fetch.3

.\"-
.\" Copyright (c) 1998-2013 Dag-Erling Smørgrav
.\" Copyright (c) 2013 Michael Gmelin <freebsd@grem.de>
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.\" $FreeBSD: stable/10/lib/libfetch/fetch.3 253805 2013-07-30 13:07:55Z des $
.\"
.Dd July 30, 2013
.Dt FETCH 3
.Os
.Sh NAME
.Nm fetchMakeURL ,
.Nm fetchParseURL ,
.Nm fetchFreeURL ,
.Nm fetchXGetURL ,
.Nm fetchGetURL ,
.Nm fetchPutURL ,
.Nm fetchStatURL ,
.Nm fetchListURL ,
.Nm fetchXGet ,
.Nm fetchGet ,
.Nm fetchPut ,
.Nm fetchStat ,
.Nm fetchList ,
.Nm fetchXGetFile ,
.Nm fetchGetFile ,
.Nm fetchPutFile ,
.Nm fetchStatFile ,
.Nm fetchListFile ,
.Nm fetchXGetHTTP ,
.Nm fetchGetHTTP ,
.Nm fetchPutHTTP ,
.Nm fetchStatHTTP ,
.Nm fetchListHTTP ,
.Nm fetchXGetFTP ,
.Nm fetchGetFTP ,
.Nm fetchPutFTP ,
.Nm fetchStatFTP ,
.Nm fetchListFTP
.Nd file transfer functions
.Sh LIBRARY
.Lb libfetch
.Sh SYNOPSIS
.In sys/param.h
.In stdio.h
.In fetch.h
.Ft struct url *
.Fn fetchMakeURL "const char *scheme" "const char *host" "int port" "const char *doc" "const char *user" "const char *pwd"
.Ft struct url *
.Fn fetchParseURL "const char *URL"
.Ft void
.Fn fetchFreeURL "struct url *u"
.Ft FILE *
.Fn fetchXGetURL "const char *URL" "struct url_stat *us" "const char *flags"
.Ft FILE *
.Fn fetchGetURL "const char *URL" "const char *flags"
.Ft FILE *
.Fn fetchPutURL "const char *URL" "const char *flags"
.Ft int
.Fn fetchStatURL "const char *URL" "struct url_stat *us" "const char *flags"
.Ft struct url_ent *
.Fn fetchListURL "const char *URL" "const char *flags"
.Ft FILE *
.Fn fetchXGet "struct url *u" "struct url_stat *us" "const char *flags"
.Ft FILE *
.Fn fetchGet "struct url *u" "const char *flags"
.Ft FILE *
.Fn fetchPut "struct url *u" "const char *flags"
.Ft int
.Fn fetchStat "struct url *u" "struct url_stat *us" "const char *flags"
.Ft struct url_ent *
.Fn fetchList "struct url *u" "const char *flags"
.Ft FILE *
.Fn fetchXGetFile "struct url *u" "struct url_stat *us" "const char *flags"
.Ft FILE *
.Fn fetchGetFile "struct url *u" "const char *flags"
.Ft FILE *
.Fn fetchPutFile "struct url *u" "const char *flags"
.Ft int
.Fn fetchStatFile "struct url *u" "struct url_stat *us" "const char *flags"
.Ft struct url_ent *
.Fn fetchListFile "struct url *u" "const char *flags"
.Ft FILE *
.Fn fetchXGetHTTP "struct url *u" "struct url_stat *us" "const char *flags"
.Ft FILE *
.Fn fetchGetHTTP "struct url *u" "const char *flags"
.Ft FILE *
.Fn fetchPutHTTP "struct url *u" "const char *flags"
.Ft int
.Fn fetchStatHTTP "struct url *u" "struct url_stat *us" "const char *flags"
.Ft struct url_ent *
.Fn fetchListHTTP "struct url *u" "const char *flags"
.Ft FILE *
.Fn fetchXGetFTP "struct url *u" "struct url_stat *us" "const char *flags"
.Ft FILE *
.Fn fetchGetFTP "struct url *u" "const char *flags"
.Ft FILE *
.Fn fetchPutFTP "struct url *u" "const char *flags"
.Ft int
.Fn fetchStatFTP "struct url *u" "struct url_stat *us" "const char *flags"
.Ft struct url_ent *
.Fn fetchListFTP "struct url *u" "const char *flags"
.Sh DESCRIPTION
These functions implement a high-level library for retrieving and
uploading files using Uniform Resource Locators (URLs).
.Pp
.Fn 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:
.Bd -literal
    <scheme>:(//(<user>(:<pwd>)?@)?<host>(:<port>)?)?/(<document>)?
.Ed
.Pp
If the URL does not seem to begin with a scheme name, the following
syntax is assumed:
.Bd -literal
    ((<user>(:<pwd>)?@)?<host>(:<port>)?)?/(<document>)?
.Ed
.Pp
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.
.Pp
.Fn fetchMakeURL
and
.Fn fetchParseURL
return a pointer to a
.Vt url
structure, which is defined as follows in
.In fetch.h :
.Bd -literal
#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;
};
.Ed
.Pp
The
.Va ims_time
field stores the time value for
.Li If-Modified-Since
HTTP requests.
.Pp
The pointer returned by
.Fn fetchMakeURL
or
.Fn fetchParseURL
should be freed using
.Fn fetchFreeURL .
.Pp
.Fn fetchXGetURL ,
.Fn fetchGetURL ,
and
.Fn fetchPutURL
constitute the recommended interface to the
.Nm 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.
.Fn fetchXGetURL
also returns the remote document's metadata in the
.Vt url_stat
structure pointed to by the
.Fa us
argument.
.Pp
The
.Fa 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.
.Pp
.Fn fetchStatURL
attempts to obtain the requested document's metadata and fill in the
structure pointed to by its second argument.
The
.Vt url_stat
structure is defined as follows in
.In fetch.h :
.Bd -literal
struct url_stat {
    off_t	 size;
    time_t	 atime;
    time_t	 mtime;
};
.Ed
.Pp
If the size could not be obtained from the server, the
.Fa size
field is set to -1.
If the modification time could not be obtained from the server, the
.Fa mtime
field is set to the epoch.
If the access time could not be obtained from the server, the
.Fa atime
field is set to the modification time.
.Pp
.Fn fetchListURL
attempts to list the contents of the directory pointed to by the URL
provided.
If successful, it returns a malloced array of
.Vt url_ent
structures.
The
.Vt url_ent
structure is defined as follows in
.In fetch.h :
.Bd -literal
struct url_ent {
    char         name[PATH_MAX];
    struct url_stat stat;
};
.Ed
.Pp
The list is terminated by an entry with an empty name.
.Pp
The pointer returned by
.Fn fetchListURL
should be freed using
.Fn free .
.Pp
.Fn fetchXGet ,
.Fn fetchGet ,
.Fn fetchPut
and
.Fn fetchStat
are similar to
.Fn fetchXGetURL ,
.Fn fetchGetURL ,
.Fn fetchPutURL
and
.Fn fetchStatURL ,
except that they expect a pre-parsed URL in the form of a pointer to
a
.Vt struct url
rather than a string.
.Pp
All of the
.Fn fetchXGetXXX ,
.Fn fetchGetXXX
and
.Fn 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
.Fn fetchXGetXXX
or
.Fn fetchGetXXX
functions is read-only, and that a stream returned by one of the
.Fn fetchPutXXX
functions is write-only.
.Sh FILE SCHEME
.Fn fetchXGetFile ,
.Fn fetchGetFile
and
.Fn fetchPutFile
provide access to documents which are files in a locally mounted file
system.
Only the <document> component of the URL is used.
.Pp
.Fn fetchXGetFile
and
.Fn fetchGetFile
do not accept any flags.
.Pp
.Fn fetchPutFile
accepts the
.Ql a
(append to file) flag.
If that flag is specified, the data written to
the stream returned by
.Fn fetchPutFile
will be appended to the previous contents of the file, instead of
replacing them.
.Sh FTP SCHEME
.Fn fetchXGetFTP ,
.Fn fetchGetFTP
and
.Fn fetchPutFTP
implement the FTP protocol as described in RFC959.
.Pp
If the
.Ql P
(not passive) flag is specified, an active (rather than passive)
connection will be attempted.
.Pp
The
.Ql p
flag is supported for compatibility with earlier versions where active
connections were the default.
It has precedence over the
.Ql P
flag, so if both are specified,
.Nm
will use a passive connection.
.Pp
If the
.Ql l
(low) flag is specified, data sockets will be allocated in the low (or
default) port range instead of the high port range (see
.Xr ip 4 ) .
.Pp
If the
.Ql d
(direct) flag is specified,
.Fn fetchXGetFTP ,
.Fn fetchGetFTP
and
.Fn fetchPutFTP
will use a direct connection even if a proxy server is defined.
.Pp
If no user name or password is given, the
.Nm fetch
library will attempt an anonymous login, with user name "anonymous"
and password "anonymous@<hostname>".
.Sh HTTP SCHEME
The
.Fn fetchXGetHTTP ,
.Fn fetchGetHTTP
and
.Fn fetchPutHTTP
functions implement the HTTP/1.1 protocol.
With a little luck, there is
even a chance that they comply with RFC2616 and RFC2617.
.Pp
If the
.Ql d
(direct) flag is specified,
.Fn fetchXGetHTTP ,
.Fn fetchGetHTTP
and
.Fn fetchPutHTTP
will use a direct connection even if a proxy server is defined.
.Pp
If the
.Ql i
(if-modified-since) flag is specified, and
the
.Va ims_time
field is set in
.Vt "struct url" ,
then
.Fn fetchXGetHTTP
and
.Fn fetchGetHTTP
will send a conditional
.Li If-Modified-Since
HTTP header to only fetch the content if it is newer than
.Va ims_time .
.Pp
Since there seems to be no good way of implementing the HTTP PUT
method in a manner consistent with the rest of the
.Nm fetch
library,
.Fn fetchPutHTTP
is currently unimplemented.
.Sh HTTPS SCHEME
Based on HTTP SCHEME.
By default the peer is verified using the CA bundle located in
.Pa /etc/ssl/cert.pem .
The file may contain multiple CA certificates.
A common source of a current CA bundle is
.Pa \%security/ca_root_nss .
.Pp
The CA bundle used for peer verification can be changed by setting the
environment variables
.Ev SSL_CA_CERT_FILE
to point to a concatenated bundle of trusted certificates and
.Ev SSL_CA_CERT_PATH
to point to a directory containing hashes of trusted CAs (see
.Xr verify 1 ) .
.Pp
A certificate revocation list (CRL) can be used by setting the
environment variable
.Ev SSL_CRL_FILE
(see
.Xr crl 1 ) .
.Pp
Peer verification can be disabled by setting the environment variable
.Ev SSL_NO_VERIFY_PEER .
Note that this also disables CRL checking.
.Pp
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
.Ev SSL_NO_VERIFY_HOSTNAME .
.Pp
Client certificate based authentication is supported.
The environment variable
.Ev SSL_CLIENT_CERT_FILE
should be set to point to a file containing key and client certificate
to be used in PEM format. In case the key is stored in a separate
file, the environment variable
.Ev SSL_CLIENT_KEY_FILE
can be set to point to the key in PEM format.
In case the key uses a password, the user will be prompted on standard
input (see
.Xr PEM 3 ) .
.Pp
By default
.Nm libfetch
allows SSLv3 and TLSv1 when negotiating the connecting with the remote
peer.
You can change this behavior by setting the environment variable
.Ev SSL_ALLOW_SSL2
to allow SSLv2 (not recommended) and
.Ev SSL_NO_SSL3
or
.Ev SSL_NO_TLS1
to disable the respective methods.
.Sh AUTHENTICATION
Apart from setting the appropriate environment variables and
specifying the user name and password in the URL or the
.Vt struct url ,
the calling program has the option of defining an authentication
function with the following prototype:
.Pp
.Ft int
.Fn myAuthMethod "struct url *u"
.Pp
The callback function should fill in the
.Fa user
and
.Fa pwd
fields in the provided
.Vt struct url
and return 0 on success, or any other value to indicate failure.
.Pp
To register the authentication callback, simply set
.Va fetchAuthMethod
to point at it.
The callback will be used whenever a site requires authentication and
the appropriate environment variables are not set.
.Pp
This interface is experimental and may be subject to change.
.Sh RETURN VALUES
.Fn fetchParseURL
returns a pointer to a
.Vt struct url
containing the individual components of the URL.
If it is
unable to allocate memory, or the URL is syntactically incorrect,
.Fn fetchParseURL
returns a NULL pointer.
.Pp
The
.Fn fetchStat
functions return 0 on success and -1 on failure.
.Pp
All other functions return a stream pointer which may be used to
access the requested document, or NULL if an error occurred.
.Pp
The following error codes are defined in
.In fetch.h :
.Bl -tag -width 18n
.It Bq Er FETCH_ABORT
Operation aborted
.It Bq Er FETCH_AUTH
Authentication failed
.It Bq Er FETCH_DOWN
Service unavailable
.It Bq Er FETCH_EXISTS
File exists
.It Bq Er FETCH_FULL
File system full
.It Bq Er FETCH_INFO
Informational response
.It Bq Er FETCH_MEMORY
Insufficient memory
.It Bq Er FETCH_MOVED
File has moved
.It Bq Er FETCH_NETWORK
Network error
.It Bq Er FETCH_OK
No error
.It Bq Er FETCH_PROTO
Protocol error
.It Bq Er FETCH_RESOLV
Resolver error
.It Bq Er FETCH_SERVER
Server error
.It Bq Er FETCH_TEMP
Temporary error
.It Bq Er FETCH_TIMEOUT
Operation timed out
.It Bq Er FETCH_UNAVAIL
File is not available
.It Bq Er FETCH_UNKNOWN
Unknown error
.It Bq Er FETCH_URL
Invalid URL
.El
.Pp
The accompanying error message includes a protocol-specific error code
and message, e.g.\& "File is not available (404 Not Found)"
.Sh ENVIRONMENT
.Bl -tag -width ".Ev FETCH_BIND_ADDRESS"
.It Ev FETCH_BIND_ADDRESS
Specifies a hostname or IP address to which sockets used for outgoing
connections will be bound.
.It Ev FTP_LOGIN
Default FTP login if none was provided in the URL.
.It Ev FTP_PASSIVE_MODE
If set to
.Ql 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.
.It Ev FTP_PASSWORD
Default FTP password if the remote server requests one and none was
provided in the URL.
.It Ev 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,
.Nm libfetch
will send
.Ql user@host
as user name to the proxy, where
.Ql user
is the real user name, and
.Ql host
is the name of the FTP server.
.Pp
If this variable is set to an empty string, no proxy will be used for
FTP requests, even if the
.Ev HTTP_PROXY
variable is set.
.It Ev ftp_proxy
Same as
.Ev FTP_PROXY ,
for compatibility.
.It Ev HTTP_ACCEPT
Specifies the value of the
.Va Accept
header for HTTP requests.
If empty, no
.Va Accept
header is sent.
The default is
.Dq */* .
.It Ev 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
.Dq basic
and
.Dq digest
authorization methods are supported.
.Pp
Both methods require two parameters: the user name and
password, in that order.
.Pp
This variable is only used if the server requires authorization and
no user name or password was specified in the URL.
.It Ev 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.
.Pp
Note that this proxy will also be used for FTP documents, unless the
.Ev FTP_PROXY
variable is set.
.It Ev http_proxy
Same as
.Ev HTTP_PROXY ,
for compatibility.
.It Ev HTTP_PROXY_AUTH
Specifies authorization parameters for the HTTP proxy in the same
format as the
.Ev HTTP_AUTH
variable.
.Pp
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.
.It Ev HTTP_REFERER
Specifies the referrer URL to use for HTTP requests.
If set to
.Dq auto ,
the document URL will be used as referrer URL.
.It Ev 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.
.It Ev NETRC
Specifies a file to use instead of
.Pa ~/.netrc
to look up login names and passwords for FTP sites.
See
.Xr ftp 1
for a description of the file format.
This feature is experimental.
.It Ev 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.
.It Ev no_proxy
Same as
.Ev NO_PROXY ,
for compatibility.
.It Ev SSL_ALLOW_SSL2
Allow SSL version 2 when negotiating the connection (not recommended).
.It Ev SSL_CA_CERT_FILE
CA certificate bundle containing trusted CA certificates.
Default value:
.Pa /etc/ssl/cert.pem .
.It Ev SSL_CA_CERT_PATH
Path containing trusted CA hashes.
.It Ev SSL_CLIENT_CERT_FILE
PEM encoded client certificate/key which will be used in
client certificate authentication.
.It Ev SSL_CLIENT_KEY_FILE
PEM encoded client key in case key and client certificate
are stored separately.
.It Ev SSL_CRL_FILE
File containing certificate revocation list.
.It Ev SSL_NO_SSL3
Don't allow SSL version 3 when negotiating the connection.
.It Ev SSL_NO_TLS1
Don't allow TLV version 1 when negotiating the connection.
.It Ev SSL_NO_VERIFY_HOSTNAME
If set, do not verify that the hostname matches the subject of the
certificate presented by the server.
.It Ev SSL_NO_VERIFY_PEER
If set, do not verify the peer certificate against trusted CAs.
.El
.Sh EXAMPLES
To access a proxy server on
.Pa proxy.example.com
port 8080, set the
.Ev HTTP_PROXY
environment variable in a manner similar to this:
.Pp
.Dl HTTP_PROXY=http://proxy.example.com:8080
.Pp
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:
.Pp
.Dl HTTP_PROXY=http://<user>:<pwd>@proxy.example.com:8080
.Pp
The second method is by using the
.Ev HTTP_PROXY_AUTH
environment variable:
.Bd -literal -offset indent
HTTP_PROXY=http://proxy.example.com:8080
HTTP_PROXY_AUTH=basic:*:<user>:<pwd>
.Ed
.Pp
To disable the use of a proxy for an HTTP server running on the local
host, define
.Ev NO_PROXY
as follows:
.Bd -literal -offset indent
NO_PROXY=localhost,127.0.0.1
.Ed
.Pp
Access HTTPS website without any certificate verification whatsoever:
.Bd -literal -offset indent
SSL_NO_VERIFY_PEER=1
SSL_NO_VERIFY_HOSTNAME=1
.Ed
.Pp
Access HTTPS website using client certificate based authentication
and a private CA:
.Bd -literal -offset indent
SSL_CLIENT_CERT_FILE=/path/to/client.pem
SSL_CA_CERT_FILE=/path/to/myca.pem
.Ed
.Sh SEE ALSO
.Xr fetch 1 ,
.Xr ftpio 3 ,
.Xr ip 4
.Rs
.%A J. Postel
.%A J. K. Reynolds
.%D October 1985
.%B File Transfer Protocol
.%O RFC959
.Re
.Rs
.%A P. Deutsch
.%A A. Emtage
.%A A. Marine.
.%D May 1994
.%T How to Use Anonymous FTP
.%O RFC1635
.Re
.Rs
.%A T. Berners-Lee
.%A L. Masinter
.%A M. McCahill
.%D December 1994
.%T Uniform Resource Locators (URL)
.%O RFC1738
.Re
.Rs
.%A R. Fielding
.%A J. Gettys
.%A J. Mogul
.%A H. Frystyk
.%A L. Masinter
.%A P. Leach
.%A T. Berners-Lee
.%D January 1999
.%B Hypertext Transfer Protocol -- HTTP/1.1
.%O RFC2616
.Re
.Rs
.%A J. Franks
.%A P. Hallam-Baker
.%A J. Hostetler
.%A S. Lawrence
.%A P. Leach
.%A A. Luotonen
.%A L. Stewart
.%D June 1999
.%B HTTP Authentication: Basic and Digest Access Authentication
.%O RFC2617
.Re
.Sh HISTORY
The
.Nm fetch
library first appeared in
.Fx 3.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm fetch
library was mostly written by
.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org
with numerous suggestions and contributions from
.An Jordan K. Hubbard Aq jkh@FreeBSD.org ,
.An Eugene Skepner Aq eu@qub.com ,
.An Hajimu Umemoto Aq ume@FreeBSD.org ,
.An Henry Whincup Aq henry@techiebod.com ,
.An Jukka A. Ukkonen Aq jau@iki.fi ,
.An Jean-Fran\(,cois Dockes Aq jf@dockes.org ,
.An Michael Gmelin Aq freebsd@grem.de
and others.
It replaces the older
.Nm ftpio
library written by
.An Poul-Henning Kamp Aq phk@FreeBSD.org
and
.An Jordan K. Hubbard Aq jkh@FreeBSD.org .
.Pp
This manual page was written by
.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org
and
.An Michael Gmelin Aq freebsd@grem.de .
.Sh BUGS
Some parts of the library are not yet implemented.
The most notable
examples of this are
.Fn fetchPutHTTP ,
.Fn fetchListHTTP ,
.Fn fetchListFTP
and FTP proxy support.
.Pp
There is no way to select a proxy at run-time other than setting the
.Ev HTTP_PROXY
or
.Ev FTP_PROXY
environment variables as appropriate.
.Pp
.Nm libfetch
does not understand or obey 305 (Use Proxy) replies.
.Pp
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.
.Pp
.Fn fetchStatFTP
does not check that the result of an MDTM command is a valid date.
.Pp
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.
.Pp
The man page is incomplete, poorly written and produces badly
formatted text.
.Pp
The error reporting mechanism is unsatisfactory.
.Pp
Some parts of the code are not fully reentrant.