Prevent crash COM_STMT_EXECUTE and invalid stmt_id

If an invalid stmt_id is passed to COM_STMT_EXECUTE , ProxySQL used to crash
due to an assert().
It seems that some buggy clients execute COM_STMT_EXECUTE with an invalid
stmt_id after an auto-reconnect.
This commit returns an error to the client.

Closes #3371
Closes #3808
Closes #4474

lib/MySQL_Session.cpp

@@ -3790,10 +3790,13 @@ void MySQL_Session::handler___status_WAITING_CLIENT_DATA___STATE_SLEEP___MYSQL_C
 		CurrentQuery.stmt_client_id=client_stmt_id;
 		stmt_global_id=client_myds->myconn->local_stmts->find_global_stmt_id_from_client(client_stmt_id);
 		if (stmt_global_id == 0) {
-			// FIXME: add error handling
-			// LCOV_EXCL_START
-			assert(0);
-			// LCOV_EXCL_STOP
+			l_free(pkt.size,pkt.ptr);
+			client_myds->setDSS_STATE_QUERY_SENT_NET();
+			string err_msg = "Unknown prepared statement handler (" + to_string(client_stmt_id) + ") given to mysql_stmt_precheck";
+			client_myds->myprot.generate_pkt_ERR(true,NULL,NULL,1,1243,(char *)"HY000", err_msg.c_str());
+			client_myds->DSS=STATE_SLEEP;
+			status=WAITING_CLIENT_DATA;
+			return;
 		}
 		CurrentQuery.stmt_global_id=stmt_global_id;
 		// now we get the statement information
@@ -3803,7 +3806,8 @@ void MySQL_Session::handler___status_WAITING_CLIENT_DATA___STATE_SLEEP___MYSQL_C
 			// we couldn't find it
 			l_free(pkt.size,pkt.ptr);
 			client_myds->setDSS_STATE_QUERY_SENT_NET();
-			client_myds->myprot.generate_pkt_ERR(true,NULL,NULL,1,1045,(char *)"28000",(char *)"Prepared statement doesn't exist", true);
+			string err_msg = "Unknown prepared statement handler (" + to_string(client_stmt_id) + ") given to mysql_stmt_precheck";
+			client_myds->myprot.generate_pkt_ERR(true,NULL,NULL,1,1243,(char *)"HY000", err_msg.c_str());
 			client_myds->DSS=STATE_SLEEP;
 			status=WAITING_CLIENT_DATA;
 			return;

test/tap/tests/reg_test_3371_prepared_statement_crash-t.cpp

@@ -0,0 +1,89 @@
+/**
+ * @file reg_test_3371_prepared_statement_crash-t.cpp
+ * @brief Tries to execute prepared statements with a not existing stmt_id.
+ * This used to crash ProxySQL , so this tap test verifies that ProxySQL
+ * doesn't crash
+ */
+
+
+#include <string>
+#include <stdio.h>
+#include <cstring>
+#include <unistd.h>
+
+#include "mysql.h"
+
+#include "tap.h"
+#include "command_line.h"
+#include "utils.h"
+
+using std::string;
+
+const int NUM_LOOPS = 100; ///< Number of loops for statement execution.
+
+int main(int argc, char** argv) {
+	CommandLine cl;
+
+	// Checking for required environmental variables
+	if (cl.getEnv()) {
+		diag("Failed to get the required environmental variables.");
+		return -1;
+	}
+
+	plan(1+NUM_LOOPS*2); // Plan for testing purposes
+
+	MYSQL* mysql = mysql_init(NULL); ///< MySQL connection object
+	if (!mysql) {
+		fprintf(stderr, "File %s, line %d, Error: %s\n", __FILE__, __LINE__, mysql_error(mysql));
+		return exit_status();
+	}
+
+	// Connecting to ProxySQL
+	diag("Connecting to '%s@%s:%d'", cl.mysql_username, cl.mysql_host, cl.port);
+	if (!mysql_real_connect(mysql, cl.mysql_host, cl.mysql_username, cl.mysql_password, NULL, cl.port, NULL, 0)) {
+		fprintf(stderr, "File %s, line %d, Error: %s\n", __FILE__, __LINE__, mysql_error(mysql));
+		return exit_status();
+	}
+
+	// Initialize and prepare all the statements
+	MYSQL_STMT* stmt = mysql_stmt_init(mysql);
+		if (!stmt) {
+			fprintf(stderr, "mysql_stmt_init(), out of memory\n");
+			return exit_status();
+		}
+
+	std::string select_query = "SELECT 1";
+	diag("select_query: %s", select_query.c_str());
+	if (mysql_stmt_prepare(stmt, select_query.c_str(), strlen(select_query.c_str()))) {
+		fprintf(stderr, "mysql_stmt_prepare at line %d failed: %s\n", __LINE__ , mysql_error(mysql));
+		mysql_close(mysql);
+		mysql_library_end();
+		return exit_status();
+	}
+
+	diag("Increasing stmt_id by 1, so that mysql_stmt_execute() must fail");
+	int rc = 0;
+	for (int i = 0; i < NUM_LOOPS ; i++) {
+		stmt->stmt_id += 1;
+		rc = mysql_stmt_execute(stmt);
+		ok (rc , "mysql_stmt_execute() must fail");
+		if (rc) {
+			unsigned int psrc = mysql_stmt_errno(stmt);
+			ok( psrc == 1243 , "mysql_stmt_execute at line %d failed: %d , %s", __LINE__ , psrc , mysql_stmt_error(stmt));
+		}
+	}
+
+	diag("Decreasing stmt_id by 1, so that mysql_stmt_execute() must succeed");
+	stmt->stmt_id -= NUM_LOOPS;
+	rc = mysql_stmt_execute(stmt);
+	ok (rc == 0 , "mysql_stmt_execute() succeeded");
+	if (rc) {
+		fprintf(stderr, "mysql_stmt_execute at line %d failed: %d , %s\n", __LINE__ , rc , mysql_stmt_error(stmt));
+		mysql_close(mysql);
+		mysql_library_end();
+		return exit_status();
+	}
+	mysql_close(mysql);
+
+	return exit_status();
+}