context.go

// 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 caddy

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"reflect"

	"github.com/mholt/certmagic"
	"go.uber.org/zap"
)

// Context is a type which defines the lifetime of modules that
// are loaded and provides access to the parent configuration
// that spawned the modules which are loaded. It should be used
// with care and wrapped with derivation functions from the
// standard context package only if you don't need the Caddy
// specific features. These contexts are cancelled when the
// lifetime of the modules loaded from it is over.
//
// Use NewContext() to get a valid value (but most modules will
// not actually need to do this).
type Context struct {
	context.Context
	moduleInstances map[string][]interface{}
	cfg             *Config
	cleanupFuncs    []func()
}

// NewContext provides a new context derived from the given
// context ctx. Normally, you will not need to call this
// function unless you are loading modules which have a
// different lifespan than the ones for the context the
// module was provisioned with. Be sure to call the cancel
// func when the context is to be cleaned up so that
// modules which are loaded will be properly unloaded.
// See standard library context package's documentation.
func NewContext(ctx Context) (Context, context.CancelFunc) {
	newCtx := Context{moduleInstances: make(map[string][]interface{}), cfg: ctx.cfg}
	c, cancel := context.WithCancel(ctx.Context)
	wrappedCancel := func() {
		cancel()

		for _, f := range ctx.cleanupFuncs {
			f()
		}

		for modName, modInstances := range newCtx.moduleInstances {
			for _, inst := range modInstances {
				if cu, ok := inst.(CleanerUpper); ok {
					err := cu.Cleanup()
					if err != nil {
						log.Printf("[ERROR] %s (%p): cleanup: %v", modName, inst, err)
					}
				}
			}
		}
	}
	newCtx.Context = c
	return newCtx, wrappedCancel
}

// OnCancel executes f when ctx is cancelled.
func (ctx *Context) OnCancel(f func()) {
	ctx.cleanupFuncs = append(ctx.cleanupFuncs, f)
}

// LoadModule loads the Caddy module(s) from the specified field of the parent struct
// pointer and returns the loaded module(s). The struct pointer and its field name as
// a string are necessary so that reflection can be used to read the struct tag on the
// field to get the module namespace and inline module name key (if specified).
//
// The field can be any one of the supported raw module types: json.RawMessage,
// []json.RawMessage, map[string]json.RawMessage, or []map[string]json.RawMessage.
// ModuleMap may be used in place of map[string]json.RawMessage. The return value's
// underlying type mirrors the input field's type:
//
//    json.RawMessage              => interface{}
//    []json.RawMessage            => []interface{}
//    map[string]json.RawMessage   => map[string]interface{}
//    []map[string]json.RawMessage => []map[string]interface{}
//
// The field must have a "caddy" struct tag in this format:
//
//    caddy:"key1=val1 key2=val2"
//
// To load modules, a "namespace" key is required. For example, to load modules
// in the "http.handlers" namespace, you'd put: `namespace=http.handlers` in the
// Caddy struct tag.
//
// The module name must also be available. If the field type is a map or slice of maps,
// then key is assumed to be the module name if an "inline_key" is NOT specified in the
// caddy struct tag. In this case, the module name does NOT need to be specified in-line
// with the module itself.
//
// If not a map, or if inline_key is non-empty, then the module name must be embedded
// into the values, which must be objects; then there must be a key in those objects
// where its associated value is the module name. This is called the "inline key",
// meaning the key containing the module's name that is defined inline with the module
// itself. You must specify the inline key in a struct tag, along with the namespace:
//
//    caddy:"namespace=http.handlers inline_key=handler"
//
// This will look for a key/value pair like `"handler": "..."` in the json.RawMessage
// in order to know the module name.
//
// To make use of the loaded module(s) (the return value), you will probably want
// to type-assert each interface{} value(s) to the types that are useful to you
// and store them on the same struct. Storing them on the same struct makes for
// easy garbage collection when your host module is no longer needed.
//
// Loaded modules have already been provisioned and validated. Upon returning
// successfully, this method clears the json.RawMessage(s) in the field since
// the raw JSON is no longer needed, and this allows the GC to free up memory.
func (ctx Context) LoadModule(structPointer interface{}, fieldName string) (interface{}, error) {
	val := reflect.ValueOf(structPointer).Elem().FieldByName(fieldName)
	typ := val.Type()

	field, ok := reflect.TypeOf(structPointer).Elem().FieldByName(fieldName)
	if !ok {
		panic(fmt.Sprintf("field %s does not exist in %#v", fieldName, structPointer))
	}

	opts, err := ParseStructTag(field.Tag.Get("caddy"))
	if err != nil {
		panic(fmt.Sprintf("malformed tag on field %s: %v", fieldName, err))
	}

	moduleNamespace, ok := opts["namespace"]
	if !ok {
		panic(fmt.Sprintf("missing 'namespace' key in struct tag on field %s", fieldName))
	}
	inlineModuleKey := opts["inline_key"]

	var result interface{}

	switch val.Kind() {
	case reflect.Slice:
		if isJSONRawMessage(typ) {
			// val is `json.RawMessage` ([]uint8 under the hood)

			if inlineModuleKey == "" {
				panic("unable to determine module name without inline_key when type is not a ModuleMap")
			}
			val, err := ctx.loadModuleInline(inlineModuleKey, moduleNamespace, val.Interface().(json.RawMessage))
			if err != nil {
				return nil, err
			}
			result = val

		} else if isJSONRawMessage(typ.Elem()) {
			// val is `[]json.RawMessage`

			if inlineModuleKey == "" {
				panic("unable to determine module name without inline_key because type is not a ModuleMap")
			}
			var all []interface{}
			for i := 0; i < val.Len(); i++ {
				val, err := ctx.loadModuleInline(inlineModuleKey, moduleNamespace, val.Index(i).Interface().(json.RawMessage))
				if err != nil {
					return nil, fmt.Errorf("position %d: %v", i, err)
				}
				all = append(all, val)
			}
			result = all

		} else if isModuleMapType(typ.Elem()) {
			// val is `[]map[string]json.RawMessage`

			var all []map[string]interface{}
			for i := 0; i < val.Len(); i++ {
				thisSet, err := ctx.loadModulesFromSomeMap(moduleNamespace, inlineModuleKey, val.Index(i))
				if err != nil {
					return nil, err
				}
				all = append(all, thisSet)
			}
			result = all
		}

	case reflect.Map:
		// val is a ModuleMap or some other kind of map
		result, err = ctx.loadModulesFromSomeMap(moduleNamespace, inlineModuleKey, val)
		if err != nil {
			return nil, err
		}

	default:
		return nil, fmt.Errorf("unrecognized type for module: %s", typ)
	}

	// we're done with the raw bytes; allow GC to deallocate
	val.Set(reflect.Zero(typ))

	return result, nil
}

// loadModulesFromSomeMap loads modules from val, which must be a type of map[string]interface{}.
// Depending on inlineModuleKey, it will be interpeted as either a ModuleMap (key is the module
// name) or as a regular map (key is not the module name, and module name is defined inline).
func (ctx Context) loadModulesFromSomeMap(namespace, inlineModuleKey string, val reflect.Value) (map[string]interface{}, error) {
	// if no inline_key is specified, then val must be a ModuleMap,
	// where the key is the module name
	if inlineModuleKey == "" {
		if !isModuleMapType(val.Type()) {
			panic(fmt.Sprintf("expected ModuleMap because inline_key is empty; but we do not recognize this type: %s", val.Type()))
		}
		return ctx.loadModuleMap(namespace, val)
	}

	// otherwise, val is a map with modules, but the module name is
	// inline with each value (the key means something else)
	return ctx.loadModulesFromRegularMap(namespace, inlineModuleKey, val)
}

// loadModulesFromRegularMap loads modules from val, where val is a map[string]json.RawMessage.
// Map keys are NOT interpreted as module names, so module names are still expected to appear
// inline with the objects.
func (ctx Context) loadModulesFromRegularMap(namespace, inlineModuleKey string, val reflect.Value) (map[string]interface{}, error) {
	mods := make(map[string]interface{})
	iter := val.MapRange()
	for iter.Next() {
		k := iter.Key()
		v := iter.Value()
		mod, err := ctx.loadModuleInline(inlineModuleKey, namespace, v.Interface().(json.RawMessage))
		if err != nil {
			return nil, fmt.Errorf("key %s: %v", k, err)
		}
		mods[k.String()] = mod
	}
	return mods, nil
}

// loadModuleMap loads modules from a ModuleMap, i.e. map[string]interface{}, where the key is the
// module name. With a module map, module names do not need to be defined inline with their values.
func (ctx Context) loadModuleMap(namespace string, val reflect.Value) (map[string]interface{}, error) {
	all := make(map[string]interface{})
	iter := val.MapRange()
	for iter.Next() {
		k := iter.Key().Interface().(string)
		v := iter.Value().Interface().(json.RawMessage)
		moduleName := namespace + "." + k
		if namespace == "" {
			moduleName = k
		}
		val, err := ctx.LoadModuleByID(moduleName, v)
		if err != nil {
			return nil, fmt.Errorf("module name '%s': %v", k, err)
		}
		all[k] = val
	}
	return all, nil
}

// LoadModuleByID decodes rawMsg into a new instance of mod and
// returns the value. If mod.New is nil, an error is returned.
// If the module implements Validator or Provisioner interfaces,
// those methods are invoked to ensure the module is fully
// configured and valid before being used.
//
// This is a lower-level method and will usually not be called
// directly by most modules. However, this method is useful when
// dynamically loading/unloading modules in their own context,
// like from embedded scripts, etc.
func (ctx Context) LoadModuleByID(id string, rawMsg json.RawMessage) (interface{}, error) {
	modulesMu.RLock()
	mod, ok := modules[id]
	modulesMu.RUnlock()
	if !ok {
		return nil, fmt.Errorf("unknown module: %s", id)
	}

	if mod.New == nil {
		return nil, fmt.Errorf("module '%s' has no constructor", mod.ID)
	}

	val := mod.New().(interface{})

	// value must be a pointer for unmarshaling into concrete type, even if
	// the module's concrete type is a slice or map; New() *should* return
	// a pointer, otherwise unmarshaling errors or panics will occur
	if rv := reflect.ValueOf(val); rv.Kind() != reflect.Ptr {
		log.Printf("[WARNING] ModuleInfo.New() for module '%s' did not return a pointer,"+
			" so we are using reflection to make a pointer instead; please fix this by"+
			" using new(Type) or &Type notation in your module's New() function.", id)
		val = reflect.New(rv.Type()).Elem().Addr().Interface().(Module)
	}

	// fill in its config only if there is a config to fill in
	if len(rawMsg) > 0 {
		err := strictUnmarshalJSON(rawMsg, &val)
		if err != nil {
			return nil, fmt.Errorf("decoding module config: %s: %v", mod, err)
		}
	}

	if val == nil {
		// returned module values are almost always type-asserted
		// before being used, so a nil value would panic; and there
		// is no good reason to explicitly declare null modules in
		// a config; it might be because the user is trying to achieve
		// a result the developer isn't expecting, which is a smell
		return nil, fmt.Errorf("module value cannot be null")
	}

	if prov, ok := val.(Provisioner); ok {
		err := prov.Provision(ctx)
		if err != nil {
			// incomplete provisioning could have left state
			// dangling, so make sure it gets cleaned up
			if cleanerUpper, ok := val.(CleanerUpper); ok {
				err2 := cleanerUpper.Cleanup()
				if err2 != nil {
					err = fmt.Errorf("%v; additionally, cleanup: %v", err, err2)
				}
			}
			return nil, fmt.Errorf("provision %s: %v", mod, err)
		}
	}

	if validator, ok := val.(Validator); ok {
		err := validator.Validate()
		if err != nil {
			// since the module was already provisioned, make sure we clean up
			if cleanerUpper, ok := val.(CleanerUpper); ok {
				err2 := cleanerUpper.Cleanup()
				if err2 != nil {
					err = fmt.Errorf("%v; additionally, cleanup: %v", err, err2)
				}
			}
			return nil, fmt.Errorf("%s: invalid configuration: %v", mod, err)
		}
	}

	ctx.moduleInstances[id] = append(ctx.moduleInstances[id], val)

	return val, nil
}

// loadModuleInline loads a module from a JSON raw message which decodes to
// a map[string]interface{}, where one of the object keys is moduleNameKey
// and the corresponding value is the module name (as a string) which can
// be found in the given scope. In other words, the module name is declared
// in-line with the module itself.
//
// This allows modules to be decoded into their concrete types and used when
// their names cannot be the unique key in a map, such as when there are
// multiple instances in the map or it appears in an array (where there are
// no custom keys). In other words, the key containing the module name is
// treated special/separate from all the other keys in the object.
func (ctx Context) loadModuleInline(moduleNameKey, moduleScope string, raw json.RawMessage) (interface{}, error) {
	moduleName, raw, err := getModuleNameInline(moduleNameKey, raw)
	if err != nil {
		return nil, err
	}

	val, err := ctx.LoadModuleByID(moduleScope+"."+moduleName, raw)
	if err != nil {
		return nil, fmt.Errorf("loading module '%s': %v", moduleName, err)
	}

	return val, nil
}

// App returns the configured app named name. If no app with
// that name is currently configured, a new empty one will be
// instantiated. (The app module must still be registered.)
func (ctx Context) App(name string) (interface{}, error) {
	if app, ok := ctx.cfg.apps[name]; ok {
		return app, nil
	}
	modVal, err := ctx.LoadModuleByID(name, nil)
	if err != nil {
		return nil, fmt.Errorf("instantiating new module %s: %v", name, err)
	}
	ctx.cfg.apps[name] = modVal.(App)
	return modVal, nil
}

// Storage returns the configured Caddy storage implementation.
func (ctx Context) Storage() certmagic.Storage {
	return ctx.cfg.storage
}

// Logger returns a logger that can be used by mod.
func (ctx Context) Logger(mod Module) *zap.Logger {
	return ctx.cfg.Logging.Logger(mod)
}