Audit log message severity levels

Motivation:

Following the SSWG guidelines for libraries and log levels, because much of the library's behavior is expressed in the language and NIO framework as errors and failed ELFs, logging at error is "verbose" and takes away control from developers.

Modifications:

Log messages have been adjusted to more accurately represent when and how the log message should be used, especially when ELFs are failed or errors are thrown.

Result:

Developers won't have log messages at error or critical unless they opt-in from their own code, unless the library has no way of expressing the failure condition through the language.

Author: Mordil

Sources/RediStack/ConnectionPool/ConnectionPool.swift

@@ -246,7 +246,7 @@ extension ConnectionPool {
     private func connectionCreationFailed(_ error: Error, backoff: TimeAmount, logger: Logger) {
         self.loop.assertInEventLoop()
 
-        logger.error("failed to create connection for pool", metadata: [
+        logger.warning("failed to create connection for pool", metadata: [
             RedisLogging.MetadataKeys.error: "\(error)"
         ])
 

Sources/RediStack/RedisConnection.swift

@@ -180,7 +180,7 @@ public final class RedisConnection: RedisClient, RedisClientWithUserContext {
             guard self.state.isConnected else { return }
 
             self.state = .closed
-            self.logger.error("connection was closed unexpectedly")
+            self.logger.warning("connection was closed unexpectedly")
             RedisMetrics.activeConnectionCount.decrement()
         }
 
@@ -239,7 +239,7 @@ extension RedisConnection {
             // log data based on the result
             switch result {
             case let .failure(error):
-                logger.error("command failed", metadata: [
+                logger.debug("command failed", metadata: [
                     RedisLogging.MetadataKeys.error: "\(error.localizedDescription)"
                 ])
 
@@ -300,7 +300,7 @@ extension RedisConnection {
             .flatMap { self.closeChannel() } // close the channel from our end
 
         notification.whenFailure {
-            logger.error("error while closing connection", metadata: [
+            logger.warning("failed to close connection", metadata: [
                 RedisLogging.MetadataKeys.error: "\($0)"
             ])
         }

docs/api-design/Logging.md

@@ -57,11 +57,11 @@ connection
 1. All log metadata keys should be added to the `RedisLogging` namespace
 1. Log messages should be in all lowercase, with no punctuation preferred
   - if a Redis command keyword (such as `QUIT`) is in the log message, it should be in all caps
-1. Log a `critical` message before any `precondition` failure
-1. Prefer single locations of `error` messages
-  - for example, only the top level `send` command on `RedisConnection` should log the error returned from Redis or from a failed `EventLoopFuture`
-1. `warning` logs should be reserved for situations that could lead to `critical` conditions
+1. `warning` logs should be reserved for situations that could lead to `error` or `critical` conditions
   - this may include leaks or bad state
+1. Only use `error` in situations where the error cannot be expressed by the language, such as by throwing an error or failing `EventLoopFuture`s.
+  - this is to avoid high severity logs that developers cannot control and must create filtering mechanisms if they want to ignore emitted logs from **RediStack**
+1. Log a `critical` message before any `preconditionFailure` or `fatalError`
 
 ### Metadata