From f175c5a82a7ddd139678c3994678931cf8dd45e1 Mon Sep 17 00:00:00 2001
From: dawkaka <yousiph77@gmail.com>
Date: Sun, 17 Jul 2022 00:19:38 +0000
Subject: [PATCH] This fixes #3241

---
 .gitignore      |  1 +
 context.go      | 10 +++++++++-
 context_test.go |  9 +++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/.gitignore b/.gitignore
index bdd50c95..3785b5fa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,4 @@ count.out
 test
 profile.out
 tmp.out
+.vscode
\ No newline at end of file
diff --git a/context.go b/context.go
index 46bf1133..c59dfeb2 100644
--- a/context.go
+++ b/context.go
@@ -1130,6 +1130,14 @@ func (c *Context) NegotiateFormat(offered ...string) string {
 		for _, offer := range offered {
 			// According to RFC 2616 and RFC 2396, non-ASCII characters are not allowed in headers,
 			// therefore we can just iterate over the string without casting it into []rune
+
+			//When the lengths are not equal,
+			//offer must end with '*'
+			//in order to avoid getting index out of range errors
+			if len(accepted) > len(offer) && offer[len(offer)-1] != '*' {
+				continue
+			}
+
 			i := 0
 			for ; i < len(accepted); i++ {
 				if accepted[i] == '*' || offer[i] == '*' {
@@ -1139,7 +1147,7 @@ func (c *Context) NegotiateFormat(offered ...string) string {
 					break
 				}
 			}
-			if i == len(accepted) {
+			if i == len(accepted) && i == len(offer) {
 				return offer
 			}
 		}
diff --git a/context_test.go b/context_test.go
index d09b0ae1..af2f8d79 100644
--- a/context_test.go
+++ b/context_test.go
@@ -1296,6 +1296,15 @@ func TestContextNegotiationFormatWithWildcardAccept(t *testing.T) {
 	assert.Equal(t, c.NegotiateFormat(MIMEJSON), "")
 	assert.Equal(t, c.NegotiateFormat(MIMEXML), "")
 	assert.Equal(t, c.NegotiateFormat(MIMEHTML), MIMEHTML)
+
+	c, _ = CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest("POST", "/", nil)
+	c.Request.Header.Add("Accept", "text/html")
+
+	assert.Equal(t, c.NegotiateFormat("text/htm"), "")
+	assert.Equal(t, c.NegotiateFormat("text/htmll"), "")
+	assert.Equal(t, c.NegotiateFormat("tex/*"), "")
+	assert.Equal(t, c.NegotiateFormat("text/html"), MIMEHTML)
 }
 
 func TestContextNegotiationFormatCustom(t *testing.T) {