Curl dns cache Either the DNS server is failing to respond, or it is throttling us back (we're sending hundreds of requests per second at peak). g. h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DNS_CACHE_TIMEOUT, long age); Description Pass a long, this sets the timeout in seconds. g; I have this curl command: curl -v www. I was going through the curl documentation and c Nov 18, 2020 · Buy commercial curl support from WolfSSL. This is not thread-safe and this uses a global variable. Jul 9, 2008 · Reply: Dan Fandrich: "Re: curl dns cache and dns changes on linux" Contemporary messages sorted: [ by date ] [ by thread ] [ by subject ] [ by author ] [ by messages with attachments ] CURLOPT_DNS_CACHE_TIMEOUT can be used together with this option to reduce DNS cache timeout or disable caching entirely if frequent reshuffling is needed. files is first in /etc/resolv. I had introduced into a Java servlet a loop that would cause the TIMEOUT on libcurl would be hit. Feb 21, 2023 · Curl does not cache any requests on the client side; therefore, any caching when using Curl occurs on the server side. 摘要1#include <curl/curl. You can set option to 0 Jun 11, 2015 · 9 Belatedly, try: curl -v -H "Cache-Control: no-cache" That will tell the web server to not cache. It can also be made shared between multiple easy handles using the share interface. CURL_LOCK_DATA_DNS Cached DNS hosts are shared across the easy handles using this shared object. Mar 18, 2024 · When we use the cURL command, we must note that cURL is only an HTTP client, and it doesn’t cache any request on the client-side. The documentation says: "Typically this means asking for both IPv4 and IPv6 addresses and there may be a whole set of those returned to libcurl. 1. Mar 19, 2013 · According to RFC 7234 - Hypertext Transfer Protocol (HTTP/1. libcurl tries its hardest to, by default, support the multi-threaded programming paradigm. The caches are kept associated with the CURL or CURLM handles, depending on which libcurl API is used, easy or multi. Oct 22, 2016 · The maintainer of curl/libcurl (https://stackoverflow. 5. h> CURLcode curl_easy_setopt (CURL *handle, CURLOPT_DNS_SERVERS, char *servers); Description Pass a char pointer that is the list of DNS servers to be used instead of the system default. com How can I ask curl to send a fresh request to not use the cache? Note: I am Jan 8, 2002 · Recently I've added a DNS cache to libcURL which will cache DNS lookups on a per-process basis, with a few exceptions/special cases also supported. Descriptions and uses for these constants are described within the curl_setopt (), curl_multi_setopt () and curl_getinfo () documentation. We help you work out your issues, debug your libcurl applications, use the API, port to new platforms, add new features and more. We rather quickly realized that having a global cache without locking was error-prone and not really advisable, so already in March 2004 we added comments in the header … Continue reading no more global dns cache in curl → I have curl installed on my ubuntu instance. May 13, 2025 · cURL: Selecting a custom DNS server to resolve domain names - curl_custom_dns. Mar 15, 2019 · The CURL_LOCK_DATA_DNS share option allows to cache DNS queries between easy handles. May 13, 2020 · I'm using curl for a while now to debug my non-prod web services. no-cache The "no-cache" request directive indicates that Oct 18, 2019 · Buy commercial curl support from WolfSSL. conf so the content of /etc/hosts will have priority over DNS queries for a given name. 62. Can any one let me know location of curl dns cache file as well the location of global cache dns file. 16 8. se> Date: Thu, 3 Aug 2023 13:26:33 -0400 hi, I am debugging an issue and need to better understand how the dns cache works. 描述传递一个long类型参数，这会设置超时时间(以秒为单位)。名称解析将保存在内存中，并使用此秒数。设置为0将完全禁用缓存，或设置为-1使缓存的 When Curl relies on the system DNS resolver (for example, when not using DNS Over HTTPS), DNS entries will be cached by the system DNS resolver too — this is the ideal way to cache DNS entries because it provides standard mechanisms to flush DNS, and is compatible with other applications that can make use of a DNS cache too. Predefined Constants ¶ The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime. 4. example. Since the addresses returned are randomly reordered, the order is not in accordance with RFC 3484 or any other deterministic order that may be generated by the system's name resolution Jun 7, 2024 · 在使用 libcurl 进行网络通信时，一个隐蔽的 bug 是由于 DNS 缓存导致的域名解析延迟。当程序重复使用相同的域名进行网络请求时，libcurl 可能会缓存 DNS 解析结果，导致后续请求的域名解析延迟增加，影响程序的性能和响应时间。 NAME CURLOPT_DNS_CACHE_TIMEOUT - life-time for DNS cache entries SYNOPSIS #include <curl/curl. CURL_LOCK_DATA_SSL_SESSION SSL sessions are shared across the easy handles using this shared object. haxx. Jul 18, 2003 · While in the process of tracking another bug (possibly not in libcurl), I ran into a problem with disabling the DNS cache on Windows XP (using CURLOPT_DNS_CACHE_TIMEOUT). Name resolve results are kept in memory and used for this number of seconds. When I'm using the --dns-servers option, I always receive an error that this feature was not found: curl --dns-servers The DNS cache is kept within the easy handle when curl_easy_perform is used, or within the multi handle when the multi interface is used. h> 2 3CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DNS_CACHE_TIMEOUT, long age); 三. Set to zero to completely disable caching, or set DNS entries have a "TTL" property but libcurl does not use that. Apr 18, 2023 · On the contrary, curl asks the OS to do the name resolution by default, and in turn the OS can take various sources to resolve name. The HTTP Cache-Control header is only available in HTTP 1. When talking HTTPS, this sends SNI for the name in the URL and curl verifies the server's response to make sure it serves for the name in the URL. , hashed wheel timer or ebtree) 3) alow to inject a custom DNS cache implementation Best --resolve inserts the address into curl's DNS cache, so it effectively makes curl believe that is the address it got when it resolved the name. 1): Caching and 5. com/users/93747/daniel-stenberg) stated in Libcurl Hostname was NOT found in DNS cache: The texts about not found in the DNS cache is just junk and is removed in a future version If the enable value is 1, it tells curl to use a global DNS cache that survives between easy handle creations and deletions. curl is powered by libcurl for all transfer Aug 8, 2015 · I would expect cUrl DNS cache to be updated with the new entry. I'm playing with CURL shared interface and shared DNS cache and it seems to work pretty well but I don't understand what is the correct way to set DNS cache timeout? DNS cache timeout is set on CURL easy handle but the cache is shared. One of these is 5. You can change the time it'll hold entries in the cache - it is only meant to aid "spikes" or rapid requests to the same host names as it doesn't get the "true" TTL values. se Sep 5, 2014 · libcurl uses its DNS cache by default as long as you re-use the handle. The system supports synchronous resolution, asynchronous resolution via c-ares, threaded resolution, and DNS-over-HTTPS (DoH). Dig itself isn't a nameserver, it is simply a tool that passes your query on to whichever nameservers you have configured, using standard DNS requests. But you can use CURLOPT_DNS_CACHE_TIMEOUT Pass a long, this sets the timeout in seconds. 2. . I am attempting to use curl's --resolve option to connect to the specified IP address when performing the HTTP request, but curl keeps reverting back to the IP address as retrieved by my local DNS cache/resolver. Therefore, by default having a global dns cache is hard, simply because, cURL, as it is now, has no concept of Aug 3, 2023 · From: Babacar Ndiaye via curl-library <curl-library_at_lists. A name resolve can easily take several hundred milliseconds and sometimes even much longer. curl_easy_setopt (handle, CURLOPT_DNS_USE_GLOBAL_CACHE, 1); or do I have to use additionally a share handle? What does the DNS cache do if it cannot resolve a domain name again and again? Does it remember that this domain is not resolveable? Is there some way to look at the DNS cache, or some entry of it? thanks for your help Mathias Received Mar 25, 2021 · 1) allow disabling DNS cache at all (I mean not just invalidation, but also addition and lookups) 2) allow configuring the initial size of the hash table used by the DNS cache 3) use a better data structure to handle the lifetime of many cache entries (e. When libcurl resolves a hostname to one or more IP addresses, that is stored in the DNS cache so that subsequent transfers in the near term do not have to redo the same resolve again. See also this mailing list discussion: How to use DNS cache in curl (1/2) How to use DNS cache in curl (2/2) [1]: which is BTW considered as evil by libcurl's TODO: Anything global is silly, and we already offer the share interface for the same functionality but done "right". Since version 8. 1, and for backward compatibility with systems that are still using HTTP 1. That set of addresses is then tried until one works, or it Name CURLOPT_DNS_USE_GLOBAL_CACHE - global DNS cache Synopsis #include <curl/curl. Therefore, any caching while using this command happens on the server-side. 101,3. Do not use. 5. Does it make sense to install some OS-wise DNS cache package to cache a single request? IP address of the service might infrequently change, so hardcoding the ip in /etc/hosts is probably not a good idea. This DNS cache timeout is entirely speculative that a name resolves to the same address for a small amount of time into the future. 0. life-time for DNS cache entriesCURLOPT_DNS_CACHE_TIMEOUT - Man Page life-time for DNS cache entries Synopsis #include <curl/curl. 0, libcurl prunes entries from the DNS cache if it exceeds 30,000 entries no matter which timeout value is used. sh Sep 27, 2025 · curl's DNS resolution system provides a unified interface for hostname resolution across multiple backends while maintaining a shared DNS cache for performance. Note that when you use the multi interface, all easy handles added to the same multi handle share the DNS cache by default without using this option. 100,192. CURL_LOCK_DATA_SSL_SESSION - the SSL session ID cache is where libcurl store resume information for SSL connections to be able to resume a previous connection faster. All transfers set to use it would share and use the same global cache. 名称CURLOPT_DNS_CACHE_TIMEOUT - 设置DNS缓存条目的生存时间 二. It is not possible to manually clean DNS cache from PHP. To bypass the server-side cache, you can use the Cache-Control HTTP header to control the caching behavior. Doesn't stop layers below caching unless it's coded to obey the headers. I think I need to work toward a local DNS cache but for now is there anything I can do to limit the bad DNS responses or DNS timeouts with curl? I was thinking, does CURLOPT_DNS_CACHE_TIMEOUT cache bad responses too? Feb 14, 2020 · 一. Name resolves will be kept in memory and used for this number of seconds. Caches and state When libcurl is used for Internet transfers, it stores data in caches and state storage in order to do subsequent transfers faster and better. To bypass the server-side cache, we can try some tweaks on the HTTP request we’re sending. 6 The Sep 1, 2020 · Buy commercial curl support from WolfSSL. 0, you can use the 'Pragma: no-cache Name curl - transfer a URL Synopsis curl [options / URLs] Description curl is a tool for transferring data from or to a server using URLs. With a team lead by the curl founder himself. Cache-Control The "Cache-Control" header field is used to specify directives for caches along the request/response chain. Set to zero to completely disable caching, or set to -1 to make the cached entries Jan 15, 2014 · There is no mechanism in the DNS protocol to force a nameserver to respond without using its cache. Set to zero to completely disable caching, or set to -1 to make the cached entries remain forever. DNS cache When libcurl resolves the IP addresses of a hostname it stores the result in its DNS cache (with a default Is there a way to tell cURL command not to use server's side cache? e. Pass a long. Apr 11, 2019 · In January 2002, we added support for a global DNS cache in libcurl. h> CURLcode curl_easy_setopt (CURL *handle, CURLOPT_DNS_USE_GLOBAL_CACHE, long enable); Description Has no function since 7. This is not thread-safe and this CURL_LOCK_DATA_DNS - the DNS cache is where libcurl stores addresses for resolved hostnames for a while to make subsequent lookups faster. Name CURLOPT_DNS_SERVERS - DNS servers to use Synopsis #include <curl/curl. Request Cache-Control Directives defines several directives to control the use of caches for a response. 1. If the enable value is 1, it tells curl to use a global DNS cache that survives between easy handle creations and deletions. It supports these protocols: DICT, FILE, FTP, FTPS, GOPHER, GOPHERS, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, MQTT, POP3, POP3S, RTMP, RTMPS, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TELNET, TFTP, WS and WSS. See full list on curl. Jul 23, 2014 · At the moment my implementation uses separate local DNS cache for every CURL easy handle. By default, libcurl caches this info for 60 seconds. The format of the dns servers option is: host[:port][,host[:port]] For example: 192. h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DNS_CACHE_TIMEOUT, long age); DESCRIPTION Pass a long, this sets the timeout in seconds. f5kn alg6 ovf7qv lseeu9t ox95 qbx s0zga0 je0b 0lqf0 33ld3