AspNetCore.Docs/aspnetcore/fundamentals/w3c-logger/index.md

title	author	description	monikerRange	ms.author	ms.date	no-loc	uid
W3CLogger in .NET Core and ASP.NET Core	wtgodbe	Learn how to create server logs in the W3C standard format.	>= aspnetcore-6.0	wigodbe	09/29/2021	Home Privacy appsettings.json ASP.NET Core Identity cookie Cookie Blazor Blazor Server Blazor WebAssembly Identity Let's Encrypt Razor SignalR	fundamentals/w3c-logger/index

W3CLogger in ASP.NET Core

W3CLogger is a middleware that writes log files in the W3C standard format. The logs contain information about HTTP requests and HTTP responses. W3CLogger provides logs of:

• HTTP request information
• Common properties
• Headers
• HTTP response information
• Metadata about the request/response pair (date/time started, time taken)

W3CLogger is valuable in several scenarios to:

• Record information about incoming requests and responses.
• Filter which parts of the request and response are logged.
• Filter which headers to log.

W3CLogger can reduce the performance of an app. Consider the performance impact when selecting fields to log - the performance reduction will increase as you log more properties. Test the performance impact of the selected logging properties.

[!WARNING] W3CLogger can potentially log personally identifiable information (PII). Consider the risk and avoid logging sensitive information. By default, fields that could contain PII are not logged.

Enabling W3CLogger

W3CLogger is enabled with UseW3CLogging, which adds the W3CLogger middleware.

[!code-csharp]

By default, W3CLogger logs common properties such as path, status-code, date, time, and protocol. All information about a single request/response pair is written to the same line.

#Version: 1.0
#Start-Date: 2021-09-29 22:18:28
#Fields: date time c-ip s-computername s-ip s-port cs-method cs-uri-stem cs-uri-query sc-status time-taken cs-version cs-host cs(User-Agent) cs(Referer)
2021-09-29 22:18:28 ::1 DESKTOP-LH3TLTA ::1 5000 GET / - 200 59.9171 HTTP/1.1 localhost:5000 Mozilla/5.0+(Windows+NT+10.0;+WOW64)+AppleWebKit/537.36+(KHTML,+like+Gecko)+Chrome/93.0.4577.82+Safari/537.36 -
2021-09-29 22:18:28 ::1 DESKTOP-LH3TLTA ::1 5000 GET / - 200 0.1802 HTTP/1.1 localhost:5000 Mozilla/5.0+(Windows+NT+10.0;+WOW64)+AppleWebKit/537.36+(KHTML,+like+Gecko)+Chrome/93.0.4577.82+Safari/537.36 -
2021-09-29 22:18:30 ::1 DESKTOP-LH3TLTA ::1 5000 GET / - 200 0.0966 HTTP/1.1 localhost:5000 Mozilla/5.0+(Windows+NT+10.0;+WOW64)+AppleWebKit/537.36+(KHTML,+like+Gecko)+Chrome/93.0.4577.82+Safari/537.36 -

W3CLogger options

To configure the W3CLogger middleware, call AddW3CLogging in ConfigureServices.

[!code-csharp]

LoggingFields

W3CLoggerOptions.LoggingFields is a bit flag enumeration that configures specific parts of the request and response to log, and other information about the connection. LoggingFields defaults to include all possible fields except UserName and Cookie.

[!code-csharp]

Flag	Description	Value
None	No logging.	0x0
Date	The date that the activity occurred.	0x1
Time	The time that the activity occurred.	0x2
ClientIpAddress	The IP address of the client that accessed the server.	0x4
UserName	The name of the authenticated user that accessed the server.	0x8
ServerName	The name of the server on which the log entry was generated.	0x10
ServerIpAddress	The IP address of the server on which the log entry was generated.	0x20
ServerPort	The port number the client is connected to.	0x40
Method	Request xref:Microsoft.AspNetCore.Http.HttpRequest.Method.	0x80
UriStem	Request Path, which includes both the xref:Microsoft.AspNetCore.Http.HttpRequest.Path and xref:Microsoft.AspNetCore.Http.HttpRequest.PathBase.	0x100
UriQuery	Request xref:Microsoft.AspNetCore.Http.HttpRequest.QueryString.	0x200
ProtocolStatus	Response xref:Microsoft.AspNetCore.Http.HttpResponse.StatusCode.	0x400
TimeTaken	The duration of time, in milliseconds, that the action consumed.	0x800
ProtocolVersion	Request xref:Microsoft.AspNetCore.Http.HttpRequest.Protocol.	0x1000
Host	Request Microsoft.AspNetCore.Http.Headers.HeaderNames.Host.	0x2000
UserAgent	Request Microsoft.AspNetCore.Http.Headers.HeaderNames.UserAgent.	0x4000
Cookie	Request Microsoft.AspNetCore.Http.Headers.HeaderNames.Cookie.	0x8000
Referer	Request Microsoft.AspNetCore.Http.Headers.HeaderNames.Referer.	0x10000
ConnectionInfoFields	Flag for logging a collection of properties, about the HTTP Connection, including ClientIpAddress, ServerIpAddress, and ServerPort.	`ClientIpAddress
RequestHeaders	Flag for logging a collection of request headers, including Host, Referer, and UserAgent.	`Host
Request	Flag for logging a collection of properties about the request, including UriStem, UriQuery, ProtocolVersion, Method, and RequestHeaders.	`UriStem
All	Flag for logging all possible fields.	`Date

FileSizeLimit

Maximum log file size in bytes. Defaults to 10 MiB.

[!code-csharp]

RetainedFileCountLimit

Maximum number of files to keep on disk before rolling, per application. Defaults to 4, capped at 10,000.

[!code-csharp]

FileName

Prefix to be used for log file name. The current date plus a file number, in the format {YYYYMMDD.X}, will be appended.

[!code-csharp]

LogDirectory

Directory where the log file will be written to. Defaults to ./logs/, relative to the app directory.

[!code-csharp]

FlushInterval

The period after which logs will be flushed to the log file. Defaults to 1 second.

[!code-csharp]