cURL send POST data-binary

Question

I have cURL command:

curl "https://pelevin.gpt.dobro.ai/generate/" --data-binary '{"prompt" : "text" , "length" : 40}

and i want to do the same thing in C++.

I tried:

  string params = "prompt=text&length=40";
  string buffer;
  CURL*  curl;
  curl = curl_easy_init();
  if (curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "https://pelevin.gpt.dobro.ai/generate/");
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_callback);
    curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, params.size());
    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, params.c_str());
    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1);
    curl_easy_perform(curl);
  }
  curl_easy_cleanup(curl);

and got message like this:

{"detail":[{"loc":["body",0],"msg":"Expecting value: line 1 column 1 (char 0)","type":"value_error.jsondecode","ctx":{"msg":"Expecting value","doc":"prompt=text&length=40","pos":0,"lineno":1,"colno":1}}]}

How can the request be made correctly?

Asteroids With Wings · Accepted Answer · 2020-11-02 11:01:01Z

1

When you went from command-line to libcurl, you changed the data you provide. Why?

First it was a JSON object string (which seems to be what the server is expecting). Now you've made it an URL-encoded string.

Just pass the right data to the server, as you did in the first example.

string params = "{\"prompt\" : \"text\" , \"length\" : 40}";

N.B. there are "better" ways to format that in modern C++, if you're up for it:

string params = R"RAW({"prompt" : "text" , "length" : 40})RAW";

BTW, it's weird to use --data-binary with data specified on the command-line. It's intended for use with file input, as it prevents newlines being stripped from the file.

answered Nov 2, 2020 at 11:01

Asteroids With Wings

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