Json logging capability (#2624)

* Support configuring the log format as json or plain.

Separately test json and plain logger. They would be competing on the
same global subscriber otherwise.

* Implement log_format for pageserver config

* Implement configurable log format for safekeeper.

libs/utils/src/logging.rs

@@ -1,11 +1,35 @@
 use std::{
     fs::{File, OpenOptions},
     path::Path,
+    str::FromStr,
 };
 
 use anyhow::{Context, Result};
+use strum_macros::{EnumString, EnumVariantNames};
 
-pub fn init(log_filename: impl AsRef<Path>, daemonize: bool) -> Result<File> {
+#[derive(EnumString, EnumVariantNames, Eq, PartialEq, Debug, Clone, Copy)]
+#[strum(serialize_all = "snake_case")]
+pub enum LogFormat {
+    Plain,
+    Json,
+}
+
+impl LogFormat {
+    pub fn from_config(s: &str) -> anyhow::Result<LogFormat> {
+        use strum::VariantNames;
+        LogFormat::from_str(s).with_context(|| {
+            format!(
+                "Unrecognized log format. Please specify one of: {:?}",
+                LogFormat::VARIANTS
+            )
+        })
+    }
+}
+pub fn init(
+    log_filename: impl AsRef<Path>,
+    daemonize: bool,
+    log_format: LogFormat,
+) -> Result<File> {
     // Don't open the same file for output multiple times;
     // the different fds could overwrite each other's output.
     let log_file = OpenOptions::new()
@@ -21,22 +45,50 @@ pub fn init(log_filename: impl AsRef<Path>, daemonize: bool) -> Result<File> {
     let env_filter = tracing_subscriber::EnvFilter::try_from_default_env()
         .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new(default_filter_str));
 
+    let x: File = log_file.try_clone().unwrap();
     let base_logger = tracing_subscriber::fmt()
         .with_env_filter(env_filter)
-        .with_target(false) // don't include event targets
-        .with_ansi(false); // don't use colors in log file;
+        .with_target(false)
+        .with_ansi(false)
+        .with_writer(move || -> Box<dyn std::io::Write> {
+            // we are cloning and returning log file in order to allow redirecting daemonized stdout and stderr to it
+            // if we do not use daemonization (e.g. in docker) it is better to log to stdout directly
+            // for example to be in line with docker log command which expects logs comimg from stdout
+            if daemonize {
+                Box::new(x.try_clone().unwrap())
+            } else {
+                Box::new(std::io::stdout())
+            }
+        });
 
-    // we are cloning and returning log file in order to allow redirecting daemonized stdout and stderr to it
-    // if we do not use daemonization (e.g. in docker) it is better to log to stdout directly
-    // for example to be in line with docker log command which expects logs comimg from stdout
-    if daemonize {
-        let x = log_file.try_clone().unwrap();
-        base_logger
-            .with_writer(move || x.try_clone().unwrap())
-            .init();
-    } else {
-        base_logger.init();
+    match log_format {
+        LogFormat::Json => base_logger.json().init(),
+        LogFormat::Plain => base_logger.init(),
     }
 
     Ok(log_file)
 }
+
+// #[cfg(test)]
+// Due to global logger, can't run tests in same process.
+// So until there's a non-global one, the tests are in ../tests/ as separate files.
+#[macro_export(local_inner_macros)]
+macro_rules! test_init_file_logger {
+    ($log_level:expr, $log_format:expr) => {{
+        use std::str::FromStr;
+        std::env::set_var("RUST_LOG", $log_level);
+
+        let tmp_dir = tempfile::TempDir::new().unwrap();
+        let log_file_path = tmp_dir.path().join("logfile");
+
+        let log_format = $crate::logging::LogFormat::from_str($log_format).unwrap();
+        let _log_file = $crate::logging::init(&log_file_path, true, log_format).unwrap();
+
+        let log_file = std::fs::OpenOptions::new()
+            .read(true)
+            .open(&log_file_path)
+            .unwrap();
+
+        log_file
+    }};
+}