Package 'curl'

Curl connection interface

Description

Drop-in replacement for base url() that supports https, ftps, gzip, deflate, etc. Default behavior is identical to url(), but request can be fully configured by passing a custom handle().

Usage

curl(url = "https://hb.cran.dev/get", open = "", handle = new_handle())

Arguments

url	character string. See examples.
open	character string. How to open the connection if it should be opened initially. Currently only "r" and "rb" are supported.
handle	a curl handle object

Details

As of version 2.3 curl connections support open(con, blocking = FALSE). In this case readBin and readLines will return immediately with data that is available without waiting. For such non-blocking connections the caller needs to call isIncomplete() to check if the download has completed yet.

Examples

## Not run: 
con <- curl("https://hb.cran.dev/get")
readLines(con)

# Auto-opened connections can be recycled
open(con, "rb")
bin <- readBin(con, raw(), 999)
close(con)
rawToChar(bin)

# HTTP error
curl("https://hb.cran.dev/status/418", "r")

# Follow redirects
readLines(curl("https://hb.cran.dev/redirect/3"))

# Error after redirect
curl("https://hb.cran.dev/redirect-to?url=https://hb.cran.dev/status/418", "r")

# Auto decompress Accept-Encoding: gzip / deflate (rfc2616 #14.3)
readLines(curl("https://hb.cran.dev/gzip"))
readLines(curl("https://hb.cran.dev/deflate"))

# Binary support
buf <- readBin(curl("https://hb.cran.dev/bytes/98765", "rb"), raw(), 1e5)
length(buf)

# Read file from disk
test <- paste0("file://", system.file("DESCRIPTION"))
readLines(curl(test))

# Other protocols
read.csv(curl("ftp://cran.r-project.org/pub/R/CRAN_mirrors.csv"))
readLines(curl("ftps://test.rebex.net:990/readme.txt"))
readLines(curl("gopher://quux.org/1"))

# Streaming data
con <- curl("http://jeroen.github.io/data/diamonds.json", "r")
while(length(x <- readLines(con, n = 5))){
  print(x)
}

# Stream large dataset over https with gzip
library(jsonlite)
con <- gzcon(curl("https://jeroen.github.io/data/nycflights13.json.gz"))
nycflights <- stream_in(con)

## End(Not run)

---

Download file to disk

Description

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().

Usage

curl_download(url, destfile, quiet = TRUE, mode = "wb", handle = new_handle())

Arguments

url	A character string naming the URL of a resource to be downloaded.
destfile	A character string with the name where the downloaded file is saved. Tilde-expansion is performed.
quiet	If TRUE, suppress status messages (if any), and the progress bar.
mode	A character string specifying the mode with which to write the file. Useful values are "w", "wb" (binary), "a" (append) and "ab".
handle	a curl handle object

Details

The main difference between curl_download and curl_fetch_disk is that curl_download checks the http status code before starting the download, and raises an error when status is non-successful. The behavior of curl_fetch_disk on the other hand is to proceed as normal and write the error page to disk in case of a non success response.

The curl_download function does support resuming and removes the temporary file if the download did not complete successfully. For a more advanced download interface which supports concurrent requests and resuming large files, have a look at the multi_download function.

Value

Path of downloaded file (invisibly).

See Also

Advanced download interface: multi_download

Examples

# Download large file
## Not run: 
url <- "http://www2.census.gov/acs2011_5yr/pums/csv_pus.zip"
tmp <- tempfile()
curl_download(url, tmp)

## End(Not run)

---

Echo Service

Description

This function is only for testing purposes. It starts a local httpuv server to echo the request body and content type in the response.

Usage

curl_echo(handle, port = find_port(), progress = interactive(), file = NULL)

find_port(range = NULL)

Arguments

handle	a curl handle object
port	the port number on which to run httpuv server
progress	show progress meter during http transfer
file	path or connection to write body. Default returns body as raw vector.
range	optional integer vector of ports to consider

Examples

if(require('httpuv')){
h <- new_handle(url = 'https://hb.cran.dev/post')
handle_setform(h, foo = "blabla", bar = charToRaw("test"),
  myfile = form_file(system.file("DESCRIPTION"), "text/description"))

# Echo the POST request data
formdata <- curl_echo(h)

# Show the multipart body
cat(rawToChar(formdata$body))

# Parse multipart
webutils::parse_http(formdata$body, formdata$content_type)
}

---

URL encoding

Description

Escape all special characters (i.e. everything except for a-z, A-Z, 0-9, '-', '.', '_' or '~') for use in URLs.

Usage

curl_escape(url)

curl_unescape(url)

Arguments

url	A character vector (typically containing urls or parameters) to be encoded/decoded

Examples

# Escape strings
out <- curl_escape("foo = bar + 5")
curl_unescape(out)

# All non-ascii characters are encoded
mu <- "\u00b5"
curl_escape(mu)
curl_unescape(curl_escape(mu))

---

Fetch the contents of a URL

Description

Low-level bindings to write data from a URL into memory, disk or a callback function.

Usage

curl_fetch_memory(url, handle = new_handle())

curl_fetch_disk(url, path, handle = new_handle())

curl_fetch_stream(url, fun, handle = new_handle())

curl_fetch_multi(
  url,
  done = NULL,
  fail = NULL,
  pool = NULL,
  data = NULL,
  handle = new_handle()
)

curl_fetch_echo(url, handle = new_handle())

Arguments

url	A character string naming the URL of a resource to be downloaded.
handle	A curl handle object.
path	Path to save results
fun	Callback function. Should have one argument, which will be a raw vector.
done	callback function for completed request. Single argument with response data in same structure as curl_fetch_memory.
fail	callback function called on failed request. Argument contains error message.
pool	a multi handle created by new_pool. Default uses a global pool.
data	(advanced) callback function, file path, or connection object for writing incoming data. This callback should only be used for streaming applications, where small pieces of incoming data get written before the request has completed. The signature for the callback function is write(data, final = FALSE). If set to NULL the entire response gets buffered internally and returned by in the done callback (which is usually what you want).

Details

The ⁠curl_fetch_*()⁠ functions automatically raise an error upon protocol problems (network, disk, TLS, etc.) but do not implement application logic. For example, you need to check the status code of HTTP requests in the response by yourself, and deal with it accordingly.

Both curl_fetch_memory() and curl_fetch_disk have a blocking and a non-blocking C implementation. The latter is slightly slower but allows for interrupting the download prematurely (using e.g. CTRL+C or ESC). Interrupting is enabled when R runs in interactive mode or when getOption("curl_interrupt") == TRUE.

The curl_fetch_multi() function is the asynchronous equivalent of curl_fetch_memory(). It wraps multi_add() to schedule requests which are executed concurrently when calling multi_run(). For each successful request, the done callback is triggered with response data. For failed requests (when curl_fetch_memory() would raise an error), the fail function is triggered with the error message.

Examples

# Load in memory
res <- curl_fetch_memory("https://hb.cran.dev/cookies/set?foo=123&bar=ftw")
res$content

# Save to disk
res <- curl_fetch_disk("https://hb.cran.dev/stream/10", tempfile())
res$content
readLines(res$content)

# Stream with callback
drip_url <- "https://hb.cran.dev/drip?duration=3&numbytes=15&code=200"
res <- curl_fetch_stream(drip_url, function(x){
  cat(rawToChar(x))
})

# Async API
data <- list()
success <- function(res){
  cat("Request done! Status:", res$status, "\n")
  data <<- c(data, list(res))
}
failure <- function(msg){
  cat("Oh noes! Request failed!", msg, "\n")
}
curl_fetch_multi("https://hb.cran.dev/get", success, failure)
curl_fetch_multi("https://hb.cran.dev/status/418", success, failure)
curl_fetch_multi("https://urldoesnotexist.xyz", success, failure)
multi_run()
str(data)

---

List curl version and options.

Description

curl_version() shows the versions of libcurl, libssl and zlib and supported protocols. curl_options() lists all options available in the current version of libcurl. The dataset curl_symbols lists all symbols (including options) provides more information about the symbols, including when support was added/removed from libcurl.

Usage

curl_options(filter = "")

curl_symbols(filter = "")

curl_version()

Arguments

filter

string: only return options with string in name

Examples

# Available options
curl_options()

# List proxy options
curl_options("proxy")

# Symbol table
curl_symbols("proxy")
# Curl/ssl version info
curl_version()

---

Normalizing URL parser

Description

Interfaces the libcurl URL parser. URLs are automatically normalized where possible, such as in the case of relative paths or url-encoded queries (see examples). When parsing hyperlinks from a HTML document, it is possible to set baseurl to the location of the document itself such that relative links can be resolved.

Usage

curl_parse_url(url, baseurl = NULL, decode = TRUE, params = TRUE)

Arguments

url	a character string of length one
baseurl	use this as the parent if url may be a relative path
decode	automatically url-decode output. Set to FALSE to get output in url-encoded format.
params	parse individual parameters assuming query is in application/x-www-form-urlencoded format.

Details

A valid URL contains at least a scheme and a host, other pieces are optional. If these are missing, the parser raises an error. Otherwise it returns a list with the following elements:

• url: the normalized input URL

• scheme: the protocol part before the ⁠://⁠ (required)

• host: name of host without port (required)

• port: decimal between 0 and 65535

• path: normalized path up till the ⁠?⁠ of the url

• query: search query: part between the ⁠?⁠ and ⁠#⁠ of the url. Use params below to get individual parameters from the query.

• fragment: the hash part after the ⁠#⁠ of the url

• user: authentication username

• password: authentication password

• params: named vector with parameters from query if set

Each element above is either a string or NULL, except for params which is always a character vector with the length equal to the number of parameters.

Note that the params field is only usable if the query is in the usual application/x-www-form-urlencoded format which is technically not part of the RFC. Some services may use e.g. a json blob as the query, in which case the parsed params field here can be ignored. There is no way for the parser to automatically infer or validate the query format, this is up to the caller.

For more details on the URL format see rfc3986 or the steps explained in the whatwg basic url parser.

On platforms that do not have a recent enough curl version (basically only RHEL-8) the Ada URL library is used as fallback. Results should be identical, though curl has nicer error messages. This is a temporary solution, we plan to remove the fallback when old systems are no longer supported.

Examples

url <- "https://jerry:[email protected]:888/foo/bar?test=123#bla"
curl_parse_url(url)

# Resolve relative links from a baseurl
curl_parse_url("/somelink", baseurl = url)

# Paths get normalized
curl_parse_url("https://foobar.com/foo/bar/../baz/../yolo")$url

# Also normalizes URL-encoding (these URLs are equivalent):
url1 <- "https://ja.wikipedia.org/wiki/\u5bff\u53f8"
url2 <- "https://ja.wikipedia.org/wiki/%e5%af%bf%e5%8f%b8"
curl_parse_url(url1)$path
curl_parse_url(url2)$path
curl_parse_url(url1, decode = FALSE)$path
curl_parse_url(url1, decode = FALSE)$path

---

Upload a File

Description

Upload a file to an ⁠http://⁠, ⁠ftp://⁠, or ⁠sftp://⁠ (ssh) server. Uploading to HTTP means performing an ⁠HTTP PUT⁠ on that URL. Be aware that sftp is only available for libcurl clients built with libssh2.

Usage

curl_upload(file, url, verbose = TRUE, reuse = TRUE, ...)

Arguments

file	connection object or path to an existing file on disk
url	where to upload, should start with e.g. ⁠ftp://⁠
verbose	emit some progress output
reuse	try to keep alive and recycle connections when possible
...	other arguments passed to handle_setopt(), for example a username and password.

Examples

## Not run: # Upload package to winbuilder:
curl_upload('mypkg_1.3.tar.gz', 'ftp://win-builder.r-project.org/R-devel/')

## End(Not run)

---

Lazy File Writer

Description

Generates a closure that writes binary (raw) data to a file.

Usage

file_writer(path, append = FALSE)

Arguments

path	file name or path on disk
append	open file in append mode

Details

The writer function automatically opens the file on the first write and closes when it goes out of scope, or explicitly by setting close = TRUE. This can be used for the data callback in multi_add() or curl_fetch_multi() such that we only keep open file handles for active downloads. This prevents running out of file descriptors when performing thousands of concurrent requests.

Value

Function with signature writer(data = raw(), close = FALSE)

Examples

# Doesn't open yet
tmp <- tempfile()
writer <- file_writer(tmp)

# Now it opens
writer(charToRaw("Hello!\n"))
writer(charToRaw("How are you?\n"))

# Close it!
writer(charToRaw("All done!\n"), close = TRUE)

# Check it worked
readLines(tmp)

---

Create and configure a curl handle

Description

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.

Usage

new_handle(...)

handle_setopt(handle, ..., .list = list())

handle_setheaders(handle, ..., .list = list())

handle_getheaders(handle)

handle_setform(handle, ..., .list = list())

handle_reset(handle)

handle_data(handle)

Arguments

...	named options / headers to be set in the handle. To send a file, see form_file(). To list all allowed options, see curl_options()
handle	Handle to modify
.list	A named list of options. This is useful if you've created a list of options elsewhere, avoiding the use of do.call().

Details

Use new_handle() to create a new clean curl handle that can be configured with custom options and headers. Note that handle_setopt appends or overrides options in the handle, whereas handle_setheaders replaces the entire set of headers with the new ones. The handle_reset function resets only options/headers/forms in the handle. It does not affect active connections, cookies or response data from previous requests. The safest way to perform multiple independent requests is by using a separate handle for each request. There is very little performance overhead in creating handles.

Value

A handle object (external pointer to the underlying curl handle). All functions modify the handle in place but also return the handle so you can create a pipeline of operations.

See Also

Other handles: handle_cookies()

Examples

h <- new_handle()
handle_setopt(h, customrequest = "PUT")
handle_setform(h, a = "1", b = "2")
r <- curl_fetch_memory("https://hb.cran.dev/put", h)
cat(rawToChar(r$content))

# Or use the list form
h <- new_handle()
handle_setopt(h, .list = list(customrequest = "PUT"))
handle_setform(h, .list = list(a = "1", b = "2"))
r <- curl_fetch_memory("https://hb.cran.dev/put", h)
cat(rawToChar(r$content))

---

Extract cookies from a handle

Description

The handle_cookies function returns a data frame with 7 columns as specified in the netscape cookie file format.

Usage

handle_cookies(handle)

Arguments

handle

a curl handle object

See Also

Other handles: handle

Examples

h <- new_handle()
handle_cookies(h)

# Server sets cookies
req <- curl_fetch_memory("https://hb.cran.dev/cookies/set?foo=123&bar=ftw", handle = h)
handle_cookies(h)

# Server deletes cookies
req <- curl_fetch_memory("https://hb.cran.dev/cookies/delete?foo", handle = h)
handle_cookies(h)

# Cookies will survive a reset!
handle_reset(h)
handle_cookies(h)

---

Internet Explorer proxy settings

Description

Lookup and mimic the system proxy settings on Windows as set by Internet Explorer. This can be used to configure curl to use the same proxy server.

Usage

ie_proxy_info()

ie_get_proxy_for_url(target_url = "http://www.google.com")

Arguments

target_url

url with host for which to lookup the proxy server

Details

The ie_proxy_info function looks up your current proxy settings as configured in IE under "Internet Options" under "LAN Settings". The ie_get_proxy_for_url determines if and which proxy should be used to connect to a particular URL. If your settings have an "automatic configuration script" this involves downloading and executing a PAC file, which can take a while.

---

Async Concurrent Requests

Description

AJAX style concurrent requests, possibly using HTTP/2 multiplexing. Results are only available via callback functions. Advanced use only! For downloading many files in parallel use multi_download instead.

Usage

multi_add(handle, done = NULL, fail = NULL, data = NULL, pool = NULL)

multi_run(timeout = Inf, poll = FALSE, pool = NULL)

multi_set(
  total_con = 50,
  host_con = 6,
  max_streams = 10,
  multiplex = TRUE,
  pool = NULL
)

multi_list(pool = NULL)

multi_cancel(handle)

new_pool(total_con = 100, host_con = 6, multiplex = TRUE)

multi_fdset(pool = NULL)

Arguments

handle	a curl handle with preconfigured url option.
done	callback function for completed request. Single argument with response data in same structure as curl_fetch_memory.
fail	callback function called on failed request. Argument contains error message.
data	(advanced) callback function, file path, or connection object for writing incoming data. This callback should only be used for streaming applications, where small pieces of incoming data get written before the request has completed. The signature for the callback function is write(data, final = FALSE). If set to NULL the entire response gets buffered internally and returned by in the done callback (which is usually what you want).
pool	a multi handle created by new_pool. Default uses a global pool.
timeout	max time in seconds to wait for results. Use 0 to poll for results without waiting at all.
poll	If TRUE then return immediately after any of the requests has completed. May also be an integer in which case it returns after n requests have completed.
total_con	max total concurrent connections.
host_con	max concurrent connections per host.
max_streams	max HTTP/2 concurrent multiplex streams per connection.
multiplex	use HTTP/2 multiplexing if supported by host and client.

Details

Requests are created in the usual way using a curl handle and added to the scheduler with multi_add. This function returns immediately and does not perform the request yet. The user needs to call multi_run which performs all scheduled requests concurrently. It returns when all requests have completed, or case of a timeout or SIGINT (e.g. if the user presses ESC or CTRL+C in the console). In case of the latter, simply call multi_run again to resume pending requests.

When the request succeeded, the done callback gets triggered with the response data. The structure if this data is identical to curl_fetch_memory. When the request fails, the fail callback is triggered with an error message. Note that failure here means something went wrong in performing the request such as a connection failure, it does not check the http status code. Just like curl_fetch_memory, the user has to implement application logic.

Raising an error within a callback function stops execution of that function but does not affect other requests.

A single handle cannot be used for multiple simultaneous requests. However it is possible to add new requests to a pool while it is running, so you can re-use a handle within the callback of a request from that same handle. It is up to the user to make sure the same handle is not used in concurrent requests.

The multi_cancel function can be used to cancel a pending request. It has no effect if the request was already completed or canceled.

The multi_fdset function returns the file descriptors curl is polling currently, and also a timeout parameter, the number of milliseconds an application should wait (at most) before proceeding. It is equivalent to the curl_multi_fdset and curl_multi_timeout calls. It is handy for applications that is expecting input (or writing output) through both curl, and other file descriptors.

See Also

Advanced download interface: multi_download

Examples

results <- list()
success <- function(x){
  results <<- append(results, list(x))
}
failure <- function(str){
  cat(paste("Failed request:", str), file = stderr())
}
# This handle will take longest (3sec)
h1 <- new_handle(url = "https://hb.cran.dev/delay/3")
multi_add(h1, done = success, fail = failure)

# This handle writes data to a file
con <- file("output.txt")
h2 <- new_handle(url = "https://hb.cran.dev/post", postfields = "bla bla")
multi_add(h2, done = success, fail = failure, data = con)

# This handle raises an error
h3 <- new_handle(url = "https://urldoesnotexist.xyz")
multi_add(h3, done = success, fail = failure)

# Actually perform the requests
multi_run(timeout = 2)
multi_run()

# Check the file
readLines("output.txt")
unlink("output.txt")

---

Advanced download interface

Description

Download multiple files concurrently, with support for resuming large files. This function is based on multi_run() and hence does not error in case any of the individual requests fail; you should inspect the return value to find out which of the downloads were completed successfully.

Usage

multi_download(
  urls,
  destfiles = NULL,
  resume = FALSE,
  progress = TRUE,
  multi_timeout = Inf,
  multiplex = FALSE,
  ...
)

Arguments

urls	vector with URLs to download. Alternatively it may also be a list of handle objects that have the url option already set.
destfiles	vector (of equal length as urls) with paths of output files, or NULL to use basename of urls.
resume	if the file already exists, resume the download. Note that this may change server responses, see details.
progress	print download progress information
multi_timeout	in seconds, passed to multi_run
multiplex	passed to new_pool
...	extra handle options passed to each request new_handle

Details

Upon completion of all requests, this function returns a data frame with results. The success column indicates if a request was successfully completed (regardless of the HTTP status code). If it failed, e.g. due to a networking issue, the error message is in the error column. A success value NA indicates that the request was still in progress when the function was interrupted or reached the elapsed multi_timeout and perhaps the download can be resumed if the server supports it.

It is also important to inspect the status_code column to see if any of the requests were successful but had a non-success HTTP code, and hence the downloaded file probably contains an error page instead of the requested content.

Note that when you set resume = TRUE you should expect HTTP-206 or HTTP-416 responses. The latter could indicate that the file was already complete, hence there was no content left to resume from the server. If you try to resume a file download but the server does not support this, success if FALSE and the file will not be touched. In fact, if we request to a download to be resumed and the server responds ⁠HTTP 200⁠ instead of ⁠HTTP 206⁠, libcurl will error and not download anything, because this probably means the server did not respect our range request and is sending us the full file.

About HTTP/2

Availability of HTTP/2 can increase the performance when making many parallel requests to a server, because HTTP/2 can multiplex many requests over a single TCP connection. Support for HTTP/2 depends on the version of libcurl that your system has, and the TLS back-end that is in use, check curl_version. For clients or servers without HTTP/2, curl makes at most 6 connections per host over which it distributes the queued downloads.

On Windows and MacOS you can switch the active TLS backend by setting an environment variable CURL_SSL_BACKEND in your ⁠~/.Renviron⁠ file. On Windows you can switch between SecureChannel (default) and OpenSSL where only the latter supports HTTP/2. On MacOS you can use either SecureTransport or LibreSSL, the default varies by MacOS version.

Value

The function returns a data frame with one row for each downloaded file and the following columns:

• success if the HTTP request was successfully performed, regardless of the response status code. This is FALSE in case of a network error, or in case you tried to resume from a server that did not support this. A value of NA means the download was interrupted while in progress.

• status_code the HTTP status code from the request. A successful download is usually 200 for full requests or 206 for resumed requests. Anything else could indicate that the downloaded file contains an error page instead of the requested content.

• resumefrom the file size before the request, in case a download was resumed.

• url final url (after redirects) of the request.

• destfile downloaded file on disk.

• error if success == FALSE this column contains an error message.

• type the Content-Type response header value.

• modified the Last-Modified response header value.

• time total elapsed download time for this file in seconds.

• headers vector with http response headers for the request.

Examples

## Not run: 
# Example: some large files
urls <- sprintf(
  "https://d37ci6vzurychx.cloudfront.net/trip-data/yellow_tripdata_2021-%02d.parquet", 1:12)
res <- multi_download(urls, resume = TRUE) # You can interrupt (ESC) and resume

# Example: revdep checker
# Download all reverse dependencies for the 'curl' package from CRAN:
pkg <- 'curl'
mirror <- 'https://cloud.r-project.org'
db <- available.packages(repos = mirror)
packages <- c(pkg, tools::package_dependencies(pkg, db = db, reverse = TRUE)[[pkg]])
versions <- db[packages,'Version']
urls <- sprintf("%s/src/contrib/%s_%s.tar.gz", mirror, packages,  versions)
res <- multi_download(urls)
all.equal(unname(tools::md5sum(res$destfile)), unname(db[packages, 'MD5sum']))
# And then you could use e.g.: tools:::check_packages_in_dir()

# Example: URL checker
pkg_url_checker <- function(dir){
  db <- tools:::url_db_from_package_sources(dir)
  res <- multi_download(db$URL, rep('/dev/null', nrow(db)), nobody=TRUE)
  db$OK <- res$status_code == 200
  db
}

# Use a local package source directory
pkg_url_checker(".")


## End(Not run)

---

POST files or data

Description

Build multipart form data elements. The form_file function uploads a file. The form_data function allows for posting a string or raw vector with a custom content-type.

Usage

form_file(path, type = NULL, name = NULL)

form_data(value, type = NULL)

Arguments

path	a string with a path to an existing file on disk
type	MIME content-type of the file.
name	a string with the file name to use for the upload
value	a character or raw vector to post

---

Lookup a hostname

Description

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.

Usage

nslookup(host, ipv4_only = FALSE, multiple = FALSE, error = TRUE)

has_internet()

Arguments

host	a string with a hostname
ipv4_only	always return ipv4 address. Set to FALSE to allow for ipv6 as well.
multiple	returns multiple ip addresses if possible
error	raise an error for failed DNS lookup. Otherwise returns NULL.

Details

The has_internet function tests for internet connectivity by performing a dns lookup. If a proxy server is detected, it will also check for connectivity by connecting via the proxy.

Examples

# Should always work if we are online
nslookup("www.r-project.org")

# If your OS supports IPv6
nslookup("ipv6.test-ipv6.com", ipv4_only = FALSE, error = FALSE)

---

Parse date/time

Description

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.

Usage

parse_date(datestring)

Arguments

datestring

a string consisting of a timestamp

Examples

# Parse dates in many formats
parse_date("Sunday, 06-Nov-94 08:49:37 GMT")
parse_date("06 Nov 1994 08:49:37")
parse_date("20040911 +0200")

---

Parse response headers

Description

Parse response header data as returned by curl_fetch, either as a set of strings or into a named list.

Usage

parse_headers(txt, multiple = FALSE)

parse_headers_list(txt)

Arguments

txt	raw or character vector with the header data
multiple	parse multiple sets of headers separated by a blank line. See details.

Details

The parse_headers_list function parses the headers into a normalized (lowercase field names, trimmed whitespace) named list.

If a request has followed redirects, the data can contain multiple sets of headers. 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.

Examples

req <- curl_fetch_memory("https://hb.cran.dev/redirect/3")
parse_headers(req$headers)
parse_headers(req$headers, multiple = TRUE)

# Parse into named list
parse_headers_list(req$headers)

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Send email

Description

Use the curl SMTP client to send an email. The message argument must be properly formatted RFC2822 email message with From/To/Subject headers and CRLF line breaks.

Usage

send_mail(
  mail_from,
  mail_rcpt,
  message,
  smtp_server = "smtp://localhost",
  use_ssl = c("try", "no", "force"),
  verbose = TRUE,
  ...
)

Arguments

mail_from	email address of the sender.
mail_rcpt	one or more recipient email addresses. Do not include names, these go into the message headers.
message	either a string or connection with (properly formatted) email message, including sender/recipient/subject headers. See example.
smtp_server	hostname or address of the SMTP server, or, an ⁠smtp://⁠ or ⁠smtps://⁠ URL. See "Specifying the server, port, and protocol" below.
use_ssl	Request to upgrade the connection to SSL using the STARTTLS command, see CURLOPT_USE_SSL for details. Default will try to SSL, proceed as normal otherwise.
verbose	print output
...	other options passed to handle_setopt(). In most cases you will need to set a username and password or login_options to authenticate with the SMTP server, see details.

Specifying the server, port, and protocol

The smtp_server argument takes a hostname, or an SMTP URL:

• mail.example.com - hostname only

• mail.example.com:587 - hostname and port

• ⁠smtp://mail.example.com⁠ - protocol and hostname

• ⁠smtp://mail.example.com:587⁠ - full SMTP URL

• ⁠smtps://mail.example.com:465⁠ - full SMTPS URL

By default, the port will be 25, unless ⁠smtps://⁠ is specified–then the default will be 465 instead.

For internet SMTP servers you probably need to pass a username and passwords option. For some servers you also need to pass a string with login_options for example login_options="AUTH=NTLM".

Encrypting connections via SMTPS or STARTTLS

There are two different ways in which SMTP can be encrypted: SMTPS servers run on a port which only accepts encrypted connections, similar to HTTPS. Alternatively, a regular insecure smtp connection can be "upgraded" to a secure TLS connection using the STARTTLS command. It is important to know which method your server expects.

If your smtp server listens on port 465, then use a ⁠smtps://hostname:465⁠ URL. The SMTPS protocol guarantees that TLS will be used to protect all communications from the start.

If your email server listens on port 25 or 587, use an ⁠smtp://⁠ URL in combination with the use_ssl parameter to control if the connection should be upgraded with STARTTLS. The default value "try" will opportunistically try to upgrade to a secure connection if the server supports it, and proceed as normal otherwise.

Examples

## Not run: # Set sender and recipients (email addresses only)
recipients <- readline("Enter your email address to receive test: ")
sender <- '[email protected]'

# Full email message in RFC2822 format
message <- 'From: "R (curl package)" <test@noreply.com>
To: "Roger Recipient" <roger@noreply.com>
Subject: Hello R user!

Dear R user,

I am sending this email using curl.'

# Send the email
send_mail(sender, recipients, message, smtp_server = 'smtps://smtp.gmail.com',
  username = 'curlpackage', password  = 'qyyjddvphjsrbnlm')
## End(Not run)

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