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Manual Reference Pages  -  FETCHFREEURL (3)


fetchMakeURL, fetchParseURL, fetchFreeURL, fetchXGetURL, fetchGetURL, fetchPutURL, fetchStatURL, fetchListURL, fetchXGet, fetchGet, fetchPut, fetchStat, fetchList, fetchXGetFile, fetchGetFile, fetchPutFile, fetchStatFile, fetchListFile, fetchXGetHTTP, fetchGetHTTP, fetchPutHTTP, fetchStatHTTP, fetchListHTTP, fetchXGetFTP, fetchGetFTP, fetchPutFTP, fetchStatFTP, fetchListFTP - file transfer functions


File Scheme
Ftp Scheme
Http Scheme
Https Scheme
Return Values
See Also


.Lb libfetch


.In sys/param.h
.In stdio.h
.In 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 * 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:


If the URL does not seem to begin with a scheme name, the following syntax is assumed:


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
.Vt url structure, which is defined as follows in
.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
.Vt 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
.Vt url_stat structure is defined as follows in
.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
.Vt url_ent structures. The
.Vt url_ent structure is defined as follows in
.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
.Vt 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 and fetchPutHTTP 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
.Vt 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.

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 /etc/ssl/cert.pem. The file may 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. In case the key is stored in a separate file, the environment variable 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 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
.Vt 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
.Vt 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
.Vt 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
.In fetch.h :
  Operation aborted
  Authentication failed
  Service unavailable
  File exists
  File system full
  Informational response
  Insufficient memory
  File has moved
  Network error
  No error
  Protocol error
  Resolver error
  Server error
  Temporary error
  Operation timed out
  File is not available
  Unknown error
  Invalid URL

The accompanying error message includes a protocol-specific error code and message, e.g. "File is not available (404 Not Found)"


  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.
SSL_ALLOW_SSL3 Allow SSL version 3 when negotiating the connection (not recommended).
SSL_CA_CERT_FILE CA certificate bundle containing trusted CA certificates. Default value: /etc/ssl/cert.pem.
SSL_CA_CERT_PATH Path containing trusted CA hashes.
  PEM encoded client certificate/key which will be used in client certificate authentication.
  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.
  If set, do not verify that the hostname matches the subject of the certificate presented by the server.
  If set, do not verify the peer certificate against trusted CAs.


To access a proxy server on port 8080, set the HTTP_PROXY environment variable in a manner similar to this:


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:


The second method is by using the HTTP_PROXY_AUTH environment variable:


To disable the use of a proxy for an HTTP server running on the local host, define NO_PROXY as follows:


Access HTTPS website without any certificate verification whatsoever:


Access HTTPS website using client certificate based authentication and a private CA:



fetch(1), ftpio(3), ip(4)
.Rs How to Use Anonymous FTP
.Rs Uniform Resource Locators (URL)


The fetch library first appeared in
.Fx 3.0 .


.An -nosplit The fetch library was mostly written by
.An Dag-Erling Sm\(/orgrav Aq with numerous suggestions and contributions from
.An Jordan K. Hubbard Aq ,
.An Eugene Skepner Aq ,
.An Hajimu Umemoto Aq ,
.An Henry Whincup Aq ,
.An Jukka A. Ukkonen Aq ,
.An Jean-Fran\(,cois Dockes Aq ,
.An Michael Gmelin Aq and others. It replaces the older ftpio library written by
.An Poul-Henning Kamp Aq and
.An Jordan K. Hubbard Aq .

This manual page was written by
.An Dag-Erling Sm\(/orgrav Aq and
.An Michael Gmelin Aq .


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.

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