log.dl

/*
Copyright (c) 2021 VMware, Inc.
SPDX-License-Identifier: MIT

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

/*
 * Logging API.
 *
 * This API has two facets.  First, it provides the `log()` function that can
 * be invoked from a DDlog rule's Inspect operator to provide more visibility
 * into the rule's evaluation.  In addition to the usual log level and log
 * message arguments, this function takes a `module` argument, which identifies
 * the module or subsystem that this log message is associated with.
 *
 * Second, it provides a Rust configuration API that can only be invoked by the
 * "host" program to set log level for individual modules and to supply a
 * logging callback for each module (see `rust/template/types/log.rs`).  This
 * way, different modules can produce separate log streams or even use different
 * logging mechanisms.
 *
 * NOTE: Internally, this library maintains a global module-to-log_callback
 * map shared by all DDlog instances running in the same address space.  The host
 * program is responsible for maintaining this mapping via the Rust API in
 * `log.rs`.
 *
 * Other related files:
 * `log4j.dl` - specializes the logging API for using log4j loggers
 * `ddlog_log.rs` - Rust logging API
 * `ddlog_log.h` - matching C bindings
 * `DDlogAPI.java (DDlogAPI.log_set_callback method)` - Java API to control
 *  logging.
 *
 * === Example ===
 *
 * In DDlog:
 * ```
 * // Declare module id's for logging purposes
 * function mod_SPAN_UUID(): log.module_t = 100
 *
 * // Use log() function in a rule
 * Span(entity, tn) :- Binding(entity, tn),
 *                     Inspect log(mod_SPAN_UUID(), 5, "Span(entity,tn) :- Binding(.entity=${deref(entity)},.tn=${deref(tn)}))").
 * ```
 *
 * In Java:
 * ```
 * // Module id declarations must match DDlog values:
 * static int MOD_SPAN_UUID1 = 100;
 * // Set logging callback and log level from Java
 * DDlogAPI.log_set_callback(
 *     MOD_SPAN_UUID1,
 *     (msg, level) -> System.err.println("Log msg from module1 (" + level + "): " + msg),
 *     5);
 * ```
 * ===============
 *
 */

/* `module_t` type identifies the subsystem or component for logging purposes.
 */
typedef module_t = signed<32>

typedef log_level_t = signed<32>

/*
 * Write to a log stream
 *
 * `module` - Identifies the subsystem writing to the log.  A log record is only
 *            produced if logging has been enabled for this subsystem (see
 *            `log.rs`)
 * `level`  - log level
 * `msg`    - error message (UTF-8)
 *
 * This function returns a `()` so that it can be used as part of an expression
 * of an Inspect operator.
 */
#[has_side_effects]
extern function log(module: module_t, level: log_level_t, msg: string)