Uploading files to the server

There are scenarios where you may want to upload new files to the server from within a browser, without having to connect to the ESP8266 over USB in order to flash a new SPIFFS image.
In this chapter, I'll show you how to use HTML forms and POST requests to upload or edit files to our little ESP server.

Client: HTML form

The easiest way to upload files is by using an HTML form, just like in the first server examples, where we used forms to turn on/off LEDs, and to send the login credentials back to the server. If you choose a file input, you automatically get a file picker, and the browser will send the right POST request to the server, with the file attached.
<form method="post" enctype="multipart/form-data">
    <input type="file" name="name">
    <input class="button" type="submit" value="Upload">
</form>

Server

In the ESP code, we have to add a handler to our server that handles POST requests to the /upload URI. When it receives a POST request, it sends a status 200 (OK) back to the client to start receiving the file, and then write it to the SPIFFS. When the file is uploaded successfully, it redirects the client to a success page.
The relevant new code is found in the
setup
and the
handleFileUpload
function.
#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <ESP8266WiFiMulti.h>
#include <ESP8266mDNS.h>
#include <ESP8266WebServer.h>
#include <FS.h>   // Include the SPIFFS library

ESP8266WiFiMulti wifiMulti;     // Create an instance of the ESP8266WiFiMulti class, called 'wifiMulti'

ESP8266WebServer server(80);    // Create a webserver object that listens for HTTP request on port 80

File fsUploadFile;              // a File object to temporarily store the received file

String getContentType(String filename); // convert the file extension to the MIME type
bool handleFileRead(String path);       // send the right file to the client (if it exists)
void handleFileUpload();                // upload a new file to the SPIFFS

void setup() {
  Serial.begin(115200);         // Start the Serial communication to send messages to the computer
  delay(10);
  Serial.println('\n');

  wifiMulti.addAP("ssid_from_AP_1", "your_password_for_AP_1");   // add Wi-Fi networks you want to connect to
  wifiMulti.addAP("ssid_from_AP_2", "your_password_for_AP_2");
  wifiMulti.addAP("ssid_from_AP_3", "your_password_for_AP_3");

  Serial.println("Connecting ...");
  int i = 0;
  while (wifiMulti.run() != WL_CONNECTED) { // Wait for the Wi-Fi to connect
    delay(1000);
    Serial.print(++i); Serial.print(' ');
  }
  Serial.println('\n');
  Serial.print("Connected to ");
  Serial.println(WiFi.SSID());              // Tell us what network we're connected to
  Serial.print("IP address:\t");
  Serial.println(WiFi.localIP());           // Send the IP address of the ESP8266 to the computer

  if (!MDNS.begin("esp8266")) {             // Start the mDNS responder for esp8266.local
    Serial.println("Error setting up MDNS responder!");
  }
  Serial.println("mDNS responder started");

  SPIFFS.begin();                           // Start the SPI Flash Files System

  server.on("/upload", HTTP_GET, []() {                 // if the client requests the upload page
    if (!handleFileRead("/upload.html"))                // send it if it exists
      server.send(404, "text/plain", "404: Not Found"); // otherwise, respond with a 404 (Not Found) error
  });

  server.on("/upload", HTTP_POST,                       // if the client posts to the upload page
    [](){ server.send(200); },                          // Send status 200 (OK) to tell the client we are ready to receive
    handleFileUpload                                    // Receive and save the file
  );

  server.onNotFound([]() {                              // If the client requests any URI
    if (!handleFileRead(server.uri()))                  // send it if it exists
      server.send(404, "text/plain", "404: Not Found"); // otherwise, respond with a 404 (Not Found) error
  });

  server.begin();                           // Actually start the server
  Serial.println("HTTP server started");
}

void loop() {
  server.handleClient();
}

String getContentType(String filename) { // convert the file extension to the MIME type
  if (filename.endsWith(".html")) return "text/html";
  else if (filename.endsWith(".css")) return "text/css";
  else if (filename.endsWith(".js")) return "application/javascript";
  else if (filename.endsWith(".ico")) return "image/x-icon";
  else if (filename.endsWith(".gz")) return "application/x-gzip";
  return "text/plain";
}

bool handleFileRead(String path) { // send the right file to the client (if it exists)
  Serial.println("handleFileRead: " + path);
  if (path.endsWith("/")) path += "index.html";          // If a folder is requested, send the index file
  String contentType = getContentType(path);             // Get the MIME type
  String pathWithGz = path + ".gz";
  if (SPIFFS.exists(pathWithGz) || SPIFFS.exists(path)) { // If the file exists, either as a compressed archive, or normal
    if (SPIFFS.exists(pathWithGz))                         // If there's a compressed version available
      path += ".gz";                                         // Use the compressed verion
    File file = SPIFFS.open(path, "r");                    // Open the file
    size_t sent = server.streamFile(file, contentType);    // Send it to the client
    file.close();                                          // Close the file again
    Serial.println(String("\tSent file: ") + path);
    return true;
  }
  Serial.println(String("\tFile Not Found: ") + path);   // If the file doesn't exist, return false
  return false;
}

void handleFileUpload(){ // upload a new file to the SPIFFS
  HTTPUpload& upload = server.upload();
  if(upload.status == UPLOAD_FILE_START){
    String filename = upload.filename;
    if(!filename.startsWith("/")) filename = "/"+filename;
    Serial.print("handleFileUpload Name: "); Serial.println(filename);
    fsUploadFile = SPIFFS.open(filename, "w");            // Open the file for writing in SPIFFS (create if it doesn't exist)
    filename = String();
  } else if(upload.status == UPLOAD_FILE_WRITE){
    if(fsUploadFile)
      fsUploadFile.write(upload.buf, upload.currentSize); // Write the received bytes to the file
  } else if(upload.status == UPLOAD_FILE_END){
    if(fsUploadFile) {                                    // If the file was successfully created
      fsUploadFile.close();                               // Close the file again
      Serial.print("handleFileUpload Size: "); Serial.println(upload.totalSize);
      server.sendHeader("Location","/success.html");      // Redirect the client to the success page
      server.send(303);
    } else {
      server.send(500, "text/plain", "500: couldn't create file");
    }
  }
}
The
handleFileUpload
function just writes the file attached to the POST request to SPIFFS.

If you wan to use other file types as well, you can just add them to the 
getContentType
 function.

Uploading files

To upload a new file to the ESP, or to update an existing file, just go to http://esp8266.local/upload, click the Choose File button, select the file you wish to upload, and click Upload. You can now enter the URL into the URL bar, and open the new file.

A note on safety

This example isn't very secure (obviously). Everyone that can connect to the ESP can upload new files, or edit the existing files and insert XSS code, for example. There's also not a lot of error checking/handling, like checking if there's enough space in the SPIFFS to upload a new file, etc. 

Advanced example

The code for these SPIFFS server examples comes (for the most part) from an example written by Hristo Gochkov. You can find it under File > Examples > ESP8266WebServer > FSBrowser. It has a web interface for browsing and editing files in your browser, and has some other nice features as well.

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