caddyhttp: Add 'skip_log' var to omit request from logs (#4691)

* caddyhttp: Implement `skip_log` handler

* Refactor to use vars middleware

Co-authored-by: Matt Holt <mholt@users.noreply.github.com>

modules/caddyhttp/logging.go

@@ -0,0 +1,144 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package caddyhttp
+
+import (
+	"errors"
+	"net"
+	"net/http"
+	"strings"
+
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+)
+
+// ServerLogConfig describes a server's logging configuration. If
+// enabled without customization, all requests to this server are
+// logged to the default logger; logger destinations may be
+// customized per-request-host.
+type ServerLogConfig struct {
+	// The default logger name for all logs emitted by this server for
+	// hostnames that are not in the LoggerNames (logger_names) map.
+	DefaultLoggerName string `json:"default_logger_name,omitempty"`
+
+	// LoggerNames maps request hostnames to a custom logger name.
+	// For example, a mapping of "example.com" to "example" would
+	// cause access logs from requests with a Host of example.com
+	// to be emitted by a logger named "http.log.access.example".
+	LoggerNames map[string]string `json:"logger_names,omitempty"`
+
+	// By default, all requests to this server will be logged if
+	// access logging is enabled. This field lists the request
+	// hosts for which access logging should be disabled.
+	SkipHosts []string `json:"skip_hosts,omitempty"`
+
+	// If true, requests to any host not appearing in the
+	// LoggerNames (logger_names) map will not be logged.
+	SkipUnmappedHosts bool `json:"skip_unmapped_hosts,omitempty"`
+
+	// If true, credentials that are otherwise omitted, will be logged.
+	// The definition of credentials is defined by https://fetch.spec.whatwg.org/#credentials,
+	// and this includes some request and response headers, i.e `Cookie`,
+	// `Set-Cookie`, `Authorization`, and `Proxy-Authorization`.
+	ShouldLogCredentials bool `json:"should_log_credentials,omitempty"`
+}
+
+// wrapLogger wraps logger in a logger named according to user preferences for the given host.
+func (slc ServerLogConfig) wrapLogger(logger *zap.Logger, host string) *zap.Logger {
+	if loggerName := slc.getLoggerName(host); loggerName != "" {
+		return logger.Named(loggerName)
+	}
+	return logger
+}
+
+func (slc ServerLogConfig) getLoggerName(host string) string {
+	tryHost := func(key string) (string, bool) {
+		// first try exact match
+		if loggerName, ok := slc.LoggerNames[key]; ok {
+			return loggerName, ok
+		}
+		// strip port and try again (i.e. Host header of "example.com:1234" should
+		// match "example.com" if there is no "example.com:1234" in the map)
+		hostOnly, _, err := net.SplitHostPort(key)
+		if err != nil {
+			return "", false
+		}
+		loggerName, ok := slc.LoggerNames[hostOnly]
+		return loggerName, ok
+	}
+
+	// try the exact hostname first
+	if loggerName, ok := tryHost(host); ok {
+		return loggerName
+	}
+
+	// try matching wildcard domains if other non-specific loggers exist
+	labels := strings.Split(host, ".")
+	for i := range labels {
+		if labels[i] == "" {
+			continue
+		}
+		labels[i] = "*"
+		wildcardHost := strings.Join(labels, ".")
+		if loggerName, ok := tryHost(wildcardHost); ok {
+			return loggerName
+		}
+	}
+
+	return slc.DefaultLoggerName
+}
+
+func (slc *ServerLogConfig) clone() *ServerLogConfig {
+	clone := &ServerLogConfig{
+		DefaultLoggerName:    slc.DefaultLoggerName,
+		LoggerNames:          make(map[string]string),
+		SkipHosts:            append([]string{}, slc.SkipHosts...),
+		SkipUnmappedHosts:    slc.SkipUnmappedHosts,
+		ShouldLogCredentials: slc.ShouldLogCredentials,
+	}
+	for k, v := range slc.LoggerNames {
+		clone.LoggerNames[k] = v
+	}
+	return clone
+}
+
+// errLogValues inspects err and returns the status code
+// to use, the error log message, and any extra fields.
+// If err is a HandlerError, the returned values will
+// have richer information.
+func errLogValues(err error) (status int, msg string, fields []zapcore.Field) {
+	var handlerErr HandlerError
+	if errors.As(err, &handlerErr) {
+		status = handlerErr.StatusCode
+		if handlerErr.Err == nil {
+			msg = err.Error()
+		} else {
+			msg = handlerErr.Err.Error()
+		}
+		fields = []zapcore.Field{
+			zap.Int("status", handlerErr.StatusCode),
+			zap.String("err_id", handlerErr.ID),
+			zap.String("err_trace", handlerErr.Trace),
+		}
+		return
+	}
+	status = http.StatusInternalServerError
+	msg = err.Error()
+	return
+}
+
+// Variable name used to indicate that this request
+// should be omitted from the access logs
+const SkipLogVar = "skip_log"