Content-type: text/html Man page of getservbyname

getservbyname

Section: Sockets Library Functions (3SOCKET)
Updated: 5 Apr 2004
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NAME

getservbyname, getservbyname_r, getservbyport, getservbyport_r, getservent, getservent_r, setservent, endservent - get service entry  

SYNOPSIS

cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]
#include <netdb.h>

struct servent *getservbyname(const char *name, const char *proto);

struct servent *getservbyname_r(const char *name, const char *proto, struct servent *result, char *buffer, int buflen);

struct servent *getservbyport(int port, const char *proto);

struct servent *getservbyport_r(int port, const char *proto, struct servent *result, char *buffer, int buflen);

struct servent *getservent(void);

struct servent *getservent_r(struct servent *result, char *buffer, int buflen);

int setservent(int stayopen);

int endservent(void);  

DESCRIPTION

These functions are used to obtain entries for Internet services. An entry may come from any of the sources for services specified in the /etc/nsswitch.conf file. See nsswitch.conf(4).

The getservbyname() and getservbyport() functions sequentially search from the beginning of the file until a matching protocol name or port number is found, or until end-of-file is encountered. If a protocol name is also supplied (non-null), searches must also match the protocol.

The getservbyname() function searches for an entry with the Internet service name specified by the name parameter.

The getservbyport() function searches for an entry with the Internet port number port.

All addresses are returned in network order. In order to interpret the addresses, byteorder(3SOCKET)

must be used for byte order conversion. The string proto is used by both getservbyname() and getservbyport() to restrict the search to entries with the specified protocol. If proto is NULL, entries with any protocol can be returned.

The functions setservent(), getservent(), and endservent() are used to enumerate entries from the services database.

The setservent() function sets (or resets) the enumeration to the beginning of the set of service entries. This function should be called before the first call to getservent(). Calls to the functions getservbyname() and getservbyport() leave the enumeration position in an indeterminate state. If the stayopen flag is non-zero, the system may keep allocated resources such as open file descriptors until a subsequent call to endservent().

The getservent() function reads the next line of the file, opening the file if necessary. getservent() opens and rewinds the file. If the stayopen flag is non-zero, the net data base will not be closed after each call to getservent() (either directly, or indirectly through one of the other "getserv" calls).

Successive calls to getservent() return either successive entries or NULL, indicating the end of the enumeration.

The endservent() function closes the file. The endservent() function can be called to indicate that the caller expects to do no further service entry retrieval operations; the system can then deallocate resources it was using. It is still allowed, but possibly less efficient, for the process to call more service entry retrieval functions after calling endservent().  

Reentrant Interfaces

The functions getservbyname(), getservbyport(), and getservent() use static storage that is re-used in each call, making these functions unsafe for use in multithreaded applications.

The functions getservbyname_r(), getservbyport_r(), and getservent_r() provide reentrant interfaces for these operations.

Each reentrant interface performs the same operation as its non-reentrant counterpart, named by removing the "_r" suffix. The reentrant interfaces, however, use buffers supplied by the caller to store returned results, and are safe for use in both single-threaded and multithreaded applications.

Each reentrant interface takes the same parameters as its non-reentrant counterpart, as well as the following additional parameters. The parameter result must be a pointer to a struct servent structure allocated by the caller. On successful completion, the function returns the service entry in this structure. The parameter buffer must be a pointer to a buffer supplied by the caller. This buffer is used as storage space for the service entry data. All of the pointers within the returned struct servent result point to data stored within this buffer. See the RETURN VALUES section of this manual page. The buffer must be large enough to hold all of the data associated with the service entry. The parameter buflen should give the size in bytes of the buffer indicated by buffer.

For enumeration in multithreaded applications, the position within the enumeration is a process-wide property shared by all threads. The setservent() function can be used in a multithreaded application but resets the enumeration position for all threads. If multiple threads interleave calls to getservent_r(), the threads will enumerate disjoint subsets of the service database.

Like their non-reentrant counterparts, getservbyname_r() and getservbyport_r() leave the enumeration position in an indeterminate state.  

RETURN VALUES

Service entries are represented by the struct servent structure defined in <netdb.h>:

struct  servent {
    char        *s_name;                      /* official name of service */
    char        **s_aliases;               /* alias list */ 
    int s_port;                    /* port service resides at */ 
    char        *s_proto;                     /* protocol to use */
};

The members of this structure are:

s_name The official name of the service.

s_aliases A zero terminated list of alternate names for the service.    

s_port The port number at which the service resides. Port numbers are                  returned in network byte order.

s_proto The name of the protocol to use when contacting the service

The functions getservbyname(), getservbyname_r(), getservbyport(), and getservbyport_r() each return a pointer to a struct servent if they successfully locate the requested entry; otherwise they return NULL.

The functions getservent() and getservent_r() each return a pointer to a struct servent if they successfully enumerate an entry; otherwise they return NULL, indicating the end of the enumeration.

The functions getservbyname(), getservbyport(), and getservent() use static storage, so returned data must be copied before a subsequent call to any of these functions if the data is to be saved.

When the pointer returned by the reentrant functions getservbyname_r(), getservbyport_r(), and getservent_r() is non-null, it is always equal to the result pointer that was supplied by the caller.  

ERRORS

The reentrant functions getservbyname_r(), getservbyport_r(), and getservent_r() return NULL and set errno to ERANGE if the length of the buffer supplied by caller is not large enough to store the result. See intro(2) for the proper usage and interpretation of errno in multithreaded applications.  

FILES

/etc/services Internet network services

/etc/netconfig network configuration file

/etc/nsswitch.conf configuration file for the name-service switch

 

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPEATTRIBUTE VALUE
MT-Level See "Reentrant Interfaces" in DESCRIPTION.

 

SEE ALSO

intro(2), intro(3), byteorder(3SOCKET), netdir(3NSL), netconfig(4), nsswitch.conf(4), services(4), attributes(5), netdb.h(3HEAD)  

WARNINGS

The reentrant interfaces getservbyname_r(), getservbyport_r(), and getservent_r() are included in this release on an uncommitted basis only, and are subject to change or removal in future minor releases.  

NOTES

The functions that return struct servent return the least significant 16-bits of the s_port field in network byte order. getservbyport() and getservbyport_r() also expect the input parameter port in the network byte order. See htons(3SOCKET) for more details on converting between host and network byte orders.

To ensure that they all return consistent results, getservbyname(), getservbyname_r(), and netdir_getbyname() are implemented in terms of the same internal library function. This function obtains the system-wide source lookup policy based on the inet family entries in netconfig(4) and the services: entry in nsswitch.conf(4). Similarly, getservbyport(), getservbyport_r(), and netdir_getbyaddr() are implemented in terms of the same internal library function. If the inet family entries in netconfig(4) have a ``-'' in the last column for nametoaddr libraries, then the entry for services in nsswitch.conf will be used; otherwise the nametoaddr libraries in that column will be used, and nsswitch.conf will not be consulted.

There is no analogue of getservent() and getservent_r() in the netdir functions, so these enumeration functions go straight to the services entry in nsswitch.conf. Thus enumeration may return results from a different source than that used by getservbyname(), getservbyname_r(), getservbyport(), and getservbyport_r().

When compiling multithreaded applications, see intro(3), Notes On Multithread Applications, for information about the use of the _REENTRANT flag.

Use of the enumeration interfaces getservent() and getservent_r() is discouraged; enumeration may not be supported for all database sources. The semantics of enumeration are discussed further in nsswitch.conf(4).


 

Index

NAME
SYNOPSIS
DESCRIPTION
Reentrant Interfaces
RETURN VALUES
ERRORS
FILES
ATTRIBUTES
SEE ALSO
WARNINGS
NOTES

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Time: 02:38:31 GMT, October 02, 2010