v2: Logging! (#2831)

* logging: Initial implementation

* logging: More encoder formats, better defaults

* logging: Fix repetition bug with FilterEncoder; add more presets

* logging: DiscardWriter; delete or no-op logs that discard their output

* logging: Add http.handlers.log module; enhance Replacer methods

The Replacer interface has new methods to customize how to handle empty
or unrecognized placeholders. Closes #2815.

* logging: Overhaul HTTP logging, fix bugs, improve filtering, etc.

* logging: General cleanup, begin transitioning to using new loggers

* Fixes after merge conflict

modules/caddyhttp/fileserver/staticfiles.go

@@ -18,6 +18,7 @@ import (
 	"bytes"
 	"fmt"
 	"html/template"
+	"io"
 	weakrand "math/rand"
 	"mime"
 	"net/http"
@@ -191,6 +192,24 @@ func (fsrv *FileServer) ServeHTTP(w http.ResponseWriter, r *http.Request, _ cadd
 		}
 	}
 
+	// if this handler exists in an error context (i.e. is
+	// part of a handler chain that is supposed to handle
+	// a previous error), we have to serve the content
+	// manually in order to write the correct status code
+	if reqErr, ok := r.Context().Value(caddyhttp.ErrorCtxKey).(error); ok {
+		statusCode := http.StatusInternalServerError
+		if handlerErr, ok := reqErr.(caddyhttp.HandlerError); ok {
+			if handlerErr.StatusCode > 0 {
+				statusCode = handlerErr.StatusCode
+			}
+		}
+		w.WriteHeader(statusCode)
+		if r.Method != "HEAD" {
+			io.Copy(w, file)
+		}
+		return nil
+	}
+
 	// let the standard library do what it does best; note, however,
 	// that errors generated by ServeContent are written immediately
 	// to the response, so we cannot handle them (but errors there