From bd0221d496475218202a889e805b40ef4afebd65 Mon Sep 17 00:00:00 2001
From: KotlinIsland <kotlinisland@users.noreply.github.com>
Date: Thu, 9 Feb 2023 15:59:49 +1000
Subject: [PATCH] blackd: fix issue for mishandling single character input

---
 CHANGES.md             | 2 ++
 src/blackd/__init__.py | 4 +++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/CHANGES.md b/CHANGES.md
index a8b556cb7e8..628f7eb28ce 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -41,6 +41,8 @@
 
 <!-- Changes to blackd -->
 
+- fix a bug where a single character would cause a 500 (#3558)
+
 ### Integrations
 
 <!-- For example, Docker, GitHub Actions, pre-commit, editors -->
diff --git a/src/blackd/__init__.py b/src/blackd/__init__.py
index ba4750b8298..24abef54b3a 100644
--- a/src/blackd/__init__.py
+++ b/src/blackd/__init__.py
@@ -146,11 +146,13 @@ async def handle(request: web.Request, executor: Executor) -> web.Response:
         )
 
         # Preserve CRLF line endings
-        if req_str[req_str.find("\n") - 1] == "\r":
+        nl = req_str.find("\n")
+        if nl > 0 and req_str[nl - 1] == "\r":
             formatted_str = formatted_str.replace("\n", "\r\n")
             # If, after swapping line endings, nothing changed, then say so
             if formatted_str == req_str:
                 raise black.NothingChanged
+        del nl
 
         # Put the source first line back
         req_str = header + req_str