local curl = require'libcurl'

libcurl is a client-side URL transfer library, supporting DICT, FILE, FTP, FTPS, Gopher, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, Telnet and TFTP. libcurl supports SSL certificates, HTTP POST, HTTP PUT, FTP uploading, HTTP form based upload, proxies, cookies, user+password authentication (Basic, Digest, NTLM, Negotiate, Kerberos), file transfer resume, http proxy tunneling and more!

API

easy interface
curl.easy(url | {opt=val}) -> etr	create an easy transfer
etr:set(opt,val | {opt=val}) -> etr	set option(s)
etr:perform() -> etr | nil,err,ecode	perform the transfer
etr:close()	close the transfer
etr:clone([url | {opt=val}]) -> etr	clone a transfer
etr:reset([{opt=val}]) -> etr	reset all options to their default values
etr:info(opt) -> val	get info about the transfer
etr:recv(buf, bufsize) -> n | nil,err,errcode	receive raw data
etr:send(buf, bufsize) -> n | nil,err,errcode	send raw data
etr:escape(s) -> s|nil	escape URL
etr:unescape(s) -> s|nil	unescape URL
etr:pause([flags])	pause transfer
multi interface
curl.multi([{opt=val}]) -> mtr	create a multi transfer
mtr:set(opt,val | {opt=val}) -> mtr	set option(s)
mtr:add(etr) -> mtr	add an easy transfer to the queue
mtr:remove(etr) -> mtr	remove an easy transfer to the queue
mtr:perform() -> transfers_left | nil,err,ecode	start/keep transfering
mtr:close()	close the transfer
mtr:wait([timeout_seconds], [extra_fds, extra_nfds]) -> numfds | nil,err,errcode	poll on all handles
mtr:fdset(read_fd_set, write_fd_set, exc_fd_set) -> max_fd | nil,err,errcode	get file descriptors
mtr:timeout() -> seconds | nil	how long to wait for socket actions
mtr:info_read() -> CURLMsg*|nil, msgs_in_queue	read multi stack info
mtr:socket_action()	read/write available data given an action
mtr:assign(sockfd, p) -> mtr	set data to associate with an internal socket
share interface
curl.share([{opt=val}]) -> shr	create a share object
shr:set(opt,val | {opt=val}) -> shr	set option(s)
shr:free()	free the share object
multipart forms
etr:mime() -> mime	create a mime object
mime:free()	free a mime object
mime:part() -> mimepart	add a mime part to a mime object
mimepart:name(name)	set mime part’s name
mimepart:filename(filename)	set mime part’s filename
mimepart:type(mimetype)	set mime part’s content type
mimepart:encoder(encoder)	set mime part’s transfer encoding
mimepart:data(s[, sz])	get mime part’s data from string or cdata buffer
mimepart:file(file)	get mime part’s data from file
mimepart:data_cb(sz, read, seek, free, arg)	get mime part’s data with callbacks
mimepart:subparts({mime1,...})	set mime part’s subparts
mimepart:headers({header=value})	set mime part’s headers
misc.
curl.C	the libcurl ffi clib object/namespace
curl.init([opt])	global init
curl.init{malloc=,free=,realloc=...}	global init with custom allocators
curl.free()	global cleanup
curl.version() -> s	get version info as a string
curl.version_info([ver]) -> t	get detailed version info as a table
curl.checkver(maj[, min[, patch]]) -> true|false	check if CURL version is >= maj.min.patch
curl.getdate(s) -> timestamp	parse a date/time to a Unix timestamp
curl.easy.strerror(errcode) -> errmsg	look-up an easy interface error code
curl.multi.strerror(errcode) -> errmsg	look-up a multi interface error code
curl.share.strerror(errcode) -> errmsg	look-up a share interface error code
curl.type(x) -> 'easy'|'multi'|'share'|nil	get curl object type

Easy vs multi interface

The easy interface is synchronous while the multi interface can do multiple transfers asynchronously. A multi transfer is set up as a list of easy transfers.

Easy interface

curl.easy(url | {opt=val}) -> etr

Create a transfer using the easy interface. Options are below (they also go for etr:set()). All options are assumed immutable and the option values are anchored internally for the lifetime of the transfer object.

How option values are converted:

• long options can be given as Lua numbers.
• char* options can be given as Lua strings (anchored).
• off_t options can be given as Lua numbers (no need for the _long suffix).
• Enum options can be given as strings (case-insensitive, no prefix).
• Bitmask options can be given as tables of form {mask_name = true|false} (again, the mask name follows the C name but case-insensitive and without the prefix).
• curl_slist options can be given as lists of strings (anchored).
• Callbacks can be given as Lua functions (anchored). The ffi callback objects are freed on etr:free() (*).

(*) Callback objects are ref-counted which means that replacing them on cloned transfers does not result in double-frees, and freeing them is deterministic, which is important since their number is hard-limited.

Main options
url	URL to work on.
curlu	set URL with CURLU object
protocols	Allowed protocols.
redir_protocols	Protocols to allow redirects to.
default_protocol	Default protocol.
port	Port number to connect to.
range	Request range: “X-Y,N-M,…”.
resume_from	Resume transfer from offset.
header	Include the header in the body output.
maxfilesize	Max. file size to get.
upload	Enable data upload.
infilesize	Size of file to send.
timecondition	Make a time-conditional request.
timevalue	Timestamp for conditional request.
Progress Tracking
noprogress	Shut off the progress meter.
progressfunction	Callback for progress meter.
progressdata	Data pointer to pass to the progress meter callback.
xferinfofunction	Callback for progress meter.
xferinfodata	Data pointer to pass to the progress meter callback.
Error Handling
verbose	Display verbose information.
stderr	stderr replacement stream.
errorbuffer	Error message buffer.
failonerror	Fail on HTTP 4xx errors.
Proxies
proxy	Proxy to use.
proxyport	Proxy port to use.
proxytype	Proxy type.
noproxy	Filter out hosts from proxy use.
httpproxytunnel	Tunnel through the HTTP proxy.
socks5_gssapi_service	Socks5 GSSAPI service name.
socks5_gssapi_nec	Socks5 GSSAPI NEC mode.
socks5_auth	set allowed methods for SOCKS5 proxy authentication
proxy_service_name	Proxy service name.
proxy_cainfo	path to proxy Certificate Authority (CA) bundle
proxy_capath	directory holding proxy CA certificates
proxy_ssl_verifypeer	verify the proxy’s SSL certificate
proxy_ssl_verifyhost	verify the proxy certificate’s name against host
proxy_sslversion	set preferred proxy TLS/SSL version
proxy_tlsauth_username	user name to use for proxy TLS authentication
proxy_tlsauth_password	password to use for proxy TLS authentication
proxy_tlsauth_type	set proxy TLS authentication methods
proxy_sslcert	set SSL proxy client certificate
proxy_sslcerttype	specify type of the proxy client SSL certificate
proxy_sslkey	specify private keyfile for TLS and SSL proxy client cert
proxy_sslkeytype	set type of the proxy private key file
proxy_keypasswd	set passphrase to proxy private key
proxy_ssl_cipher_list	specify ciphers to use for proxy TLS
proxy_crlfile	specify a proxy Certificate Revocation List file
proxy_ssl_options	set proxy SSL behavior options
pre_proxy	set pre-proxy to use
proxy_pinnedpublickey	set pinned public key for https proxy
suppress_connect_headers	Suppress proxy CONNECT response headers from user callbacks
haproxyprotocol	send HAProxy PROXY protocol v1 header
proxy_tls13_ciphers	Ciphers suites for proxy TLS 1.3
I/O Callbacks
writefunction	Callback for writing data.
writedata	Data pointer to pass to the write callback.
readfunction	Callback for reading data.
readdata	Data pointer to pass to the read callback.
seekfunction	Callback for seek operations.
seekdata	Data pointer to pass to the seek callback.
Speed Limits
low_speed_limit	Low speed limit to abort transfer.
low_speed_time	Time to be below the speed to trigger low speed abort.
max_send_speed	Cap the upload speed.
max_recv_speed	Cap the download speed.
Authentication
netrc	Enable .netrc parsing.
netrc_file	.netrc file name.
userpwd	User name and password.
proxyuserpwd	Proxy user name and password.
username	User name.
password	Password.
login_options	Login options.
proxyusername	Proxy user name.
proxypassword	Proxy password.
httpauth	HTTP server authentication methods.
tlsauth_username	TLS authentication user name.
tlsauth_password	TLS authentication password.
tlsauth_type	TLS authentication methods.
proxyauth	HTTP proxy authentication methods.
sasl_ir	Enable SASL initial response.
xoauth2_bearer	OAuth2 bearer token.
sasl_authzid	Authorisation identity (identity to act as)
HTTP Protocol
autoreferer	Automatically set Referer: header.
accept_encoding	Accept-Encoding and automatic decompressing data.
transfer_encoding	Request Transfer-Encoding.
followlocation	Follow HTTP redirects.
unrestricted_auth	Do not restrict authentication to original host.
maxredirs	Maximum number of redirects to follow.
postredir	How to act on redirects after POST.
put	Issue a HTTP PUT request.
post	Issue a HTTP POST request.
httpget	Do a HTTP GET request.
postfields	Send a POST with this data.
postfieldsize	The POST data is this big.
copypostfields	Send a POST with this data - and copy it.
httppost	Multipart formpost HTTP POST.
referer	Referer: header.
useragent	User-Agent: header.
httpheader	Custom HTTP headers.
headeropt	Control custom headers.
proxyheader	Custom HTTP headers sent to proxy.
http200aliases	Alternative versions of 200 OK.
cookie	Cookie(s) to send.
cookiefile	File to read cookies from.
cookiejar	File to write cookies to.
cookiesession	Start a new cookie session.
cookielist	Add or control cookies.
http_version	HTTP version to use.
ignore_content_length	Ignore Content-Length.
http_content_decoding	Disable Content decoding.
http_transfer_decoding	Disable Transfer decoding.
expect_100_timeout_ms	100-continue timeout in ms.
pipewait	Wait on connection to pipeline on it.
keep_sending_on_error	Keep sending on early HTTP response >= 300
request_target	Specify an alternative target for this request
mimepost	Set post/send data from mime structure
disallow_username_in_url	Disallow specifying username in the url
trailerfunction	Set callback for sending trailing headers
trailerdata	Custom pointer passed to the trailing headers callback
http09_allowed	Allow HTTP/0.9 response
HTTP/2 Protocol
stream_weight	Set numerical stream weight
stream_depends	Set stream this transfer depends on
stream_depends_e	Set stream this transfer depends on exclusively
Connection
interface	Bind connection locally to this.
localport	Bind connection locally to this port.
localportrange	Bind connection locally to port range.
tcp_nodelay	Disable the Nagle algorithm.
tcp_keepalive	Enable TCP keep-alive.
tcp_keepidle	Idle time before sending keep-alive.
tcp_keepintvl	Interval between keep-alive probes.
tcp_fastopen	enable TCP Fast Open
address_scope	IPv6 scope for local addresses.
unix_socket_path	Path to a Unix domain socket.
abstract_unix_socket	Set an abstract Unix domain socket
dns_interface	Bind name resolves to an interface.
dns_cache_timeout	Timeout for DNS cache.
dns_local_ip4	Bind name resolves to an IP4 address.
dns_local_ip6	Bind name resolves to an IP6 address.
dns_servers	Preferred DNS servers.
dns_use_global_cache	OBSOLETE Enable global DNS cache.
timeout	Timeout for the entire request in seconds.
timeout_ms	Timeout for the entire request in ms.
connecttimeout	Timeout for the connection phase in seconds.
connecttimeout_ms	Timeout for the connection phase in ms.
accepttimeout_ms	Timeout for a connection be accepted.
server_response_timeout
fresh_connect	Use a new connection.
forbid_reuse	Prevent subsequent connections from re-using this connection.
connect_only	Only connect, nothing else.
resolve	Provide fixed/fake name resolves.
conv_from_network_function	Callback for code base conversion.
conv_to_network_function	Callback for code base conversion.
conv_from_utf8_function	Callback for code base conversion.
opensocketfunction
opensocketdata
closesocketfunction
closesocketdata
sockoptfunction	Callback for sockopt operations.
sockoptdata	Data pointer to pass to the sockopt callback.
connect_to	Connect to a specific host and port instead of the URL’s host and port
happy_eyeballs_timeout_ms	Head start for ipv6 for happy eyeballs
resolver_start_function	Set callback to be called before a new resolve request is started
resolver_start_data	Custom pointer passed to the resolver start callback
dns_shuffle_addresses	Shuffle addresses when a hostname returns more than one
doh_url	Provide the DNS-over-HTTPS URL
upkeep_interval_ms	Connection upkeep interval
maxage_conn	Max idle time allowed for reusing a connection
SSH Protocol
ssh_auth_types	SSH authentication types.
ssh_public_keyfile	File name of public key.
ssh_private_keyfile	File name of private key.
ssh_knownhosts	File name with known hosts.
ssh_keyfunction	Callback for known hosts handling.
ssh_keydata	Custom pointer to pass to ssh key callback.
ssh_host_public_key_md5	MD5 of host’s public key.
ssh_compression	enables compression / decompression of SSH traffic
SMTP Protocol
mail_from	Address of the sender.
mail_rcpt	Address of the recipients.
mail_auth	Authentication address.
TFTP Protocol
tftp_blksize	TFTP block size.
tftp_no_options	Do not send TFTP options requests.
SSL
use_ssl	Use TLS/SSL.
sslcert	Client cert.
sslversion	SSL version to use.
sslcerttype	Client cert type.
sslkey	Client key.
sslkeytype	Client key type.
keypasswd	Client key password.
sslengine	Use identifier with SSL engine.
sslengine_default	Default SSL engine.
ssl_options	Control SSL behavior.
ssl_falsestart	Enable TLS False Start.
ssl_cipher_list	Ciphers to use.
ssl_verifyhost	Verify the host name in the SSL certificate.
ssl_verifypeer	Verify the SSL certificate.
ssl_verifystatus	Verify the SSL certificate’s status.
ssl_ctx_function	Callback for SSL context logic.
ssl_ctx_data	Data pointer to pass to the SSL context callback.
ssl_sessionid_cache	Disable SSL session-id cache.
ssl_enable_npn
ssl_enable_alpn
cainfo	CA cert bundle.
capath	Path to CA cert bundle.
crlfile	Certificate Revocation List.
issuercert	Issuer certificate.
certinfo	Extract certificate info.
pinnedpublickey	Set pinned SSL public key.
krblevel	Kerberos security level.
random_file	Provide source for entropy random data.
egdsocket	Identify EGD socket for entropy.
gssapi_delegation	Disable GSS-API delegation.
tls13_ciphers	Specify ciphers suites to use for TLS 1.3
altsvc_ctrl	Control alt-svc behavior
altsvc	Set alt-svc cache file name
FTP Protocol
ftpport	Use active FTP.
quote	Commands to run before transfer.
postquote	Commands to run after transfer.
prequote	Commands to run just before transfer.
append	Append to remote file.
ftp_use_eprt	Use EPTR.
ftp_use_epsv	Use EPSV.
ftp_use_pret	Use PRET.
ftp_create_missing_dirs	Create missing directories on the remote server.
ftp_response_timeout	Timeout for FTP responses.
ftp_alternative_to_user	Alternative to USER.
ftp_skip_pasv_ip	Ignore the IP address in the PASV response.
ftpsslauth	Control how to do TLS.
ftp_ssl_ccc	Back to non-TLS again after authentication.
ftp_account	Send ACCT command.
ftp_filemethod	Specify how to reach files.
transfertext	Use text transfer.
proxy_transfer_mode	Add transfer mode to URL over proxy.
RTSP Protocol
rtsp_request	RTSP request.
rtsp_session_id	RTSP session-id.
rtsp_stream_uri	RTSP stream URI.
rtsp_transport	RTSP Transport:
rtsp_client_cseq	Client CSEQ number.
rtsp_server_cseq	CSEQ number for RTSP Server->Client request.
interleavefunction	Callback for RTSP interleaved data.
interleavedata	Data pointer to pass to the RTSP interleave callback.
Misc. Options
path_as_is	Disable squashing /../ and /./ sequences in the path.
buffersize	Ask for smaller buffer size.
nosignal	Do not install signal handlers.
share	Share object to use.
private	Private pointer to store.
ipresolve	IP version to resolve to.
ioctlfunction	Callback for I/O operations.
ioctldata	Data pointer to pass to the I/O callback.
service_name	SPNEGO service name.
crlf	Convert newlines.
customrequest	Custom request/method.
filetime	Request file modification date and time.
dirlistonly	List only.
nobody	Do not get the body contents.
new_file_perms	Mode for creating new remote files.
new_directory_perms	Mode for creating new remote directories.
chunk_bgn_function	Callback for wildcard download start of chunk.
chunk_end_function	Callback for wildcard download end of chunk.
chunk_data	Data pointer to pass to the chunk callbacks.
fnmatch_function	Callback for wildcard matching.
fnmatch_data	Data pointer to pass to the wildcard matching callback.
wildcardmatch	Transfer multiple files according to a file name pattern.
telnetoptions	TELNET options.
maxconnects	Maximum number of connections in the connection pool.
headerfunction	Callback for writing received headers.
headerdata	Data pointer to pass to the header callback.
upload_buffersize	Set preferred upload buffer size
Debugging
debugfunction	Callback for debug information.
debugdata	Data pointer to pass to the debug callback.

Multi interface

curl.multi([{etr1,..., opt=val}]) -> mtr

Create a transfer using the multi interface. The details are the same as with the easy interface except that the list of options is different (see below). Also, if the options table has any elements in the array part, mtr:add() is called for/with each element.

There’s a section on the libcurl tutorial on how to use the multi interface.

socketfunction	Callback about what to wait for
socketdata	Custom pointer passed to the socket callback
pipelining	enable/disable HTTP pipelining
timerfunction	Set callback to receive timeout values
timerdata	Custom pointer to pass to timer callback
maxconnects	Set size of connection cache
max_host_connections	Set max number of connections to a single host
max_pipeline_length	Maximum number of requests in a pipeline
content_length_penalty_size	Size threshold for pipelining penalty
chunk_length_penalty_size	Chunk length threshold for pipelining
pipelining_site_bl	Pipelining host blacklist (list of strings)
pipelining_server_bl	Pipelining server blacklist (list of strings)
max_total_connections	Max simultaneously open connections
pushfunction	Callback that approves or denies server pushes
pushdata	Pointer to pass to push callback

Share interface

curl.share([{opt=val}]) -> shr

Create a share object. Options below (also for shr:set()):

lockfunc	lock data callback
unlockfunc	unlock data callback
share	what tyoe of data to share
unshare	what type of data not to share
userdata	pointer to pass to lock and unlock functions

Binaries

The included libcurl binaries are compiled to use the SSL/TLS APIs provided by the host OS by default but can also use luapower’s openssl as SSL backend provided libcurl is initalized manually with curl.init{sslbackend='openssl'}.

The decision to ship OpenSSL even on Linux is because OpenSSL is not ABI-compatible between versions and distros don’t usually ship multiple versions of it (sigh, Linux).

DNS resolving is asynchronous using the multi-threaded resolver.

Features that were not compiled in:

• SFTP and SCP (requires libssh2).
• HTTP2 (requires ng-http2).
• IDN (requires libidn).
• RTMP (requires librtmp).
• PSL (requires libpsl).
• LDAP.

Last updated: 19 months ago | Edit on GitHub