Demo 39: ESP32/8266 multipart upload a file and download a file via HTTP

1. Introduction
In previous demos, I showed you how to use MQTT/MQTTS and how to update firmware OTA (TCP/UDP and HTTP). In this demo, I will show you another interesting topic. That is how to download and multi-part upload a file via HTTP.

Figure: multipart upload and download a file via http

Based on this demo, you can build an application that can download the new firmware or the configuration file to memory card that is attached to client board for using later. Or you can upload the log file that records occurred events in run time to a server.
This is the requirement of this demo: a ESP32 will download a file from internet and after finish downloading, upload it to local apache server. The downloaded file will be stored in sdcard.
In order to make it easy, I created a library here in github. You just install and use it.
Note: this library can be apply for ESP8266.
2. Software
The library is simple to use. It has 2 APIs: upload() and download() with parameters. The parameters are:
- url of uploading and downloading file.
- progress displaying callback function.
- response processing callback function.
- reading and writing data to storage (sdcard, SPIFFS, ...) callback functions.
You should change them accordingly to your application.
Note: The url parser of this library is quite simple and it will be updated later.

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#include "UDHttp.h" #include "mySD.h" const char* ssid = "dd-wrt"; const char* password = "0000000000"; File root; //these callbacks will be invoked to read and write data to sdcard //and process response //and showing progress int responsef(uint8_t *buffer, int len){ Serial.printf("%s\n", buffer); return 0; } //read data callback int rdataf(uint8_t *buffer, int len){ //read file to upload if (root.available()) { return root.read(buffer, len); } return 0; } //write data callback int wdataf(uint8_t *buffer, int len){ //write downloaded data to file return root.write(buffer, len); } void progressf(int percent){ Serial.printf("%d\n", percent); } void setup() { // put your setup code here, to run once: Serial.begin(115200); WiFi.begin(ssid, password); while (WiFi.status() != WL_CONNECTED) { delay(500); Serial.print("."); } Serial.println(""); Serial.println("WiFi connected"); Serial.println("IP address: "); Serial.println(WiFi.localIP()); Serial.print("Initializing SD card..."); if (!SD.begin(32, 14, 12, 27)) { Serial.println("initialization failed!"); return; } Serial.println("initialization done."); SD.remove("test.pdf"); { UDHttp udh; //open file on sdcard to write root = SD.open("test.pdf", FILE_WRITE); if (!root) { Serial.println("can not open file!"); return; } //download the file from url udh.download("http://www.smart-words.org/linking-words/linking-words.pdf", wdataf, progressf); root.close(); Serial.printf("done downloading\n"); } { UDHttp udh; //open file on sdcard to read root = SD.open("test.pdf"); if (!root) { Serial.println("can not open file!"); return; } //upload downloaded file to local server udh.upload("http://192.168.1.107:80/upload/upload.php", "test.pdf", root.size(), rdataf, progressf, responsef); root.close(); Serial.printf("done uploading\n"); } } void loop() { // put your main code here, to run repeatedly: }

And the php script was used for this demo:

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<?php $target_path = "uploads/"; $target_path = $target_path . basename( $_FILES['data']['name']); if(move_uploaded_file($_FILES['data']['tmp_name'], $target_path)) { echo "The file ". basename( $_FILES['data']['name']). " has been uploaded"; } else{ echo "There was an error uploading the file, please try again!"; } ?>

Note: The variable $_FILES['data']['name'] has fixed 'data' field name (similar to html form ""). The downloaded file will be stored in sub-folder 'uploads' which is relative to folder where the php script located. Reference this post to install local apache server. 
3. Hardware
For harware connection please refer here.

4. Result

Figure: start downloading with progress displaying