Download an SDcard file (ESP8266)

[arjenv]

Dear readers. I have searched the net now for over 4 hours, and tried several suggestions. Alas nothing works.

Using an ESP8266 (Yes obsolete but I have several of them an it suits my needs). Platformio.

lib_deps =
me-no-dev/ESPAsyncTCP@^2.0.0
me-no-dev/ESPAsyncWebServer@^3.6.0

The ESP is programmed as a webserver. Wrote an application in which I can upload/download/delete/rename files that are in Flash. I am trying to duplicate these functions to an SD card I attached. I can now open the SD card and list the files. Next in line is the 'delete' function. With LittleFS the following snippet is used:
(part of an AsyncWebServerRequest following a XMLHttpRequest from a webpage)

request->send(LittleFS, fileName, "application/octet-stream", true);

That works fine with files in the flash. Now I thought that replacing 'LittleFS' with 'SD' would do the trick, I found that in a number of examples, but that is where I got stuck and searched the net for the last 4 hours.

so:
request->send(SD, fileName, "application/octet-stream", true);

Does NOT work....
It gives me an error:

no instance of overloaded function "AsyncWebServerRequest::send" matches the argument list

I read somewhere that this has to do with the ESP8266 but I cannot verify that.
Tried different suggestions as 'open the SD file and send that as a respond' and tried the 'chunked' example to no avail.

What else can I try? Roll back to an older version of the lib?
Thanks

[mathieucarbou]

lib_deps =
me-no-dev/ESPAsyncTCP@^2.0.0
me-no-dev/ESPAsyncWebServer@^3.6.0

You are not using the official libraries.

Please look at the README and use the right ones. We do not support the olds ones or any fork.

Thanks!

[arjenv]

Thank you for your reply
Thought these were the official libraries.

So I changed the lib deps to:

lib_deps =
ESP32Async/ESPAsyncTCP
ESP32Async/ESPAsyncWebServer

However, I am getting the exact same error as described in the 1st section.

[mathieucarbou]

Did you try to look at all the many examples inside the project ?

[arjenv]

Yes I did, I spent 4 hours looking for the solution. Do you have s specific example in mind I might have missed?

Why is 'SD' not working whereas 'LittleFS' is? They are both filesystems I think?

[mathieucarbou]

Yes! If you have an ESP32 with SDCard support and an SD Card plugged in it should work.... SD is a FS implementation, but only on ESP32. On 8266, there is SDFS (i think). Either way, switch to ESP32 and don't loose time like you did with old 8266 specificities. They don't even have 2 cores.

[arjenv]

Follow up question: I managed to get it to work with the following:

server.on("/SDfile", HTTP_GET, [](AsyncWebServerRequest * request) {

... <some checks whether the file exists etc>

      if (strcmp(fileAction, "download") == 0) {
          logmessage += " downloaded";
          Serial.println();Serial.println(fileName);Serial.println();
          SDfile = SD.open(fileName, FILE_READ);
          request->send(SDfile, fileName, "application/octet-stream", true);
         // SDfile.close();  // OBSERVE THIS IS COMMENTED OUT!
    }
}

At first I closed the file directly after 'request->send..", but that wont work because it is asynchronous. So I commented out the SDfile.close() command altogether. However, I am now concerned that a file is still open. Will it close automatically after this function or do I have to check for the file to have downloaded completely and then close the file. And if so: How?

[mathieucarbou]

At first I closed the file directly after 'request->send..", but that wont work because it is asynchronous.

exactly!
The real sending happens after ;-)
The file is closed by the library after the response is sent, no worry ;-)

In any case, if you happen one day to have some cleanup to do for a request, you can use request->onDisconnect(cb) :

    request->onDisconnect([]() {
      Serial.printf("Request was disconnected!\n");
    });

[arjenv]

Thanks. Very clear answer. :-)