v2: Module documentation; refactor LoadModule(); new caddy struct tags (#2924)

This commit goes a long way toward making automated documentation of
Caddy config and Caddy modules possible. It's a broad, sweeping change,
but mostly internal. It allows us to automatically generate docs for all
Caddy modules (including future third-party ones) and make them viewable
on a web page; it also doubles as godoc comments.

As such, this commit makes significant progress in migrating the docs
from our temporary wiki page toward our new website which is still under
construction.

With this change, all host modules will use ctx.LoadModule() and pass in
both the struct pointer and the field name as a string. This allows the
reflect package to read the struct tag from that field so that it can
get the necessary information like the module namespace and the inline
key.

This has the nice side-effect of unifying the code and documentation. It
also simplifies module loading, and handles several variations on field
types for raw module fields (i.e. variations on json.RawMessage, such as
arrays and maps).

I also renamed ModuleInfo.Name -> ModuleInfo.ID, to make it clear that
the ID is the "full name" which includes both the module namespace and
the name. This clarity is helpful when describing module hierarchy.

As of this change, Caddy modules are no longer an experimental design.
I think the architecture is good enough to go forward.

4 files changed, 67 insertions, 46 deletions

diff --git a/modules/logging/encoders.go b/modules/logging/encoders.go
index c3c8aba..28cda55 100644
--- a/modules/logging/encoders.go
+++ b/modules/logging/encoders.go
@@ -43,8 +43,8 @@ type ConsoleEncoder struct {
 // CaddyModule returns the Caddy module information.
 func (ConsoleEncoder) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "caddy.logging.encoders.console",
-		New:  func() caddy.Module { return new(ConsoleEncoder) },
+		ID:  "caddy.logging.encoders.console",
+		New: func() caddy.Module { return new(ConsoleEncoder) },
 	}
 }
 
@@ -63,8 +63,8 @@ type JSONEncoder struct {
 // CaddyModule returns the Caddy module information.
 func (JSONEncoder) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "caddy.logging.encoders.json",
-		New:  func() caddy.Module { return new(JSONEncoder) },
+		ID:  "caddy.logging.encoders.json",
+		New: func() caddy.Module { return new(JSONEncoder) },
 	}
 }
 
@@ -84,8 +84,8 @@ type LogfmtEncoder struct {
 // CaddyModule returns the Caddy module information.
 func (LogfmtEncoder) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "caddy.logging.encoders.logfmt",
-		New:  func() caddy.Module { return new(LogfmtEncoder) },
+		ID:  "caddy.logging.encoders.logfmt",
+		New: func() caddy.Module { return new(LogfmtEncoder) },
 	}
 }
 
@@ -102,25 +102,24 @@ func (lfe *LogfmtEncoder) Provision(_ caddy.Context) error {
 type StringEncoder struct {
 	zapcore.Encoder
 	FieldName   string          `json:"field,omitempty"`
-	FallbackRaw json.RawMessage `json:"fallback,omitempty"`
+	FallbackRaw json.RawMessage `json:"fallback,omitempty" caddy:"namespace=caddy.logging.encoders inline_key=format"`
 }
 
 // CaddyModule returns the Caddy module information.
 func (StringEncoder) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "caddy.logging.encoders.string",
-		New:  func() caddy.Module { return new(StringEncoder) },
+		ID:  "caddy.logging.encoders.string",
+		New: func() caddy.Module { return new(StringEncoder) },
 	}
 }
 
 // Provision sets up the encoder.
 func (se *StringEncoder) Provision(ctx caddy.Context) error {
 	if se.FallbackRaw != nil {
-		val, err := ctx.LoadModuleInline("format", "caddy.logging.encoders", se.FallbackRaw)
+		val, err := ctx.LoadModule(se, "FallbackRaw")
 		if err != nil {
 			return fmt.Errorf("loading fallback encoder module: %v", err)
 		}
-		se.FallbackRaw = nil // allow GC to deallocate
 		se.Encoder = val.(zapcore.Encoder)
 	}
 	if se.Encoder == nil {
diff --git a/modules/logging/filewriter.go b/modules/logging/filewriter.go
index 6957b6a..cc60c64 100644
--- a/modules/logging/filewriter.go
+++ b/modules/logging/filewriter.go
@@ -28,22 +28,42 @@ func init() {
 	caddy.RegisterModule(FileWriter{})
 }
 
-// FileWriter can write logs to files.
+// FileWriter can write logs to files. By default, log files
+// are rotated ("rolled") when they get large, and old log
+// files get deleted, to ensure that the process does not
+// exhaust disk space.
 type FileWriter struct {
-	Filename      string `json:"filename,omitempty"`
-	Roll          *bool  `json:"roll,omitempty"`
-	RollSizeMB    int    `json:"roll_size_mb,omitempty"`
-	RollCompress  *bool  `json:"roll_gzip,omitempty"`
-	RollLocalTime bool   `json:"roll_local_time,omitempty"`
-	RollKeep      int    `json:"roll_keep,omitempty"`
-	RollKeepDays  int    `json:"roll_keep_days,omitempty"`
+	// Filename is the name of the file to write.
+	Filename string `json:"filename,omitempty"`
+
+	// Roll toggles log rolling or rotation, which is
+	// enabled by default.
+	Roll *bool `json:"roll,omitempty"`
+
+	// When a log file reaches approximately this size,
+	// it will be rotated.
+	RollSizeMB int `json:"roll_size_mb,omitempty"`
+
+	// Whether to compress rolled files. Default: true
+	RollCompress *bool `json:"roll_gzip,omitempty"`
+
+	// Whether to use local timestamps in rolled filenames.
+	// Default: false
+	RollLocalTime bool `json:"roll_local_time,omitempty"`
+
+	// The maximum number of rolled log files to keep.
+	// Default: 10
+	RollKeep int `json:"roll_keep,omitempty"`
+
+	// How many days to keep rolled log files. Default: 90
+	RollKeepDays int `json:"roll_keep_days,omitempty"`
 }
 
 // CaddyModule returns the Caddy module information.
 func (FileWriter) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "caddy.logging.writers.file",
-		New:  func() caddy.Module { return new(FileWriter) },
+		ID:  "caddy.logging.writers.file",
+		New: func() caddy.Module { return new(FileWriter) },
 	}
 }
 
diff --git a/modules/logging/filterencoder.go b/modules/logging/filterencoder.go
index eff0279..6680019 100644
--- a/modules/logging/filterencoder.go
+++ b/modules/logging/filterencoder.go
@@ -29,13 +29,17 @@ func init() {
 	caddy.RegisterModule(FilterEncoder{})
 }
 
-// FilterEncoder wraps an underlying encoder. It does
-// not do any encoding itself, but it can manipulate
-// (filter) fields before they are actually encoded.
-// A wrapped encoder is required.
+// FilterEncoder can filter (manipulate) fields on
+// log entries before they are actually encoded by
+// an underlying encoder.
 type FilterEncoder struct {
-	WrappedRaw json.RawMessage            `json:"wrap,omitempty"`
-	FieldsRaw  map[string]json.RawMessage `json:"fields,omitempty"`
+	// The underlying encoder that actually
+	// encodes the log entries. Required.
+	WrappedRaw json.RawMessage `json:"wrap,omitempty" caddy:"namespace=caddy.logging.encoders inline_key=format"`
+
+	// A map of field names to their filters. Note that this
+	// is not a module map; the keys are field names.
+	FieldsRaw map[string]json.RawMessage `json:"fields,omitempty" caddy:"namespace=caddy.logging.encoders.filter inline_key=filter"`
 
 	wrapped zapcore.Encoder
 	Fields  map[string]LogFieldFilter `json:"-"`
@@ -47,8 +51,8 @@ type FilterEncoder struct {
 // CaddyModule returns the Caddy module information.
 func (FilterEncoder) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "caddy.logging.encoders.filter",
-		New:  func() caddy.Module { return new(FilterEncoder) },
+		ID:  "caddy.logging.encoders.filter",
+		New: func() caddy.Module { return new(FilterEncoder) },
 	}
 }
 
@@ -59,28 +63,23 @@ func (fe *FilterEncoder) Provision(ctx caddy.Context) error {
 	}
 
 	// set up wrapped encoder (required)
-	val, err := ctx.LoadModuleInline("format", "caddy.logging.encoders", fe.WrappedRaw)
+	val, err := ctx.LoadModule(fe, "WrappedRaw")
 	if err != nil {
 		return fmt.Errorf("loading fallback encoder module: %v", err)
 	}
-	fe.WrappedRaw = nil // allow GC to deallocate
 	fe.wrapped = val.(zapcore.Encoder)
 
 	// set up each field filter
 	if fe.Fields == nil {
 		fe.Fields = make(map[string]LogFieldFilter)
 	}
-	for field, filterRaw := range fe.FieldsRaw {
-		if filterRaw == nil {
-			continue
-		}
-		val, err := ctx.LoadModuleInline("filter", "caddy.logging.encoders.filter", filterRaw)
-		if err != nil {
-			return fmt.Errorf("loading log filter module: %v", err)
-		}
-		fe.Fields[field] = val.(LogFieldFilter)
-	}
-	fe.FieldsRaw = nil // allow GC to deallocate
+	vals, err := ctx.LoadModule(fe, "FieldsRaw")
+	if err != nil {
+		return fmt.Errorf("loading log filter modules: %v", err)
+	}
+	for fieldName, modIface := range vals.(map[string]interface{}) {
+		fe.Fields[fieldName] = modIface.(LogFieldFilter)
+	}
 
 	return nil
 }
diff --git a/modules/logging/filters.go b/modules/logging/filters.go
index b44e084..52db2fe 100644
--- a/modules/logging/filters.go
+++ b/modules/logging/filters.go
@@ -41,8 +41,8 @@ type DeleteFilter struct{}
 // CaddyModule returns the Caddy module information.
 func (DeleteFilter) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "caddy.logging.encoders.filter.delete",
-		New:  func() caddy.Module { return new(DeleteFilter) },
+		ID:  "caddy.logging.encoders.filter.delete",
+		New: func() caddy.Module { return new(DeleteFilter) },
 	}
 }
 
@@ -55,15 +55,18 @@ func (DeleteFilter) Filter(in zapcore.Field) zapcore.Field {
 // IPMaskFilter is a Caddy log field filter that
 // masks IP addresses.
 type IPMaskFilter struct {
+	// The IPv4 range in CIDR notation.
 	IPv4CIDR int `json:"ipv4_cidr,omitempty"`
+
+	// The IPv6 range in CIDR notation.
 	IPv6CIDR int `json:"ipv6_cidr,omitempty"`
 }
 
 // CaddyModule returns the Caddy module information.
 func (IPMaskFilter) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "caddy.logging.encoders.filter.ip_mask",
-		New:  func() caddy.Module { return new(IPMaskFilter) },
+		ID:  "caddy.logging.encoders.filter.ip_mask",
+		New: func() caddy.Module { return new(IPMaskFilter) },
 	}
 }