Eliminate fixed token-length limit in hba.c.

Historically, hba.c limited tokens in the authentication configuration
files (pg_hba.conf and pg_ident.conf) to less than 256 bytes.  We have
seen a few reports of this limit causing problems; notably, for
moderately-complex LDAP configurations.  Let's get rid of the fixed
limit by using a StringInfo instead of a fixed-size buffer.
This actually takes less code than before, since we can get rid of
a nontrivial error recovery stanza.  It's doubtless a hair slower,
but parsing the content of the HBA files should in no way be
performance-critical.

Although this is a pretty straightforward patch, it doesn't seem
worth the risk to back-patch given the small number of complaints
to date.  In released branches, we'll just raise MAX_TOKEN to
ameliorate the problem.

Discussion: https://postgr.es/m/1588937.1690221208@sss.pgh.pa.us

src/backend/libpq/hba.c

@@ -56,8 +56,6 @@
 #endif
 
 
-#define MAX_TOKEN	256
-
 /* callback data for check_network_callback */
 typedef struct check_network_data
 {
@@ -161,8 +159,8 @@ pg_isblank(const char c)
  * commas, beginning of line, and end of line.  Blank means space or tab.
  *
  * Tokens can be delimited by double quotes (this allows the inclusion of
- * blanks or '#', but not newlines).  As in SQL, write two double-quotes
+ * commas, blanks, and '#', but not newlines).  As in SQL, write two
- * to represent a double quote.
+ * double-quotes to represent a double quote.
  *
  * Comments (started by an unquoted '#') are skipped, i.e. the remainder
  * of the line is ignored.
@@ -171,8 +169,8 @@ pg_isblank(const char c)
  * Thus, if a continuation occurs within quoted text or a comment, the
  * quoted text or comment is considered to continue to the next line.)
  *
- * The token, if any, is returned at *buf (a buffer of size bufsz), and
+ * The token, if any, is returned into buf (replacing any previous
- * *lineptr is advanced past the token.
+ * contents), and *lineptr is advanced past the token.
  *
  * Also, we set *initial_quote to indicate whether there was quoting before
  * the first character.  (We use that to prevent "@x" from being treated
@@ -180,30 +178,25 @@ pg_isblank(const char c)
  * we want to allow that to support embedded spaces in file paths.)
  *
  * We set *terminating_comma to indicate whether the token is terminated by a
- * comma (which is not returned).
+ * comma (which is not returned, nor advanced over).
  *
- * In event of an error, log a message at ereport level elevel, and also
+ * The only possible error condition is lack of terminating quote, but we
- * set *err_msg to a string describing the error.  Currently the only
+ * currently do not detect that, but just return the rest of the line.
- * possible error is token too long for buf.
  *
- * If successful: store null-terminated token at *buf and return true.
+ * If successful: store dequoted token in buf and return true.
- * If no more tokens on line: set *buf = '\0' and return false.
+ * If no more tokens on line: set buf to empty and return false.
- * If error: fill buf with truncated or misformatted token and return false.
  */
 static bool
-next_token(char **lineptr, char *buf, int bufsz,
+next_token(char **lineptr, StringInfo buf,
-		   bool *initial_quote, bool *terminating_comma,
+		   bool *initial_quote, bool *terminating_comma)
-		   int elevel, char **err_msg)
 {
 	int			c;
-	char	   *start_buf = buf;
-	char	   *end_buf = buf + (bufsz - 1);
 	bool		in_quote = false;
 	bool		was_quote = false;
 	bool		saw_quote = false;
 
-	Assert(end_buf > start_buf);
+	/* Initialize output parameters */
-
+	resetStringInfo(buf);
 	*initial_quote = false;
 	*terminating_comma = false;
 
@@ -226,22 +219,6 @@ next_token(char **lineptr, char *buf, int bufsz,
 			break;
 		}
 
-		if (buf >= end_buf)
-		{
-			*buf = '\0';
-			ereport(elevel,
-					(errcode(ERRCODE_CONFIG_FILE_ERROR),
-					 errmsg("authentication file token too long, skipping: \"%s\"",
-							start_buf)));
-			*err_msg = "authentication file token too long";
-			/* Discard remainder of line */
-			while ((c = (*(*lineptr)++)) != '\0')
-				;
-			/* Un-eat the '\0', in case we're called again */
-			(*lineptr)--;
-			return false;
-		}
-
 		/* we do not pass back a terminating comma in the token */
 		if (c == ',' && !in_quote)
 		{
@@ -250,7 +227,7 @@ next_token(char **lineptr, char *buf, int bufsz,
 		}
 
 		if (c != '"' || was_quote)
-			*buf++ = c;
+			appendStringInfoChar(buf, c);
 
 		/* Literal double-quote is two double-quotes */
 		if (in_quote && c == '"')
@@ -262,7 +239,7 @@ next_token(char **lineptr, char *buf, int bufsz,
 		{
 			in_quote = !in_quote;
 			saw_quote = true;
-			if (buf == start_buf)
+			if (buf->len == 0)
 				*initial_quote = true;
 		}
 
@@ -275,9 +252,7 @@ next_token(char **lineptr, char *buf, int bufsz,
 	 */
 	(*lineptr)--;
 
-	*buf = '\0';
+	return (saw_quote || buf->len > 0);
-
-	return (saw_quote || buf > start_buf);
 }
 
 /*
@@ -409,21 +384,22 @@ static List *
 next_field_expand(const char *filename, char **lineptr,
 				  int elevel, int depth, char **err_msg)
 {
-	char		buf[MAX_TOKEN];
+	StringInfoData buf;
 	bool		trailing_comma;
 	bool		initial_quote;
 	List	   *tokens = NIL;
 
+	initStringInfo(&buf);
+
 	do
 	{
-		if (!next_token(lineptr, buf, sizeof(buf),
+		if (!next_token(lineptr, &buf,
-						&initial_quote, &trailing_comma,
+						&initial_quote, &trailing_comma))
-						elevel, err_msg))
 			break;
 
 		/* Is this referencing a file? */
-		if (!initial_quote && buf[0] == '@' && buf[1] != '\0')
+		if (!initial_quote && buf.len > 1 && buf.data[0] == '@')
-			tokens = tokenize_expand_file(tokens, filename, buf + 1,
+			tokens = tokenize_expand_file(tokens, filename, buf.data + 1,
 										  elevel, depth + 1, err_msg);
 		else
 		{
@@ -434,11 +410,13 @@ next_field_expand(const char *filename, char **lineptr,
 			 * for the list of tokens.
 			 */
 			oldcxt = MemoryContextSwitchTo(tokenize_context);
-			tokens = lappend(tokens, make_auth_token(buf, initial_quote));
+			tokens = lappend(tokens, make_auth_token(buf.data, initial_quote));
 			MemoryContextSwitchTo(oldcxt);
 		}
 	} while (trailing_comma && (*err_msg == NULL));
 
+	pfree(buf.data);
+
 	return tokens;
 }