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Fixes body encoding and prompt type issues in LanguageModelFailurePlugin #1643

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Merged
waldekmastykarz merged 2 commits into from
May 3, 2026
+16 −6
Merged

Fixes body encoding and prompt type issues in LanguageModelFailurePlugin #1643

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14ff1a2
Fixes body encoding and prompt type issues in LanguageModelFailurePlugin
waldekmastykarz May 2, 2026
bf56c6c
Merge branch 'main' into fix-llm-failure
waldekmastykarz May 3, 2026
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22 changes: 16 additions & 6 deletions DevProxy.Plugins/Behavior/LanguageModelFailurePlugin.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -73,7 +73,11 @@ public override async Task BeforeRequestAsync(ProxyRequestArgs e, CancellationTo
return;
}

if (!OpenAIRequest.TryGetCompletionLikeRequest(request.BodyString, Logger, out var openAiRequest))
Logger.LogDebug("Request encoding: {Encoding}", request.Encoding?.EncodingName ?? "null");
var originalBody = System.Text.Encoding.UTF8.GetString(request.Body);
Logger.LogDebug("Original request body:\n{Body}", originalBody);
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if (!OpenAIRequest.TryGetCompletionLikeRequest(originalBody, Logger, out var openAiRequest))
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{
Logger.LogRequest("Skipping non-OpenAI request", MessageType.Skipped, new LoggingContext(e.Session));
return;
Expand All @@ -91,15 +95,17 @@ public override async Task BeforeRequestAsync(ProxyRequestArgs e, CancellationTo
completionRequest.Prompt += "\n\n" + faultPrompt;
Logger.LogDebug("Modified completion request prompt: {Prompt}", completionRequest.Prompt);
Logger.LogRequest($"Simulating fault {faultName}", MessageType.Chaos, new LoggingContext(e.Session));
e.Session.SetRequestBodyString(JsonSerializer.Serialize(completionRequest, ProxyUtils.JsonSerializerOptions));
var modifiedBody = JsonSerializer.Serialize(completionRequest, ProxyUtils.JsonSerializerOptions);
Logger.LogDebug("Modified request body:\n{Body}", modifiedBody);
e.Session.SetRequestBodyString(modifiedBody);
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}
else if (openAiRequest is OpenAIChatCompletionRequest chatRequest)
{
var messages = new List<OpenAIChatCompletionMessage>(chatRequest.Messages)
{
new()
{
Role = "user",
Role = "system",
Content = faultPrompt
}
};
Expand All @@ -114,15 +120,17 @@ public override async Task BeforeRequestAsync(ProxyRequestArgs e, CancellationTo

Logger.LogDebug("Added fault prompt to messages: {Prompt}", faultPrompt);
Logger.LogRequest($"Simulating fault {faultName}", MessageType.Chaos, new LoggingContext(e.Session));
e.Session.SetRequestBodyString(JsonSerializer.Serialize(newRequest, ProxyUtils.JsonSerializerOptions));
var modifiedBody = JsonSerializer.Serialize(newRequest, ProxyUtils.JsonSerializerOptions);
Logger.LogDebug("Modified request body:\n{Body}", modifiedBody);
e.Session.SetRequestBodyString(modifiedBody);
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}
else if (openAiRequest is OpenAIResponsesRequest responsesRequest)
{
var inputItems = new List<OpenAIResponsesInputItem>(responsesRequest.Input ?? [])
{
new()
{
Role = "user",
Role = "system",
Content = faultPrompt
}
};
Expand All @@ -144,7 +152,9 @@ public override async Task BeforeRequestAsync(ProxyRequestArgs e, CancellationTo

Logger.LogDebug("Added fault prompt to Responses API input: {Prompt}", faultPrompt);
Logger.LogRequest($"Simulating fault {faultName}", MessageType.Chaos, new LoggingContext(e.Session));
e.Session.SetRequestBodyString(JsonSerializer.Serialize(newRequest, ProxyUtils.JsonSerializerOptions));
var modifiedBody = JsonSerializer.Serialize(newRequest, ProxyUtils.JsonSerializerOptions);
Logger.LogDebug("Modified request body:\n{Body}", modifiedBody);
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e.Session.SetRequestBodyString(modifiedBody);
}
else
{
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