From d85cc2ec103de72658c55ba74197337c99bd1f74 Mon Sep 17 00:00:00 2001
From: Omar Ramadan <omar@blockcast.net>
Date: Mon, 10 Jun 2024 08:03:24 -0700
Subject: [PATCH] logging: Customizable zap cores (#6381)

---
 caddyconfig/httpcaddyfile/builtins.go      | 17 ++++++++++
 caddyconfig/httpcaddyfile/builtins_test.go |  6 ++--
 logging.go                                 | 12 ++++++++
 modules/logging/cores.go                   | 36 ++++++++++++++++++++++
 4 files changed, 69 insertions(+), 2 deletions(-)
 create mode 100644 modules/logging/cores.go

diff --git a/caddyconfig/httpcaddyfile/builtins.go b/caddyconfig/httpcaddyfile/builtins.go
index 35a08ef2782..e1e95e00a37 100644
--- a/caddyconfig/httpcaddyfile/builtins.go
+++ b/caddyconfig/httpcaddyfile/builtins.go
@@ -849,6 +849,7 @@ func parseInvoke(h Helper) (caddyhttp.MiddlewareHandler, error) {
 //	log <logger_name> {
 //	    hostnames <hostnames...>
 //	    output <writer_module> ...
+//	    core   <core_module> ...
 //	    format <encoder_module> ...
 //	    level  <level>
 //	}
@@ -960,6 +961,22 @@ func parseLogHelper(h Helper, globalLogNames map[string]struct{}) ([]ConfigValue
 			}
 			cl.WriterRaw = caddyconfig.JSONModuleObject(wo, "output", moduleName, h.warnings)
 
+		case "core":
+			if !h.NextArg() {
+				return nil, h.ArgErr()
+			}
+			moduleName := h.Val()
+			moduleID := "caddy.logging.cores." + moduleName
+			unm, err := caddyfile.UnmarshalModule(h.Dispenser, moduleID)
+			if err != nil {
+				return nil, err
+			}
+			core, ok := unm.(zapcore.Core)
+			if !ok {
+				return nil, h.Errf("module %s (%T) is not a zapcore.Core", moduleID, unm)
+			}
+			cl.CoreRaw = caddyconfig.JSONModuleObject(core, "module", moduleName, h.warnings)
+
 		case "format":
 			if !h.NextArg() {
 				return nil, h.ArgErr()
diff --git a/caddyconfig/httpcaddyfile/builtins_test.go b/caddyconfig/httpcaddyfile/builtins_test.go
index 70f347dd9dc..cf746348487 100644
--- a/caddyconfig/httpcaddyfile/builtins_test.go
+++ b/caddyconfig/httpcaddyfile/builtins_test.go
@@ -25,11 +25,12 @@ func TestLogDirectiveSyntax(t *testing.T) {
 		{
 			input: `:8080 {
 				log {
+					core mock
 					output file foo.log
 				}
 			}
 			`,
-			output:      `{"logging":{"logs":{"default":{"exclude":["http.log.access.log0"]},"log0":{"writer":{"filename":"foo.log","output":"file"},"include":["http.log.access.log0"]}}},"apps":{"http":{"servers":{"srv0":{"listen":[":8080"],"logs":{"default_logger_name":"log0"}}}}}}`,
+			output:      `{"logging":{"logs":{"default":{"exclude":["http.log.access.log0"]},"log0":{"writer":{"filename":"foo.log","output":"file"},"core":{"module":"mock"},"include":["http.log.access.log0"]}}},"apps":{"http":{"servers":{"srv0":{"listen":[":8080"],"logs":{"default_logger_name":"log0"}}}}}}`,
 			expectError: false,
 		},
 		{
@@ -53,11 +54,12 @@ func TestLogDirectiveSyntax(t *testing.T) {
 		{
 			input: `:8080 {
 				log name-override {
+					core mock
 					output file foo.log
 				}
 			}
 			`,
-			output:      `{"logging":{"logs":{"default":{"exclude":["http.log.access.name-override"]},"name-override":{"writer":{"filename":"foo.log","output":"file"},"include":["http.log.access.name-override"]}}},"apps":{"http":{"servers":{"srv0":{"listen":[":8080"],"logs":{"default_logger_name":"name-override"}}}}}}`,
+			output:      `{"logging":{"logs":{"default":{"exclude":["http.log.access.name-override"]},"name-override":{"writer":{"filename":"foo.log","output":"file"},"core":{"module":"mock"},"include":["http.log.access.name-override"]}}},"apps":{"http":{"servers":{"srv0":{"listen":[":8080"],"logs":{"default_logger_name":"name-override"}}}}}}`,
 			expectError: false,
 		},
 	} {
diff --git a/logging.go b/logging.go
index d3e7bf32b56..ca10beeeddc 100644
--- a/logging.go
+++ b/logging.go
@@ -292,6 +292,10 @@ type BaseLog struct {
 	// The encoder is how the log entries are formatted or encoded.
 	EncoderRaw json.RawMessage `json:"encoder,omitempty" caddy:"namespace=caddy.logging.encoders inline_key=format"`
 
+	// Tees entries through a zap.Core module which can extract
+	// log entry metadata and fields for further processing.
+	CoreRaw json.RawMessage `json:"core,omitempty" caddy:"namespace=caddy.logging.cores inline_key=module"`
+
 	// Level is the minimum level to emit, and is inclusive.
 	// Possible levels: DEBUG, INFO, WARN, ERROR, PANIC, and FATAL
 	Level string `json:"level,omitempty"`
@@ -366,6 +370,14 @@ func (cl *BaseLog) provisionCommon(ctx Context, logging *Logging) error {
 		cl.encoder = newDefaultProductionLogEncoder(cl.writerOpener)
 	}
 	cl.buildCore()
+	if cl.CoreRaw != nil {
+		mod, err := ctx.LoadModule(cl, "CoreRaw")
+		if err != nil {
+			return fmt.Errorf("loading log core module: %v", err)
+		}
+		core := mod.(zapcore.Core)
+		cl.core = zapcore.NewTee(cl.core, core)
+	}
 	return nil
 }
 
diff --git a/modules/logging/cores.go b/modules/logging/cores.go
new file mode 100644
index 00000000000..49aa7640ce3
--- /dev/null
+++ b/modules/logging/cores.go
@@ -0,0 +1,36 @@
+package logging
+
+import (
+	"go.uber.org/zap/zapcore"
+
+	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
+)
+
+func init() {
+	caddy.RegisterModule(MockCore{})
+}
+
+// MockCore is a no-op module, purely for testing
+type MockCore struct {
+	zapcore.Core `json:"-"`
+}
+
+// CaddyModule returns the Caddy module information.
+func (MockCore) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "caddy.logging.cores.mock",
+		New: func() caddy.Module { return new(MockCore) },
+	}
+}
+
+func (lec *MockCore) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
+	return nil
+}
+
+// Interface guards
+var (
+	_ zapcore.Core          = (*MockCore)(nil)
+	_ caddy.Module          = (*MockCore)(nil)
+	_ caddyfile.Unmarshaler = (*MockCore)(nil)
+)