__pmParseHostAttrsSpec(3) host and attributes specification parser

Other Alias

__pmUnparseHostAttrsSpec, __pmFreeHostAttrsSpec, __pmFreeAttrsSpec


#include <pcp/pmapi.h>
#include <pcp/impl.h>

int __pmParseHostAttrsSpec(const char *string, pmHostSpec **hostsp, int *count, __pmHashCtl *attrs, char **errmsg);

int __pmUnparseHostAttrsSpec(pmHostSpec *hostsp, int *count, __pmHashCtl *attrs, char *string, size_t size);

void __pmFreeHostAttrsSpec(pmHostSpec *hosts, int count, __pmHashCtl *attrs);

void __pmFreeAttrsSpec(__pmHashCtl *attrs);

cc ... -lpcp


__pmParseHostAttrsSpec accepts a string specifying the location of a PCP performance metric collector daemon, and any attributes that should be associated with the connection to that daemon.

The syntax allows the optional specification of a protocol (native PCP protocol, encrypted PCP protocol or unix domain socket protocol).

If the specified protocol is native PCP protocol, or encrypted PCP protocol, an initial pmcd(1) hostname with optional port numbers and optional proxy host, and optional attributes which are to be associated with the connection may be specified. Some examples follow:

pcp://nas1.servers.com:[email protected]?compress

If the specified protocol is a unix domain socket protocol, the path to the socket in the local file system may be specified along with optional attributes which are to be associated with the connection. For example:


If the optional protocol component is not specified, then the default setting will be used - which is the native PCP binary protocol. However, this can still be overwritten via the environment as described in PCPIntro(1). If the protocol prefix is specified, it must be one of either "pcp://" (clear), "pcps://" (secure, encrypted), "unix://" (authenticated local) or "local://" ("unix://" then "pcp://").

The path specified for the "unix://" and "local://" protocols will always be interpreted as an absolute path name. For example, the following are all interpreted identically as $PCP_RUN_DIR/pmcd.socket.


Refer to __pmParseHostSpec(3) for further details of the host and proxy host components.

If any optional connection attributes are to be specified, these are separated from the hostname component via the '?' character. Each attribute is separated by the '&' character, and each can be either a simple attribute flag (such as "compress") or a name=value pair (such as "username=fred").

__pmParseHostAttrsSpec takes a null-terminated host-and-attributes specification string and returns an array of pmHostSpec structures, where the array has count entries, and an attrs hash table containing any attributes (including the optional protocol, if it was specified).

Full details of the pmHostSpec structures are provided in __pmParseHostSpec(3).

The __pmHashCtl structure that is filled out on return via attributes, represents each individual attribute in the specification string with any associated value. It should be considered an opaque structure and should be zeroed beforehand.

The returned hash table control structure can be iterated using one of the supplied iteration mechanisms - __pmHashWalkCB (a callback-based mechanism) or __pmHashWalk (a simple procedural mechanism). These provide access to the individual hash nodes, as __pmHashNode entries, which provide access to decoded attributes and their (optional) values.

    typedef struct __pmHashNode {
        __pmHashNode    *next;    /* next node in hash bucket (internal) */
        unsigned int    key;      /* key identifying particular attribute */
        void            *data;    /* attributes value (optional, string) */
    } __pmHashNode;

There are a set number of valid attributes, however these may be extended in future releases as new connection parameters become needed. These can be identified via the PCP_ATTR_* macros in the PCP header files.

__pmUnparseHostSpec performs the inverse operation, creating a string representation from hosts and attributes structures. The size of the supplied string buffer must be provided by the caller using the size parameter.


If the given string is successfully parsed __pmParseHostAttrsSpec returns zero. In this case the dynamic storage allocated by __pmParseHostAttrsSpec can be released by calling __pmFreeHostAttrsSpec using the addresses returned from __pmParseHostAttrsSpec

Alternatively, the hosts and attributes memory can be freed separately, using __pmFreeHostSpec(3) and __pmFreeAttrsSpec.

__pmParseHostAttrsSpec returns PM_ERR_GENERIC and a dynamically allocated error message string in errmsg, if the given string does not parse, and the user-supplied errmsg pointer is non-null. Be sure to free(3) the error message string in this situation.

In the case of an error, both hosts and attributes are undefined. In the case of success, errmsg is undefined.

On success __pmUnparseHostAttrsSpec returns a positive value indicating the number of characters written into the supplied buffer. However, if the supplied buffer was too small, a negative status code of -E2BIG will be returned.