Fixes bug in har responses encoding

DevProxy.Plugins/Generation/HarGeneratorPlugin.cs

@@ -6,6 +6,7 @@
 using DevProxy.Abstractions.Proxy;
 using DevProxy.Abstractions.Utils;
 using DevProxy.Plugins.Models;
+using DevProxy.Plugins.Utils;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.Logging;
 using System.Diagnostics;
@@ -128,11 +129,11 @@ private HarEntry CreateHarEntry(RequestLog log)
                         return new HarCookie { Name = parts[0].Trim(), Value = parts.Length > 1 ? parts[1].Trim() : "" };
                     })],
                 HeadersSize = request.Headers?.ToString()?.Length ?? 0,
-                BodySize = request.HasBody ? (request.BodyString?.Length ?? 0) : 0,
+                BodySize = request.HasBody ? (request.Body?.Length ?? 0) : 0,
                 PostData = request.HasBody ? new HarPostData
                 {
                     MimeType = request.ContentType,
-                    Text = request.BodyString ?? ""
+                    Text = request.Body is not null ? HttpUtils.GetBodyString(request.ContentType, request.Body) : ""
                 }
                     : null
             },
@@ -152,12 +153,12 @@ private HarEntry CreateHarEntry(RequestLog log)
                     })],
                 Content = new HarContent
                 {
-                    Size = response.HasBody ? (response.BodyString?.Length ?? 0) : 0,
+                    Size = response.HasBody ? (response.Body?.Length ?? 0) : 0,
                     MimeType = response.ContentType ?? "",
-                    Text = Configuration.IncludeResponse && response.HasBody ? response.BodyString : null
+                    Text = Configuration.IncludeResponse && response.HasBody && response.Body is not null ? HttpUtils.GetBodyString(response.ContentType, response.Body) : null
                 },
                 HeadersSize = response.Headers?.ToString()?.Length ?? 0,
-                BodySize = response.HasBody ? (response.BodyString?.Length ?? 0) : 0
+                BodySize = response.HasBody ? (response.Body?.Length ?? 0) : 0
             } : null
         };
 

DevProxy.Plugins/Inspection/DevToolsPlugin.cs

@@ -6,6 +6,7 @@
 using DevProxy.Abstractions.Plugins;
 using DevProxy.Abstractions.Utils;
 using DevProxy.Plugins.Inspection.CDP;
+using DevProxy.Plugins.Utils;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.Logging;
 using System.Collections.Concurrent;
@@ -119,7 +120,7 @@ public override async Task BeforeRequestAsync(ProxyRequestArgs e, CancellationTo
                     Url = e.Session.HttpClient.Request.Url,
                     Method = e.Session.HttpClient.Request.Method,
                     Headers = headers,
-                    PostData = e.Session.HttpClient.Request.HasBody ? GetBodyString(e.Session.HttpClient.Request.ContentType, e.Session.HttpClient.Request.Body) : null
+                    PostData = e.Session.HttpClient.Request.HasBody ? HttpUtils.GetBodyString(e.Session.HttpClient.Request.ContentType, e.Session.HttpClient.Request.Body) : null
                 },
                 Timestamp = (double)DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() / 1000,
                 WallTime = DateTimeOffset.UtcNow.ToUnixTimeSeconds(),
@@ -173,7 +174,7 @@ public override async Task AfterResponseAsync(ProxyResponseArgs e, CancellationT
         {
             if (IsTextResponse(e.Session.HttpClient.Response.ContentType))
             {
-                body.Body = GetBodyString(e.Session.HttpClient.Response.ContentType, e.Session.HttpClient.Response.Body);
+                body.Body = HttpUtils.GetBodyString(e.Session.HttpClient.Response.ContentType, e.Session.HttpClient.Response.Body);
                 body.Base64Encoded = false;
             }
             else
@@ -1062,33 +1063,6 @@ private static bool IsTextResponse(string? contentType)
         return isTextResponse;
     }
 
-    // Decodes an HTTP message body (request or response) to a string.
-    // If the Content-Type header specifies a charset, that encoding is used.
-    // Otherwise, the body is decoded as UTF-8. The underlying proxy library
-    // defaults to ISO-8859-1 per the obsolete RFC 2616, but modern standards
-    // (RFC 7231, RFC 8259) treat UTF-8 as the default for JSON and most web content.
-    private static string GetBodyString(string? contentType, byte[] body)
-    {
-        if (contentType is not null)
-        {
-            try
-            {
-                var ct = new System.Net.Mime.ContentType(contentType);
-                if (!string.IsNullOrEmpty(ct.CharSet))
-                {
-                    return Encoding.GetEncoding(ct.CharSet).GetString(body);
-                }
-            }
-            catch
-            {
-                // Malformed Content-Type or unsupported charset; fall through
-                // to UTF-8 default
-            }
-        }
-
-        return Encoding.UTF8.GetString(body);
-    }
-
     protected override void Dispose(bool disposing)
     {
         if (disposing)

DevProxy.Plugins/Utils/HttpUtils.cs

@@ -3,12 +3,50 @@
 // See the LICENSE file in the project root for more information.
 
 using Microsoft.Extensions.Logging;
+using System.Text;
 using Titanium.Web.Proxy.Http;
 
 namespace DevProxy.Plugins.Utils;
 
 internal sealed class HttpUtils
 {
+    // Decodes an HTTP message body (request or response) to a string.
+    // If the Content-Type header specifies a charset, that encoding is used.
+    // Otherwise, tries strict UTF-8 decoding first. If the body contains
+    // invalid UTF-8 sequences, falls back to Latin-1 (ISO-8859-1) which is a
+    // lossless 1:1 byte-to-char mapping that preserves raw byte values.
+    // The underlying proxy library defaults to ISO-8859-1 per the obsolete
+    // RFC 2616, but modern standards (RFC 7231, RFC 8259) treat UTF-8 as the
+    // default for JSON and most web content.
+    public static string GetBodyString(string? contentType, byte[] body)
+    {
+        if (contentType is not null)
+        {
+            try
+            {
+                var ct = new System.Net.Mime.ContentType(contentType);
+                if (!string.IsNullOrEmpty(ct.CharSet))
+                {
+                    return Encoding.GetEncoding(ct.CharSet).GetString(body);
+                }
+            }
+            catch
+            {
+                // Malformed Content-Type or unsupported charset; fall through
+                // to UTF-8/Latin-1 default
+            }
+        }
+
+        try
+        {
+            return new UTF8Encoding(encoderShouldEmitUTF8Identifier: false, throwOnInvalidBytes: true).GetString(body);
+        }
+        catch (DecoderFallbackException)
+        {
+            return Encoding.Latin1.GetString(body);
+        }
+    }
+
     public static string GetBodyFromStreamingResponse(Response response, ILogger logger)
     {
         logger.LogTrace("{Method} called", nameof(GetBodyFromStreamingResponse));