@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/libpq.sgml,v 1.209 2006/05/17 21:50:54 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/libpq.sgml,v 1.210 2006/05/21 20:19:23 tgl Exp $ -->
<chapter id="libpq">
<title><application>libpq</application> - C Library</title>
@ -2187,15 +2187,16 @@ It is not thread-safe.
<sect2 id="libpq-exec-escape-string">
<title>Escaping Strings for Inclusion in SQL Commands</title>
<indexterm zone="libpq-exec-escape-string"><primary>PQescapeStringConn</></>
<indexterm zone="libpq-exec-escape-string"><primary>PQescapeString</></>
<indexterm zone="libpq-exec-escape-string"><primary>escaping strings</></>
<para>
<function>PQescapeString</function> escapes a string for use within an SQL
<function>PQescapeStringConn </function> escapes a string for use within an SQL
command. This is useful when inserting data values as literal constants
in SQL commands. Certain characters (such as quotes and backslashes) must
be escaped to prevent them from being interpreted specially by the SQL parser.
<function>PQescapeString</> performs this operation.
<function>PQescapeStringConn </> performs this operation.
</para>
<tip>
@ -2213,36 +2214,68 @@ value is passed as a separate parameter in <function>PQexecParams</> or
its sibling routines.
<synopsis>
size_t PQescapeString (char *to, const char *from, size_t length);
size_t PQescapeStringConn (PGconn *conn,
char *to, const char *from, size_t length,
int *error);
</synopsis>
</para>
<para>
<function>PQescapeStringConn</> writes an escaped
version of the <parameter>from</> string to the <parameter>to</>
buffer, escaping special characters so that they cannot cause any
harm, and adding a terminating zero byte. The single quotes that
must surround <productname>PostgreSQL</> string literals are not
included in the result string; they should be provided in the SQL
command that the result is inserted into.
The parameter <parameter>from</> points to the first character of the string
that is to be escaped, and the <parameter>length</> parameter gives the
number of characters in this string. A terminating zero byte is not
number of byte s in this string. A terminating zero byte is not
required, and should not be counted in <parameter>length</>. (If
a terminating zero byte is found before <parameter>length</> bytes are
processed, <function>PQescapeString</> stops at the zero; the behavior
processed, <function>PQescapeStringConn </> stops at the zero; the behavior
is thus rather like <function>strncpy</>.)
<parameter>to</> shall point to a
buffer that is able to hold at least one more character than twice
buffer that is able to hold at least one more byte than twice
the value of <parameter>length</>, otherwise the behavior is
undefined. A call to <function>PQescapeString</> writes an escaped
version of the <parameter>from</> string to the <parameter>to</>
buffer, replacing special characters so that they cannot cause any
harm, and adding a terminating zero byte. The single quotes that
must surround <productname>PostgreSQL</> string literals are not
included in the result string; they should be provided in the SQL
command that the result is inserted into.
undefined.
Behavior is likewise undefined if the <parameter>to</> and <parameter>from</>
strings overlap.
</para>
<para>
If the <parameter>error</> parameter is not NULL, then <literal>*error</>
is set to zero on success, nonzero on error. Presently the only possible
error conditions involve invalid multibyte encoding in the source string.
The output string is still generated on error, but it can be expected that
the server will reject it as malformed. On error, a suitable message is
stored in the <parameter>conn</> object, whether or not <parameter>error</>
is NULL.
</para>
<para>
<function>PQescapeString</> returns the number of characters written
<function>PQescapeStringConn</> returns the number of byte s written
to <parameter>to</>, not including the terminating zero byte.
</para>
<para>
Behavior is undefined if the <parameter>to</> and <parameter>from</>
strings overlap.
<synopsis>
size_t PQescapeString (char *to, const char *from, size_t length);
</synopsis>
</para>
<para>
<function>PQescapeString</> is an older, deprecated version of
<function>PQescapeStringConn</>; the difference is that it does not
take <parameter>conn</> or <parameter>error</> parameters. Because of this,
it cannot adjust its behavior depending on the connection properties (such as
character encoding) and therefore <emphasis>it may give the wrong results</>.
Also, it has no way to report error conditions.
</para>
<para>
<function>PQescapeString</> can be used safely in single-threaded client
programs that work with only one <productname>PostgreSQL</> connection at
a time (in this case it can find out what it needs to know <quote>behind the
scenes</>). In other contexts it is a security hazard and should be avoided
in favor of <function>PQescapeStringConn</>.
</para>
</sect2>
@ -2257,16 +2290,17 @@ strings overlap.
<variablelist>
<varlistentry>
<term><function>PQescapeBytea</function><indexterm><primary>PQescapeBytea</></></term>
<term><function>PQescapeByteaConn </function><indexterm><primary>PQescapeByteaConn </></></term>
<listitem>
<para>
Escapes binary data for use within an SQL command with the type
<type>bytea</type>. As with <function>PQescapeString</function>,
<type>bytea</type>. As with <function>PQescapeStringConn </function>,
this is only used when inserting data directly into an SQL command string.
<synopsis>
unsigned char *PQescapeBytea(const unsigned char *from,
size_t from_length,
size_t *to_length);
unsigned char *PQescapeByteaConn(PGconn *conn,
const unsigned char *from,
size_t from_length,
size_t *to_length);
</synopsis>
</para>
@ -2276,10 +2310,10 @@ unsigned char *PQescapeBytea(const unsigned char *from,
of a <type>bytea</type> literal in an <acronym>SQL</acronym>
statement. In general, to escape a byte, it is converted into the
three digit octal number equal to the octet value, and preceded by
two backslashes. The single quote (<literal>'</>) and backslash
one or two backslashes. The single quote (<literal>'</>) and backslash
(<literal>\</>) characters have special alternative escape
sequences. See <xref linkend="datatype-binary"> for more
information. <function>PQescapeBytea</function> performs this
information. <function>PQescapeByteaConn </function> performs this
operation, escaping only the minimally required bytes.
</para>
@ -2290,16 +2324,15 @@ unsigned char *PQescapeBytea(const unsigned char *from,
bytes in this binary string. (A terminating zero byte is
neither necessary nor counted.) The <parameter>to_length</parameter>
parameter points to a variable that will hold the resultant
escaped string length. The result string length includes the terminating
escaped string length. This result string length includes the terminating
zero byte of the result.
</para>
<para>
<function>PQescapeBytea</> returns an escaped version of the
<function>PQescapeByteaConn </> returns an escaped version of the
<parameter>from</parameter> parameter binary string in memory
allocated with <function>malloc()</> (a null pointer is returned if
memory could not be allocated). This memory must be freed using
<function>PQfreemem</> when the result is no longer needed. The
allocated with <function>malloc()</>. This memory must be freed using
<function>PQfreemem()</> when the result is no longer needed. The
return string has all special characters replaced so that they can
be properly processed by the <productname>PostgreSQL</productname>
string literal parser, and the <type>bytea</type> input function. A
@ -2307,6 +2340,45 @@ unsigned char *PQescapeBytea(const unsigned char *from,
surround <productname>PostgreSQL</productname> string literals are
not part of the result string.
</para>
<para>
On error, a NULL pointer is returned, and a suitable error message
is stored in the <parameter>conn</> object. Currently, the only
possible error is insufficient memory for the result string.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><function>PQescapeBytea</function><indexterm><primary>PQescapeBytea</></></term>
<listitem>
<para>
<function>PQescapeBytea</> is an older, deprecated version of
<function>PQescapeByteaConn</>.
<synopsis>
unsigned char *PQescapeBytea(const unsigned char *from,
size_t from_length,
size_t *to_length);
</synopsis>
</para>
<para>
The only difference from <function>PQescapeByteaConn</> is that
<function>PQescapeBytea</> does not
take a <structname>PGconn</> parameter. Because of this, it cannot adjust
its behavior depending on the connection properties (in particular,
whether standard-conforming strings are enabled)
and therefore <emphasis>it may give the wrong results</>. Also, it
has no way to return an error message on failure.
</para>
<para>
<function>PQescapeBytea</> can be used safely in single-threaded client
programs that work with only one <productname>PostgreSQL</> connection at
a time (in this case it can find out what it needs to know <quote>behind the
scenes</>). In other contexts it is a security hazard and should be
avoided in favor of <function>PQescapeByteaConn</>.
</para>
</listitem>
</varlistentry>
@ -2314,7 +2386,7 @@ unsigned char *PQescapeBytea(const unsigned char *from,
<term><function>PQunescapeBytea</function><indexterm><primary>PQunescapeBytea</></></term>
<listitem>
<para>
Converts an escaped string representation of binary data into binary
Converts a string representation of binary data into binary
data — the reverse of <function>PQescapeBytea</function>.
This is needed when retrieving <type>bytea</type> data in text format,
but not when retrieving it in binary format.
@ -2324,16 +2396,24 @@ unsigned char *PQunescapeBytea(const unsigned char *from, size_t *to_length);
</synopsis>
</para>
<para>
The <parameter>from</parameter> parameter points to an escaped string
such as might be returned by <function>PQgetvalue</function> when applied to a
<type>bytea</type> column. <function>PQunescapeBytea</function> converts
this string representation into its binary representation.
<para>
The <parameter>from</parameter> parameter points to a string
such as might be returned by <function>PQgetvalue</function> when applied
to a <type>bytea</type> column. <function>PQunescapeBytea</function>
converts this string representation into its binary representation.
It returns a pointer to a buffer allocated with
<function>malloc()</function>, or null on error, and puts the size of
the buffer in <parameter>to_length</parameter>. The result must be
freed using <function>PQfreemem</> when it is no longer needed.
</para>
<para>
This conversion is not exactly the inverse of
<function>PQescapeBytea</function>, because the string is not expected
to be <quote>escaped</> when received from <function>PQgetvalue</function>.
In particular this means there is no need for string quoting considerations,
and so no need for a <structname>PGconn</> parameter.
</para>
</listitem>
</varlistentry>
@ -2349,6 +2429,7 @@ void PQfreemem(void *ptr);
<para>
Frees memory allocated by <application>libpq</>, particularly
<function>PQescapeByteaConn</function>,
<function>PQescapeBytea</function>,
<function>PQunescapeBytea</function>,
and <function>PQnotifies</function>.
@ -4000,9 +4081,9 @@ current connection parameters will be used. (Therefore, put more-specific
entries first when you are using wildcards.)
If an entry needs to contain <literal>:</literal> or
<literal>\</literal>, escape this character with <literal>\</literal>.
A hostname of <literal>localhost</> matches both TCP <literal>host</> (hostname <literal>localhost</>)
and Unix domain socket <literal>local</> (<literal>pghost</> empty or the default socket directory)
connections coming from the local machine.
A hostname of <literal>localhost</> matches both TCP (hostname
<literal>localhost </>) and Unix domain socket (<literal>pghost</> empty or the
default socket directory) connections coming from the local machine.
</para>
<para>