C# Implementation (#2)
C# implementation of SEP-1763 --------- Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
This commit is contained in:
Peder Holdgaard Pedersen
GitHub
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1 changed files with 13862 additions and 21 deletions
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using ModelContextProtocol.Interceptors;
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using ModelContextProtocol.Interceptors.Client;
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using ModelContextProtocol.Protocol;
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using System.Text.Json;
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using System.Text.Json.Nodes;
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/// <summary>
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/// Sample mutation interceptors for MCP client operations.
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/// These interceptors demonstrate argument transformation and response filtering.
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/// </summary>
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[McpClientInterceptorType]
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public class ClientMutationInterceptors
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{
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/// <summary>
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/// Normalizes tool arguments by trimming whitespace and converting empty strings to null.
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/// </summary>
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[McpClientInterceptor(
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Name = "argument-normalizer",
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Description = "Normalizes tool arguments (trim whitespace, handle empty strings)",
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Type = InterceptorType.Mutation,
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Events = [InterceptorEvents.ToolsCall],
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Phase = InterceptorPhase.Request,
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PriorityHint = -100)] // Normalization runs before validation
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public MutationInterceptorResult NormalizeArguments(JsonNode? payload)
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{
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if (payload is null)
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{
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return MutationInterceptorResult.Unchanged(payload);
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}
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// Parse the tool call
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CallToolRequestParams? toolCall;
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try
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{
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toolCall = payload.Deserialize<CallToolRequestParams>();
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}
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catch (JsonException)
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{
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return MutationInterceptorResult.Unchanged(payload);
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}
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if (toolCall?.Arguments is null || toolCall.Arguments.Count == 0)
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{
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return MutationInterceptorResult.Unchanged(payload);
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}
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bool modified = false;
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var normalizedArgs = new Dictionary<string, JsonElement>();
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foreach (var arg in toolCall.Arguments)
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{
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var value = arg.Value;
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// Trim string values
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if (value.ValueKind == JsonValueKind.String)
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{
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var stringValue = value.GetString();
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if (stringValue is not null)
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{
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var trimmed = stringValue.Trim();
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if (trimmed != stringValue)
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{
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modified = true;
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// Convert empty strings to null
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if (string.IsNullOrEmpty(trimmed))
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{
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normalizedArgs[arg.Key] = JsonDocument.Parse("null").RootElement;
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}
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else
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{
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normalizedArgs[arg.Key] = JsonDocument.Parse($"\"{EscapeJsonString(trimmed)}\"").RootElement;
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}
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continue;
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}
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}
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}
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normalizedArgs[arg.Key] = value;
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}
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if (!modified)
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{
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return MutationInterceptorResult.Unchanged(payload);
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}
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// Rebuild the payload with normalized arguments
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var mutatedPayload = new JsonObject
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{
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["name"] = toolCall.Name,
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["arguments"] = JsonSerializer.SerializeToNode(normalizedArgs)
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};
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if (toolCall.Meta is not null)
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{
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mutatedPayload["_meta"] = JsonSerializer.SerializeToNode(toolCall.Meta);
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}
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return MutationInterceptorResult.Mutated(mutatedPayload);
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}
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/// <summary>
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/// Adds a timestamp to all outgoing tool call requests for audit purposes.
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/// </summary>
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[McpClientInterceptor(
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Name = "request-timestamp",
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Description = "Adds timestamp metadata to tool call requests",
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Type = InterceptorType.Mutation,
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Events = [InterceptorEvents.ToolsCall],
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Phase = InterceptorPhase.Request,
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PriorityHint = 100)] // Runs after normalization/validation
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public MutationInterceptorResult AddTimestamp(JsonNode? payload)
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{
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if (payload is not JsonObject obj)
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{
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return MutationInterceptorResult.Unchanged(payload);
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}
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// Create or update _meta with timestamp
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var meta = obj["_meta"]?.AsObject() ?? new JsonObject();
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meta["clientTimestamp"] = DateTimeOffset.UtcNow.ToString("o");
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meta["clientVersion"] = "1.0.0";
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obj["_meta"] = meta;
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return MutationInterceptorResult.Mutated(obj);
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}
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/// <summary>
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/// Redacts sensitive information from tool responses before returning to caller.
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/// </summary>
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[McpClientInterceptor(
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Name = "response-redactor",
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Description = "Redacts sensitive patterns from tool responses",
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Type = InterceptorType.Mutation,
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Events = [InterceptorEvents.ToolsCall],
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Phase = InterceptorPhase.Response,
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PriorityHint = 50)]
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public MutationInterceptorResult RedactResponse(JsonNode? payload)
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{
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if (payload is null)
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{
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return MutationInterceptorResult.Unchanged(payload);
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}
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// Parse the result
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CallToolResult? result;
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try
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{
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result = payload.Deserialize<CallToolResult>();
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}
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catch (JsonException)
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{
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return MutationInterceptorResult.Unchanged(payload);
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}
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if (result?.Content is null)
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{
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return MutationInterceptorResult.Unchanged(payload);
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}
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bool modified = false;
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var newContent = new List<ContentBlock>();
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foreach (var content in result.Content)
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{
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if (content is TextContentBlock textBlock)
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{
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var redactedText = RedactSensitivePatterns(textBlock.Text);
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if (redactedText != textBlock.Text)
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{
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modified = true;
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newContent.Add(new TextContentBlock { Text = redactedText });
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continue;
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}
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}
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newContent.Add(content);
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}
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if (!modified)
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{
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return MutationInterceptorResult.Unchanged(payload);
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}
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// Rebuild result with redacted content
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var mutatedResult = new JsonObject
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{
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["content"] = JsonSerializer.SerializeToNode(newContent),
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["isError"] = result.IsError
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};
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return MutationInterceptorResult.Mutated(mutatedResult);
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}
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private static string RedactSensitivePatterns(string? text)
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{
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if (string.IsNullOrEmpty(text))
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{
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return text ?? string.Empty;
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}
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// Redact API keys (common patterns)
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text = System.Text.RegularExpressions.Regex.Replace(
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text,
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@"(?i)(api[_-]?key|apikey|secret|password|token)[""']?\s*[:=]\s*[""']?[\w\-\.]+[""']?",
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"$1=***REDACTED***");
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// Redact bearer tokens
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text = System.Text.RegularExpressions.Regex.Replace(
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text,
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@"(?i)bearer\s+[\w\-\.]+",
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"Bearer ***REDACTED***");
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return text;
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}
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private static string EscapeJsonString(string value)
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{
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return value
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.Replace("\\", "\\\\")
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.Replace("\"", "\\\"")
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.Replace("\n", "\\n")
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.Replace("\r", "\\r")
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.Replace("\t", "\\t");
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}
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}
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