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/** |
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* example C code using libcurl and json-c |
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* to post and return a payload using |
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* http://jsonplaceholder.typicode.com |
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* |
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* Requirements: |
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* |
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* json-c - https://github.com/json-c/json-c |
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* libcurl - http://curl.haxx.se/libcurl/c |
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* |
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* Build: |
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* |
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* cc curltest.c -lcurl -ljson-c -o curltest |
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* |
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* Run: |
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* |
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* ./curltest |
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* |
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*/ |
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/* standard includes */ |
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#include <stdio.h> |
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#include <stdlib.h> |
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#include <stdarg.h> |
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#include <string.h> |
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/* json-c (https://github.com/json-c/json-c) */ |
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#include <json-c/json.h> |
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/* libcurl (http://curl.haxx.se/libcurl/c) */ |
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#include <curl/curl.h> |
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/* holder for curl fetch */ |
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struct curl_fetch_st { |
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char *payload; |
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size_t size; |
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}; |
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/* callback for curl fetch */ |
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size_t curl_callback (void *contents, size_t size, size_t nmemb, void *userp) { |
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size_t realsize = size * nmemb; /* calculate buffer size */ |
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struct curl_fetch_st *p = (struct curl_fetch_st *) userp; /* cast pointer to fetch struct */ |
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/* expand buffer */ |
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p->payload = (char *) realloc(p->payload, p->size + realsize + 1); |
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/* check buffer */ |
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if (p->payload == NULL) { |
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/* this isn't good */ |
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fprintf(stderr, "ERROR: Failed to expand buffer in curl_callback"); |
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/* free buffer */ |
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free(p->payload); |
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/* return */ |
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return -1; |
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} |
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/* copy contents to buffer */ |
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memcpy(&(p->payload[p->size]), contents, realsize); |
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/* set new buffer size */ |
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p->size += realsize; |
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/* ensure null termination */ |
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p->payload[p->size] = 0; |
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/* return size */ |
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return realsize; |
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} |
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/* fetch and return url body via curl */ |
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CURLcode curl_fetch_url(CURL *ch, const char *url, struct curl_fetch_st *fetch) { |
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CURLcode rcode; /* curl result code */ |
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/* init payload */ |
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fetch->payload = (char *) calloc(1, sizeof(fetch->payload)); |
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/* check payload */ |
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if (fetch->payload == NULL) { |
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/* log error */ |
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fprintf(stderr, "ERROR: Failed to allocate payload in curl_fetch_url"); |
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/* return error */ |
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return CURLE_FAILED_INIT; |
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} |
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/* init size */ |
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fetch->size = 0; |
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/* set url to fetch */ |
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curl_easy_setopt(ch, CURLOPT_URL, url); |
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/* set calback function */ |
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curl_easy_setopt(ch, CURLOPT_WRITEFUNCTION, curl_callback); |
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/* pass fetch struct pointer */ |
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curl_easy_setopt(ch, CURLOPT_WRITEDATA, (void *) fetch); |
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/* set default user agent */ |
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curl_easy_setopt(ch, CURLOPT_USERAGENT, "libcurl-agent/1.0"); |
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/* set timeout */ |
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curl_easy_setopt(ch, CURLOPT_TIMEOUT, 5); |
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/* enable location redirects */ |
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curl_easy_setopt(ch, CURLOPT_FOLLOWLOCATION, 1); |
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/* set maximum allowed redirects */ |
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curl_easy_setopt(ch, CURLOPT_MAXREDIRS, 1); |
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/* fetch the url */ |
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rcode = curl_easy_perform(ch); |
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/* return */ |
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return rcode; |
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} |
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int main(int argc, char *argv[]) { |
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CURL *ch; /* curl handle */ |
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CURLcode rcode; /* curl result code */ |
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json_object *json; /* json post body */ |
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enum json_tokener_error jerr = json_tokener_success; /* json parse error */ |
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struct curl_fetch_st curl_fetch; /* curl fetch struct */ |
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struct curl_fetch_st *cf = &curl_fetch; /* pointer to fetch struct */ |
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struct curl_slist *headers = NULL; /* http headers to send with request */ |
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/* url to test site */ |
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char *url = "http://jsonplaceholder.typicode.com/posts/"; |
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/* init curl handle */ |
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if ((ch = curl_easy_init()) == NULL) { |
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/* log error */ |
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fprintf(stderr, "ERROR: Failed to create curl handle in fetch_session"); |
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/* return error */ |
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return 1; |
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} |
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/* set content type */ |
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headers = curl_slist_append(headers, "Accept: application/json"); |
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headers = curl_slist_append(headers, "Content-Type: application/json"); |
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/* create json object for post */ |
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json = json_object_new_object(); |
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/* build post data */ |
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json_object_object_add(json, "title", json_object_new_string("testies")); |
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json_object_object_add(json, "body", json_object_new_string("testies ... testies ... 1,2,3")); |
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json_object_object_add(json, "userId", json_object_new_int(133)); |
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/* set curl options */ |
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curl_easy_setopt(ch, CURLOPT_CUSTOMREQUEST, "POST"); |
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curl_easy_setopt(ch, CURLOPT_HTTPHEADER, headers); |
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curl_easy_setopt(ch, CURLOPT_POSTFIELDS, json_object_to_json_string(json)); |
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/* fetch page and capture return code */ |
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rcode = curl_fetch_url(ch, url, cf); |
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/* cleanup curl handle */ |
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curl_easy_cleanup(ch); |
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/* free headers */ |
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curl_slist_free_all(headers); |
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/* free json object */ |
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json_object_put(json); |
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/* check return code */ |
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if (rcode != CURLE_OK || cf->size < 1) { |
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/* log error */ |
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fprintf(stderr, "ERROR: Failed to fetch url (%s) - curl said: %s", |
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url, curl_easy_strerror(rcode)); |
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/* return error */ |
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return 2; |
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} |
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/* check payload */ |
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if (cf->payload != NULL) { |
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/* print result */ |
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printf("CURL Returned: \n%s\n", cf->payload); |
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/* parse return */ |
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json = json_tokener_parse_verbose(cf->payload, &jerr); |
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/* free payload */ |
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free(cf->payload); |
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} else { |
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/* error */ |
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fprintf(stderr, "ERROR: Failed to populate payload"); |
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/* free payload */ |
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free(cf->payload); |
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/* return */ |
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return 3; |
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} |
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/* check error */ |
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if (jerr != json_tokener_success) { |
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/* error */ |
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fprintf(stderr, "ERROR: Failed to parse json string"); |
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/* free json object */ |
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json_object_put(json); |
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/* return */ |
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return 4; |
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} |
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/* debugging */ |
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printf("Parsed JSON: %s\n", json_object_to_json_string(json)); |
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/* exit */ |
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return 0; |
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} |
aaronhurt created this gist