c++ libcurl json rest

Question

I am trying to download a json file from a REST webpage in C++ with libcurl. The following code works if I go to the webpage but it doesnt download if I try to access the json ....

I think it should be an easy fix but I cant find any reference to this ...

If I go to webpage it opens the json but this code only returns text/html; charset=utf-8

??????????

CURL *curl;
CURLcode res;
    struct curl_slist *headers=NULL; // init to NULL is important 
    headers = curl_slist_append(headers, "Accept: application/json");   

curl = curl_easy_init();
if(curl) {

    curl_easy_setopt(curl, CURLOPT_URL, "http://web.com/api/json/123");
            curl_easy_setopt(curl, CURLOPT_HTTPGET,1);
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
    //curl_easy_setopt(curl, CURLOPT_URL, "http://web.com/123.html");//this works!!!
    res = curl_easy_perform(curl);

    if(CURLE_OK == res) {
        char *ct;
        /* ask for the content-type */
        res = curl_easy_getinfo(curl, CURLINFO_CONTENT_TYPE, &ct);
        if((CURLE_OK == res) && ct)
            printf("We received Content-Type: %s\n", ct);
    }
}
/* always cleanup */ 
curl_easy_cleanup(curl);

score 20 · Accepted Answer · edited Feb 29 '20 at 12:58

20

std::string ServerContent::DownloadJSON(std::string URL)
{   
    CURL *curl;
    CURLcode res;
    struct curl_slist *headers=NULL; // init to NULL is important 
    std::ostringstream oss;
    headers = curl_slist_append(headers, "Accept: application/json");  
    headers = curl_slist_append(headers, "Content-Type: application/json");
    headers = curl_slist_append(headers, "charset: utf-8"); 
    curl = curl_easy_init();

    if (curl) 
    {
        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
        curl_easy_setopt(curl, CURLOPT_URL, URL.c_str());
        curl_easy_setopt(curl, CURLOPT_HTTPGET,1); 
        curl_easy_setopt(curl,CURLOPT_WRITEFUNCTION,writer);
        res = curl_easy_perform(curl);

        if (CURLE_OK == res) 
        { 
            char *ct;         
            res = curl_easy_getinfo(curl, CURLINFO_CONTENT_TYPE, &ct);
            if((CURLE_OK == res) && ct)
                return *DownloadedResponse;
        }
    }

    curl_slist_free_all(headers);
}


static std::string *DownloadedResponse;

static int writer(char *data, size_t size, size_t nmemb, std::string *buffer_in)
{

    // Is there anything in the buffer?  
    if (buffer_in != NULL)  
    {
        // Append the data to the buffer    
        buffer_in->append(data, size * nmemb);

        // How much did we write?   
        DownloadedResponse = buffer_in;

        return size * nmemb;  
    }

    return 0;

}

edited Feb 29 '20 at 12:58

Jens A. Koch

39,862
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answered Apr 25 '11 at 16:39

Philip

579
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3

You have two calls to `curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);` I believe the second one is not needed. – Ivaylo Strandjev May 10 '13 at 07:19
2

Also from my experience it seems you should assign the return value of curl_slist_append back to headers in order to modify the list. – Ivaylo Strandjev May 10 '13 at 07:41
3

you are missing a call to `curl_slist_free(headers)` so this code leaks the header list – Pete Kirkham Jun 06 '13 at 10:58
1

@PeteKirkham you are missing _all. curl_slist_free_all(headers); – lumingjing Sep 23 '13 at 03:29
Your `curl_slist_append` calls aren't appending anything: you're ignoring the return value. – Emil Laine Mar 21 '17 at 00:09
must be a slow day at the convienent store lol – deadcow Jun 02 '22 at 07:52

score 1 · Answer 2 · answered Apr 18 '11 at 22:52

1

I think this has to do with the configuration on the HTTP server. First, you should be sending some type of indication of what type you're expecting, for example, adding an Accept header like this:

Accept: application/json

If you don't specify what you're expecting, the server may return the default HTML in the response header Content-Type, and that's what curl says to you.

answered Apr 18 '11 at 22:52

Diego Sevilla

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I tried to add the following but I cant get to the actually data from the server response.... struct curl_slist *headers=NULL; // init to NULL is important headers = curl_slist_append(headers, "Accept: application/json"); curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers); – Philip Apr 20 '11 at 16:38

score 0 · Answer 3 · answered Apr 18 '11 at 22:44

0

Have you tried this approach from the tutorial code at the curl site? http://curl.haxx.se/libcurl/c/sepheaders.html

answered Apr 18 '11 at 22:44

holtavolt

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I want to read the json not put it, is there a CURLOPT_READHEADER or something to read the stream of data returned from server? btw this worls for me on the command line curl -i -H "Accept: application/json" -X GET web.com/api/json/123 – Philip Apr 18 '11 at 23:24

c++ libcurl json rest

3 Answers3

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