Added ${aspnet-request-headers} for rendering headers

src/Shared/LayoutRenderers/AspNetRequestHeadersLayoutRenderer.cs

@@ -0,0 +1,115 @@
+using System.Collections.Generic;
+using System.Text;
+using NLog.Config;
+using NLog.LayoutRenderers;
+using NLog.Web.Internal;
+using System;
+#if !ASP_NET_CORE
+using System.Collections.Specialized;
+using System.Linq;
+#else
+using Microsoft.AspNetCore.Http;
+#endif
+
+namespace NLog.Web.LayoutRenderers
+{
+    /// <summary>
+    /// ASP.NET Request Headers
+    /// </summary>
+    /// <para>Example usage of ${aspnet-request-headers}</para>
+    /// <example>
+    /// <code lang="NLog Layout Renderer">
+    /// ${aspnet-request-headers:OutputFormat=Flat}
+    /// ${aspnet-request-headers:OutputFormat=Json}
+    /// ${aspnet-request-headers:OutputFormat=Json:HeaderNames=username}
+    /// ${aspnet-request-headers:OutputFormat=Json:Exclude=access_token}
+    /// </code>
+    /// </example>
+    [LayoutRenderer("aspnet-request-headers")]
+    [ThreadSafe]
+    public class AspNetRequestHeadersLayoutRenderer : AspNetLayoutMultiValueRendererBase
+    {
+        /// <summary>
+        /// Header names to be rendered.
+        /// If <c>null</c> or empty array, all headers will be rendered.
+        /// </summary>
+        public List<string> HeaderNames { get; set; }
+
+        /// <summary>
+        /// Gets or sets the keys to exclude from the output. If omitted, none are excluded.
+        /// </summary>
+        /// <docgen category='Rendering Options' order='10' />
+#if ASP_NET_CORE
+        public ISet<string> Exclude { get; set; }
+#else
+        public HashSet<string> Exclude { get; set; }
+#endif
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="AspNetRequestHeadersLayoutRenderer" /> class.
+        /// </summary>
+        public AspNetRequestHeadersLayoutRenderer()
+        {
+            Exclude = new HashSet<string>(new[] { "ALL_HTTP", "ALL_RAW", "AUTH_PASSWORD" }, StringComparer.OrdinalIgnoreCase);
+        }
+
+        /// <summary>
+        /// Renders the ASP.NET Headers appends it to the specified <see cref="StringBuilder" />.
+        /// </summary>
+        /// <param name="builder">The <see cref="StringBuilder" /> to append the rendered data to.</param>
+        /// <param name="logEvent">Logging event.</param>
+        protected override void DoAppend(StringBuilder builder, LogEventInfo logEvent)
+        {
+            var httpRequest = HttpContextAccessor.HttpContext.TryGetRequest();
+            if (httpRequest == null)
+            {
+                return;
+            }
+
+            var headers = httpRequest.Headers;
+            if (headers?.Count > 0)
+            {
+                bool excludeKeys = (HeaderNames == null || HeaderNames.Count == 0) && Exclude?.Count > 0;
+                var headerValues = GetHeaderValues(headers, excludeKeys);
+                SerializePairs(headerValues, builder, logEvent);
+            }
+        }
+
+#if !ASP_NET_CORE
+        private IEnumerable<KeyValuePair<string, string>> GetHeaderValues(NameValueCollection headers, bool excludeKeys)
+        {
+            var headerNames = HeaderNames?.Count > 0 ? HeaderNames : headers.Keys.Cast<string>().ToList();
+            foreach (var headerName in headerNames)
+            {
+                if (excludeKeys && Exclude.Contains(headerName))
+                    continue;
+
+                var headerValue = headers[headerName];
+                if (headerValue == null)
+                {
+                    continue;
+                }
+
+                yield return new KeyValuePair<string, string>(headerName, headerValue);
+            }
+        }
+#else
+        private IEnumerable<KeyValuePair<string, string>> GetHeaderValues(IHeaderDictionary headers, bool excludeKeys)
+        {
+            var headerNames = HeaderNames?.Count > 0 ? HeaderNames : headers.Keys;
+            foreach (var headerName in headerNames)
+            {
+                if (excludeKeys && Exclude.Contains(headerName))
+                    continue;
+
+                if (!headers.TryGetValue(headerName, out var headerValue))
+                {
+                    continue;
+                }
+
+                yield return new KeyValuePair<string, string>(headerName, headerValue);
+            }
+        }
+#endif
+    }
+}