From 24a6740de1e6529dbd4bb4dded00814eb78ead28 Mon Sep 17 00:00:00 2001
From: Moritz Peters <maritz.peters@gmail.com>
Date: Wed, 10 Jan 2018 18:56:22 +0100
Subject: [PATCH 1/3] fix: change usage of _header to headersSernt

---
 index.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/index.js b/index.js
index f190c689..c5fa036c 100644
--- a/index.js
+++ b/index.js
@@ -80,7 +80,7 @@ function compression (options) {
         return false
       }
 
-      if (!this._header) {
+      if (!this.headersSent) {
         this._implicitHeader()
       }
 
@@ -94,7 +94,7 @@ function compression (options) {
         return false
       }
 
-      if (!this._header) {
+      if (!this.headersSent) {
         // estimate the length
         if (!this.getHeader('Content-Length')) {
           length = chunkLength(chunk, encoding)

From 14271613dedd9ab714d294a1cb180cea5101ded2 Mon Sep 17 00:00:00 2001
From: Sebastian Beltran <bjohansebas@gmail.com>
Date: Sun, 3 Nov 2024 17:38:44 -0500
Subject: [PATCH 2/3] improve logic

---
 index.js | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/index.js b/index.js
index 9f14082a..c518c6e8 100644
--- a/index.js
+++ b/index.js
@@ -80,7 +80,7 @@ function compression (options) {
         return false
       }
 
-      if (!this.headersSent) {
+      if (!headersSent(res)) {
         this._implicitHeader()
       }
 
@@ -94,7 +94,7 @@ function compression (options) {
         return false
       }
 
-      if (!this.headersSent) {
+      if (!headersSent(res)) {
         // estimate the length
         if (!this.getHeader('Content-Length')) {
           length = chunkLength(chunk, encoding)
@@ -281,3 +281,17 @@ function toBuffer (chunk, encoding) {
     ? Buffer.from(chunk, encoding)
     : chunk
 }
+
+/**
+ * Determine if the response headers have been sent.
+ *
+ * @param {object} res
+ * @returns {boolean}
+ * @private
+ */
+
+function headersSent (res) {
+  return typeof res.headersSent !== 'boolean'
+    ? Boolean(res._header)
+    : res.headersSent
+}

From 9c96376ee11ec382c654afbaea1ceaa4139dfb1f Mon Sep 17 00:00:00 2001
From: Sebastian Beltran <bjohansebas@gmail.com>
Date: Sun, 3 Nov 2024 17:40:36 -0500
Subject: [PATCH 3/3] update history

---
 HISTORY.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/HISTORY.md b/HISTORY.md
index 7f625d08..3d224eda 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -1,3 +1,7 @@
+unreleased
+==========
+  * Use `res.headersSent` when available
+
 1.7.5 / 2024-10-31
 ==========