Fix: Correct content-length header for responses with multi-byte characters (#12702)

Move content-length computation outside the headers null check in CDP
so it is always set when body data is present. Also use InvariantCulture
for number formatting and align the BiDi implementation. Add tests for
correct content-length with string and binary bodies containing emoji.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kblok

lib/PuppeteerSharp.Tests/RequestInterceptionTests/RequestRespondTests.cs

@@ -148,6 +148,40 @@ await e.Request.RespondAsync(new ResponseData
             Assert.That(error.Message, Does.Match("Invalid header|Expected \"header\"|invalid argument"));
         }
 
+        [Test, PuppeteerTest("requestinterception.spec", "Request.respond", "should report correct content-length header with string")]
+        public async Task ShouldReportCorrectContentLengthHeaderWithString()
+        {
+            await Page.SetRequestInterceptionAsync(true);
+            Page.Request += async (_, e) =>
+            {
+                await e.Request.RespondAsync(new ResponseData
+                {
+                    Status = HttpStatusCode.OK,
+                    Body = "Correct length \U0001F4CF?",
+                });
+            };
+            var response = await Page.GoToAsync(TestConstants.EmptyPage);
+            var headers = response.Headers;
+            Assert.That(headers["content-length"], Is.EqualTo("20"));
+        }
+
+        [Test, PuppeteerTest("requestinterception.spec", "Request.respond", "should report correct content-length header with binary body")]
+        public async Task ShouldReportCorrectContentLengthHeaderWithBinaryBody()
+        {
+            await Page.SetRequestInterceptionAsync(true);
+            Page.Request += async (_, e) =>
+            {
+                await e.Request.RespondAsync(new ResponseData
+                {
+                    Status = HttpStatusCode.OK,
+                    BodyData = System.Text.Encoding.UTF8.GetBytes("Correct length \U0001F4CF?"),
+                });
+            };
+            var response = await Page.GoToAsync(TestConstants.EmptyPage);
+            var headers = response.Headers;
+            Assert.That(headers["content-length"], Is.EqualTo("20"));
+        }
+
         [Test, PuppeteerTest("requestinterception.spec", "Request.respond", "should stringify intercepted request response headers")]
         public async Task ShouldStringifyInterceptedRequestResponseHeaders()
         {

lib/PuppeteerSharp/Bidi/BidiHttpRequest.cs

@@ -487,7 +487,7 @@ private async Task RespondInternalAsync(ResponseData response)
             }
 
             // Add content-length if not present and we have body data
-            if (!hasContentLength && response.BodyData != null)
+            if (!hasContentLength && response.BodyData is { Length: > 0 })
             {
                 responseHeaders.Add(new Header("content-length", response.BodyData.Length.ToString(CultureInfo.InvariantCulture)));
             }

lib/PuppeteerSharp/Cdp/CdpHttpRequest.cs

@@ -355,11 +355,11 @@ private async Task RespondInternalAsync(ResponseData response)
                     responseHeaders.Add(new Header { Name = keyValuePair.Key, Value = keyValuePair.Value.ToString() });
                 }
             }
+        }
 
-            if (!response.Headers.ContainsKey("content-length") && response.BodyData != null)
-            {
-                responseHeaders.Add(new Header { Name = "content-length", Value = response.BodyData.Length.ToString(CultureInfo.CurrentCulture) });
-            }
+        if (response.BodyData is { Length: > 0 } && (response.Headers == null || !response.Headers.ContainsKey("content-length")))
+        {
+            responseHeaders.Add(new Header { Name = "content-length", Value = response.BodyData.Length.ToString(CultureInfo.InvariantCulture) });
         }
 
         if (response.ContentType != null)