add config plugin ability

config/provider.go

@@ -1,3 +1,6 @@
+// Copyright (c) Roman Atachiants and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for details.
+//
 // Copyright (c) 2019,CAOHONGJU All rights reserved.
 // Use of this source code is governed by a MIT-style
 // license that can be found in the LICENSE file.
@@ -6,7 +9,13 @@ package config
 
 import (
 	"errors"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"plugin"
 	"strings"
+	"time"
 )
 
 // Provider 提供者接口
@@ -33,8 +42,38 @@ func (c *ProviderConfig) Load(builtins ...Provider) (Provider, error) {
 		}
 	}
 
-	// TODO: load a plugin provider
-	return nil, errors.New("The provider '" + c.Provider + "' could not be loaded. ")
+	// Attempt to load a plugin provider
+	p, err := plugin.Open(resolvePath(c.Provider))
+	if err != nil {
+		return nil, errors.New("The provider plugin '" + c.Provider + "' could not be opened. " + err.Error())
+	}
+
+	// Get the symbol
+	sym, err := p.Lookup("New")
+	if err != nil {
+		return nil, errors.New("The provider '" + c.Provider + "' does not contain 'func New() interface{}' symbol")
+	}
+
+	// Resolve the
+	pFactory, validFunc := sym.(*func() interface{})
+	if !validFunc {
+		return nil, errors.New("The provider '" + c.Provider + "' does not contain 'func New() interface{}' symbol")
+	}
+
+	// Construct the provider
+	provider, validProv := ((*pFactory)()).(Provider)
+	if !validProv {
+		return nil, errors.New("The provider '" + c.Provider + "' does not implement 'Provider'")
+	}
+
+	// Configure the provider
+	err = provider.Configure(c.Config)
+	if err != nil {
+		return nil, errors.New("The provider '" + c.Provider + "' could not be configured")
+	}
+
+	// Succesfully opened and configured a provider
+	return provider, nil
 }
 
 // LoadOrPanic 加载 Provider 如果失败直接 panics.
@@ -58,3 +97,49 @@ func LoadProvider(config *ProviderConfig, providers ...Provider) Provider {
 	// Load the provider according to the configuration
 	return config.LoadOrPanic(providers...)
 }
+
+func resolvePath(path string) string {
+	// If it's an url, download the file
+	if strings.HasPrefix(path, "http") {
+		f, err := httpFile(path)
+		if err != nil {
+			panic(err)
+		}
+
+		// Get the downloaded file path
+		path = f.Name()
+	}
+
+	// Make sure the path is absolute
+	path, _ = filepath.Abs(path)
+	return path
+}
+
+// DefaultClient used for http with a shorter timeout.
+var defaultClient = &http.Client{
+	Timeout: 5 * time.Second,
+}
+
+// httpFile downloads a file from HTTP
+var httpFile = func(url string) (*os.File, error) {
+	tokens := strings.Split(url, "/")
+	fileName := tokens[len(tokens)-1]
+
+	output, err := os.Create(fileName)
+	if err != nil {
+		return nil, err
+	}
+	defer output.Close()
+
+	response, err := http.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer response.Body.Close()
+
+	if _, err := io.Copy(output, response.Body); err != nil {
+		return nil, err
+	}
+
+	return output, nil
+}

config/tls.go

@@ -9,7 +9,6 @@ import (
 	"errors"
 	"io/ioutil"
 	"os"
-	"path/filepath"
 	"strings"
 )
 
@@ -50,9 +49,3 @@ func (c *TLSConfig) Load() (*tls.Config, error) {
 		Certificates: []tls.Certificate{cer},
 	}, err
 }
-
-func resolvePath(path string) string {
-	// Make sure the path is absolute
-	path, _ = filepath.Abs(path)
-	return path
-}