apk-tools/libfetch/fetch.3

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.\" Copyright (c) 2010 Joerg Sonnenberger <joerg@NetBSD.org>
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.\" $FreeBSD: fetch.3,v 1.64 2007/12/18 11:03:26 des Exp $
.\" $NetBSD: fetch.3,v 1.17 2016/05/31 18:02:36 abhinav Exp $
.\"
.Dd January 22, 2010
.Dt FETCH 3
.Os
.Sh NAME
.Nm fetchMakeURL ,
.Nm fetchParseURL ,
.Nm fetchCopyURL ,
.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
.Nm fetchInitURLList ,
.Nm fetchFreeURLList ,
.Nm fetchUnquotePath ,
.Nm fetchUnquoteFilename ,
.Nm fetchStringifyURL ,
.Nm fetchConnectionCacheInit ,
.Nm fetchConnectionCacheClose ,
.Nm fetch
.Nd file transfer functions
.Sh LIBRARY
.Lb libfetch
.Sh SYNOPSIS
.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 struct url *
.Fn fetchCopyURL "const struct url *u"
.Ft void
.Fn fetchFreeURL "struct url *u"
.Ft fetchIO *
.Fn fetchXGetURL "const char *URL" "struct url_stat *us" "const char *flags"
.Ft fetchIO *
.Fn fetchGetURL "const char *URL" "const char *flags"
.Ft fetchIO *
.Fn fetchPutURL "const char *URL" "const char *flags"
.Ft int
.Fn fetchStatURL "const char *URL" "struct url_stat *us" "const char *flags"
.Ft int
.Fn fetchListURL "struct url_list *list" "const char *URL" "const char *pattern" "const char *flags"
.Ft fetchIO *
.Fn fetchXGet "struct url *u" "struct url_stat *us" "const char *flags"
.Ft fetchIO *
.Fn fetchGet "struct url *u" "const char *flags"
.Ft fetchIO *
.Fn fetchPut "struct url *u" "const char *flags"
.Ft int
.Fn fetchStat "struct url *u" "struct url_stat *us" "const char *flags"
.Ft int
.Fn fetchList "struct url_list *list" "struct url *u" "const char *pattern" "const char *flags"
.Ft fetchIO *
.Fn fetchXGetFile "struct url *u" "struct url_stat *us" "const char *flags"
.Ft fetchIO *
.Fn fetchGetFile "struct url *u" "const char *flags"
.Ft fetchIO *
.Fn fetchPutFile "struct url *u" "const char *flags"
.Ft int
.Fn fetchStatFile "struct url *u" "struct url_stat *us" "const char *flags"
.Ft int
.Fn fetchListFile "struct url_list *list" "struct url *u" "const char *pattern" "const char *flags"
.Ft fetchIO *
.Fn fetchXGetHTTP "struct url *u" "struct url_stat *us" "const char *flags"
.Ft fetchIO *
.Fn fetchGetHTTP "struct url *u" "const char *flags"
.Ft fetchIO *
.Fn fetchPutHTTP "struct url *u" "const char *flags"
.Ft int
.Fn fetchStatHTTP "struct url *u" "struct url_stat *us" "const char *flags"
.Ft int
.Fn fetchListHTTP "struct url_list *list" "struct url *u" "const char *pattern" "const char *flags"
.Ft fetchIO *
.Fn fetchXGetFTP "struct url *u" "struct url_stat *us" "const char *flags"
.Ft fetchIO *
.Fn fetchGetFTP "struct url *u" "const char *flags"
.Ft fetchIO *
.Fn fetchPutFTP "struct url *u" "const char *flags"
.Ft int
.Fn fetchStatFTP "struct url *u" "struct url_stat *us" "const char *flags"
.Ft int
.Fn fetchListFTP "struct url_list *list" "struct url *u" "const char *pattern" "const char *flags"
.Ft void
.Fn fetchInitURLList "struct url_list *ul"
.Ft int
.Fn fetchAppendURLList "struct url_list *dst" "const struct url_list *src"
.Ft void
.Fn fetchFreeURLList "struct url_list *ul"
.Ft char *
.Fn fetchUnquotePath "struct url *u"
.Ft char *
.Fn fetchUnquoteFilename "struct url *u"
.Ft char *
.Fn fetchStringifyURL "const struct url *u"
.Ft void
.Fn fetchConnectionCacheInit "int global" "int per_host"
.Ft void
.Fn fetchConnectionCacheClose "void"
.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 RFC 1738.
A regular expression which produces this syntax is:
.Bd -literal -offset indent
\*[Lt]scheme\*[Gt]:(//(\*[Lt]user\*[Gt](:\*[Lt]pwd\*[Gt])?@)?\*[Lt]host\*[Gt](:\*[Lt]port\*[Gt])?)?/(\*[Lt]doc\*[Gt])?
.Ed
.Pp
If the URL does not seem to begin with a scheme name, it is assumed to be a local path.
Only absolute path names are accepted.
.Pp
Note that some components of the URL are not necessarily relevant to
all URL schemes.
For instance, the file scheme only needs the
.Aq scheme
and
.Aq doc
components.
.Fn fetchParseURL
quotes any unsafe character in the URL automatically.
This is not done by
.Fn fetchMakeURL .
.Fn fetchCopyURL
copies an existing
.Vt url
structure.
.Pp
.Fn fetchMakeURL ,
.Fn fetchParseURL ,
and
.Fn fetchCopyURL
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
#define URL_HOSTLEN 255

struct url {
    char	 scheme[URL_SCHEMELEN + 1];
    char	 user[URL_USERLEN + 1];
    char	 pwd[URL_PWDLEN + 1];
    char	 host[URL_HOSTLEN + 1];
    int		 port;
    char	*doc;
    off_t	 offset;
    size_t	 length;
    time_t	 last_modified;
};
.Ed
.Pp
The pointer returned by
.Fn fetchMakeURL ,
.Fn fetchCopyURL ,
and
.Fn fetchParseURL
should be freed using
.Fn fetchFreeURL .
The size of
.Vt struct URL
is not part of the ABI.
.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.
The pattern can be a simple glob-like expression as hint.
Callers should not depend on the server to filter names.
If successful, it appends the list of entries to the
.Vt url_list
structure.
The
.Vt url_list
structure is defined as follows in
.In fetch.h :
.Bd -literal
struct url_list {
    size_t	length;
    size_t	alloc_size;
    struct url	*urls;
};
.Ed
.Pp
The list should be initialized by calling
.Fn fetchInitURLList
and the entries be freed by calling
.Fn fetchFreeURLList .
The function
.Fn fetchAppendURLList
can be used to append one URL lists to another.
If the
.Ql c
(cache result) flag is specified, the library is allowed to internally
cache the result.
.Pp
.Fn fetchStringifyURL
returns the URL as string.
.Fn fetchUnquotePath
returns the path name part of the URL with any quoting undone.
Query arguments and fragment identifiers are not included.
.Fn fetchUnquoteFilename
returns the last component of the path name as returned by
.Fn fetchUnquotePath .
.Fn fetchStringifyURL ,
.Fn fetchUnquotePath ,
and
.Fn fetchUnquoteFilename
return a string that should be deallocated with
.Fn free
after use.
.Pp
.Fn fetchConnectionCacheInit
enables the connection cache.
The first argument specifies the global limit on cached connections.
The second argument specifies the host limit.
Entries are considered to specify the same host, if the host name
from the URL is identical, indepent of the address or address family.
.Fn fetchConnectionCacheClose
flushed the connection cache and closes all cached connections.
.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 PROTOCOL INDEPENDENT FLAGS
If the
.Ql i
(if-modified-since) flag is specified, the library will try to fetch
the content only if it is newer than
.Va last_modified .
For HTTP an
.Li If-Modified-Since
HTTP header is sent.
For FTP a
.Li MTDM
command is sent first and compared locally.
For FILE the source file is compared.
.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
.Aq 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 RFC 959.
.Pp
By default
.Nm libfetch
will attempt to use passive mode first and only fallback to active mode
if the server reports a syntax error.
If the
.Ql a
(active) flag is specified, a passive connection is not tried and active mode
is used directly.
.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@\*[Lt]hostname\*[Gt]".
.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 RFC 2616 and RFC 2617.
.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
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 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
.Dv 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
.Dv 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 host name 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 anything but
.Ql no ,
forces the FTP code to use passive 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_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, only basic authorization is supported.
.Pp
Basic authorization requires 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.
.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://\*[Lt]user\*[Gt]:\*[Lt]pwd\*[Gt]@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:*:\*[Lt]user\*[Gt]:\*[Lt]pwd\*[Gt]
.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
.Sh SEE ALSO
.\" .Xr fetch 1 ,
.\" .Xr ftpio 3 ,
.Xr ftp 1 ,
.Xr ip 4
.Rs
.%A J. Postel
.%A J. K. Reynolds
.%D October 1985
.%B File Transfer Protocol
.%O RFC 959
.Re
.Rs
.%A P. Deutsch
.%A A. Emtage
.%A A. Marine
.%D May 1994
.%T How to Use Anonymous FTP
.%O RFC 1635
.Re
.Rs
.%A T. Berners-Lee
.%A L. Masinter
.%A M. McCahill
.%D December 1994
.%T Uniform Resource Locators (URL)
.%O RFC 1738
.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 RFC 2616
.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 RFC 2617
.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 Mt des@FreeBSD.org
with numerous suggestions from
.An Jordan K. Hubbard Aq Mt jkh@FreeBSD.org ,
.An Eugene Skepner Aq Mt eu@qub.com
and other
.Fx
developers.
It replaces the older
.Nm ftpio
library written by
.An Poul-Henning Kamp Aq Mt phk@FreeBSD.org
and
.An Jordan K. Hubbard Aq Mt jkh@FreeBSD.org .
.Pp
This manual page was written by
.An Dag-Erling Sm\(/orgrav Aq Mt des@FreeBSD.org .
.Sh BUGS
Some parts of the library are not yet implemented.
The most notable
examples of this are
.Fn fetchPutHTTP
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
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.