Introduce two new libpq connection functions, PQconnectdbParams and

PQconnectStartParams. These are analogous to PQconnectdb and PQconnectStart
respectively. They differ from the legacy functions in that they accept
two NULL-terminated arrays, keywords and values, rather than conninfo
strings. This avoids the need to build the conninfo string in cases
where it might be inconvenient to do so. Includes documentation.

Also modify psql to utilize PQconnectdbParams rather than PQsetdbLogin.
This allows the new config parameter application_name to be set, which
in turn is displayed in the pg_stat_activity view and included in CSV
log entries. This will also ensure both new functions get regularly
exercised.

Patch by Guillaume Lelarge with review and minor adjustments by
Joe Conway.

1 files changed, 84 insertions, 33 deletions

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 1d13e8b0b4e..a698ab1958d 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/libpq.sgml,v 1.295 2010/01/21 14:58:52 rhaas Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/libpq.sgml,v 1.296 2010/01/28 06:28:26 joe Exp $ -->
 
 <chapter id="libpq">
  <title><application>libpq</application> - C Library</title>
@@ -56,7 +56,8 @@
    one time.  (One reason to do that is to access more than one
    database.)  Each connection is represented by a
    <structname>PGconn</><indexterm><primary>PGconn</></> object, which
-   is obtained from the function <function>PQconnectdb</> or
+   is obtained from the function <function>PQconnectdb</>,
+   <function>PQconnectdbParams</>, or
    <function>PQsetdbLogin</>.  Note that these functions will always
    return a non-null object pointer, unless perhaps there is too
    little memory even to allocate the <structname>PGconn</> object.
@@ -91,35 +92,33 @@
 
    <variablelist>
     <varlistentry>
-     <term><function>PQconnectdb</function><indexterm><primary>PQconnectdb</></></term>
+     <term><function>PQconnectdbParams</function><indexterm><primary>PQconnectdbParams</></></term>
      <listitem>
       <para>
        Makes a new connection to the database server.
 
        <synopsis>
-        PGconn *PQconnectdb(const char *conninfo);
+        PGconn *PQconnectdbParams(const char **keywords, const char **values);
        </synopsis>
       </para>
 
       <para>
        This function opens a new database connection using the parameters taken
-       from the string <literal>conninfo</literal>.  Unlike <function>PQsetdbLogin</> below,
-       the parameter set can be extended without changing the function signature,
-       so use of this function (or its nonblocking analogues <function>PQconnectStart</>
-       and <function>PQconnectPoll</function>) is preferred for new application programming.
+       from two <symbol>NULL</symbol>-terminated arrays. The first,
+       <literal>keywords</literal>, is defined as an array of strings, each one
+       being a key word. The second, <literal>values</literal>, gives the value
+       for each key word. Unlike <function>PQsetdbLogin</> below, the parameter
+       set can be extended without changing the function signature, so use of
+       this function (or its nonblocking analogs <function>PQconnectStartParams</>
+       and <function>PQconnectPoll</function>) is preferred for new application
+       programming.
       </para>
 
       <para>
-       The passed string
-       can be empty to use all default parameters, or it can contain one or more
-       parameter settings separated by whitespace.
-       Each parameter setting is in the form <literal>keyword = value</literal>.
-       Spaces around the equal sign are optional.
-       To write an empty value or a value containing
-       spaces, surround it with single quotes, e.g.,
-       <literal>keyword = 'a value'</literal>.
-       Single quotes and backslashes within the value must be escaped with a
-       backslash, i.e., <literal>\'</literal> and <literal>\\</literal>.
+       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-<symbol>NULL</symbol> element
+       of the <literal>keywords</literal> array.
       </para>
 
       <para>
@@ -478,6 +477,39 @@
     </varlistentry>
 
     <varlistentry>
+     <term><function>PQconnectdb</function><indexterm><primary>PQconnectdb</></></term>
+     <listitem>
+      <para>
+       Makes a new connection to the database server.
+
+       <synopsis>
+        PGconn *PQconnectdb(const char *conninfo);
+       </synopsis>
+      </para>
+
+      <para>
+       This function opens a new database connection using the parameters taken
+       from the string <literal>conninfo</literal>.
+      </para>
+
+      <para>
+       The passed string can be empty to use all default parameters, or it can
+       contain one or more parameter settings separated by whitespace.
+       Each parameter setting is in the form <literal>keyword = value</literal>.
+       Spaces around the equal sign are optional. To write an empty value,
+       or a value containing spaces, surround it with single quotes, e.g.,
+       <literal>keyword = 'a value'</literal>. Single quotes and backslashes
+       within the value must be escaped with a backslash, i.e.,
+       <literal>\'</literal> and <literal>\\</literal>.
+      </para>
+
+      <para>
+       The currently recognized parameter key words are the same as above.
+      </para>
+     </listitem>
+    </varlistentry>
+
+    <varlistentry>
      <term><function>PQsetdbLogin</function><indexterm><primary>PQsetdbLogin</></></term>
      <listitem>
       <para>
@@ -532,6 +564,7 @@ PGconn *PQsetdb(char *pghost,
     </varlistentry>
 
     <varlistentry>
+     <term><function>PQconnectStartParams</function><indexterm><primary>PQconnectStartParams</></></term>
      <term><function>PQconnectStart</function><indexterm><primary>PQconnectStart</></></term>
      <term><function>PQconnectPoll</function><indexterm><primary>PQconnectPoll</></></term>
      <listitem>
@@ -540,6 +573,10 @@ PGconn *PQsetdb(char *pghost,
        Make a connection to the database server in a nonblocking manner.
 
        <synopsis>
+        PGconn *PQconnectStartParams(const char **keywords, const char **values);
+       </synopsis>
+
+       <synopsis>
         PGconn *PQconnectStart(const char *conninfo);
        </synopsis>
 
@@ -549,29 +586,37 @@ PGconn *PQsetdb(char *pghost,
       </para>
 
       <para>
-       These two functions are used to open a connection to a database server such
+       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
-       <function>PQconnectdb</>, and so the application can manage this
-       operation in parallel with other activities.
+       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
+       <function>PQconnectdbParams</> or <function>PQconnectdb</>, and so the
+       application can manage this operation in parallel with other activities.
       </para>
 
       <para>
-       The database connection is made using the parameters taken from the string
-       <literal>conninfo</literal>, passed to <function>PQconnectStart</function>. This string is in
-       the same format as described above for <function>PQconnectdb</function>.
+       With <function>PQconnectStartParams</function>, the database connection is made
+       using the parameters taken from the <literal>keywords</literal> and
+       <literal>values</literal> arrays, as described above for
+       <function>PQconnectdbParams</function>.
       </para>
+
       <para>
-       Neither <function>PQconnectStart</function> nor <function>PQconnectPoll</function> will block, so long as a number of
+       With <function>PQconnectStart</function>, the database connection is made
+       using the parameters taken from the string <literal>conninfo</literal> as
+       described above for <function>PQconnectdb</function>.
+      </para>
+
+      <para>
+       Neither <function>PQconnectStartParams</function> nor <function>PQconnectStart</function>
+       nor <function>PQconnectPoll</function> will block, so long as a number of
        restrictions are met:
        <itemizedlist>
         <listitem>
          <para>
           The <literal>hostaddr</> and <literal>host</> parameters are used appropriately to ensure that
           name and reverse name queries are not made. See the documentation of
-          these parameters under <function>PQconnectdb</function> above for details.
+          these parameters under <function>PQconnectdbParams</function> above for details.
          </para>
         </listitem>
 
@@ -592,6 +637,11 @@ PGconn *PQsetdb(char *pghost,
       </para>
 
       <para>
+       Note: use of <function>PQconnectStartParams</> is analogous to
+       <function>PQconnectStart</> shown below.
+      </para>
+
+      <para>
        To begin a nonblocking connection request, call <literal>conn = PQconnectStart("<replaceable>connection_info_string</>")</literal>.
        If <varname>conn</varname> is null, then <application>libpq</> has been unable to allocate a new <structname>PGconn</>
        structure. Otherwise, a valid <structname>PGconn</> pointer is returned (though not yet
@@ -883,7 +933,8 @@ PQconninfoOption *PQconninfoParse(const char *conninfo, char **errmsg);
        parameters previously used. This can be useful for error recovery if a
        working connection is lost. They differ from <function>PQreset</function> (above) in that they
        act in a nonblocking manner. These functions suffer from the same
-       restrictions as <function>PQconnectStart</> and <function>PQconnectPoll</>.
+       restrictions as <function>PQconnectStartParams</>, <function>PQconnectStart</>
+       and <function>PQconnectPoll</>.
       </para>
 
       <para>
@@ -1096,9 +1147,9 @@ PQconninfoOption *PQconninfoParse(const char *conninfo, char **errmsg);
       </para>
 
       <para>
-       See the entry for <function>PQconnectStart</> and <function>PQconnectPoll</> with regards
-       to other status codes
-       that might be seen.
+       See the entry for <function>PQconnectStartParams</>, <function>PQconnectStart</>
+       and <function>PQconnectPoll</> with regards to other status codes that
+       might be seen.
       </para>
      </listitem>
     </varlistentry>