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github.go
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github.go
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// github.go - ham fisted accesses to github /user with caching.
package main
import (
"encoding/json"
"fmt"
"io/ioutil"
"net/http"
"os"
"path/filepath"
"time"
)
const (
// Maximum time an item is considered valid in the cache.
maxAgeDays = 30
cacheDir = "/tmp/scoreboard.cache"
)
// GithubUserResponse holds information about a particular github user.
type GithubUserResponse struct {
Login string `json:"login"`
ID int `json:"id"`
NodeID string `json:"node_id"`
AvatarURL string `json:"avatar_url"`
GravatarID string `json:"gravatar_id"`
URL string `json:"url"`
HTMLURL string `json:"html_url"`
FollowersURL string `json:"followers_url"`
FollowingURL string `json:"following_url"`
GistsURL string `json:"gists_url"`
StarredURL string `json:"starred_url"`
SubscriptionsURL string `json:"subscriptions_url"`
OrganizationsURL string `json:"organizations_url"`
ReposURL string `json:"repos_url"`
EventsURL string `json:"events_url"`
ReceivedEventsURL string `json:"received_events_url"`
Type string `json:"type"`
SiteAdmin bool `json:"site_admin"`
Name string `json:"name"`
Company interface{} `json:"company"`
Blog string `json:"blog"`
Location string `json:"location"`
Email interface{} `json:"email"`
Hireable interface{} `json:"hireable"`
Bio interface{} `json:"bio"`
PublicRepos int `json:"public_repos"`
PublicGists int `json:"public_gists"`
Followers int `json:"followers"`
Following int `json:"following"`
CreatedAt time.Time `json:"created_at"`
UpdatedAt time.Time `json:"updated_at"`
}
// readFromNegativeCache attempts to read data for a given username from the
// negative cache files. If we have a hit there, the user is considered as
// "non-existent" and attempts to fetch from github should not happen (or it
// will eat our quota).
func readFromNegativeCache(username string) (bool, error) {
_, cached, err := cached(negativeCacheFile(username), maxAgeDays*24*time.Hour)
if err != nil {
return false, fmt.Errorf("negative cache read error for %q: %v", username, err)
}
return cached, nil
}
// readFromCache attempts to read data for a given username from the cache
// files. Returns the data read from the cache file, a bool indicating whether
// the user data was found (and is valid) and an error.
func readFromCache(username string) ([]byte, bool, error) {
jdata, ok, err := cached(cacheFile(username), maxAgeDays*24*time.Hour)
if err != nil {
return nil, false, fmt.Errorf("cache read error for %q: %v", username, err)
}
if !ok {
return nil, false, nil
}
return jdata, true, nil
}
// readFromGithub reads data from a user using the github API (v3). If a 404 is
// returned, we save the user to the negative cache to avoid future accesses to
// this user. Returns the data read from Github (json), a boolean indicating
// whether we found a valid user or not, and an error.
func readFromGithub(username string) ([]byte, bool, error) {
r, err := http.Get("https://api.github.com/users/" + username)
if err != nil {
return nil, false, fmt.Errorf("error retrieving github user %q: %v", username, err)
}
// Save username in our negative cache if we get a 404.
if r.StatusCode == http.StatusNotFound {
if err = cachesave(negativeCacheFile(username), []byte{}); err != nil {
return nil, false, fmt.Errorf("negative cache write error for %q: %v", username, err)
}
return nil, false, nil
}
if r.StatusCode < 200 || r.StatusCode > 299 {
return nil, false, fmt.Errorf("github returned status %d (%s) for user %q", r.StatusCode, r.Status, username)
}
jdata, err := ioutil.ReadAll(r.Body)
if err != nil {
return nil, false, fmt.Errorf("error reading http body for user %q: %v", username, err)
}
return jdata, true, nil
}
// githubUserInfo returns github information about a given username. A boolean
// flag is returned to indicate if the user was found (either in the cache or
// in github). All other unexpected conditions return an error.
func githubUserInfo(username string) (GithubUserResponse, bool, error) {
// Attempt to read from negative cache (user deleted, etc).
// Return a not found response if the user is in the negative cache.
cached, err := readFromNegativeCache(username)
if err != nil || cached {
return GithubUserResponse{}, false, err
}
// Attempt to read from cache.
jdata, cached, err := readFromCache(username)
if err != nil {
return GithubUserResponse{}, false, err
}
// Not in cache. Fetch from github.
if !cached {
jdata, cached, err = readFromGithub(username)
if err != nil || !cached {
return GithubUserResponse{}, false, err
}
}
// Unmarshal the JSON and run very basic checks. If everything OK, save
// this to the cache.
var resp GithubUserResponse
if err := json.Unmarshal(jdata, &resp); err != nil {
return GithubUserResponse{}, false, fmt.Errorf("error decoding github data: %v", err)
}
if resp.Login == "" {
return GithubUserResponse{}, false, fmt.Errorf("got bad json from github: %s", string(jdata))
}
if err := cachesave(cacheFile(username), jdata); err != nil {
return GithubUserResponse{}, false, fmt.Errorf("cache write error for %q: %v", username, err)
}
return resp, true, nil
}
// cached returns the data cached in a file. A duration specifies for how long
// data in the cache is valid. Three values are returned: a slice of bytes
// containing the data in the cache file (if considered valid), a boolean
// indicating whether the data is valid or not (expired, etc), and an error.
func cached(cachefile string, exp time.Duration) ([]byte, bool, error) {
fi, err := os.Stat(cachefile)
if err != nil {
// Return no error on not exists condition (use the boolean to signal).
if os.IsNotExist(err) {
err = nil
}
return nil, false, err
}
// Is this file older than maxAgeDays?
if time.Now().After(fi.ModTime().Add(exp)) {
return nil, false, nil
}
data, err := ioutil.ReadFile(cachefile)
if err != nil {
return nil, false, err
}
return data, true, err
}
// cachesave saves cache data into a file, creating the required directory
// structure, if needed.
func cachesave(cachefile string, data []byte) error {
dir, _ := filepath.Split(cachefile)
// Create the entire directory structure (if needed).
if err := os.MkdirAll(dir, 0777); err != nil {
return err
}
if err := ioutil.WriteFile(cachefile, data, 0777); err != nil {
return err
}
return nil
}
// cacheFile returns the name of the cache file for a given user.
func cacheFile(username string) string {
return filepath.Join(cacheDir, username+".cache")
}
// negativeCachefile returns the name of the negative cache file for a given
// user.
func negativeCacheFile(username string) string {
return filepath.Join(cacheDir, username+".negcache")
}