requestHead.length() + 1);
      client.write(charBuf1);
      //Serial.print("send request buffer=");
      //Serial.println(charBuf1);

// create file buffer
      const int bufSize = 2048;
      byte clientBuf[bufSize];
      int clientCount = 0;
    
// send myFile:
      while (myFile.available()) 
      {
        clientBuf[clientCount] = myFile.read();
        clientCount++;
        if (clientCount > (bufSize - 1)) 
        {
          client.write((const uint8_t *)clientBuf, bufSize);
          clientCount = 0;
        }
      }
      if (clientCount > 0) 
      {
        client.write((const uint8_t *)clientBuf, clientCount);
        //Serial.println("Sent LAST buffer");
      }

// send tail
      char charBuf3[tail.length() + 1];
      tail.toCharArray(charBuf3, tail.length() + 1);
      client.write(charBuf3);
      //Serial.print(charBuf3);
    } 
 }
//print response 
  while(client.connected())
  {
    while(client.available()) 
    {
        String line = client.readStringUntil('\r');       
        Serial.print(line);       
    }
 }
 myFile.close();
 Serial.println("closing connection");
}