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@@ -0,0 +1,129 @@

+package utils

+

+import (

+	"bytes"

+	"io"

+	"net/http"

+	"strings"

+)

+

+// VersionInfo is used to model entities which has a version.

+// It is basically a tupple with name and version.

+type VersionInfo interface {

+	Name() string

+	Version() string

+}

+

+func validVersion(version VersionInfo) bool {

+	stopChars := " \t\r\n/"

+	if strings.ContainsAny(version.Name(), stopChars) {

+		return false

+	}

+	if strings.ContainsAny(version.Version(), stopChars) {

+		return false

+	}

+	return true

+}

+

+// Convert versions to a string and append the string to the string base.

+//

+// Each VersionInfo will be converted to a string in the format of

+// "product/version", where the "product" is get from the Name() method, while

+// version is get from the Version() method. Several pieces of verson information

+// will be concatinated and separated by space.

+func appendVersions(base string, versions ...VersionInfo) string {

+	if len(versions) == 0 {

+		return base

+	}

+

+	var buf bytes.Buffer

+	if len(base) > 0 {

+		buf.Write([]byte(base))

+	}

+

+	for _, v := range versions {

+		name := []byte(v.Name())

+		version := []byte(v.Version())

+

+		if len(name) == 0 || len(version) == 0 {

+			continue

+		}

+		if !validVersion(v) {

+			continue

+		}

+		buf.Write([]byte(v.Name()))

+		buf.Write([]byte("/"))

+		buf.Write([]byte(v.Version()))

+		buf.Write([]byte(" "))

+	}

+	return buf.String()

+}

+

+// HTTPRequestDecorator is used to change an instance of

+// http.Request. It could be used to add more header fields,

+// change body, etc.

+type HTTPRequestDecorator interface {

+	// ChangeRequest() changes the request accordingly.

+	// The changed request will be returned or err will be non-nil

+	// if an error occur.

+	ChangeRequest(req *http.Request) (newReq *http.Request, err error)

+}

+

+// HTTPUserAgentDecorator appends the product/version to the user agent field

+// of a request.

+type HTTPUserAgentDecorator struct {

+	versions []VersionInfo

+}

+

+func NewHTTPUserAgentDecorator(versions ...VersionInfo) HTTPRequestDecorator {

+	ret := new(HTTPUserAgentDecorator)

+	ret.versions = versions

+	return ret

+}

+

+func (self *HTTPUserAgentDecorator) ChangeRequest(req *http.Request) (newReq *http.Request, err error) {

+	if req == nil {

+		return req, nil

+	}

+

+	userAgent := appendVersions(req.UserAgent(), self.versions...)

+	if len(userAgent) > 0 {

+		req.Header.Set("User-Agent", userAgent)

+	}

+	return req, nil

+}

+

+// HTTPRequestFactory creates an HTTP request

+// and applies a list of decorators on the request.

+type HTTPRequestFactory struct {

+	decorators []HTTPRequestDecorator

+}

+

+func NewHTTPRequestFactory(d ...HTTPRequestDecorator) *HTTPRequestFactory {

+	ret := new(HTTPRequestFactory)

+	ret.decorators = d

+	return ret

+}

+

+// NewRequest() creates a new *http.Request,

+// applies all decorators in the HTTPRequestFactory on the request,

+// then applies decorators provided by d on the request.

+func (self *HTTPRequestFactory) NewRequest(method, urlStr string, body io.Reader, d ...HTTPRequestDecorator) (*http.Request, error) {

+	req, err := http.NewRequest(method, urlStr, body)

+	if err != nil {

+		return nil, err

+	}

+	for _, dec := range self.decorators {

+		req, err = dec.ChangeRequest(req)

+		if err != nil {

+			return nil, err

+		}

+	}

+	for _, dec := range d {

+		req, err = dec.ChangeRequest(req)

+		if err != nil {

+			return nil, err

+		}

+	}

+	return req, err

+}