PQescapeIdentifier

Christopher Kings-Lynne wrote:

TODO item done for 8.2:

* Add PQescapeIdentifier() to libpq

Someone probably needs to check this :)

Updated patch applied. Thanks.

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Index: doc/src/sgml/libpq.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/libpq.sgml,v
retrieving revision 1.211
diff -c -c -r1.211 libpq.sgml
*** doc/src/sgml/libpq.sgml	23 May 2006 22:13:19 -0000	1.211
--- doc/src/sgml/libpq.sgml	26 Jun 2006 23:54:12 -0000
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*** 2279,2284 ****
--- 2279,2347 ----
</para>
</sect2>

+ <sect2 id="libpq-exec-escape-identifier">
+   <title>Escaping Identifier for Inclusion in SQL Commands</title>
+ 
+    <indexterm zone="libpq-exec-escape-identifier"><primary>PQescapeIdentifier</></>
+    <indexterm zone="libpq-exec-escape-identifier"><primary>escaping strings</></>
+ 
+ <para>
+ <function>PQescapeIdentifier</function> escapes a string for use 
+ as an identifier name within an SQL command.  For example; table names,
+ column names, view names and user names are all identifiers.
+ Double quotes (") must be escaped to prevent them from being interpreted 
+ specially by the SQL parser. <function>PQescapeIdentifier</> performs this 
+ operation.
+ </para>
+ 
+ <tip>
+ <para>
+ It is especially important to do proper escaping when handling strings that
+ were received from an untrustworthy source.  Otherwise there is a security
+ risk: you are vulnerable to <quote>SQL injection</> attacks wherein unwanted
+ SQL commands are fed to your database.
+ </para>
+ </tip>
+ 
+ <para>
+ Note that it is still necessary to do escaping of identifiers when
+ using functions that support parameterized queries such as <function>PQexecParams</> or
+ its sibling routines. Only literal values are automatically escaped
+ using these functions, not identifiers.
+ 
+ <synopsis>
+ size_t PQescapeIdentifier (char *to, const char *from, size_t length);
+ </synopsis>
+ </para>
+ 
+ <para>
+ 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
+ required, and should not be counted in <parameter>length</>.  (If
+ a terminating zero byte is found before <parameter>length</> bytes are
+ processed, <function>PQescapeIdentifier</> 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
+ the value of <parameter>length</>, otherwise the behavior is
+ undefined.  A call to <function>PQescapeIdentifier</> 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 double quotes that
+ may surround <productname>PostgreSQL</> identifiers are not
+ included in the result string; they should be provided in the SQL
+ command that the result is inserted into.
+ </para>
+ <para>
+ <function>PQescapeIdentifier</> returns the number of characters written
+ to <parameter>to</>, not including the terminating zero byte.
+ </para>
+ <para>
+ Behavior is undefined if the <parameter>to</> and <parameter>from</>
+ strings overlap.
+ </para>
+ </sect2>

<sect2 id="libpq-exec-escape-bytea">
<title>Escaping Binary Strings for Inclusion in SQL Commands</title>
Index: src/interfaces/libpq/exports.txt
===================================================================
RCS file: /cvsroot/pgsql/src/interfaces/libpq/exports.txt,v
retrieving revision 1.11
diff -c -c -r1.11 exports.txt
*** src/interfaces/libpq/exports.txt	28 May 2006 22:42:05 -0000	1.11
--- src/interfaces/libpq/exports.txt	26 Jun 2006 23:54:20 -0000
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*** 130,132 ****
--- 130,134 ----
PQencryptPassword         128
PQisthreadsafe            129
enlargePQExpBuffer        130
+ PQescapeIdentifier        131
+ 
Index: src/interfaces/libpq/fe-exec.c
===================================================================
RCS file: /cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v
retrieving revision 1.186
diff -c -c -r1.186 fe-exec.c
*** src/interfaces/libpq/fe-exec.c	28 May 2006 21:13:54 -0000	1.186
--- src/interfaces/libpq/fe-exec.c	26 Jun 2006 23:54:21 -0000
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*** 2516,2521 ****
--- 2516,2557 ----
}

/*
+  * Escaping arbitrary strings to get valid SQL identifier strings.
+  *
+  * Replaces " with "".
+  *
+  * length is the length of the source string.  (Note: if a terminating NUL
+  * is encountered sooner, PQescapeIdentifier stops short of "length"; the behavior
+  * is thus rather like strncpy.)
+  *
+  * For safety the buffer at "to" must be at least 2*length + 1 bytes long.
+  * A terminating NUL character is added to the output string, whether the
+  * input is NUL-terminated or not.
+  *
+  * Returns the actual length of the output (not counting the terminating NUL).
+  */
+ size_t
+ PQescapeIdentifier(char *to, const char *from, size_t length)
+ {
+ 	const char *source = from;
+ 	char	   *target = to;
+ 	size_t		remaining = length;
+ 
+ 	while (remaining > 0 && *source != '\0')
+ 	{
+ 		if (*source  == '"')
+ 			*target++ = *source;
+ 		*target++ = *source++;
+ 		remaining--;
+ 	}
+ 
+ 	/* Write the terminating NUL character. */
+ 	*target = '\0';
+ 
+ 	return target - to;
+ }
+ 
+ /*
*		PQescapeBytea	- converts from binary string to the
*		minimal encoding necessary to include the string in an SQL
*		INSERT statement with a bytea type column as the target.
Index: src/interfaces/libpq/libpq-fe.h
===================================================================
RCS file: /cvsroot/pgsql/src/interfaces/libpq/libpq-fe.h,v
retrieving revision 1.129
diff -c -c -r1.129 libpq-fe.h
*** src/interfaces/libpq/libpq-fe.h	23 May 2006 22:13:19 -0000	1.129
--- src/interfaces/libpq/libpq-fe.h	26 Jun 2006 23:54:21 -0000
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*** 436,441 ****
--- 436,443 ----
size_t *to_length);
extern unsigned char *PQunescapeBytea(const unsigned char *strtext,
size_t *retbuflen);
+ extern size_t PQescapeIdentifier(char *to, const char *from, size_t length);
+ 
/* These forms are deprecated! */
extern size_t PQescapeString(char *to, const char *from, size_t length);
extern unsigned char *PQescapeBytea(const unsigned char *from, size_t from_length,