Implement logging to file

.gitignore

@@ -2,3 +2,4 @@
 /config.json
 events/
 /*.data
+/log

src/logging.rs

@@ -0,0 +1,64 @@
+// Copied and edited based on https://github.com/estk/log4rs/pull/295
+
+use anyhow::Context;
+use log::LevelFilter;
+use log4rs::Handle;
+use log4rs::{
+    append::{
+        console::{ConsoleAppender, Target},
+        rolling_file::policy::compound::{
+            roll::fixed_window::FixedWindowRoller, trigger::size::SizeTrigger, CompoundPolicy,
+        },
+    },
+    config::{Appender, Config, Root},
+    encode::pattern::PatternEncoder,
+    filter::threshold::ThresholdFilter,
+};
+
+pub fn init_logging(level: LevelFilter) -> anyhow::Result<Handle> {
+    let file_path = "log/file.log";
+    let archive_pattern = "log/file_{}.log";
+    // Pattern: https://docs.rs/log4rs/*/log4rs/append/rolling_file/policy/compound/roll/fixed_window/struct.FixedWindowRollerBuilder.html#method.build
+
+    // Build a stderr logger.
+    let stderr = ConsoleAppender::builder().target(Target::Stderr).build();
+
+    // Create a policy to use with the file logging
+    let trigger = SizeTrigger::new(4096); // 4kb (4 * 1024)
+    let roller = FixedWindowRoller::builder()
+        .build(archive_pattern, 10) // Roll based on pattern and max 10 archive files
+        .expect("Failed to create FixedWindowRoller");
+    let policy = CompoundPolicy::new(Box::new(trigger), Box::new(roller));
+
+    // Logging to log file. (with rolling)
+    let log_file = log4rs::append::rolling_file::RollingFileAppender::builder()
+        // Pattern: https://docs.rs/log4rs/*/log4rs/encode/pattern/index.html
+        .encoder(Box::new(PatternEncoder::new(
+            "{d(%Y-%m-%d %H:%M:%S)} {l} - {m}\n",
+        )))
+        .build(file_path, Box::new(policy))
+        .unwrap();
+
+    let config = Config::builder()
+        .appender(Appender::builder().build("log_file", Box::new(log_file)))
+        .appender(
+            Appender::builder()
+                .filter(Box::new(ThresholdFilter::new(level)))
+                .build("stderr", Box::new(stderr)),
+        )
+        .build(
+            Root::builder()
+                .appender("log_file")
+                .appender("stderr")
+                .build(level),
+        )
+        .context("Failed to configure logging")?;
+
+    // Use this to change log levels at runtime.
+    // This means you can change the default log level to trace
+    // if you are trying to debug an issue and need more logs on then turn it off
+    // once you are done.
+    let handle = log4rs::init_config(config).context("Failed to init_config")?;
+
+    Ok(handle)
+}