Provided by: nbdkit_1.34.4-1ubuntu1_amd64
NAME
nbdkit-curl-plugin - nbdkit curl plugin (HTTP, FTP and other protocols)
SYNOPSIS
nbdkit -r curl [url=]http://example.com/disk.img
DESCRIPTION
"nbdkit-curl-plugin" is a plugin for nbdkit(1) which turns content served over HTTP, FTP, and more, into a Network Block Device. It uses a library called libcurl (also known as cURL) to read data from URLs. The exact list of protocols that libcurl can handle depends on how it was compiled, but most versions will handle HTTP, HTTPS, FTP, FTPS and more (see: "curl -V"). Note: This plugin supports writes. However for HTTP, you may not want nbdkit to issue PUT requests to the remote server (which probably doesn't understand them). To force nbdkit to use a readonly connection, pass the -r flag. Using the -r flag also enables NBD multi- conn, which usually performs much better (if the client supports it). Although this plugin can access SFTP (ie. SSH) servers, it is much better to use nbdkit-ssh-plugin(1). This plugin can be used to access "file:///" URLs, but you should use nbdkit-file-plugin(1) instead.
EXAMPLE
nbdkit -r curl http://example.com/disk.img serves the remote disk image as NBD on TCP port 10809 (to control ports and protocols used to serve NBD see nbdkit(1)).
PARAMETERS
cainfo=FILENAME (nbdkit ≥ 1.18) Configure CA bundle for libcurl. See CURLOPT_CAINFO(3) for details. Pass empty string in order to not use the default certificate store that libcurl is compiled with. capath=PATH (nbdkit ≥ 1.18) Set CA certificates directory location for libcurl. See CURLOPT_CAPATH(3) for more information. connections=N (nbdkit ≥ 1.34) Open up to "N" curl connections to the web server. The default is 4. Curl connections are shared between all NBD clients, so you may wish to increase this if you expect many simultaneous NBD clients (or a single client using many multi-conn connections). See "NBD CONNECTIONS AND CURL HANDLES" below. cookie=COOKIE cookie=+FILENAME cookie=- cookie=-FD (nbdkit ≥ 1.12) Set a cookie in the request header when connecting to the remote server. A typical example is: cookie='vmware_soap_session="52a01262-bf93-ccce-d379-8dabb3e55560"' This option can be used at most once. It only works for HTTP and HTTPS transports. To set multiple cookies you must concatenate them yourself, eg: cookie='name1=content1; name2=content2' See CURLOPT_COOKIE(3) for more information about this. The format is quite strict and must consist of "key=value", each cookie separated by exactly "; " (semicolon and space). If the cookie is used for authentication then passing it on the command line is not secure on shared machines. Use the alternate "+FILENAME" syntax to pass it in a file, "-" to read the cookie interactively, or "-FD" to read it from a file descriptor. cookiefile= (nbdkit ≥ 1.26) Enable cookie processing (eg. when following redirects), starting with an empty list of cookies. This is equivalent to calling CURLOPT_COOKIEFILE(3) with an empty string. cookiefile=FILENAME (nbdkit ≥ 1.26) Enable cookie processing (eg. when following redirects), prepopulating cookies from the given file. The file can contain cookies in any format supported by curl, see CURLOPT_COOKIEFILE(3). Cookies sent by the server are not saved when nbdkit exits. cookiejar=FILENAME (nbdkit ≥ 1.26) Enable cookie processing (eg. when following redirects), prepopulating cookies from the given file, and writing server cookies back to the file when the NBD handle is closed. The file can contain cookies in any format supported by curl, see CURLOPT_COOKIEJAR(3). There is some advice on the internet telling you to set this to /dev/null, but you should not do this because it can corrupt /dev/null. If you don't want a cookiejar, omit this option. If you want to enable cookie processing without updating a permanent cookiejar, use the "cookiefile=" option instead. cookie-script=SCRIPT cookie-script-renew=SECS (nbdkit ≥ 1.22, not Windows) Run "SCRIPT" (a command or shell script fragment) to generate the HTTP/HTTPS cookies. "cookie-script" cannot be used with "cookie". See "HEADER AND COOKIE SCRIPTS" below. followlocation=false (nbdkit ≥ 1.26) Do not follow redirects from the server. The default is true (follow redirects). You can follow redirects but avoid redirecting to a less secure protocol (eg. HTTPS redirecting to FTP) by using the "protocols" parameter instead. header=HEADER (nbdkit ≥ 1.22) For HTTP/HTTPS, send a custom header, or remove a header that curl has added. To add a custom header: header='X-My-Name: John Doe' To remove a header that curl has added, add the header followed by a colon and no value: header='User-Agent:' To add a custom header that has no value, you have to use a semicolon instead of colon. This adds an "X-Empty:" header with no value: header='X-Empty;' See CURLOPT_HTTPHEADER(3). You can use this option multiple times in order to add several headers. Note this sends the header in all requests, even when following a redirect, which can cause headers (eg. containing sensitive authorization information) to be sent to hosts other than the one originally requested. header-script=SCRIPT header-script-renew=SECS (nbdkit ≥ 1.22, not Windows) Run "SCRIPT" (a command or shell script fragment) to generate the HTTP/HTTPS headers. "header-script" cannot be used with "header". See "HEADER AND COOKIE SCRIPTS" below. http-version=none http-version=1.0 http-version=1.1 http-version=2.0 http-version=2TLS http-version=2-prior-knowledge http-version=3 http-version=3only (nbdkit ≥ 1.34) Force curl to use a particular HTTP protocol. The default is "none" meaning curl will negotiate the best protocol with the server. The other settings are mainly for testing. See CURLOPT_HTTP_VERSION(3) for details. password=PASSWORD Set the password to use when connecting to the remote server. Note that passing this on the command line is not secure on shared machines. password=- Ask for the password (interactively) when nbdkit starts up. password=+FILENAME Read the password from the named file. This is a secure method to supply a password, as long as you set the permissions on the file appropriately. password=-FD Read the password from file descriptor number "FD", inherited from the parent process when nbdkit starts up. This is also a secure method to supply a password. protocols=PROTO,PROTO,... (nbdkit ≥ 1.12) Limit the protocols that are allowed in the URL. Use this option for extra security if the URL comes from an untrusted source and you want to avoid security isues in the more obscure protocols that curl supports. (See qemu CVE-2013-0249 for an example of a security bug introduced by allowing unrestricted protocols). For example if you only intend HTTP and HTTPS URLs to be used, then add this parameter: "protocols=http,https" This restriction also applies if the plugin follows a redirect to another protocol (eg. you start with an "https://" URL which the server redirects to "ftp://"). To prevent redirects altogether see the "followlocation" parameter. The value of this parameter is a comma-separated list of protocols, for example "protocols=https", or "protocols=http,https", or "protocols=file,ftp,gopher". For a list of known protocols, see the libcurl manual (CURLOPT_PROTOCOLS_STR(3)). The default is to allow any protocol. proxy=PROXY (nbdkit ≥ 1.20) Set the proxy. See CURLOPT_PROXY(3). proxy-password=PASSWORD proxy-password=- proxy-password=+FILENAME proxy-password=-FD proxy-user=USERNAME (nbdkit ≥ 1.12) Set the proxy username and password. sslverify=false Don't verify the SSL certificate of the remote host. ssl-cipher-list=CIPHER[:CIPHER...] ssl-version=default ssl-version=tlsv1 ssl-version=sslv2 ssl-version=sslv3 ssl-version=tlsv1.0 ssl-version=tlsv1.1 ssl-version=tlsv1.2 ssl-version=tlsv1.3 ssl-version=max-default ssl-version=max-tlsv1.0 ssl-version=max-tlsv1.1 ssl-version=max-tlsv1.2 ssl-version=max-tlsv1.3 Set the SSL ciphers and TLS version. For further information see CURLOPT_SSL_CIPHER_LIST(3) and CURLOPT_SSLVERSION(3). tcp-keepalive=true (nbdkit ≥ 1.20) Enable TCP keepalives. tcp-nodelay=false (nbdkit ≥ 1.20) Enable Nagle’s algorithm. Small writes on the network socket will not be sent immediately but will be held in a local buffer and coalesced if possible. This is more efficient for the network but can cause increased latency. The default (in libcurl ≥ 7.50.2) is that Nagle’s algorithm is disabled for better latency at the expense of network efficiency. See CURLOPT_TCP_NODELAY(3). timeout=SECS Set the timeout for requests. timeout=0 Use the default libcurl timeout for requests. tls13-ciphers=CIPHER[:CIPHER...] Select TLSv1.3 ciphers available. See CURLOPT_TLS13_CIPHERS(3) and https://curl.se/docs/ssl-ciphers.html unix-socket-path=PATH (nbdkit ≥ 1.10) Instead of using a TCP connection, connect to the server over the named Unix domain socket. See CURLOPT_UNIX_SOCKET_PATH(3). [url=]URL The URL of the remote disk image. This is passed to libcurl directly via CURLOPT_URL(3). This parameter is required. "url=" is a magic config key and may be omitted in most cases. See "Magic parameters" in nbdkit(1). user=USERNAME Set the username to use when connecting to the remote server. This may also be set in the URL (eg. "http://foo@example.com/disk.img") user-agent=USER-AGENT (nbdkit ≥ 1.22) Send user-agent header when using HTTP or HTTPS. The default is no user-agent header.
NBD CONNECTIONS AND CURL HANDLES
nbdkit ≤ 1.32 used a simple model where a new NBD connection would create a new libcurl handle. In practice this meant there was a 1-to-1 relationship between NBD connections and HTTP connections to the remote web server (assuming http: or https: URL). nbdkit ≥ 1.34 changed to using a fixed pool of libcurl handles shared across all NBD connections. You can control the maximum number of curl handles in the pool with the "connections" parameter (default 4). Note that if there are more than 4 NBD connections, they will share the 4 web server connections, unless you adjust "connections".
HEADER AND COOKIE SCRIPTS
While the "header" and "cookie" parameters can be used to specify static headers and cookies which are used in every HTTP/HTTPS request, the alternate "header-script" and "cookie-script" parameters can be used to run an external script or program to generate headers and/or cookies. This is particularly useful to access services which require an authorization token. In addition the "header-script-renew" and "cookie-script-renew" parameters allow you to renew the authorization token by rerunning the script periodically. "header-script" is incompatible with "header", and "cookie-script" is incompatible with "cookie". Header script The header script should print zero or more HTTP headers, each line of output in the same format as the "header" parameter. The headers printed by the script are passed to CURLOPT_HTTPHEADER(3). In the following example, an imaginary web service requires authentication using a token fetched from a separate login server. The token expires after 60 seconds, so we also tell the plugin that it must renew the token (by re-running the script) if more than 50 seconds have elapsed since the last request: nbdkit curl https://service.example.com/disk.img \ header-script=' printf "Authorization: Bearer " curl -s -X POST https://auth.example.com/login | jq -r .token ' \ header-script-renew=50 Cookie script The cookie script should print a single line in the same format as the "cookie" parameter. This is passed to CURLOPT_COOKIE(3). Header and cookie script shell variables Within the "header-script" and "cookie-script" the following shell variables are available: $iteration The number of times that the script has been called. The first time the script is called this contains 0. $url The URL as passed to the plugin. Example: VMware ESXi cookies VMware ESXi’s web server can expose both VMDK and raw format disk images, but requires you to log in using HTTP Basic Authentication. While you can use the "user" and "password" parameters to send HTTP Basic Authentication headers in every request, tests have shown that it is faster to accept the cookie which the server returns and send that instead. (It is not clear why it is faster, but one theory is that VMware has to do a more expensive username and password check each time.) The web server can be accessed as below. Since the cookie expires after a certain period of time, we use "cookie-script-renew", and because the server uses a self-signed certificate we must use --insecure and "sslverify=false". SERVER=esx.example.com DCPATH=data DS=datastore1 GUEST=guest-name URL="https://$SERVER/folder/$GUEST/$GUEST-flat.vmdk?dcPath=$DCPATH&dsName=$DS" nbdkit curl "$URL" \ cookie-script=' curl --head -s --insecure -u root:password "$url" | sed -ne "{ s/^Set-Cookie: \([^;]*\);.*/\1/ip }" ' \ cookie-script-renew=500 \ sslverify=false Example: Docker Hub authorization tokens Accessing objects like container layers from Docker Hub requires that you first fetch an authorization token, even for anonymous access. These tokens expire after about 5 minutes (300 seconds) so must be periodically renewed. You will need this authorization script (/tmp/auth.sh): #!/bin/sh - IMAGE=library/fedora curl -s "https://auth.docker.io/token?service=registry.docker.io&scope=repository:$IMAGE:pull" | jq -r .token You will also need this script to get the blobSum of the layer (/tmp/blobsum.sh): #!/bin/sh - TOKEN=`/tmp/auth.sh` IMAGE=library/fedora curl -s -X GET -H "Authorization: Bearer $TOKEN" \ "https://registry-1.docker.io/v2/$IMAGE/manifests/latest" | jq -r '.fsLayers[0].blobSum' Both scripts must be executable, and both can be run on their own to check they are working. To run nbdkit: IMAGE=library/fedora BLOBSUM=`/tmp/blobsum.sh` URL="https://registry-1.docker.io/v2/$IMAGE/blobs/$BLOBSUM" nbdkit curl "$URL" \ header-script=' printf "Authorization: Bearer "; /tmp/auth.sh ' \ header-script-renew=200 \ --filter=gzip Note that this exposes a tar file over NBD. See also nbdkit-tar-filter(1).
DEBUG FLAGS
-D curl.scripts=1 This prints out the headers and cookies generated by the "header-script" and "cookie-script" options, which can be useful when debugging these scripts. -D curl.verbose=1 This enables very verbose curl debugging. See CURLOPT_VERBOSE(3). This is mainly useful if you suspect there is a bug inside libcurl itself.
FILES
$plugindir/nbdkit-curl-plugin.so The plugin. Use "nbdkit --dump-config" to find the location of $plugindir.
VERSION
"nbdkit-curl-plugin" first appeared in nbdkit 1.2.
SEE ALSO
curl(1), libcurl(3), CURLOPT_CAINFO(3), CURLOPT_CAPATH(3), CURLOPT_COOKIE(3), CURLOPT_COOKIEFILE(3), CURLOPT_COOKIEJAR(3), CURLOPT_FOLLOWLOCATION(3), CURLOPT_HTTPHEADER(3), CURLOPT_PROXY(3), CURLOPT_SSL_CIPHER_LIST(3), CURLOPT_SSLVERSION(3), CURLOPT_TCP_KEEPALIVE(3), CURLOPT_TCP_NODELAY(3), CURLOPT_TLS13_CIPHERS(3), CURLOPT_URL(3), CURLOPT_UNIX_SOCKET_PATH(3), CURLOPT_USERAGENT(3), CURLOPT_VERBOSE(3), nbdkit(1), nbdkit-extentlist-filter(1), nbdkit-file-plugin(1), nbdkit-retry-filter(1), nbdkit-retry-request-filter(1), nbdkit-ssh-plugin(1), nbdkit-torrent-plugin(1), nbdkit-plugin(3), http://curl.haxx.se, https://curl.se/docs/ssl-ciphers.html
AUTHORS
Richard W.M. Jones Parts derived from Alexander Graf's "QEMU Block driver for CURL images".
COPYRIGHT
Copyright Red Hat
LICENSE
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. • Neither the name of Red Hat nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.