From 793fd983ef937d2bea1edf5d8d855e2a452a4aa7 Mon Sep 17 00:00:00 2001
From: Nan Monnand Deng <monnand@gmail.com>
Date: Fri, 2 Aug 2013 02:47:58 -0400
Subject: [PATCH] http utils

---
 utils/http.go | 129 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 129 insertions(+)
 create mode 100644 utils/http.go

diff --git a/utils/http.go b/utils/http.go
new file mode 100644
index 0000000000..61fdbff04e
--- /dev/null
+++ b/utils/http.go
@@ -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
+}