How can I write HTTP POST request multipart/form-data myself? - http

Question

I want to send a POST request to server in multipart/form-data contents.
I have to write the request statement myself, without any high-level API
because it has to be sent as an AT command of the modem.
The curl command below is a command to test the server's API, and this is what I want to construct myself.
# This is what I want to construct myself.
curl -X POST $API_ENDPOINT \
-F time=yyyy-mm-dd-hh:mm:ss \
-F event=1 \
-F rssi=31 \
-F battery=80 \
-F filename=test.jpg \
-F files=#test.jpg \ # Send an image from my local file system to server.
-w %{http_code}
echo "\r\n"
And the below is what I sent to my modem.
/* This is form for multipart/form-data. Is it right?
POST $API_ENDPOINT HTTP/1.1
Host: $HOST
Content-Length: $body_length
Content-Type: multipart/form-data; boundary="boundary"
--boundary
Content-Disposition: form-data; name="files"; filename="example.jpg"
Content-Type: image/jpg
--boundary--
*/
// Below C++ code was written for the above POST request.
std::string filename = "example.jpg";
std::string filePath = "example.jpg";
std::string body =
std::string("--boundary\r\n") +
"Content-Disposition: form-data; name=\"files\"; filename=\"" + filePath + "\"\r\n" +
"Content-Type: image/jpg\r\n" +
"\r\n" +
"--boundary--\r\n";
std::string header =
std::string("POST ") + url + " HTTP/1.1\r\n" +
"Host: " + host + "\r\n" +
"Content-Length: " + std::to_string(body.length()) + "\r\n" +
"Content-Type: multipart/form-data; boundary=\"boundary\"\r\n" +
"\r\n";
std::string data = header + body;
... and this is the server log.
Error: MultipartParser.end(): stream ended unexpectedly: state = PART_DATA
This is my question.
How can I add fields(time, event, rssi, etc) in the request body? The server seems getting each fields as <key: value> format. How can I add it in multipart/form-data?
Is it correct to attach an image file like that? In the curl command, I wrote the path of my local image file (-F files) and the name that this image file will be stored on the server (-F filename). How should I reflect this in my request form?
Thanks brothers

Answer 1

I did it! Right that.
/*
POST $API_ENDPOINT HTTP/1.1
Host: $HOST
Content-Length: $body_length
Content-Type: multipart/form-data; boundary="boundary"
--boundary
Content-Type: text/plain
Content-Disposition: form-data; name="time"
yyyy-mm-dd-hh:mm:ss
--boundary
Content-Type: text/plain
Content-Disposition: form-data; name="event"
1
--boundary
Content-Type: text/plain
Content-Disposition: form-data; name="rssi"
31
--boundary
Content-Type: text/plain
Content-Disposition: form-data; name="battery"
99
--boundary
Content-Type: text/plain
Content-Disposition: form-data; name="filename"
example.jpg
--boundary
Content-Type: image/jpg
Content-Disposition: form-data; name="files"; filename="example.jpg"
....binary bytes of example.jpg...
--boundary--
*/
const int fd = // File descriptor of my serial port
const std::string host = // host
const std::string uri = // uri
const int tryout = 10 // for modem
std::string filename = "1996-03-05.jpg";
std::string filePath = "1996-03-05.jpg";
std::ifstream bin(filePath, std::ios::binary);
std::string imageBin((std::istreambuf_iterator<char>(bin)), std::istreambuf_iterator<char>());
std::string TIMESTAMP = "1996-03-05";
std::string event = "1";
std::string rssi = "31";
std::string battery = "90";
atcmd::__sendATcmd(fd, "AT+QHTTPCFG=\"contextid\",1\r");
atcmd::__readBufferUntil(fd, "\r\nOK\r\n", tryout);
atcmd::__sendATcmd(fd, "AT+QHTTPCFG=\"contenttype\",3\r"); // 3: multipart/form-data
atcmd::__readBufferUntil(fd, "\r\nOK\r\n", tryout);
atcmd::__sendATcmd(fd, "AT+QHTTPCFG=\"requestheader\",1\r");
atcmd::__readBufferUntil(fd, "\r\nOK\r\n", tryout);
const std::string fullUrl = "http://" + host + uri;
atcmd::__sendATcmd(fd, ("AT+QHTTPURL=" + std::to_string(fullUrl.length()) + "\r").c_str());
atcmd::__readBufferUntil(fd, "\r\nCONNECT\r\n", tryout);
atcmd::__sendATcmd(fd, fullUrl.c_str());
atcmd::__readBufferUntil(fd, "\r\nOK\r\n", tryout);
std::string body_fields = (
std::string("--boundary\r\n") +
"Content-Type: text/plain\r\n" +
"Content-Disposition: form/data; name=\"time\"\r\n" +
"\r\n" +
TIMESTAMP + "\r\n" +
"--boundary\r\n" +
"Content-Type: text/plain\r\n" +
"Content-Disposition: form/data; name=\"event\"\r\n" +
"\r\n" +
event + "\r\n" +
"--boundary\r\n" +
"Content-Type: text/plain\r\n" +
"Content-Disposition: form/data; name=\"rssi\"\r\n" +
"\r\n" +
rssi + "\r\n" +
"--boundary\r\n" +
"Content-Type: text/plain\r\n" +
"Content-Disposition: form/data; name=\"battery\"\r\n" +
"\r\n" +
battery + "\r\n" +
"--boundary\r\n" +
"Content-Type: text/plain\r\n" +
"Content-Disposition: form/data; name=\"filename\"\r\n" +
"\r\n" +
filename + "\r\n"
);
std::string body_image = (
std::string("--boundary\r\n") +
"Content-Type: image/jpeg\r\n" +
"Content-Disposition: form-data; name=\"files\"; filename=\"" + filePath + "\"\r\n" +
"\r\n" +
imageBin + "\r\n" +
"--boundary--\r\n"
);
int bodyLen = body_fields.length() + body_image.length();
std::string header = (
std::string("POST ") + uri + " HTTP/1.1\r\n" +
"Host: " + host + "\r\n" +
"Content-Length: " + std::to_string(bodyLen) + "\r\n" +
"Content-Type: multipart/form-data; boundary=\"boundary\"\r\n" +
"\r\n"
);
const std::string dataLen = std::to_string(header.length() + bodyLen);
std::string maxInputBodyTime = "80";
std::string maxResponseTime = "80";
atcmd::__sendATcmd(fd, ("AT+QHTTPPOST="
+ dataLen + ","
+ maxInputBodyTime + ","
+ maxResponseTime + "\r").c_str());
atcmd::__readBufferUntil(fd, "\r\nCONNECT\r\n", tryout);
atcmd::__sendATcmd(fd, header.c_str());
atcmd::__sendATcmd(fd, body_fields.c_str());
atcmd::__sendATcmd(fd, body_image.c_str(), body_image.length());
atcmd::__readBufferUntil(fd, "\r\nOK\r\n", tryout);
atcmd::__sendATcmd(fd, "AT+QHTTPREAD=80\r");
std::cout << atcmd::__readBuffer(fd) << std::endl;