Send file post request from the ESP32

Question

Is it impossible to send a file post request from the ESP32 using the SPIFFS file system? ESP32 freezes while sending.

Code example:

File file = SPIFFS.open("/Images/test.bmp", FILE_READ);
String start_request = ""; String end_request = "";
start_request = start_request +
 "\n--AaB03x\n" +
 "Content-Disposition: form-data; name=\"userfile\"; filename=\"CAM.bmp\"\n" +
 "Content-Transfer-Encoding: binary\n\n";
end_request = end_request + "\n--AaB03x--\n";
uint16_t full_length;
full_length = start_request.length() + file.size() + end_request.length();
WiFiClient client;
if (!client.connect("server_name", 80)) {
 Serial.println("Connected FILED!");
 return;
}
Serial.println("Connected ok!");
client.println("POST /Home/Index HTTP/1.1");
client.println("Host: example.com");
client.println("User-Agent: ESP32");
client.println("Content-Type: multipart/form-data; boundary=AaB03x");
client.print("Content-Length: "); client.println(full_length);
client.print(start_request);
while (file.available()){
 client.write(file.read());
}
Serial.println(">>><<<");
client.println(end_request);

• Juraj: HTTP requires an empty line after the headers. add an empty line with client.println() before client.print(start_request);

Answer 1

One can send a POST request with data fields appended with binary data as shown in the code below. The presented code was made to make a POST request to a Dataverse repository, however, can be easily adapted to any other POST request. Finally, the code below is optimized for Tensilica's Xtensa LX6/7 microprocessors, vis-a-vis ESP32.

The full code can be found here:

https://github.com/aeonSolutions/openScienceResearch-Smart-DAQ-Device-able-to-Upload-Live-Experimental-Sensor-Data-to-a-Data-Repo

// *********************************************************
// Upload Dataset to Harvard's Dataverse
// *********************************************************
void UploadToDataverse() {
 //Check WiFi connection status
 if(WiFi.status() != WL_CONNECTED){
 mserial.printStrln("WiFi Disconnected");
 if (connect2WIFInetowrk()){
 UploadToDataverse();
 }
 }
 // Start sending dataset file
 File datasetFile = FFat.open("/"+EXPERIMENTAL_DATA_FILENAME, FILE_READ);
 if (!datasetFile){
 mserial.printStrln("Dataset file not found");
 return;
 }
 
 String boundary = "7MA4YWxkTrZu0gW";
 String contentType = "text/csv";
 // DATASET_REPOSITORY_URL = "/api/files/:persistentId/replace?persistentId=" +PERSISTENT_ID;
 DATASET_REPOSITORY_URL = "/api/datasets/:persistentId/add?persistentId="+PERSISTENT_ID;
 
 String datasetFileName = datasetFile.name();
 String datasetFileSize = String(datasetFile.size());
 mserial.printStrln("Dataset File Details:");
 mserial.printStrln("Filename:" + datasetFileName);
 mserial.printStrln("size (bytes): "+ datasetFileSize);
 mserial.printStrln("");
 
 WiFiClientSecure client;
 int str_len = SERVER_URL.length() + 1; // Length (with one extra character for the null terminator)
 char SERVER_URL_char [str_len]; // Prepare the character array (the buffer) 
 SERVER_URL.toCharArray(SERVER_URL_char, str_len); // Copy it over 
 
 client.stop();
 client.setCACert(HARVARD_ROOT_CA_RSA_SHA1);
 if (!client.connect(SERVER_URL_char, SERVER_PORT)) {
 mserial.printStrln("Cloud server URL connection FAILED!");
 mserial.printStrln(SERVER_URL_char);
 int server_status = client.connected();
 mserial.printStrln("Server status code: " + String(server_status));
 return;
 }
 mserial.printStrln("Connected to the dataverse of Harvard University"); 
 mserial.printStrln("");
 // We now create a URI for the request
 mserial.printStr("Requesting URL: ");
 mserial.printStrln(DATASET_REPOSITORY_URL);
 // Make a HTTP request and add HTTP headers 
 // post header
 String postHeader = "POST " + DATASET_REPOSITORY_URL + " HTTP/1.1\r\n";
 postHeader += "Host: " + SERVER_URL + ":" + String(SERVER_PORT) + "\r\n";
 postHeader += "X-Dataverse-key: " + API_TOKEN + "\r\n";
 postHeader += "Content-Type: multipart/form-data; boundary=" + boundary + "\r\n";
 postHeader += "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n";
 postHeader += "Accept-Encoding: gzip,deflate\r\n";
 postHeader += "Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7\r\n";
 postHeader += "User-Agent: AeonLabs LDAD Smart DAQ device\r\n";
 postHeader += "Keep-Alive: 300\r\n";
 postHeader += "Connection: keep-alive\r\n";
 postHeader += "Accept-Language: en-us\r\n";
 // jsonData header
 String jsonData = "{\"description\":\"LIVE Experimental data upload from LDAD Smart 12bit DAQ \",\"categories\":[\"Data\"], \"restrict\":\"false\", \"tabIngest\":\"false\"}"; 
 String jsonDataHeader = "--" + boundary + "\r\n";
 jsonDataHeader += "Content-Disposition: form-data; name=\"jsonData\"\r\n\r\n";
 jsonDataHeader += jsonData+"\r\n";
 // dataset header
 String datasetHead = "--" + boundary + "\r\n";
 datasetHead += "Content-Disposition: form-data; name=\"file\"; filename=\"" + datasetFileName + "\"\r\n";
 datasetHead += "Content-Type: " + contentType + "\r\n\r\n";
 // request tail
 String tail = "\r\n--" + boundary + "--\r\n\r\n";
 // content length
 int contentLength = jsonDataHeader.length() + datasetHead.length() + datasetFile.size() + tail.length();
 postHeader += "Content-Length: " + String(contentLength, DEC) + "\n\n";
 
 // send post header
 int postHeader_len=postHeader.length() + 1; 
 char charBuf0[postHeader_len];
 postHeader.toCharArray(charBuf0, postHeader_len);
 client.print(charBuf0);
 mserial.printStr(charBuf0);
 // send key header
 char charBufKey[jsonDataHeader.length() + 1];
 jsonDataHeader.toCharArray(charBufKey, jsonDataHeader.length() + 1);
 client.print(charBufKey);
 mserial.printStr(charBufKey);
 // send request buffer
 char charBuf1[datasetHead.length() + 1];
 datasetHead.toCharArray(charBuf1, datasetHead.length() + 1);
 client.print(charBuf1);
 mserial.printStr(charBuf1);
 // create buffer
 const int bufSize = 2048;
 byte clientBuf[bufSize];
 int clientCount = 0;
 while (datasetFile.available()) {
 clientBuf[clientCount] = datasetFile.read();
 clientCount++;
 if (clientCount > (bufSize - 1)) {
 client.write((const uint8_t *)clientBuf, bufSize);
 clientCount = 0;
 }
 }
 datasetFile.close();
 
 if (clientCount > 0) {
 client.write((const uint8_t *)clientBuf, clientCount);
 mserial.printStrln("[binary data]");
 }
 // send tail
 char charBuf3[tail.length() + 1];
 tail.toCharArray(charBuf3, tail.length() + 1);
 client.print(charBuf3);
 mserial.printStr(charBuf3);
 // Read all the lines of the reply from server and print them to mserial
 mserial.printStrln("");
 mserial.printStrln("Response Headers:");
 String responseHeaders = "";
 while (client.connected()) {
 // mserial.printStrln("while client connected");
 responseHeaders = client.readStringUntil('\n');
 mserial.printStrln(responseHeaders);
 if (responseHeaders == "\r") {
 mserial.printStrln("====== end of headers ======");
 break;
 }
 }
 String responseContent = client.readStringUntil('\n');
 mserial.printStrln("Harvard University's Dataverse reply was:");
 mserial.printStrln("==========");
 mserial.printStrln(responseContent);
 mserial.printStrln("==========");
 mserial.printStrln("closing connection");
 client.stop();
 }