From 8c6c24192cc6ef7e2199daa1ddb2853277ccc8cb Mon Sep 17 00:00:00 2001
From: Vincent Weevers <mail@vincentweevers.nl>
Date: Sat, 12 Mar 2022 23:46:03 +0100
Subject: [PATCH] Document error codes of `classic-level` and `many-level`

Ref https://github.com/Level/classic-level/pull/8
---
 README.md | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index df77e2d..93f29d6 100644
--- a/README.md
+++ b/README.md
@@ -78,9 +78,15 @@
     - [`LEVEL_INVALID_KEY`](#level_invalid_key)
     - [`LEVEL_INVALID_VALUE`](#level_invalid_value)
     - [`LEVEL_CORRUPTION`](#level_corruption)
+    - [`LEVEL_IO_ERROR`](#level_io_error)
     - [`LEVEL_INVALID_PREFIX`](#level_invalid_prefix)
     - [`LEVEL_NOT_SUPPORTED`](#level_not_supported)
     - [`LEVEL_LEGACY`](#level_legacy)
+    - [`LEVEL_LOCKED`](#level_locked)
+    - [`LEVEL_READONLY`](#level_readonly)
+    - [`LEVEL_ASSERT`](#level_assert)
+    - [`LEVEL_CONNECTION_LOST`](#level_connection_lost)
+    - [`LEVEL_REMOTE_ERROR`](#level_remote_error)
   - [Shared Access](#shared-access)
 - [Private API For Implementors](#private-api-for-implementors)
   - [Example](#example)
@@ -809,7 +815,10 @@ try {
   await db.open()
 } catch (err) {
   console.error(err.code) // 'LEVEL_DATABASE_NOT_OPEN'
-  console.error(err.cause) // 'Error: Failed to acquire lock'
+
+  if (err.cause && err.cause.code === 'LEVEL_LOCKED') {
+    // Another process or instance has opened the database
+  }
 }
 ```
 
@@ -864,6 +873,10 @@ When a value is `null`, `undefined` or (if an implementation deems it so) otherw
 
 Data could not be read (from an underlying store) due to a corruption.
 
+#### `LEVEL_IO_ERROR`
+
+Data could not be read (from an underlying store) due to an input/output error, for example from the filesystem.
+
 #### `LEVEL_INVALID_PREFIX`
 
 When a sublevel prefix contains characters outside of the supported byte range.
@@ -890,6 +903,26 @@ module.exports = function plugin (db) {
 
 When a method, option or other property was used that has been removed from the API.
 
+#### `LEVEL_LOCKED`
+
+When an attempt was made to open a database that is already open in another process or instance. Used by `classic-level` and other implementations of `abstract-level` that use exclusive locks.
+
+#### `LEVEL_READONLY`
+
+When an attempt was made to write data to a read-only database. Used by `many-level`.
+
+#### `LEVEL_ASSERT`
+
+When an internal assertion failed. This could indicate a bug. If so, please open a detailed issue in the relevant repository or [`Level/community`](https://github.com/Level/community) when in doubt. Be sure to include steps to reproduce.
+
+#### `LEVEL_CONNECTION_LOST`
+
+When a database relies on a connection to a remote party and that connection has been lost. Used by `many-level`.
+
+#### `LEVEL_REMOTE_ERROR`
+
+When a remote party encountered an unexpected condition that it can't reflect with a more specific code. Used by `many-level`.
+
 ### Shared Access
 
 Unless documented otherwise, implementations of `abstract-level` do _not_ support accessing a database from multiple processes running in parallel. That includes Node.js clusters and Electron renderer processes.