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Fix bogus behavior of PQsslAttribute(conn, "library").
Commit ebc8b7d intended to change the behavior of PQsslAttribute(NULL, "library"), but accidentally also changed what happens with a non-NULL conn pointer. Undo that so that only the intended behavior change happens. Clarify some associated documentation. Per bug #17625 from Heath Lord. Back-patch to v15. Discussion: https://postgr.es/m/17625-fc47c78b7d71b534@postgresql.org
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‎doc/src/sgml/libpq.sgml‎

Lines changed: 22 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -2515,8 +2515,9 @@ const char *PQsslAttribute(const PGconn *conn, const char *attribute_name);
25152515

25162516
<para>
25172517
The list of available attributes varies depending on the SSL library
2518-
being used, and the type of connection. If an attribute is not
2519-
available, returns NULL.
2518+
being used and the type of connection. Returns NULL if the connection
2519+
does not use SSL or the specified attribute name is not defined for the
2520+
library in use.
25202521
</para>
25212522

25222523
<para>
@@ -2575,12 +2576,15 @@ const char *PQsslAttribute(const PGconn *conn, const char *attribute_name);
25752576

25762577
<para>
25772578
As a special case, the <literal>library</literal> attribute may be
2578-
queried without an existing connection by passing NULL as the
2579-
<literal>conn</literal> argument. The historical behavior was to return
2580-
NULL for any attribute when a NULL <literal>conn</literal> was provided;
2581-
client programs needing to differentiate between the newer and older
2582-
implementations may check the
2583-
<literal>LIBPQ_HAS_SSL_LIBRARY_DETECTION</literal> feature macro.
2579+
queried without a connection by passing NULL as
2580+
the <literal>conn</literal> argument. The result will be the default
2581+
SSL library name, or NULL if <application>libpq</application> was
2582+
compiled without any SSL support. (Prior
2583+
to <productname>PostgreSQL</productname> version 15, passing NULL as
2584+
the <literal>conn</literal> argument always resulted in NULL.
2585+
Client programs needing to differentiate between the newer and older
2586+
implementations of this case may check the
2587+
<literal>LIBPQ_HAS_SSL_LIBRARY_DETECTION</literal> feature macro.)
25842588
</para>
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</listitem>
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</varlistentry>
@@ -2589,7 +2593,8 @@ const char *PQsslAttribute(const PGconn *conn, const char *attribute_name);
25892593
<term><function>PQsslAttributeNames</function><indexterm><primary>PQsslAttributeNames</primary></indexterm></term>
25902594
<listitem>
25912595
<para>
2592-
Return an array of SSL attribute names available. The array is terminated by a NULL pointer.
2596+
Returns an array of SSL attribute names available.
2597+
The array is terminated by a NULL pointer.
25932598
<synopsis>
25942599
const char * const * PQsslAttributeNames(const PGconn *conn);
25952600
</synopsis>
@@ -2601,17 +2606,20 @@ const char * const * PQsslAttributeNames(const PGconn *conn);
26012606
<term><function>PQsslStruct</function><indexterm><primary>PQsslStruct</primary></indexterm></term>
26022607
<listitem>
26032608
<para>
2604-
Return a pointer to an SSL-implementation-specific object describing
2605-
the connection.
2609+
Returns a pointer to an SSL-implementation-specific object describing
2610+
the connection. Returns NULL if the connection is not encrypted
2611+
or the requested type of object is not available from the connection's
2612+
SSL implementation.
26062613
<synopsis>
26072614
void *PQsslStruct(const PGconn *conn, const char *struct_name);
26082615
</synopsis>
26092616
</para>
26102617
<para>
26112618
The struct(s) available depend on the SSL implementation in use.
26122619
For <productname>OpenSSL</productname>, there is one struct,
2613-
available under the name "OpenSSL", and it returns a pointer to the
2614-
<productname>OpenSSL</productname> <literal>SSL</literal> struct.
2620+
available under the name <literal>OpenSSL</literal>,
2621+
and it returns a pointer to
2622+
<productname>OpenSSL</productname>'s <literal>SSL</literal> struct.
26152623
To use this function, code along the following lines could be used:
26162624
<programlisting><![CDATA[
26172625
#include <libpq-fe.h>
@@ -2644,7 +2652,7 @@ void *PQsslStruct(const PGconn *conn, const char *struct_name);
26442652
<listitem>
26452653
<para>
26462654
<indexterm><primary>SSL</primary><secondary sortas="libpq">in libpq</secondary></indexterm>
2647-
Returns the SSL structure used in the connection, or null
2655+
Returns the SSL structure used in the connection, or NULL
26482656
if SSL is not in use.
26492657

26502658
<synopsis>

‎src/interfaces/libpq/fe-secure-openssl.c‎

Lines changed: 10 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1747,14 +1747,21 @@ PQsslAttributeNames(PGconn *conn)
17471747
const char *
17481748
PQsslAttribute(PGconn *conn, const char *attribute_name)
17491749
{
1750-
if (strcmp(attribute_name, "library") == 0)
1751-
return "OpenSSL";
1752-
17531750
if (!conn)
1751+
{
1752+
/* PQsslAttribute(NULL, "library") reports the default SSL library */
1753+
if (strcmp(attribute_name, "library") == 0)
1754+
return "OpenSSL";
17541755
return NULL;
1756+
}
1757+
1758+
/* All attributes read as NULL for a non-encrypted connection */
17551759
if (conn->ssl == NULL)
17561760
return NULL;
17571761

1762+
if (strcmp(attribute_name, "library") == 0)
1763+
return "OpenSSL";
1764+
17581765
if (strcmp(attribute_name, "key_bits") == 0)
17591766
{
17601767
static char sslbits_str[12];

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