Provide self-registering storage system (#12978)
	
		
	
				
					
				
			* Provide self-registering storage system Signed-off-by: Andrew Thornton <art27@cantab.net> * More simplification Signed-off-by: Andrew Thornton <art27@cantab.net> * Remove old strings from setting Signed-off-by: Andrew Thornton <art27@cantab.net> * oops attachments not attachment Signed-off-by: Andrew Thornton <art27@cantab.net> Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>tokarchuk/v1.17
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// Copyright 2020 The Gitea Authors. All rights reserved.
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// Use of this source code is governed by a MIT-style
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// license that can be found in the LICENSE file.
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package storage | 
				
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import ( | 
				
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	"encoding/json" | 
				
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	"reflect" | 
				
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) | 
				
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// Mappable represents an interface that can MapTo another interface
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type Mappable interface { | 
				
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	MapTo(v interface{}) error | 
				
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} | 
				
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// toConfig will attempt to convert a given configuration cfg into the provided exemplar type.
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//
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// It will tolerate the cfg being passed as a []byte or string of a json representation of the
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// exemplar or the correct type of the exemplar itself
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func toConfig(exemplar, cfg interface{}) (interface{}, error) { | 
				
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	// First of all check if we've got the same type as the exemplar - if so it's all fine.
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	if reflect.TypeOf(cfg).AssignableTo(reflect.TypeOf(exemplar)) { | 
				
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		return cfg, nil | 
				
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	} | 
				
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	// Now if not - does it provide a MapTo function we can try?
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	if mappable, ok := cfg.(Mappable); ok { | 
				
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		newVal := reflect.New(reflect.TypeOf(exemplar)) | 
				
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		if err := mappable.MapTo(newVal.Interface()); err == nil { | 
				
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			return newVal.Elem().Interface(), nil | 
				
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		} | 
				
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		// MapTo has failed us ... let's try the json route ...
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	} | 
				
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	// OK we've been passed a byte array right?
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	configBytes, ok := cfg.([]byte) | 
				
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	if !ok { | 
				
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		// oh ... it's a string then?
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		var configStr string | 
				
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		configStr, ok = cfg.(string) | 
				
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		configBytes = []byte(configStr) | 
				
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	} | 
				
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	if !ok { | 
				
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		// hmm ... can we marshal it to json?
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		var err error | 
				
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		configBytes, err = json.Marshal(cfg) | 
				
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		ok = (err == nil) | 
				
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	} | 
				
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	if !ok { | 
				
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		// no ... we've tried hard enough at this point - throw an error!
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		return nil, ErrInvalidConfiguration{cfg: cfg} | 
				
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	} | 
				
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	// OK unmarshal the byte array into a new copy of the exemplar
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	newVal := reflect.New(reflect.TypeOf(exemplar)) | 
				
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	if err := json.Unmarshal(configBytes, newVal.Interface()); err != nil { | 
				
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		// If we can't unmarshal it then return an error!
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		return nil, ErrInvalidConfiguration{cfg: cfg, err: err} | 
				
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	} | 
				
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	return newVal.Elem().Interface(), nil | 
				
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} | 
				
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