FETCH(3) FreeBSD Library Functions Manual FETCH(3)
NAME
fetchMakeURL, fetchParseURL, fetchFreeURL, fetchXGetURL, fetchGetURL,
fetchPutURL, fetchStatURL, fetchListURL, fetchXGet, fetchGet, fetchPut,
fetchStat, fetchList, fetchXGetFile, fetchGetFile, fetchPutFile,
fetchStatFile, fetchListFile, fetchXGetHTTP, fetchGetHTTP, fetchPutHTTP,
fetchStatHTTP, fetchListHTTP, fetchReqHTTP, fetchXGetFTP, fetchGetFTP,
fetchPutFTP, fetchStatFTP, fetchListFTP - file transfer functions
LIBRARY
File Transfer Library (libfetch, -lfetch)
SYNOPSIS
#include <sys/param.h>
#include <stdio.h>
#include <fetch.h>
struct url *
fetchMakeURL(const char *scheme, const char *host, int port,
const char *doc, const char *user, const char *pwd);
struct url *
fetchParseURL(const char *URL);
void
fetchFreeURL(struct url *u);
FILE *
fetchXGetURL(const char *URL, struct url_stat *us, const char *flags);
FILE *
fetchGetURL(const char *URL, const char *flags);
FILE *
fetchPutURL(const char *URL, const char *flags);
int
fetchStatURL(const char *URL, struct url_stat *us, const char *flags);
struct url_ent *
fetchListURL(const char *URL, const char *flags);
FILE *
fetchXGet(struct url *u, struct url_stat *us, const char *flags);
FILE *
fetchGet(struct url *u, const char *flags);
FILE *
fetchPut(struct url *u, const char *flags);
int
fetchStat(struct url *u, struct url_stat *us, const char *flags);
struct url_ent *
fetchList(struct url *u, const char *flags);
FILE *
fetchXGetFile(struct url *u, struct url_stat *us, const char *flags);
FILE *
fetchGetFile(struct url *u, const char *flags);
FILE *
fetchPutFile(struct url *u, const char *flags);
int
fetchStatFile(struct url *u, struct url_stat *us, const char *flags);
struct url_ent *
fetchListFile(struct url *u, const char *flags);
FILE *
fetchXGetHTTP(struct url *u, struct url_stat *us, const char *flags);
FILE *
fetchGetHTTP(struct url *u, const char *flags);
FILE *
fetchPutHTTP(struct url *u, const char *flags);
int
fetchStatHTTP(struct url *u, struct url_stat *us, const char *flags);
struct url_ent *
fetchListHTTP(struct url *u, const char *flags);
FILE *
fetchReqHTTP(struct url *u, const char *method, const char *flags,
const char *content_type, const char *body);
FILE *
fetchXGetFTP(struct url *u, struct url_stat *us, const char *flags);
FILE *
fetchGetFTP(struct url *u, const char *flags);
FILE *
fetchPutFTP(struct url *u, const char *flags);
int
fetchStatFTP(struct url *u, struct url_stat *us, const char *flags);
struct url_ent *
fetchListFTP(struct url *u, const char *flags);
DESCRIPTION
These functions implement a high-level library for retrieving and
uploading files using Uniform Resource Locators (URLs).
fetchParseURL() takes a URL in the form of a null-terminated string and
splits it into its components function according to the Common Internet
Scheme Syntax detailed in RFC1738. A regular expression which produces
this syntax is:
<scheme>:(//(<user>(:<pwd>)?@)?<host>(:<port>)?)?/(<document>)?
If the URL does not seem to begin with a scheme name, the following
syntax is assumed:
((<user>(:<pwd>)?@)?<host>(:<port>)?)?/(<document>)?
Note that some components of the URL are not necessarily relevant to all
URL schemes. For instance, the file scheme only needs the <scheme> and
<document> components.
fetchMakeURL() and fetchParseURL() return a pointer to a url structure,
which is defined as follows in <fetch.h>:
#define URL_SCHEMELEN 16
#define URL_USERLEN 256
#define URL_PWDLEN 256
struct url {
char scheme[URL_SCHEMELEN+1];
char user[URL_USERLEN+1];
char pwd[URL_PWDLEN+1];
char host[MAXHOSTNAMELEN+1];
int port;
char *doc;
off_t offset;
size_t length;
time_t ims_time;
};
The ims_time field stores the time value for If-Modified-Since HTTP
requests.
The pointer returned by fetchMakeURL() or fetchParseURL() should be freed
using fetchFreeURL().
fetchXGetURL(), fetchGetURL(), and fetchPutURL() constitute the
recommended interface to the fetch library. They examine the URL passed
to them to determine the transfer method, and call the appropriate lower-
level functions to perform the actual transfer. fetchXGetURL() also
returns the remote document's metadata in the url_stat structure pointed
to by the us argument.
The flags argument is a string of characters which specify transfer
options. The meaning of the individual flags is scheme-dependent, and is
detailed in the appropriate section below.
fetchStatURL() attempts to obtain the requested document's metadata and
fill in the structure pointed to by its second argument. The url_stat
structure is defined as follows in <fetch.h>:
struct url_stat {
off_t size;
time_t atime;
time_t mtime;
};
If the size could not be obtained from the server, the size field is set
to -1. If the modification time could not be obtained from the server,
the mtime field is set to the epoch. If the access time could not be
obtained from the server, the atime field is set to the modification
time.
fetchListURL() attempts to list the contents of the directory pointed to
by the URL provided. If successful, it returns a malloced array of
url_ent structures. The url_ent structure is defined as follows in
<fetch.h>:
struct url_ent {
char name[PATH_MAX];
struct url_stat stat;
};
The list is terminated by an entry with an empty name.
The pointer returned by fetchListURL() should be freed using free().
fetchXGet(), fetchGet(), fetchPut() and fetchStat() are similar to
fetchXGetURL(), fetchGetURL(), fetchPutURL() and fetchStatURL(), except
that they expect a pre-parsed URL in the form of a pointer to a struct
url rather than a string.
All of the fetchXGetXXX(), fetchGetXXX() and fetchPutXXX() functions
return a pointer to a stream which can be used to read or write data from
or to the requested document, respectively. Note that although the
implementation details of the individual access methods vary, it can
generally be assumed that a stream returned by one of the fetchXGetXXX()
or fetchGetXXX() functions is read-only, and that a stream returned by
one of the fetchPutXXX() functions is write-only.
FILE SCHEME
fetchXGetFile(), fetchGetFile() and fetchPutFile() provide access to
documents which are files in a locally mounted file system. Only the
<document> component of the URL is used.
fetchXGetFile() and fetchGetFile() do not accept any flags.
fetchPutFile() accepts the `a' (append to file) flag. If that flag is
specified, the data written to the stream returned by fetchPutFile() will
be appended to the previous contents of the file, instead of replacing
them.
FTP SCHEME
fetchXGetFTP(), fetchGetFTP() and fetchPutFTP() implement the FTP
protocol as described in RFC959.
If the `P' (not passive) flag is specified, an active (rather than
passive) connection will be attempted.
The `p' flag is supported for compatibility with earlier versions where
active connections were the default. It has precedence over the `P'
flag, so if both are specified, fetchMakeURL will use a passive
connection.
If the `l' (low) flag is specified, data sockets will be allocated in the
low (or default) port range instead of the high port range (see ip(4)).
If the `d' (direct) flag is specified, fetchXGetFTP(), fetchGetFTP() and
fetchPutFTP() will use a direct connection even if a proxy server is
defined.
If no user name or password is given, the fetch library will attempt an
anonymous login, with user name "anonymous" and password
"anonymous@<hostname>".
HTTP SCHEME
The fetchXGetHTTP(), fetchGetHTTP(), fetchPutHTTP() and fetchReqHTTP()
functions implement the HTTP/1.1 protocol. With a little luck, there is
even a chance that they comply with RFC2616 and RFC2617.
If the `d' (direct) flag is specified, fetchXGetHTTP(), fetchGetHTTP()
and fetchPutHTTP() will use a direct connection even if a proxy server is
defined.
If the `i' (if-modified-since) flag is specified, and the ims_time field
is set in struct url, then fetchXGetHTTP() and fetchGetHTTP() will send a
conditional If-Modified-Since HTTP header to only fetch the content if it
is newer than ims_time.
The function fetchReqHTTP() can be used to make requests with an
arbitrary HTTP verb, including POST, DELETE, CONNECT, OPTIONS, TRACE or
PATCH. This can be done by setting the argument method to the intended
verb, such as `POST', and body to the content.
Since there seems to be no good way of implementing the HTTP PUT method
in a manner consistent with the rest of the fetch library, fetchPutHTTP()
is currently unimplemented.
HTTPS SCHEME
Based on HTTP SCHEME. By default the peer is verified using the CA
bundle located in /usr/local/etc/ssl/cert.pem. If this file does not
exist, /etc/ssl/cert.pem is used instead. If neither file exists, and
SSL_CA_CERT_PATH has not been set, OpenSSL's default CA cert and path
settings apply. The certificate bundle can contain multiple CA
certificates. A common source of a current CA bundle is
security/ca_root_nss.
The CA bundle used for peer verification can be changed by setting the
environment variables SSL_CA_CERT_FILE to point to a concatenated bundle
of trusted certificates and SSL_CA_CERT_PATH to point to a directory
containing hashes of trusted CAs (see verify(1)).
A certificate revocation list (CRL) can be used by setting the
environment variable SSL_CRL_FILE (see crl(1)).
Peer verification can be disabled by setting the environment variable
SSL_NO_VERIFY_PEER. Note that this also disables CRL checking.
By default the service identity is verified according to the rules
detailed in RFC6125 (also known as hostname verification). This feature
can be disabled by setting the environment variable
SSL_NO_VERIFY_HOSTNAME.
Client certificate based authentication is supported. The environment
variable SSL_CLIENT_CERT_FILE should be set to point to a file containing
key and client certificate to be used in PEM format. When a PEM-format
key is in a separate file from the client certificate, the environment
variable SSL_CLIENT_KEY_FILE can be set to point to the key file. In
case the key uses a password, the user will be prompted on standard input
(see PEM(3)).
By default libfetch allows TLSv1 and newer when negotiating the
connecting with the remote peer. You can change this behavior by setting
the SSL_NO_TLS1, SSL_NO_TLS1_1 and SSL_NO_TLS1_2 environment variables to
disable TLS 1.0, 1.1 and 1.2 respectively.
AUTHENTICATION
Apart from setting the appropriate environment variables and specifying
the user name and password in the URL or the struct url, the calling
program has the option of defining an authentication function with the
following prototype:
int myAuthMethod(struct url *u)
The callback function should fill in the user and pwd fields in the
provided struct url and return 0 on success, or any other value to
indicate failure.
To register the authentication callback, simply set fetchAuthMethod to
point at it. The callback will be used whenever a site requires
authentication and the appropriate environment variables are not set.
This interface is experimental and may be subject to change.
RETURN VALUES
fetchParseURL() returns a pointer to a struct url containing the
individual components of the URL. If it is unable to allocate memory, or
the URL is syntactically incorrect, fetchParseURL() returns a NULL
pointer.
The fetchStat() functions return 0 on success and -1 on failure.
All other functions return a stream pointer which may be used to access
the requested document, or NULL if an error occurred.
The following error codes are defined in <fetch.h>:
[FETCH_ABORT] Operation aborted
[FETCH_AUTH] Authentication failed
[FETCH_DOWN] Service unavailable
[FETCH_EXISTS] File exists
[FETCH_FULL] File system full
[FETCH_INFO] Informational response
[FETCH_MEMORY] Insufficient memory
[FETCH_MOVED] File has moved
[FETCH_NETWORK] Network error
[FETCH_OK] No error
[FETCH_PROTO] Protocol error
[FETCH_RESOLV] Resolver error
[FETCH_SERVER] Server error
[FETCH_TEMP] Temporary error
[FETCH_TIMEOUT] Operation timed out
[FETCH_UNAVAIL] File is not available
[FETCH_UNKNOWN] Unknown error
[FETCH_URL] Invalid URL
The accompanying error message includes a protocol-specific error code
and message, like "File is not available (404 Not Found)"
ENVIRONMENT
FETCH_BIND_ADDRESS Specifies a hostname or IP address to which
sockets used for outgoing connections will be
bound.
FTP_LOGIN Default FTP login if none was provided in the
URL.
FTP_PASSIVE_MODE If set to `no', forces the FTP code to use active
mode. If set to any other value, forces passive
mode even if the application requested active
mode.
FTP_PASSWORD Default FTP password if the remote server
requests one and none was provided in the URL.
FTP_PROXY URL of the proxy to use for FTP requests. The
document part is ignored. FTP and HTTP proxies
are supported; if no scheme is specified, FTP is
assumed. If the proxy is an FTP proxy, libfetch
will send `user@host' as user name to the proxy,
where `user' is the real user name, and `host' is
the name of the FTP server.
If this variable is set to an empty string, no
proxy will be used for FTP requests, even if the
HTTP_PROXY variable is set.
ftp_proxy Same as FTP_PROXY, for compatibility.
HTTP_ACCEPT Specifies the value of the Accept header for HTTP
requests. If empty, no Accept header is sent.
The default is "*/*".
HTTP_AUTH Specifies HTTP authorization parameters as a
colon-separated list of items. The first and
second item are the authorization scheme and
realm respectively; further items are scheme-
dependent. Currently, the "basic" and "digest"
authorization methods are supported.
Both methods require two parameters: the user
name and password, in that order.
This variable is only used if the server requires
authorization and no user name or password was
specified in the URL.
HTTP_PROXY URL of the proxy to use for HTTP requests. The
document part is ignored. Only HTTP proxies are
supported for HTTP requests. If no port number
is specified, the default is 3128.
Note that this proxy will also be used for FTP
documents, unless the FTP_PROXY variable is set.
http_proxy Same as HTTP_PROXY, for compatibility.
HTTP_PROXY_AUTH Specifies authorization parameters for the HTTP
proxy in the same format as the HTTP_AUTH
variable.
This variable is used if and only if connected to
an HTTP proxy, and is ignored if a user and/or a
password were specified in the proxy URL.
HTTP_REFERER Specifies the referrer URL to use for HTTP
requests. If set to "auto", the document URL
will be used as referrer URL.
HTTP_USER_AGENT Specifies the User-Agent string to use for HTTP
requests. This can be useful when working with
HTTP origin or proxy servers that differentiate
between user agents. If defined but empty, no
User-Agent header is sent.
NETRC Specifies a file to use instead of ~/.netrc to
look up login names and passwords for FTP and
HTTP sites as well as HTTP proxies. See ftp(1)
for a description of the file format.
NO_PROXY Either a single asterisk, which disables the use
of proxies altogether, or a comma- or whitespace-
separated list of hosts for which proxies should
not be used.
no_proxy Same as NO_PROXY, for compatibility.
SOCKS5_PROXY Uses SOCKS version 5 to make connection. The
format must be the IP or hostname followed by a
colon for the port. IPv6 addresses must enclose
the address in brackets. If no port is
specified, the default is 1080. This setting
will supercede a connection to an HTTP_PROXY.
SSL_CA_CERT_FILE CA certificate bundle containing trusted CA
certificates. Default value: See HTTPS SCHEME
above.
SSL_CA_CERT_PATH Path containing trusted CA hashes.
SSL_CLIENT_CERT_FILE PEM encoded client certificate/key which will be
used in client certificate authentication.
SSL_CLIENT_KEY_FILE PEM encoded client key in case key and client
certificate are stored separately.
SSL_CRL_FILE File containing certificate revocation list.
SSL_NO_TLS1 Do not allow TLS version 1.0 when negotiating the
connection.
SSL_NO_TLS1_1 Do not allow TLS version 1.1 when negotiating the
connection.
SSL_NO_TLS1_2 Do not allow TLS version 1.2 when negotiating the
connection.
SSL_NO_VERIFY_HOSTNAME If set, do not verify that the hostname matches
the subject of the certificate presented by the
server.
SSL_NO_VERIFY_PEER If set, do not verify the peer certificate
against trusted CAs.
EXAMPLES
To access a proxy server on proxy.example.com port 8080, set the
HTTP_PROXY environment variable in a manner similar to this:
HTTP_PROXY=http://proxy.example.com:8080
If the proxy server requires authentication, there are two options
available for passing the authentication data. The first method is by
using the proxy URL:
HTTP_PROXY=http://<user>:<pwd>@proxy.example.com:8080
The second method is by using the HTTP_PROXY_AUTH environment variable:
HTTP_PROXY=http://proxy.example.com:8080
HTTP_PROXY_AUTH=basic:*:<user>:<pwd>
To disable the use of a proxy for an HTTP server running on the local
host, define NO_PROXY as follows:
NO_PROXY=localhost,127.0.0.1
To use a SOCKS5 proxy, set the SOCKS5_PROXY environment variable to a
valid host or IP followed by an optional colon and the port. IPv6
addresses must be enclosed in brackets. The following are examples of
valid settings:
SOCKS5_PROXY=proxy.example.com
SOCKS5_PROXY=proxy.example.com:1080
SOCKS5_PROXY=192.0.2.0
SOCKS5_PROXY=198.51.100.0:1080
SOCKS5_PROXY=[2001:db8::1]
SOCKS5_PROXY=[2001:db8::2]:1080
Access HTTPS website without any certificate verification whatsoever:
SSL_NO_VERIFY_PEER=1
SSL_NO_VERIFY_HOSTNAME=1
Access HTTPS website using client certificate based authentication and a
private CA:
SSL_CLIENT_CERT_FILE=/path/to/client.pem
SSL_CA_CERT_FILE=/path/to/myca.pem
SEE ALSO
fetch(1), ip(4)
J. Postel and J. K. Reynolds, File Transfer Protocol, October 1985,
RFC959.
P. Deutsch, A. Emtage, and A. Marine., How to Use Anonymous FTP, May
1994, RFC1635.
T. Berners-Lee, L. Masinter, and M. McCahill, Uniform Resource Locators
(URL), December 1994, RFC1738.
R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach, and
T. Berners-Lee, Hypertext Transfer Protocol -- HTTP/1.1, January 1999,
RFC2616.
J. Franks, P. Hallam-Baker, J. Hostetler, S. Lawrence, P. Leach, A.
Luotonen, and L. Stewart, HTTP Authentication: Basic and Digest Access
Authentication, June 1999, RFC2617.
HISTORY
The fetch library first appeared in FreeBSD 3.0.
AUTHORS
The fetch library was mostly written by Dag-Erling Sm/rgrav
<des@FreeBSD.org> with numerous suggestions and contributions from Jordan
K. Hubbard <jkh@FreeBSD.org>, Eugene Skepner <eu@qub.com>, Hajimu Umemoto
<ume@FreeBSD.org>, Henry Whincup <henry@techiebod.com>, Jukka A. Ukkonen
<jau@iki.fi>, Jean-Fran,ois Dockes <jf@dockes.org>, Michael Gmelin
<freebsd@grem.de> and others. It replaces the older ftpio library
written by Poul-Henning Kamp <phk@FreeBSD.org> and Jordan K. Hubbard
<jkh@FreeBSD.org>.
This manual page was written by Dag-Erling Sm/rgrav <des@FreeBSD.org> and
Michael Gmelin <freebsd@grem.de>.
BUGS
Some parts of the library are not yet implemented. The most notable
examples of this are fetchPutHTTP(), fetchListHTTP(), fetchListFTP() and
FTP proxy support.
There is no way to select a proxy at run-time other than setting the
HTTP_PROXY or FTP_PROXY environment variables as appropriate.
libfetch does not understand or obey 305 (Use Proxy) replies.
Error numbers are unique only within a certain context; the error codes
used for FTP and HTTP overlap, as do those used for resolver and system
errors. For instance, error code 202 means "Command not implemented,
superfluous at this site" in an FTP context and "Accepted" in an HTTP
context.
fetchStatFTP() does not check that the result of an MDTM command is a
valid date.
In case password protected keys are used for client certificate based
authentication the user is prompted for the password on each and every
fetch operation.
The man page is incomplete, poorly written and produces badly formatted
text.
The error reporting mechanism is unsatisfactory.
Some parts of the code are not fully reentrant.
FreeBSD 13.1-RELEASE-p6 November 24, 2020 FreeBSD 13.1-RELEASE-p6
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