| FETCH(3) | MidnightBSD Library Functions Manual | FETCH(3) |
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
File Transfer Library (libfetch, -lfetch)
#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);
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.
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.
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>".
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.
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_ALLOW_SSL3 environment
variable to allow SSLv3 and SSL_NO_TLS1,
SSL_NO_TLS1_1 and
SSL_NO_TLS1_2 to disable TLS 1.0, 1.1 and 1.2
respectively.
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.
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]FETCH_AUTH]FETCH_DOWN]FETCH_EXISTS]FETCH_FULL]FETCH_INFO]FETCH_MEMORY]FETCH_MOVED]FETCH_NETWORK]FETCH_OK]FETCH_PROTO]FETCH_RESOLV]FETCH_SERVER]FETCH_TEMP]FETCH_TIMEOUT]FETCH_UNAVAIL]FETCH_UNKNOWN]FETCH_URL]The accompanying error message includes a protocol-specific error code and message, like "File is not available (404 Not Found)"
FETCH_BIND_ADDRESSFTP_LOGINFTP_PASSIVE_MODEno’, 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_PASSWORDFTP_PROXYlibfetch
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_proxyFTP_PROXY, for compatibility.HTTP_ACCEPTHTTP_AUTHBoth 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_PROXYNote that this proxy will also be used for FTP documents,
unless the FTP_PROXY variable is set.
http_proxyHTTP_PROXY, for compatibility.HTTP_PROXY_AUTHHTTP_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_REFERERHTTP_USER_AGENTNETRCNO_PROXYno_proxyNO_PROXY, for compatibility.SSL_ALLOW_SSL3SSL_CA_CERT_FILESSL_CA_CERT_PATHSSL_CLIENT_CERT_FILESSL_CLIENT_KEY_FILESSL_CRL_FILESSL_NO_TLS1SSL_NO_TLS1_1SSL_NO_TLS1_2SSL_NO_VERIFY_HOSTNAMESSL_NO_VERIFY_PEERTo 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:8080If 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:8080The 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
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
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.
The fetch library first appeared in
FreeBSD 3.0.
The fetch library was mostly written by
Dag-Erling Smørgrav
<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-François 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 Smørgrav <des@FreeBSD.org> and Michael Gmelin <freebsd@grem.de>.
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.
| August 28, 2019 | midnightbsd-3.1 |