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urlgen.go
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package amazonproduct
import (
"crypto/hmac"
"crypto/sha256"
"encoding/base64"
"fmt"
"io/ioutil"
"net/http"
"net/url"
"sort"
"strings"
"time"
)
type AmazonProductAPI struct {
AccessKey string
SecretKey string
AssociateTag string
Host string
Client *http.Client
}
func (api AmazonProductAPI) genSignAndFetch(Operation string, Parameters map[string]string) (string, error) {
genUrl, err := GenerateAmazonUrl(api, Operation, Parameters)
if err != nil {
return "", err
}
SetTimestamp(genUrl)
signedurl, err := SignAmazonUrl(genUrl, api)
if err != nil {
return "", err
}
if api.Client == nil {
api.Client = http.DefaultClient
}
resp, err := api.Client.Get(signedurl)
if err != nil {
return "", err
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
return "", err
}
return string(body), nil
}
func GenerateAmazonUrl(api AmazonProductAPI, Operation string, Parameters map[string]string) (finalUrl *url.URL, err error) {
result, err := url.Parse(api.Host)
if err != nil {
return nil, err
}
result.Host = api.Host
result.Scheme = "http"
result.Path = "/onca/xml"
values := url.Values{}
values.Add("Operation", Operation)
values.Add("Service", "AWSECommerceService")
values.Add("AWSAccessKeyId", api.AccessKey)
values.Add("Version", "2013-08-01")
values.Add("AssociateTag", api.AssociateTag)
for k, v := range Parameters {
values.Set(k, v)
}
params := values.Encode()
result.RawQuery = params
return result, nil
}
func SetTimestamp(origUrl *url.URL) (err error) {
values, err := url.ParseQuery(origUrl.RawQuery)
if err != nil {
return err
}
values.Set("Timestamp", time.Now().UTC().Format(time.RFC3339))
origUrl.RawQuery = values.Encode()
return nil
}
func SignAmazonUrl(origUrl *url.URL, api AmazonProductAPI) (signedUrl string, err error) {
escapeUrl := strings.Replace(origUrl.RawQuery, ",", "%2C", -1)
escapeUrl = strings.Replace(escapeUrl, ":", "%3A", -1)
params := strings.Split(escapeUrl, "&")
sort.Strings(params)
sortedParams := strings.Join(params, "&")
toSign := fmt.Sprintf("GET\n%s\n%s\n%s", origUrl.Host, origUrl.Path, sortedParams)
hasher := hmac.New(sha256.New, []byte(api.SecretKey))
_, err = hasher.Write([]byte(toSign))
if err != nil {
return "", err
}
hash := base64.StdEncoding.EncodeToString(hasher.Sum(nil))
hash = url.QueryEscape(hash)
newParams := fmt.Sprintf("%s&Signature=%s", sortedParams, hash)
origUrl.RawQuery = newParams
return origUrl.String(), nil
}