CURLOPT_TCP_KEEPALIVE - Man Page

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TCP_KEEPALIVE, long probe);

Pass a long. If set to 1, TCP keepalive probes will be sent. The delay and frequency of these probes can be controlled by the CURLOPT_TCP_KEEPIDLE(3) and CURLOPT_TCP_KEEPINTVL(3) options, provided the operating system supports them. Set to 0 (default behavior) to disable keepalive probes

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CURL *curl = curl_easy_init();
if(curl) {
  curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

  /* enable TCP keep-alive for this transfer */
  curl_easy_setopt(curl, CURLOPT_TCP_KEEPALIVE, 1L);

  /* keep-alive idle time to 120 seconds */
  curl_easy_setopt(curl, CURLOPT_TCP_KEEPIDLE, 120L);

  /* interval time between keep-alive probes: 60 seconds */
  curl_easy_setopt(curl, CURLOPT_TCP_KEEPINTVL, 60L);

  curl_easy_perform(curl);
}

Added in 7.25.0

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

CURLOPT_TCP_KEEPIDLE(3), CURLOPT_TCP_KEEPINTVL(3),

curl_easy_setopt(3), curl_easy_upkeep(3), CURLOPT_TCP_KEEPIDLE(3), CURLOPT_TCP_KEEPINTVL(3), CURLOPT_TCP_NODELAY(3), CURLOPT_UPKEEP_INTERVAL_MS(3), nbdkit-curl-plugin(1).