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CLASS="APPLICATION"
>libpq</SPAN
> - C Library</TD
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="LIBPQ-CONNECT"
>31.1. Database Connection Control Functions</A
></H1
><P
> The following functions deal with making a connection to a
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> backend server. An
application program can have several backend connections open at
one time. (One reason to do that is to access more than one
database.) Each connection is represented by a
<TT
CLASS="STRUCTNAME"
>PGconn</TT
> object, which
is obtained from the function <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
>,
<CODE
CLASS="FUNCTION"
>PQconnectdbParams</CODE
>, or
<CODE
CLASS="FUNCTION"
>PQsetdbLogin</CODE
>. Note that these functions will always
return a non-null object pointer, unless perhaps there is too
little memory even to allocate the <TT
CLASS="STRUCTNAME"
>PGconn</TT
> object.
The <CODE
CLASS="FUNCTION"
>PQstatus</CODE
> function should be called to check
the return value for a successful connection before queries are sent
via the connection object.
<DIV
CLASS="WARNING"
><P
></P
><TABLE
CLASS="WARNING"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Warning</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> On Unix, forking a process with open libpq connections can lead to
unpredictable results because the parent and child processes share
the same sockets and operating system resources. For this reason,
such usage is not recommended, though doing an <CODE
CLASS="FUNCTION"
>exec</CODE
> from
the child process to load a new executable is safe.
</P
></TD
></TR
></TABLE
></DIV
>
</P><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> On Windows, there is a way to improve performance if a single
database connection is repeatedly started and shutdown. Internally,
libpq calls <CODE
CLASS="FUNCTION"
>WSAStartup()</CODE
> and <CODE
CLASS="FUNCTION"
>WSACleanup()</CODE
> for connection startup
and shutdown, respectively. <CODE
CLASS="FUNCTION"
>WSAStartup()</CODE
> increments an internal
Windows library reference count which is decremented by <CODE
CLASS="FUNCTION"
>WSACleanup()</CODE
>.
When the reference count is just one, calling <CODE
CLASS="FUNCTION"
>WSACleanup()</CODE
> frees
all resources and all DLLs are unloaded. This is an expensive
operation. To avoid this, an application can manually call
<CODE
CLASS="FUNCTION"
>WSAStartup()</CODE
> so resources will not be freed when the last database
connection is closed.
</P
></BLOCKQUOTE
></DIV
><P>
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQCONNECTDBPARAMS"
></A
><CODE
CLASS="FUNCTION"
>PQconnectdbParams</CODE
></DT
><DD
><P
> Makes a new connection to the database server.
</P><PRE
CLASS="SYNOPSIS"
>PGconn *PQconnectdbParams(const char * const *keywords,
const char * const *values,
int expand_dbname);</PRE
><P>
</P
><P
> This function opens a new database connection using the parameters taken
from two <TT
CLASS="SYMBOL"
>NULL</TT
>-terminated arrays. The first,
<TT
CLASS="LITERAL"
>keywords</TT
>, is defined as an array of strings, each one
being a key word. The second, <TT
CLASS="LITERAL"
>values</TT
>, gives the value
for each key word. Unlike <CODE
CLASS="FUNCTION"
>PQsetdbLogin</CODE
> below, the parameter
set can be extended without changing the function signature, so use of
this function (or its nonblocking analogs <CODE
CLASS="FUNCTION"
>PQconnectStartParams</CODE
>
and <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>) is preferred for new application
programming.
</P
><P
> The currently recognized parameter key words are listed in
<A
HREF="libpq-connect.html#LIBPQ-PARAMKEYWORDS"
>Section 31.1.2</A
>.
</P
><P
> When <TT
CLASS="LITERAL"
>expand_dbname</TT
> is non-zero, the
<TT
CLASS="PARAMETER"
>dbname</TT
> key word value is allowed to be recognized
as a connection string. Only the first occurrence of
<TT
CLASS="PARAMETER"
>dbname</TT
> is expanded this way, any subsequent
<TT
CLASS="PARAMETER"
>dbname</TT
> value is processed as plain database name. More
details on the possible connection string formats appear in
<A
HREF="libpq-connect.html#LIBPQ-CONNSTRING"
>Section 31.1.1</A
>.
</P
><P
> The passed arrays can be empty to use all default parameters, or can
contain one or more parameter settings. They should be matched in length.
Processing will stop with the last non-<TT
CLASS="SYMBOL"
>NULL</TT
> element
of the <TT
CLASS="LITERAL"
>keywords</TT
> array.
</P
><P
> If any parameter is unspecified, then the corresponding
environment variable (see <A
HREF="libpq-envars.html"
>Section 31.14</A
>)
is checked. If the environment variable is not set either,
then the indicated built-in defaults are used.
</P
><P
> In general key words are processed from the beginning of these arrays in index
order. The effect of this is that when key words are repeated, the last processed
value is retained. Therefore, through careful placement of the
<TT
CLASS="PARAMETER"
>dbname</TT
> key word, it is possible to determine what may
be overridden by a <TT
CLASS="PARAMETER"
>conninfo</TT
> string, and what may not.
</P
></DD
><DT
><A
NAME="LIBPQ-PQCONNECTDB"
></A
><CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
></DT
><DD
><P
> Makes a new connection to the database server.
</P><PRE
CLASS="SYNOPSIS"
>PGconn *PQconnectdb(const char *conninfo);</PRE
><P>
</P
><P
> This function opens a new database connection using the parameters taken
from the string <TT
CLASS="LITERAL"
>conninfo</TT
>.
</P
><P
> The passed string can be empty to use all default parameters, or it can
contain one or more parameter settings separated by whitespace,
or it can contain a <ACRONYM
CLASS="ACRONYM"
>URI</ACRONYM
>.
See <A
HREF="libpq-connect.html#LIBPQ-CONNSTRING"
>Section 31.1.1</A
> for details.
</P
></DD
><DT
><A
NAME="LIBPQ-PQSETDBLOGIN"
></A
><CODE
CLASS="FUNCTION"
>PQsetdbLogin</CODE
></DT
><DD
><P
> Makes a new connection to the database server.
</P><PRE
CLASS="SYNOPSIS"
>PGconn *PQsetdbLogin(const char *pghost,
const char *pgport,
const char *pgoptions,
const char *pgtty,
const char *dbName,
const char *login,
const char *pwd);</PRE
><P>
</P
><P
> This is the predecessor of <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
> with a fixed
set of parameters. It has the same functionality except that the
missing parameters will always take on default values. Write <TT
CLASS="SYMBOL"
>NULL</TT
> or an
empty string for any one of the fixed parameters that is to be defaulted.
</P
><P
> If the <TT
CLASS="PARAMETER"
>dbName</TT
> contains
an <TT
CLASS="SYMBOL"
>=</TT
> sign or has a valid connection <ACRONYM
CLASS="ACRONYM"
>URI</ACRONYM
> prefix, it
is taken as a <TT
CLASS="PARAMETER"
>conninfo</TT
> string in exactly the same way as
if it had been passed to <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
>, and the remaining
parameters are then applied as specified for <CODE
CLASS="FUNCTION"
>PQconnectdbParams</CODE
>.
</P
></DD
><DT
><A
NAME="LIBPQ-PQSETDB"
></A
><CODE
CLASS="FUNCTION"
>PQsetdb</CODE
></DT
><DD
><P
> Makes a new connection to the database server.
</P><PRE
CLASS="SYNOPSIS"
>PGconn *PQsetdb(char *pghost,
char *pgport,
char *pgoptions,
char *pgtty,
char *dbName);</PRE
><P>
</P
><P
> This is a macro that calls <CODE
CLASS="FUNCTION"
>PQsetdbLogin</CODE
> with null pointers
for the <TT
CLASS="PARAMETER"
>login</TT
> and <TT
CLASS="PARAMETER"
>pwd</TT
> parameters. It is provided
for backward compatibility with very old programs.
</P
></DD
><DT
><A
NAME="LIBPQ-PQCONNECTSTARTPARAMS"
></A
><CODE
CLASS="FUNCTION"
>PQconnectStartParams</CODE
><BR><CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
><BR><CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
></DT
><DD
><P
>
Make a connection to the database server in a nonblocking manner.
</P><PRE
CLASS="SYNOPSIS"
>PGconn *PQconnectStartParams(const char * const *keywords,
const char * const *values,
int expand_dbname);
PGconn *PQconnectStart(const char *conninfo);
PostgresPollingStatusType PQconnectPoll(PGconn *conn);</PRE
><P>
</P
><P
> These three functions are used to open a connection to a database server such
that your application's thread of execution is not blocked on remote I/O
whilst doing so. The point of this approach is that the waits for I/O to
complete can occur in the application's main loop, rather than down inside
<CODE
CLASS="FUNCTION"
>PQconnectdbParams</CODE
> or <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
>, and so the
application can manage this operation in parallel with other activities.
</P
><P
> With <CODE
CLASS="FUNCTION"
>PQconnectStartParams</CODE
>, the database connection is made
using the parameters taken from the <TT
CLASS="LITERAL"
>keywords</TT
> and
<TT
CLASS="LITERAL"
>values</TT
> arrays, and controlled by <TT
CLASS="LITERAL"
>expand_dbname</TT
>,
as described above for <CODE
CLASS="FUNCTION"
>PQconnectdbParams</CODE
>.
</P
><P
> With <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
>, the database connection is made
using the parameters taken from the string <TT
CLASS="LITERAL"
>conninfo</TT
> as
described above for <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
>.
</P
><P
> Neither <CODE
CLASS="FUNCTION"
>PQconnectStartParams</CODE
> nor <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
>
nor <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
> will block, so long as a number of
restrictions are met:
<P
></P
></P><UL
><LI
><P
> The <TT
CLASS="LITERAL"
>hostaddr</TT
> and <TT
CLASS="LITERAL"
>host</TT
> parameters are used appropriately to ensure that
name and reverse name queries are not made. See the documentation of
these parameters in <A
HREF="libpq-connect.html#LIBPQ-PARAMKEYWORDS"
>Section 31.1.2</A
> for details.
</P
></LI
><LI
><P
> If you call <CODE
CLASS="FUNCTION"
>PQtrace</CODE
>, ensure that the stream object
into which you trace will not block.
</P
></LI
><LI
><P
> You ensure that the socket is in the appropriate state
before calling <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>, as described below.
</P
></LI
></UL
><P>
</P
><P
> Note: use of <CODE
CLASS="FUNCTION"
>PQconnectStartParams</CODE
> is analogous to
<CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> shown below.
</P
><P
> To begin a nonblocking connection request, call <TT
CLASS="LITERAL"
>conn = PQconnectStart("<TT
CLASS="REPLACEABLE"
><I
>connection_info_string</I
></TT
>")</TT
>.
If <TT
CLASS="VARNAME"
>conn</TT
> is null, then <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> has been unable to allocate a new <TT
CLASS="STRUCTNAME"
>PGconn</TT
>
structure. Otherwise, a valid <TT
CLASS="STRUCTNAME"
>PGconn</TT
> pointer is returned (though not yet
representing a valid connection to the database). On return from
<CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
>, call <TT
CLASS="LITERAL"
>status = PQstatus(conn)</TT
>. If <TT
CLASS="VARNAME"
>status</TT
> equals
<TT
CLASS="SYMBOL"
>CONNECTION_BAD</TT
>, <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> has failed.
</P
><P
> If <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> succeeds, the next stage is to poll
<SPAN
CLASS="APPLICATION"
>libpq</SPAN
> so that it can proceed with the connection sequence.
Use <CODE
CLASS="FUNCTION"
>PQsocket(conn)</CODE
> to obtain the descriptor of the
socket underlying the database connection.
Loop thus: If <CODE
CLASS="FUNCTION"
>PQconnectPoll(conn)</CODE
> last returned
<TT
CLASS="SYMBOL"
>PGRES_POLLING_READING</TT
>, wait until the socket is ready to
read (as indicated by <CODE
CLASS="FUNCTION"
>select()</CODE
>, <CODE
CLASS="FUNCTION"
>poll()</CODE
>, or
similar system function).
Then call <CODE
CLASS="FUNCTION"
>PQconnectPoll(conn)</CODE
> again.
Conversely, if <CODE
CLASS="FUNCTION"
>PQconnectPoll(conn)</CODE
> last returned
<TT
CLASS="SYMBOL"
>PGRES_POLLING_WRITING</TT
>, wait until the socket is ready
to write, then call <CODE
CLASS="FUNCTION"
>PQconnectPoll(conn)</CODE
> again.
If you have yet to call
<CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>, i.e., just after the call to
<CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
>, behave as if it last returned
<TT
CLASS="SYMBOL"
>PGRES_POLLING_WRITING</TT
>. Continue this loop until
<CODE
CLASS="FUNCTION"
>PQconnectPoll(conn)</CODE
> returns
<TT
CLASS="SYMBOL"
>PGRES_POLLING_FAILED</TT
>, indicating the connection procedure
has failed, or <TT
CLASS="SYMBOL"
>PGRES_POLLING_OK</TT
>, indicating the connection
has been successfully made.
</P
><P
> At any time during connection, the status of the connection can be
checked by calling <CODE
CLASS="FUNCTION"
>PQstatus</CODE
>. If this call returns <TT
CLASS="SYMBOL"
>CONNECTION_BAD</TT
>, then the
connection procedure has failed; if the call returns <CODE
CLASS="FUNCTION"
>CONNECTION_OK</CODE
>, then the
connection is ready. Both of these states are equally detectable
from the return value of <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>, described above. Other states might also occur
during (and only during) an asynchronous connection procedure. These
indicate the current stage of the connection procedure and might be useful
to provide feedback to the user for example. These statuses are:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-CONNECTION-STARTED"
></A
><TT
CLASS="SYMBOL"
>CONNECTION_STARTED</TT
></DT
><DD
><P
> Waiting for connection to be made.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECTION-MADE"
></A
><TT
CLASS="SYMBOL"
>CONNECTION_MADE</TT
></DT
><DD
><P
> Connection OK; waiting to send.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECTION-AWAITING-RESPONSE"
></A
><TT
CLASS="SYMBOL"
>CONNECTION_AWAITING_RESPONSE</TT
></DT
><DD
><P
> Waiting for a response from the server.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECTION-AUTH-OK"
></A
><TT
CLASS="SYMBOL"
>CONNECTION_AUTH_OK</TT
></DT
><DD
><P
> Received authentication; waiting for backend start-up to finish.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECTION-SSL-STARTUP"
></A
><TT
CLASS="SYMBOL"
>CONNECTION_SSL_STARTUP</TT
></DT
><DD
><P
> Negotiating SSL encryption.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECTION-SETENV"
></A
><TT
CLASS="SYMBOL"
>CONNECTION_SETENV</TT
></DT
><DD
><P
> Negotiating environment-driven parameter settings.
</P
></DD
></DL
></DIV
><P>
Note that, although these constants will remain (in order to maintain
compatibility), an application should never rely upon these occurring in a
particular order, or at all, or on the status always being one of these
documented values. An application might do something like this:
</P><PRE
CLASS="PROGRAMLISTING"
>switch(PQstatus(conn))
{
case CONNECTION_STARTED:
feedback = "Connecting...";
break;
case CONNECTION_MADE:
feedback = "Connected to server...";
break;
.
.
.
default:
feedback = "Connecting...";
}</PRE
><P>
</P
><P
> The <TT
CLASS="LITERAL"
>connect_timeout</TT
> connection parameter is ignored
when using <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>; it is the application's
responsibility to decide whether an excessive amount of time has elapsed.
Otherwise, <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> followed by a
<CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
> loop is equivalent to
<CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
>.
</P
><P
> Note that if <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> returns a non-null pointer, you must call
<CODE
CLASS="FUNCTION"
>PQfinish</CODE
> when you are finished with it, in order to dispose of
the structure and any associated memory blocks. This must be done even if
the connection attempt fails or is abandoned.
</P
></DD
><DT
><A
NAME="LIBPQ-PQCONNDEFAULTS"
></A
><CODE
CLASS="FUNCTION"
>PQconndefaults</CODE
></DT
><DD
><P
> Returns the default connection options.
</P><PRE
CLASS="SYNOPSIS"
>PQconninfoOption *PQconndefaults(void);
typedef struct
{
char *keyword; /* The keyword of the option */
char *envvar; /* Fallback environment variable name */
char *compiled; /* Fallback compiled in default value */
char *val; /* Option's current value, or NULL */
char *label; /* Label for field in connect dialog */
char *dispchar; /* Indicates how to display this field
in a connect dialog. Values are:
"" Display entered value as is
"*" Password field - hide value
"D" Debug option - don't show by default */
int dispsize; /* Field size in characters for dialog */
} PQconninfoOption;</PRE
><P>
</P
><P
> Returns a connection options array. This can be used to determine
all possible <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
> options and their
current default values. The return value points to an array of
<TT
CLASS="STRUCTNAME"
>PQconninfoOption</TT
> structures, which ends
with an entry having a null <TT
CLASS="STRUCTFIELD"
>keyword</TT
> pointer. The
null pointer is returned if memory could not be allocated. Note that
the current default values (<TT
CLASS="STRUCTFIELD"
>val</TT
> fields)
will depend on environment variables and other context. Callers
must treat the connection options data as read-only.
</P
><P
> After processing the options array, free it by passing it to
<CODE
CLASS="FUNCTION"
>PQconninfoFree</CODE
>. If this is not done, a small amount of memory
is leaked for each call to <CODE
CLASS="FUNCTION"
>PQconndefaults</CODE
>.
</P
></DD
><DT
><A
NAME="LIBPQ-PQCONNINFOPARSE"
></A
><CODE
CLASS="FUNCTION"
>PQconninfoParse</CODE
></DT
><DD
><P
> Returns parsed connection options from the provided connection string.
</P><PRE
CLASS="SYNOPSIS"
>PQconninfoOption *PQconninfoParse(const char *conninfo, char **errmsg);</PRE
><P>
</P
><P
> Parses a connection string and returns the resulting options as an
array; or returns <TT
CLASS="SYMBOL"
>NULL</TT
> if there is a problem with the connection
string. This function can be used to extract
the <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
> options in the provided
connection string. The return value points to an array of
<TT
CLASS="STRUCTNAME"
>PQconninfoOption</TT
> structures, which ends
with an entry having a null <TT
CLASS="STRUCTFIELD"
>keyword</TT
> pointer.
</P
><P
> All legal options will be present in the result array, but the
<TT
CLASS="LITERAL"
>PQconninfoOption</TT
> for any option not present
in the connection string will have <TT
CLASS="LITERAL"
>val</TT
> set to
<TT
CLASS="LITERAL"
>NULL</TT
>; default values are not inserted.
</P
><P
> If <TT
CLASS="LITERAL"
>errmsg</TT
> is not <TT
CLASS="SYMBOL"
>NULL</TT
>, then <TT
CLASS="LITERAL"
>*errmsg</TT
> is set
to <TT
CLASS="SYMBOL"
>NULL</TT
> on success, else to a <CODE
CLASS="FUNCTION"
>malloc</CODE
>'d error string explaining
the problem. (It is also possible for <TT
CLASS="LITERAL"
>*errmsg</TT
> to be
set to <TT
CLASS="SYMBOL"
>NULL</TT
> and the function to return <TT
CLASS="SYMBOL"
>NULL</TT
>;
this indicates an out-of-memory condition.)
</P
><P
> After processing the options array, free it by passing it to
<CODE
CLASS="FUNCTION"
>PQconninfoFree</CODE
>. If this is not done, some memory
is leaked for each call to <CODE
CLASS="FUNCTION"
>PQconninfoParse</CODE
>.
Conversely, if an error occurs and <TT
CLASS="LITERAL"
>errmsg</TT
> is not <TT
CLASS="SYMBOL"
>NULL</TT
>,
be sure to free the error string using <CODE
CLASS="FUNCTION"
>PQfreemem</CODE
>.
</P
></DD
><DT
><A
NAME="LIBPQ-PQFINISH"
></A
><CODE
CLASS="FUNCTION"
>PQfinish</CODE
></DT
><DD
><P
> Closes the connection to the server. Also frees
memory used by the <TT
CLASS="STRUCTNAME"
>PGconn</TT
> object.
</P><PRE
CLASS="SYNOPSIS"
>void PQfinish(PGconn *conn);</PRE
><P>
</P
><P
> Note that even if the server connection attempt fails (as
indicated by <CODE
CLASS="FUNCTION"
>PQstatus</CODE
>), the application should call <CODE
CLASS="FUNCTION"
>PQfinish</CODE
>
to free the memory used by the <TT
CLASS="STRUCTNAME"
>PGconn</TT
> object.
The <TT
CLASS="STRUCTNAME"
>PGconn</TT
> pointer must not be used again after
<CODE
CLASS="FUNCTION"
>PQfinish</CODE
> has been called.
</P
></DD
><DT
><A
NAME="LIBPQ-PQRESET"
></A
><CODE
CLASS="FUNCTION"
>PQreset</CODE
></DT
><DD
><P
> Resets the communication channel to the server.
</P><PRE
CLASS="SYNOPSIS"
>void PQreset(PGconn *conn);</PRE
><P>
</P
><P
> This function will close the connection
to the server and attempt to reestablish a new
connection to the same server, using all the same
parameters previously used. This might be useful for
error recovery if a working connection is lost.
</P
></DD
><DT
><A
NAME="LIBPQ-PQRESETSTART"
></A
><CODE
CLASS="FUNCTION"
>PQresetStart</CODE
><BR><CODE
CLASS="FUNCTION"
>PQresetPoll</CODE
></DT
><DD
><P
> Reset the communication channel to the server, in a nonblocking manner.
</P><PRE
CLASS="SYNOPSIS"
>int PQresetStart(PGconn *conn);
PostgresPollingStatusType PQresetPoll(PGconn *conn);</PRE
><P>
</P
><P
> These functions will close the connection to the server and attempt to
reestablish a new connection to the same server, using all the same
parameters previously used. This can be useful for error recovery if a
working connection is lost. They differ from <CODE
CLASS="FUNCTION"
>PQreset</CODE
> (above) in that they
act in a nonblocking manner. These functions suffer from the same
restrictions as <CODE
CLASS="FUNCTION"
>PQconnectStartParams</CODE
>, <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
>
and <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>.
</P
><P
> To initiate a connection reset, call
<CODE
CLASS="FUNCTION"
>PQresetStart</CODE
>. If it returns 0, the reset has
failed. If it returns 1, poll the reset using
<CODE
CLASS="FUNCTION"
>PQresetPoll</CODE
> in exactly the same way as you
would create the connection using <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>.
</P
></DD
><DT
><A
NAME="LIBPQ-PQPINGPARAMS"
></A
><CODE
CLASS="FUNCTION"
>PQpingParams</CODE
></DT
><DD
><P
> <CODE
CLASS="FUNCTION"
>PQpingParams</CODE
> reports the status of the
server. It accepts connection parameters identical to those of
<CODE
CLASS="FUNCTION"
>PQconnectdbParams</CODE
>, described above. It is not, however,
necessary to supply correct user name, password, or database name
values to obtain the server status.
</P><PRE
CLASS="SYNOPSIS"
>PGPing PQpingParams(const char * const *keywords,
const char * const *values,
int expand_dbname);</PRE
><P>
The function returns one of the following values:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQPINGPARAMS-PQPING-OK"
></A
><TT
CLASS="LITERAL"
>PQPING_OK</TT
></DT
><DD
><P
> The server is running and appears to be accepting connections.
</P
></DD
><DT
><A
NAME="LIBPQ-PQPINGPARAMS-PQPING-REJECT"
></A
><TT
CLASS="LITERAL"
>PQPING_REJECT</TT
></DT
><DD
><P
> The server is running but is in a state that disallows connections
(startup, shutdown, or crash recovery).
</P
></DD
><DT
><A
NAME="LIBPQ-PQPINGPARAMS-PQPING-NO-RESPONSE"
></A
><TT
CLASS="LITERAL"
>PQPING_NO_RESPONSE</TT
></DT
><DD
><P
> The server could not be contacted. This might indicate that the
server is not running, or that there is something wrong with the
given connection parameters (for example, wrong port number), or
that there is a network connectivity problem (for example, a
firewall blocking the connection request).
</P
></DD
><DT
><A
NAME="LIBPQ-PQPINGPARAMS-PQPING-NO-ATTEMPT"
></A
><TT
CLASS="LITERAL"
>PQPING_NO_ATTEMPT</TT
></DT
><DD
><P
> No attempt was made to contact the server, because the supplied
parameters were obviously incorrect or there was some client-side
problem (for example, out of memory).
</P
></DD
></DL
></DIV
><P>
</P
></DD
><DT
><A
NAME="LIBPQ-PQPING"
></A
><CODE
CLASS="FUNCTION"
>PQping</CODE
></DT
><DD
><P
> <CODE
CLASS="FUNCTION"
>PQping</CODE
> reports the status of the
server. It accepts connection parameters identical to those of
<CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
>, described above. It is not, however,
necessary to supply correct user name, password, or database name
values to obtain the server status.
</P><PRE
CLASS="SYNOPSIS"
>PGPing PQping(const char *conninfo);</PRE
><P>
</P
><P
> The return values are the same as for <CODE
CLASS="FUNCTION"
>PQpingParams</CODE
>.
</P
></DD
></DL
></DIV
><P>
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-CONNSTRING"
>31.1.1. Connection Strings</A
></H2
><P
> Several <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> functions parse a user-specified string to obtain
connection parameters. There are two accepted formats for these strings:
plain <TT
CLASS="LITERAL"
>keyword = value</TT
> strings
and <A
HREF="http://www.ietf.org/rfc/rfc3986.txt"
TARGET="_top"
>RFC
3986</A
> URIs.
</P
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN38669"
>31.1.1.1. Keyword/Value Connection Strings</A
></H3
><P
> In the first format, each parameter setting is in the form
<TT
CLASS="LITERAL"
>keyword = value</TT
>. Spaces around the equal sign are
optional. To write an empty value, or a value containing spaces, surround it
with single quotes, e.g., <TT
CLASS="LITERAL"
>keyword = 'a value'</TT
>. Single
quotes and backslashes within
the value must be escaped with a backslash, i.e., <TT
CLASS="LITERAL"
>\'</TT
> and
<TT
CLASS="LITERAL"
>\\</TT
>.
</P
><P
> Example:
</P><PRE
CLASS="PROGRAMLISTING"
>host=localhost port=5432 dbname=mydb connect_timeout=10</PRE
><P>
</P
><P
> The recognized parameter key words are listed in <A
HREF="libpq-connect.html#LIBPQ-PARAMKEYWORDS"
>Section 31.1.2</A
>.
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN38680"
>31.1.1.2. Connection URIs</A
></H3
><P
> The general form for a connection <ACRONYM
CLASS="ACRONYM"
>URI</ACRONYM
> is:
</P><PRE
CLASS="SYNOPSIS"
>postgresql://[user[:password]@][netloc][:port][/dbname][?param1=value1&...]</PRE
><P>
</P
><P
> The <ACRONYM
CLASS="ACRONYM"
>URI</ACRONYM
> scheme designator can be either
<TT
CLASS="LITERAL"
>postgresql://</TT
> or <TT
CLASS="LITERAL"
>postgres://</TT
>. Each
of the <ACRONYM
CLASS="ACRONYM"
>URI</ACRONYM
> parts is optional. The following examples
illustrate valid <ACRONYM
CLASS="ACRONYM"
>URI</ACRONYM
> syntax uses:
</P><PRE
CLASS="PROGRAMLISTING"
>postgresql://
postgresql://localhost
postgresql://localhost:5433
postgresql://localhost/mydb
postgresql://user@localhost
postgresql://user:secret@localhost
postgresql://other@localhost/otherdb?connect_timeout=10&application_name=myapp</PRE
><P>
Components of the hierarchical part of the <ACRONYM
CLASS="ACRONYM"
>URI</ACRONYM
> can also
be given as parameters. For example:
</P><PRE
CLASS="PROGRAMLISTING"
>postgresql:///mydb?host=localhost&port=5433</PRE
><P>
</P
><P
> Percent-encoding may be used to include symbols with special meaning in any
of the <ACRONYM
CLASS="ACRONYM"
>URI</ACRONYM
> parts.
</P
><P
> Any connection parameters not corresponding to key words listed in <A
HREF="libpq-connect.html#LIBPQ-PARAMKEYWORDS"
>Section 31.1.2</A
> are ignored and a warning message about them
is sent to <TT
CLASS="FILENAME"
>stderr</TT
>.
</P
><P
> For improved compatibility with JDBC connection <ACRONYM
CLASS="ACRONYM"
>URI</ACRONYM
>s,
instances of parameter <TT
CLASS="LITERAL"
>ssl=true</TT
> are translated into
<TT
CLASS="LITERAL"
>sslmode=require</TT
>.
</P
><P
> The host part may be either host name or an IP address. To specify an
IPv6 host address, enclose it in square brackets:
</P><PRE
CLASS="SYNOPSIS"
>postgresql://[2001:db8::1234]/database</PRE
><P>
</P
><P
> The host component is interpreted as described for the parameter <A
HREF="libpq-connect.html#LIBPQ-CONNECT-HOST"
>host</A
>. In particular, a Unix-domain socket
connection is chosen if the host part is either empty or starts with a
slash, otherwise a TCP/IP connection is initiated. Note, however, that the
slash is a reserved character in the hierarchical part of the URI. So, to
specify a non-standard Unix-domain socket directory, either omit the host
specification in the URI and specify the host as a parameter, or
percent-encode the path in the host component of the URI:
</P><PRE
CLASS="PROGRAMLISTING"
>postgresql:///dbname?host=/var/lib/postgresql
postgresql://%2Fvar%2Flib%2Fpostgresql/dbname</PRE
><P>
</P
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-PARAMKEYWORDS"
>31.1.2. Parameter Key Words</A
></H2
><P
> The currently recognized parameter key words are:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-CONNECT-HOST"
></A
><TT
CLASS="LITERAL"
>host</TT
></DT
><DD
><P
> Name of host to connect to.
If this begins with a slash, it specifies Unix-domain
communication rather than TCP/IP communication; the value is the
name of the directory in which the socket file is stored. The
default behavior when <TT
CLASS="LITERAL"
>host</TT
> is not specified
is to connect to a Unix-domain
socket in
<TT
CLASS="FILENAME"
>/tmp</TT
> (or whatever socket directory was specified
when <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> was built). On machines without
Unix-domain sockets, the default is to connect to <TT
CLASS="LITERAL"
>localhost</TT
>.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-HOSTADDR"
></A
><TT
CLASS="LITERAL"
>hostaddr</TT
></DT
><DD
><P
> Numeric IP address of host to connect to. This should be in the
standard IPv4 address format, e.g., <TT
CLASS="LITERAL"
>172.28.40.9</TT
>. If
your machine supports IPv6, you can also use those addresses.
TCP/IP communication is
always used when a nonempty string is specified for this parameter.
</P
><P
> Using <TT
CLASS="LITERAL"
>hostaddr</TT
> instead of <TT
CLASS="LITERAL"
>host</TT
> allows the
application to avoid a host name look-up, which might be important
in applications with time constraints. However, a host name is
required for Kerberos, GSSAPI, or SSPI authentication
methods, as well as for <TT
CLASS="LITERAL"
>verify-full</TT
> SSL
certificate verification. The following rules are used:
<P
></P
></P><UL
><LI
><P
> If <TT
CLASS="LITERAL"
>host</TT
> is specified without <TT
CLASS="LITERAL"
>hostaddr</TT
>,
a host name lookup occurs.
</P
></LI
><LI
><P
> If <TT
CLASS="LITERAL"
>hostaddr</TT
> is specified without <TT
CLASS="LITERAL"
>host</TT
>,
the value for <TT
CLASS="LITERAL"
>hostaddr</TT
> gives the server network address.
The connection attempt will fail if the authentication
method requires a host name.
</P
></LI
><LI
><P
> If both <TT
CLASS="LITERAL"
>host</TT
> and <TT
CLASS="LITERAL"
>hostaddr</TT
> are specified,
the value for <TT
CLASS="LITERAL"
>hostaddr</TT
> gives the server network address.
The value for <TT
CLASS="LITERAL"
>host</TT
> is ignored unless the
authentication method requires it, in which case it will be
used as the host name.
</P
></LI
></UL
><P>
Note that authentication is likely to fail if <TT
CLASS="LITERAL"
>host</TT
>
is not the name of the server at network address <TT
CLASS="LITERAL"
>hostaddr</TT
>.
Also, note that <TT
CLASS="LITERAL"
>host</TT
> rather than <TT
CLASS="LITERAL"
>hostaddr</TT
>
is used to identify the connection in <TT
CLASS="FILENAME"
>~/.pgpass</TT
> (see
<A
HREF="libpq-pgpass.html"
>Section 31.15</A
>).
</P
><P
> Without either a host name or host address,
<SPAN
CLASS="APPLICATION"
>libpq</SPAN
> will connect using a
local Unix-domain socket; or on machines without Unix-domain
sockets, it will attempt to connect to <TT
CLASS="LITERAL"
>localhost</TT
>.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-PORT"
></A
><TT
CLASS="LITERAL"
>port</TT
></DT
><DD
><P
> Port number to connect to at the server host, or socket file
name extension for Unix-domain
connections.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-DBNAME"
></A
><TT
CLASS="LITERAL"
>dbname</TT
></DT
><DD
><P
> The database name. Defaults to be the same as the user name.
In certain contexts, the value is checked for extended
formats; see <A
HREF="libpq-connect.html#LIBPQ-CONNSTRING"
>Section 31.1.1</A
> for more details on
those.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-USER"
></A
><TT
CLASS="LITERAL"
>user</TT
></DT
><DD
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> user name to connect as.
Defaults to be the same as the operating system name of the user
running the application.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-PASSWORD"
></A
><TT
CLASS="LITERAL"
>password</TT
></DT
><DD
><P
> Password to be used if the server demands password authentication.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-CONNECT-TIMEOUT"
></A
><TT
CLASS="LITERAL"
>connect_timeout</TT
></DT
><DD
><P
> Maximum wait for connection, in seconds (write as a decimal integer
string). Zero or not specified means wait indefinitely. It is not
recommended to use a timeout of less than 2 seconds.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-CLIENT-ENCODING"
></A
><TT
CLASS="LITERAL"
>client_encoding</TT
></DT
><DD
><P
> This sets the <TT
CLASS="VARNAME"
>client_encoding</TT
>
configuration parameter for this connection. In addition to
the values accepted by the corresponding server option, you
can use <TT
CLASS="LITERAL"
>auto</TT
> to determine the right
encoding from the current locale in the client
(<TT
CLASS="ENVAR"
>LC_CTYPE</TT
> environment variable on Unix
systems).
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-OPTIONS"
></A
><TT
CLASS="LITERAL"
>options</TT
></DT
><DD
><P
> Adds command-line options to send to the server at run-time.
For example, setting this to <TT
CLASS="LITERAL"
>-c geqo=off</TT
> sets the
session's value of the <TT
CLASS="VARNAME"
>geqo</TT
> parameter to
<TT
CLASS="LITERAL"
>off</TT
>. For a detailed discussion of the available
options, consult <A
HREF="runtime-config.html"
>Chapter 18</A
>.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-APPLICATION-NAME"
></A
><TT
CLASS="LITERAL"
>application_name</TT
></DT
><DD
><P
> Specifies a value for the <A
HREF="runtime-config-logging.html#GUC-APPLICATION-NAME"
>application_name</A
>
configuration parameter.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-FALLBACK-APPLICATION-NAME"
></A
><TT
CLASS="LITERAL"
>fallback_application_name</TT
></DT
><DD
><P
> Specifies a fallback value for the <A
HREF="runtime-config-logging.html#GUC-APPLICATION-NAME"
>application_name</A
> configuration parameter.
This value will be used if no value has been given for
<TT
CLASS="LITERAL"
>application_name</TT
> via a connection parameter or the
<TT
CLASS="ENVAR"
>PGAPPNAME</TT
> environment variable. Specifying
a fallback name is useful in generic utility programs that
wish to set a default application name but allow it to be
overridden by the user.
</P
></DD
><DT
><A
NAME="LIBPQ-KEEPALIVES"
></A
><TT
CLASS="LITERAL"
>keepalives</TT
></DT
><DD
><P
> Controls whether client-side TCP keepalives are used. The default
value is 1, meaning on, but you can change this to 0, meaning off,
if keepalives are not wanted. This parameter is ignored for
connections made via a Unix-domain socket.
</P
></DD
><DT
><A
NAME="LIBPQ-KEEPALIVES-IDLE"
></A
><TT
CLASS="LITERAL"
>keepalives_idle</TT
></DT
><DD
><P
> Controls the number of seconds of inactivity after which TCP should
send a keepalive message to the server. A value of zero uses the
system default. This parameter is ignored for connections made via a
Unix-domain socket, or if keepalives are disabled.
It is only supported on systems where <TT
CLASS="SYMBOL"
>TCP_KEEPIDLE</TT
> or
an equivalent socket option is available, and on Windows; on other
systems, it has no effect.
</P
></DD
><DT
><A
NAME="LIBPQ-KEEPALIVES-INTERVAL"
></A
><TT
CLASS="LITERAL"
>keepalives_interval</TT
></DT
><DD
><P
> Controls the number of seconds after which a TCP keepalive message
that is not acknowledged by the server should be retransmitted. A
value of zero uses the system default. This parameter is ignored for
connections made via a Unix-domain socket, or if keepalives are disabled.
It is only supported on systems where <TT
CLASS="SYMBOL"
>TCP_KEEPINTVL</TT
> or
an equivalent socket option is available, and on Windows; on other
systems, it has no effect.
</P
></DD
><DT
><A
NAME="LIBPQ-KEEPALIVES-COUNT"
></A
><TT
CLASS="LITERAL"
>keepalives_count</TT
></DT
><DD
><P
> Controls the number of TCP keepalives that can be lost before the
client's connection to the server is considered dead. A value of
zero uses the system default. This parameter is ignored for
connections made via a Unix-domain socket, or if keepalives are disabled.
It is only supported on systems where <TT
CLASS="SYMBOL"
>TCP_KEEPCNT</TT
> or
an equivalent socket option is available; on other systems, it has no
effect.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-TTY"
></A
><TT
CLASS="LITERAL"
>tty</TT
></DT
><DD
><P
> Ignored (formerly, this specified where to send server debug output).
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-SSLMODE"
></A
><TT
CLASS="LITERAL"
>sslmode</TT
></DT
><DD
><P
> This option determines whether or with what priority a secure
<ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> TCP/IP connection will be negotiated with the
server. There are six modes:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>disable</TT
></DT
><DD
><P
> only try a non-<ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection
</P
></DD
><DT
><TT
CLASS="LITERAL"
>allow</TT
></DT
><DD
><P
> first try a non-<ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection; if that
fails, try an <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection
</P
></DD
><DT
><TT
CLASS="LITERAL"
>prefer</TT
> (default)</DT
><DD
><P
> first try an <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection; if that fails,
try a non-<ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection
</P
></DD
><DT
><TT
CLASS="LITERAL"
>require</TT
></DT
><DD
><P
> only try an <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection. If a root CA
file is present, verify the certificate in the same way as
if <TT
CLASS="LITERAL"
>verify-ca</TT
> was specified
</P
></DD
><DT
><TT
CLASS="LITERAL"
>verify-ca</TT
></DT
><DD
><P
> only try an <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection, and verify that
the server certificate is issued by a trusted
certificate authority (<ACRONYM
CLASS="ACRONYM"
>CA</ACRONYM
>)
</P
></DD
><DT
><TT
CLASS="LITERAL"
>verify-full</TT
></DT
><DD
><P
> only try an <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection, verify that the
server certificate is issued by a
trusted <ACRONYM
CLASS="ACRONYM"
>CA</ACRONYM
> and that the server host name
matches that in the certificate
</P
></DD
></DL
></DIV
><P>
See <A
HREF="libpq-ssl.html"
>Section 31.18</A
> for a detailed description of how
these options work.
</P
><P
> <TT
CLASS="LITERAL"
>sslmode</TT
> is ignored for Unix domain socket
communication.
If <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is compiled without SSL support,
using options <TT
CLASS="LITERAL"
>require</TT
>, <TT
CLASS="LITERAL"
>verify-ca</TT
>, or
<TT
CLASS="LITERAL"
>verify-full</TT
> will cause an error, while
options <TT
CLASS="LITERAL"
>allow</TT
> and <TT
CLASS="LITERAL"
>prefer</TT
> will be
accepted but <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> will not actually attempt
an <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
>
connection.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-REQUIRESSL"
></A
><TT
CLASS="LITERAL"
>requiressl</TT
></DT
><DD
><P
> This option is deprecated in favor of the <TT
CLASS="LITERAL"
>sslmode</TT
>
setting.
</P
><P
> If set to 1, an <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection to the server
is required (this is equivalent to <TT
CLASS="LITERAL"
>sslmode</TT
>
<TT
CLASS="LITERAL"
>require</TT
>). <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> will then refuse
to connect if the server does not accept an
<ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection. If set to 0 (default),
<SPAN
CLASS="APPLICATION"
>libpq</SPAN
> will negotiate the connection type with
the server (equivalent to <TT
CLASS="LITERAL"
>sslmode</TT
>
<TT
CLASS="LITERAL"
>prefer</TT
>). This option is only available if
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is compiled with SSL support.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-SSLCOMPRESSION"
></A
><TT
CLASS="LITERAL"
>sslcompression</TT
></DT
><DD
><P
> If set to 1 (default), data sent over SSL connections will be
compressed (this requires <SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
> version
0.9.8 or later).
If set to 0, compression will be disabled (this requires
<SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
> 1.0.0 or later).
This parameter is ignored if a connection without SSL is made,
or if the version of <SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
> used does not support
it.
</P
><P
> Compression uses CPU time, but can improve throughput if
the network is the bottleneck.
Disabling compression can improve response time and throughput
if CPU performance is the limiting factor.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-SSLCERT"
></A
><TT
CLASS="LITERAL"
>sslcert</TT
></DT
><DD
><P
> This parameter specifies the file name of the client SSL
certificate, replacing the default
<TT
CLASS="FILENAME"
>~/.postgresql/postgresql.crt</TT
>.
This parameter is ignored if an SSL connection is not made.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-SSLKEY"
></A
><TT
CLASS="LITERAL"
>sslkey</TT
></DT
><DD
><P
> This parameter specifies the location for the secret key used for
the client certificate. It can either specify a file name that will
be used instead of the default
<TT
CLASS="FILENAME"
>~/.postgresql/postgresql.key</TT
>, or it can specify a key
obtained from an external <SPAN
CLASS="QUOTE"
>"engine"</SPAN
> (engines are
<SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
> loadable modules). An external engine
specification should consist of a colon-separated engine name and
an engine-specific key identifier. This parameter is ignored if an
SSL connection is not made.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-SSLROOTCERT"
></A
><TT
CLASS="LITERAL"
>sslrootcert</TT
></DT
><DD
><P
> This parameter specifies the name of a file containing SSL
certificate authority (<ACRONYM
CLASS="ACRONYM"
>CA</ACRONYM
>) certificate(s).
If the file exists, the server's certificate will be verified
to be signed by one of these authorities. The default is
<TT
CLASS="FILENAME"
>~/.postgresql/root.crt</TT
>.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-SSLCRL"
></A
><TT
CLASS="LITERAL"
>sslcrl</TT
></DT
><DD
><P
> This parameter specifies the file name of the SSL certificate
revocation list (CRL). Certificates listed in this file, if it
exists, will be rejected while attempting to authenticate the
server's certificate. The default is
<TT
CLASS="FILENAME"
>~/.postgresql/root.crl</TT
>.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-REQUIREPEER"
></A
><TT
CLASS="LITERAL"
>requirepeer</TT
></DT
><DD
><P
> This parameter specifies the operating-system user name of the
server, for example <TT
CLASS="LITERAL"
>requirepeer=postgres</TT
>.
When making a Unix-domain socket connection, if this
parameter is set, the client checks at the beginning of the
connection that the server process is running under the specified
user name; if it is not, the connection is aborted with an error.
This parameter can be used to provide server authentication similar
to that available with SSL certificates on TCP/IP connections.
(Note that if the Unix-domain socket is in
<TT
CLASS="FILENAME"
>/tmp</TT
> or another publicly writable location,
any user could start a server listening there. Use this parameter
to ensure that you are connected to a server run by a trusted user.)
This option is only supported on platforms for which the
<TT
CLASS="LITERAL"
>peer</TT
> authentication method is implemented; see
<A
HREF="auth-methods.html#AUTH-PEER"
>Section 19.3.7</A
>.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-KRBSRVNAME"
></A
><TT
CLASS="LITERAL"
>krbsrvname</TT
></DT
><DD
><P
> Kerberos service name to use when authenticating with Kerberos 5
or GSSAPI.
This must match the service name specified in the server
configuration for Kerberos authentication to succeed. (See also
<A
HREF="auth-methods.html#KERBEROS-AUTH"
>Section 19.3.5</A
> and <A
HREF="auth-methods.html#GSSAPI-AUTH"
>Section 19.3.3</A
>.)
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-GSSLIB"
></A
><TT
CLASS="LITERAL"
>gsslib</TT
></DT
><DD
><P
> GSS library to use for GSSAPI authentication. Only used on Windows.
Set to <TT
CLASS="LITERAL"
>gssapi</TT
> to force libpq to use the GSSAPI
library for authentication instead of the default SSPI.
</P
></DD
><DT
><A
NAME="LIBPQ-CONNECT-SERVICE"
></A
><TT
CLASS="LITERAL"
>service</TT
></DT
><DD
><P
> Service name to use for additional parameters. It specifies a service
name in <TT
CLASS="FILENAME"
>pg_service.conf</TT
> that holds additional connection parameters.
This allows applications to specify only a service name so connection parameters
can be centrally maintained. See <A
HREF="libpq-pgservice.html"
>Section 31.16</A
>.
</P
></DD
></DL
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