From 933c7164fe03b1b5fd2196eaac1345128df0381a Mon Sep 17 00:00:00 2001
From: sunface <cto@188.com>
Date: Mon, 4 Apr 2022 21:52:12 +0800
Subject: [PATCH] =?UTF-8?q?=E6=96=B0=E5=A2=9E=E7=AB=A0=20[Cookbook=20-=20?=
 =?UTF-8?q?=E6=97=A5=E5=BF=97]?=
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---
 src/cookbook/devtools/log.md | 126 +++++++++++++++++++++++++++++++++++
 1 file changed, 126 insertions(+)

diff --git a/src/cookbook/devtools/log.md b/src/cookbook/devtools/log.md
index 65c2dbdd..adc6616a 100644
--- a/src/cookbook/devtools/log.md
+++ b/src/cookbook/devtools/log.md
@@ -1 +1,127 @@
 # 日志
+
+## log 包
+[log](https://docs.rs/crate/log/0.4.16) 提供了日志相关的实用工具。
+
+### 在控制台打印 debug 信息
+`env_logger` 通过环境变量来配置日志。[log::debug!](https://docs.rs/log/0.4.16/log/macro.debug.html) 使用起来跟 [std::fmt](https://doc.rust-lang.org/std/fmt/) 中的格式化字符串很像。
+
+```rust
+fn execute_query(query: &str) {
+    log::debug!("Executing query: {}", query);
+}
+
+fn main() {
+    env_logger::init();
+
+    execute_query("DROP TABLE students");
+}
+```
+
+如果大家运行代码，会发现没有任何日志输出，原因是默认的日志级别是 `error`，因此我们需要通过 `RUST_LOG` 环境变量来设置下新的日志级别：
+```shell
+$ RUST_LOG=debug cargo run
+```
+
+然后你将成功看到以下输出:
+```shell
+DEBUG:main: Executing query: DROP TABLE students
+```
+
+### 将错误日志输出到控制台
+下面我们通过 [log::error!](https://docs.rs/log/0.4.16/log/macro.error.html) 将错误日志输出到标准错误 `stderr`。
+
+```rust
+fn execute_query(_query: &str) -> Result<(), &'static str> {
+    Err("I'm afraid I can't do that")
+}
+
+fn main() {
+    env_logger::init();
+
+    let response = execute_query("DROP TABLE students");
+    if let Err(err) = response {
+        log::error!("Failed to execute query: {}", err);
+    }
+}
+```
+
+### 将错误输出到标准输出 stdout
+默认的错误会输出到标准错误输出 `stderr`，下面我们通过自定的配置来让错误输出到标准输出 `stdout`。
+
+```rust,editable
+use env_logger::{Builder, Target};
+
+fn main() {
+    Builder::new()
+        .target(Target::Stdout)
+        .init();
+
+    log::error!("This error has been printed to Stdout");
+}
+```
+
+### 使用自定义 logger
+下面的代码将实现一个自定义 logger `ConsoleLogger`，输出到标准输出 `stdout`。为了使用日志宏，`ConsoleLogger` 需要实现 [log::Log](https://docs.rs/log/*/log/trait.Log.html) 特征，然后使用 [log::set_logger](https://docs.rs/log/*/log/fn.set_logger.html) 来安装使用。
+
+```rust,editable
+use log::{Record, Level, Metadata, LevelFilter, SetLoggerError};
+
+static CONSOLE_LOGGER: ConsoleLogger = ConsoleLogger;
+
+struct ConsoleLogger;
+
+impl log::Log for ConsoleLogger {
+  fn enabled(&self, metadata: &Metadata) -> bool {
+     metadata.level() <= Level::Info
+    }
+
+    fn log(&self, record: &Record) {
+        if self.enabled(record.metadata()) {
+            println!("Rust says: {} - {}", record.level(), record.args());
+        }
+    }
+
+    fn flush(&self) {}
+}
+
+fn main() -> Result<(), SetLoggerError> {
+    log::set_logger(&CONSOLE_LOGGER)?;
+    log::set_max_level(LevelFilter::Info);
+
+    log::info!("hello log");
+    log::warn!("warning");
+    log::error!("oops");
+    Ok(())
+}
+```
+
+### 输出到 Unix syslog
+下面的代码将使用 [syslog](https://docs.rs/crate/syslog/6.0.1) 包将日志输出到 [Unix Syslog](https://www.gnu.org/software/libc/manual/html_node/Overview-of-Syslog.html).
+
+```rust,editable
+#[cfg(target_os = "linux")]
+#[cfg(target_os = "linux")]
+use syslog::{Facility, Error};
+
+#[cfg(target_os = "linux")]
+fn main() -> Result<(), Error> {
+    // 初始化 logger
+    syslog::init(Facility::LOG_USER,
+                 log::LevelFilter::Debug,
+                 // 可选的应用名称
+                 Some("My app name"))?;
+    log::debug!("this is a debug {}", "message");
+    log::error!("this is an error!");
+    Ok(())
+}
+
+#[cfg(not(target_os = "linux"))]
+fn main() {
+    println!("So far, only Linux systems are supported.");
+}
+```
+
+
+## tracing
+@todo
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