The nslookup function is similar to nsl but works on all platforms and can resolve ipv6 addresses if supported by the OS. Default behavior raises an error if lookup fails. The has_internet function tests the internet connection by resolving a random address.
Parse response header data as returned by curl_fetch If the request has followed redirects, the data can contain multiple sets of headers. Therefore when multiple = TRUE, the function returns a list with the response headers for each request. By default it only returns the headers of the final request.
handle
(Package: curl) :
Create and configure a curl handle
Handles are the work horses of libcurl. A handle is used to configure a request with custom options, headers and payload. Once the handle has been set up, it can be passed to any of the download functions such as curl ,curl_download or curl_fetch_memory. The handle will maintain state in between requests, including keep-alive connections, cookies and settings.
Libcurl implementation of C_download (the "internal" download method) with added support for https, ftps, gzip, etc. Default behavior is identical to download.file, but request can be fully configured by passing a custom handle.
Low-level bindings to write data from a URL into memory, disk or a callback function. These are mainly intended for httr, most users will be better off using the curl or curl_download function, or the http specific wrappers in the httr package.
Can be used to parse dates appearing in http response headers such as Expires or Last-Modified. Automatically recognizes most common formats. If the format is known, strptime might be easier.
providing 
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