Manual browser: fetch(3)

FETCH(3) Library Functions Manual FETCH(3)


fetchMakeURL, fetchParseURL, fetchCopyURL, 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 fetchInitURLList, fetchFreeURLList, fetchUnquotePath, fetchUnquoteFilename, fetchStringifyURL, fetchConnectionCacheInit, fetchConnectionCacheClose, fetchfile transfer functions


File Transfer Library (libfetch, -lfetch)


#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);

struct url *
fetchCopyURL(const struct url *u);

fetchFreeURL(struct url *u);

fetchIO *
fetchXGetURL(const char *URL, struct url_stat *us, const char *flags);

fetchIO *
fetchGetURL(const char *URL, const char *flags);

fetchIO *
fetchPutURL(const char *URL, const char *flags);

fetchStatURL(const char *URL, struct url_stat *us, const char *flags);

fetchListURL(struct url_list *list, const char *URL, const char *flags);

fetchIO *
fetchXGet(struct url *u, struct url_stat *us, const char *flags);

fetchIO *
fetchGet(struct url *u, const char *flags);

fetchIO *
fetchPut(struct url *u, const char *flags);

fetchStat(struct url *u, struct url_stat *us, const char *flags);

fetchList(struct url_list *list, struct url *u, const char *flags);

fetchIO *
fetchXGetFile(struct url *u, struct url_stat *us, const char *flags);

fetchIO *
fetchGetFile(struct url *u, const char *flags);

fetchIO *
fetchPutFile(struct url *u, const char *flags);

fetchStatFile(struct url *u, struct url_stat *us, const char *flags);

fetchListFile(struct url_list *list, struct url *u, const char *flags);

fetchIO *
fetchXGetHTTP(struct url *u, struct url_stat *us, const char *flags);

fetchIO *
fetchGetHTTP(struct url *u, const char *flags);

fetchIO *
fetchPutHTTP(struct url *u, const char *flags);

fetchStatHTTP(struct url *u, struct url_stat *us, const char *flags);

fetchListHTTP(struct url_list *list, struct url *u, const char *flags);

fetchIO *
fetchXGetFTP(struct url *u, struct url_stat *us, const char *flags);

fetchIO *
fetchGetFTP(struct url *u, const char *flags);

fetchIO *
fetchPutFTP(struct url *u, const char *flags);

fetchStatFTP(struct url *u, struct url_stat *us, const char *flags);

fetchListFTP(struct url_list *list, struct url *u, const char *flags);

fetchInitURLList(struct url_list *ul);

fetchAppendURLList(struct url_list *dst, const struct url_list *src);

fetchFreeURLList(struct url_list *ul);

char *
fetchUnquotePath(struct url *u);

char *
fetchUnquoteFilename(struct url *u);

char *
fetchStringifyURL(const struct url *u);

fetchConnectionCacheInit(int global, int per_host);



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 RFC 1738. A regular expression which produces this syntax is:


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.

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. fetchParseURL() quotes any unsafe character in the URL automatically. This is not done by fetchMakeURL(). fetchCopyURL() copies an existing url structure.

fetchMakeURL(), fetchParseURL(), and fetchCopyURL() 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 
#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; 

The pointer returned by fetchMakeURL(), fetchCopyURL(), and fetchParseURL() should be freed using fetchFreeURL(). The size of struct URL is not part of the ABI.

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. 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 url_list structure. The url_list structure is defined as follows in <fetch.h>:

struct url_list { 
    size_t	length; 
    size_t	alloc_size; 
    struct url	*urls; 

The list should be initialized by calling fetchInitURLList() and the entries be freed by calling fetchFreeURLList(). The function fetchAppendURLList() can be used to append one URL lists to another. If the ‘c’ (cache result) flag is specified, the library is allowed to internally cache the result.

fetchStringifyURL() returns the URL as string. fetchUnquotePath() returns the path name part of the URL with any quoting undone. Query arguments and fragment identifiers are not included. fetchUnquoteFilename() returns the last component of the path name as returned by fetchUnquotePath(). fetchStringifyURL(), fetchUnquotePath(), and fetchUnquoteFilename() return a string that should be deallocated with free() after use.

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. fetchConnectionCacheClose() flushed the connection cache and closes all cached connections.

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.


If the ‘i’ (if-modified-since) flag is specified, the library will try to fetch the content only if it is newer than last_modified. For HTTP an If-Modified-Since HTTP header is sent. For FTP a MTDM command is sent first and compared locally. For FILE the source file is compared.


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 RFC 959.

By default libfetch will attempt to use passive mode first and only fallback to active mode if the server reports a syntax error. If the ‘a’ (active) flag is specified, a passive connection is not tried and active mode is used directly.

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 RFC 2616 and RFC 2617.

If the ‘d’ (direct) flag is specified, fetchXGetHTTP(), fetchGetHTTP(), and fetchPutHTTP() will use a direct connection even if a proxy server is defined.

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.


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>:

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 host name or IP address to which sockets used for outgoing connections will be bound.
Default FTP login if none was provided in the URL.
If set to anything but ‘no’, forces the FTP code to use passive mode.
Default FTP password if the remote server requests one and none was provided in the URL.
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.

Same as FTP_PROXY, for compatibility.
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.

Basic authorization requires 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.

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.

Same as HTTP_PROXY, for compatibility.
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.

Specifies the referrer URL to use for HTTP requests. If set to “auto”, the document URL will be used as referrer URL.
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.
Specifies a file to use instead of ~/.netrc to look up login names and passwords for FTP sites. See ftp(1) for a description of the file format. This feature is experimental.
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.
Same as NO_PROXY, for compatibility.


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:



ftp(1), ip(4)

J. Postel and J. K. Reynolds, File Transfer Protocol, October 1985, RFC 959.

P. Deutsch, A. Emtage, and A. Marine, How to Use Anonymous FTP, May 1994, RFC 1635.

T. Berners-Lee, L. Masinter, and M. McCahill, Uniform Resource Locators (URL), December 1994, RFC 1738.

R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach, and T. Berners-Lee, Hypertext Transfer Protocol -- HTTP/1.1, January 1999, RFC 2616.

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, RFC 2617.


The fetch library first appeared in FreeBSD 3.0.


The fetch library was mostly written by Dag-Erling Smørgrav <> with numerous suggestions from Jordan K. Hubbard <>, Eugene Skepner <> and other FreeBSD developers. It replaces the older ftpio library written by Poul-Henning Kamp <> and Jordan K. Hubbard <>.

This manual page was written by Dag-Erling Smørgrav <>.


Some parts of the library are not yet implemented. The most notable examples of this are fetchPutHTTP() 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.

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.

January 22, 2010 NetBSD 7.0