logging: Implement `log_append` handler (#6066)

* logging: Implement `extra_log` handler

* Rename to `log_append`

* Rename `skip_log` to `log_skip`

---------

Co-authored-by: Matt Holt <[email protected]>

9 files changed, 239 insertions, 12 deletions

diff --git a/caddyconfig/httpcaddyfile/builtins.go b/caddyconfig/httpcaddyfile/builtins.go
index 5040924df..505885d2d 100644
--- a/caddyconfig/httpcaddyfile/builtins.go
+++ b/caddyconfig/httpcaddyfile/builtins.go
@@ -49,7 +49,8 @@ func init() {
 	RegisterDirective("handle_errors", parseHandleErrors)
 	RegisterHandlerDirective("invoke", parseInvoke)
 	RegisterDirective("log", parseLog)
-	RegisterHandlerDirective("skip_log", parseSkipLog)
+	RegisterHandlerDirective("skip_log", parseLogSkip)
+	RegisterHandlerDirective("log_skip", parseLogSkip)
 }
 
 // parseBind parses the bind directive. Syntax:
@@ -1038,13 +1039,19 @@ func parseLogHelper(h Helper, globalLogNames map[string]struct{}) ([]ConfigValue
 	return configValues, nil
 }
 
-// parseSkipLog parses the skip_log directive. Syntax:
+// parseLogSkip parses the log_skip directive. Syntax:
 //
-//	skip_log [<matcher>]
-func parseSkipLog(h Helper) (caddyhttp.MiddlewareHandler, error) {
+//	log_skip [<matcher>]
+func parseLogSkip(h Helper) (caddyhttp.MiddlewareHandler, error) {
 	h.Next() // consume directive name
+
+	// "skip_log" is deprecated, replaced by "log_skip"
+	if h.Val() == "skip_log" {
+		caddy.Log().Named("config.adapter.caddyfile").Warn("the 'skip_log' directive is deprecated, please use 'log_skip' instead!")
+	}
+
 	if h.NextArg() {
 		return nil, h.ArgErr()
 	}
-	return caddyhttp.VarsMiddleware{"skip_log": true}, nil
+	return caddyhttp.VarsMiddleware{"log_skip": true}, nil
 }
diff --git a/caddyconfig/httpcaddyfile/directives.go b/caddyconfig/httpcaddyfile/directives.go
index 9a549a18e..13026fa4e 100644
--- a/caddyconfig/httpcaddyfile/directives.go
+++ b/caddyconfig/httpcaddyfile/directives.go
@@ -43,7 +43,8 @@ var directiveOrder = []string{
 	"vars",
 	"fs",
 	"root",
-	"skip_log",
+	"log_append",
+	"log_skip",
 
 	"header",
 	"copy_response_headers", // only in reverse_proxy's handle_response
diff --git a/caddytest/integration/caddyfile_adapt/log_add.caddyfiletest b/caddytest/integration/caddyfile_adapt/log_add.caddyfiletest
new file mode 100644
index 000000000..4f91e4644
--- /dev/null
+++ b/caddytest/integration/caddyfile_adapt/log_add.caddyfiletest
@@ -0,0 +1,71 @@
+:80 {
+	log
+
+	vars foo foo
+
+	log_append const bar
+	log_append vars foo
+	log_append placeholder {path}
+
+	log_append /only-for-this-path secret value
+}
+----------
+{
+	"apps": {
+		"http": {
+			"servers": {
+				"srv0": {
+					"listen": [
+						":80"
+					],
+					"routes": [
+						{
+							"handle": [
+								{
+									"foo": "foo",
+									"handler": "vars"
+								}
+							]
+						},
+						{
+							"match": [
+								{
+									"path": [
+										"/only-for-this-path"
+									]
+								}
+							],
+							"handle": [
+								{
+									"handler": "log_append",
+									"key": "secret",
+									"value": "value"
+								}
+							]
+						},
+						{
+							"handle": [
+								{
+									"handler": "log_append",
+									"key": "const",
+									"value": "bar"
+								},
+								{
+									"handler": "log_append",
+									"key": "vars",
+									"value": "foo"
+								},
+								{
+									"handler": "log_append",
+									"key": "placeholder",
+									"value": "{http.request.uri.path}"
+								}
+							]
+						}
+					],
+					"logs": {}
+				}
+			}
+		}
+	}
+}
diff --git a/caddytest/integration/caddyfile_adapt/log_except_catchall_blocks.caddyfiletest b/caddytest/integration/caddyfile_adapt/log_except_catchall_blocks.caddyfiletest
index 6fbc6c7c8..e1362f8fb 100644
--- a/caddytest/integration/caddyfile_adapt/log_except_catchall_blocks.caddyfiletest
+++ b/caddytest/integration/caddyfile_adapt/log_except_catchall_blocks.caddyfiletest
@@ -1,7 +1,7 @@
 http://localhost:2020 {
 	log
-	skip_log /first-hidden*
-	skip_log /second-hidden*
+	log_skip /first-hidden*
+	log_skip /second-hidden*
 	respond 200
 }
 
@@ -34,7 +34,7 @@ http://localhost:2020 {
 											"handle": [
 												{
 													"handler": "vars",
-													"skip_log": true
+													"log_skip": true
 												}
 											],
 											"match": [
@@ -49,7 +49,7 @@ http://localhost:2020 {
 											"handle": [
 												{
 													"handler": "vars",
-													"skip_log": true
+													"log_skip": true
 												}
 											],
 											"match": [
diff --git a/modules/caddyhttp/logging.go b/modules/caddyhttp/logging.go
index 728befd2b..81b2830fc 100644
--- a/modules/caddyhttp/logging.go
+++ b/modules/caddyhttp/logging.go
@@ -166,7 +166,7 @@ func (e *ExtraLogFields) Set(field zap.Field) {
 const (
 	// Variable name used to indicate that this request
 	// should be omitted from the access logs
-	SkipLogVar string = "skip_log"
+	LogSkipVar string = "log_skip"
 
 	// For adding additional fields to the access logs
 	ExtraLogFieldsCtxKey caddy.CtxKey = "extra_log_fields"
diff --git a/modules/caddyhttp/logging/caddyfile.go b/modules/caddyhttp/logging/caddyfile.go
new file mode 100644
index 000000000..010b48919
--- /dev/null
+++ b/modules/caddyhttp/logging/caddyfile.go
@@ -0,0 +1,53 @@
+// 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 logging
+
+import (
+	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
+	"github.com/caddyserver/caddy/v2/caddyconfig/httpcaddyfile"
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
+)
+
+func init() {
+	httpcaddyfile.RegisterHandlerDirective("log_append", parseCaddyfile)
+}
+
+// parseCaddyfile sets up the log_append handler from Caddyfile tokens. Syntax:
+//
+//	log_append [<matcher>] <key> <value>
+func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error) {
+	handler := new(LogAppend)
+	err := handler.UnmarshalCaddyfile(h.Dispenser)
+	return handler, err
+}
+
+// UnmarshalCaddyfile implements caddyfile.Unmarshaler.
+func (h *LogAppend) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
+	d.Next() // consume directive name
+	if !d.NextArg() {
+		return d.ArgErr()
+	}
+	h.Key = d.Val()
+	if !d.NextArg() {
+		return d.ArgErr()
+	}
+	h.Value = d.Val()
+	return nil
+}
+
+// Interface guards
+var (
+	_ caddyfile.Unmarshaler = (*LogAppend)(nil)
+)
diff --git a/modules/caddyhttp/logging/logadd.go b/modules/caddyhttp/logging/logadd.go
new file mode 100644
index 000000000..3b554367f
--- /dev/null
+++ b/modules/caddyhttp/logging/logadd.go
@@ -0,0 +1,94 @@
+// 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 logging
+
+import (
+	"net/http"
+	"strings"
+
+	"go.uber.org/zap"
+
+	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
+)
+
+func init() {
+	caddy.RegisterModule(LogAppend{})
+}
+
+// LogAppend implements a middleware that takes a key and value, where
+// the key is the name of a log field and the value is a placeholder,
+// or variable key, or constant value to use for that field.
+type LogAppend struct {
+	// Key is the name of the log field.
+	Key string `json:"key,omitempty"`
+
+	// Value is the value to use for the log field.
+	// If it is a placeholder (with surrounding `{}`),
+	// it will be evaluated when the log is written.
+	// If the value is a key that exists in the `vars`
+	// map, the value of that key will be used. Otherwise
+	// the value will be used as-is as a constant string.
+	Value string `json:"value,omitempty"`
+}
+
+// CaddyModule returns the Caddy module information.
+func (LogAppend) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "http.handlers.log_append",
+		New: func() caddy.Module { return new(LogAppend) },
+	}
+}
+
+func (h LogAppend) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
+	// Run the next handler in the chain first.
+	// If an error occurs, we still want to add
+	// any extra log fields that we can, so we
+	// hold onto the error and return it later.
+	handlerErr := next.ServeHTTP(w, r)
+
+	// On the way back up the chain, add the extra log field
+	ctx := r.Context()
+
+	vars := ctx.Value(caddyhttp.VarsCtxKey).(map[string]any)
+	repl := ctx.Value(caddy.ReplacerCtxKey).(*caddy.Replacer)
+	extra := ctx.Value(caddyhttp.ExtraLogFieldsCtxKey).(*caddyhttp.ExtraLogFields)
+
+	var varValue any
+	if strings.HasPrefix(h.Value, "{") &&
+		strings.HasSuffix(h.Value, "}") &&
+		strings.Count(h.Value, "{") == 1 {
+		// the value looks like a placeholder, so get its value
+		varValue, _ = repl.Get(strings.Trim(h.Value, "{}"))
+	} else if val, ok := vars[h.Value]; ok {
+		// the value is a key in the vars map
+		varValue = val
+	} else {
+		// the value is a constant string
+		varValue = h.Value
+	}
+
+	// Add the field to the extra log fields.
+	// We use zap.Any because it will reflect
+	// to the correct type for us.
+	extra.Add(zap.Any(h.Key, varValue))
+
+	return handlerErr
+}
+
+// Interface guards
+var (
+	_ caddyhttp.MiddlewareHandler = (*LogAppend)(nil)
+)
diff --git a/modules/caddyhttp/server.go b/modules/caddyhttp/server.go
index 9ea04acb9..04ae003a7 100644
--- a/modules/caddyhttp/server.go
+++ b/modules/caddyhttp/server.go
@@ -715,7 +715,7 @@ func (s *Server) logRequest(
 	repl *caddy.Replacer, bodyReader *lengthReader, shouldLogCredentials bool,
 ) {
 	// this request may be flagged as omitted from the logs
-	if skipLog, ok := GetVar(r.Context(), SkipLogVar).(bool); ok && skipLog {
+	if skip, ok := GetVar(r.Context(), LogSkipVar).(bool); ok && skip {
 		return
 	}
 
diff --git a/modules/caddyhttp/standard/imports.go b/modules/caddyhttp/standard/imports.go
index d7bb2800c..236e7be1e 100644
--- a/modules/caddyhttp/standard/imports.go
+++ b/modules/caddyhttp/standard/imports.go
@@ -10,6 +10,7 @@ import (
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/encode/zstd"
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/fileserver"
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/headers"
+	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/logging"
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/map"
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/proxyprotocol"
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/push"