Fix extended query Bind handling when a single parameter format is provided

PostgreSQL allows a Bind message to specify a single parameter format
(num_param_formats = 1), which applies to all parameters.

libpq, however, always expects a format entry per parameter and previously
sent uninitialized values for the remaining parameters when only one format
was specified. This caused ProxySQL to forward malformed Bind packets to
backend.

ProxySQL now detects this case and propagates the single provided parameter
format to all parameters, matching PostgreSQL semantics.

lib/PgSQL_Connection.cpp

@@ -1839,7 +1839,29 @@ void PgSQL_Connection::stmt_execute_start() {
 					"Failed to read param format", false);
 				return;
 			}
-			param_formats[i] = format;
+			param_formats[i] = format; // 0 = text, 1 = binary
+		}
+	}
+
+	// Normalize param formats for libpq:
+	// According to the PostgreSQL Bind message specification:
+	// https://www.postgresql.org/docs/current/protocol-message-formats.html#PROTOCOL-MESSAGE-FORMATS-BIND
+	//  - num_param_formats = 0 -> all parameters are TEXT
+	//  - num_param_formats = 1 -> the single format applies to all parameters
+	//  - num_param_formats = num_param_values -> formats are applied per-parameter in order
+	// Any other number of parameter formats is a protocol error.
+	if (!param_formats.empty()) {
+		if (param_formats.size() == 1 && param_values.size() > 1) {
+			// PostgreSQL protocol allows 1 format for all params,
+			// libpq DOES NOT, we must expand
+			int fmt = param_formats[0];
+			param_formats.resize(param_values.size(), fmt);
+		} else if (param_formats.size() != param_values.size()) {
+			proxy_error("Invalid param format count: got %zu, expected %zu\n",
+				param_formats.size(), param_values.size());
+			set_error(PGSQL_ERROR_CODES::ERRCODE_INVALID_PARAMETER_VALUE,
+				"Invalid parameter format count", false);
+			return;
 		}
 	}
 
@@ -1858,8 +1880,13 @@ void PgSQL_Connection::stmt_execute_start() {
 		}
 	}
 
+	// If the client did not send any parameter formats (num_param_formats = 0),
+	// PostgreSQL protocol defines this as "all parameters are TEXT".
+	// libpq represents this case by passing paramFormats = nullptr.
+	const int* param_formats_data = (param_formats.empty() == false ? param_formats.data() : nullptr);
+
 	if (PQsendQueryPrepared(pgsql_conn, query.backend_stmt_name, param_values.size(),
-		param_values.data(), param_lengths.data(), param_formats.data(),
+		param_values.data(), param_lengths.data(), param_formats_data,
 		(result_formats.size() > 0) ? result_formats[0] : 0) == 0) {
 		set_error_from_PQerrorMessage();
 		proxy_error("Failed to send execute prepared statement. %s\n", get_error_code_with_message().c_str());