Add http_proxy support for http client (#5571)

- if 'http_proxy' environment variable is set, respect it when creating http client
- otherwise initialize a http client with timeout settings

Add ogjson to cache even when it fails

in this way we can prevent from requesting unparsable urls repeatedly

Extend expire time of cached link preview data to a week

There's no need to invalidate cache and send request again frequently

Revert timeout

Revert cache_expire_time

api/post.go

@@ -530,11 +530,11 @@ func getOpenGraphMetadata(c *Context, w http.ResponseWriter, r *http.Request) {
 	og := app.GetOpenGraphMetadata(url)
 
 	ogJSON, err := og.ToJSON()
+	openGraphDataCache.AddWithExpiresInSecs(props["url"], ogJSON, 3600) // Cache would expire after 1 hour
 	if err != nil {
 		w.Write([]byte(`{"url": ""}`))
 		return
 	}
 
-	openGraphDataCache.AddWithExpiresInSecs(props["url"], ogJSON, 3600) // Cache would expire after 1 houre
 	w.Write(ogJSON)
 }

app/post.go

@@ -4,7 +4,10 @@
 package app
 
 import (
+	"net"
 	"net/http"
+	"net/url"
+	"os"
 	"regexp"
 	"time"
 
@@ -17,13 +20,35 @@ import (
 )
 
 var (
-	c = &http.Client{
-		Timeout: 5 * time.Second,
-	}
+	httpClient *http.Client
 
+	httpTimeout       = time.Duration(5 * time.Second)
 	linkWithTextRegex = regexp.MustCompile(`<([^<\|]+)\|([^>]+)>`)
 )
 
+func dialTimeout(network, addr string) (net.Conn, error) {
+	return net.DialTimeout(network, addr, httpTimeout)
+}
+
+func init() {
+	p, ok := os.LookupEnv("HTTP_PROXY")
+	if ok {
+		if u, err := url.Parse(p); err == nil {
+			httpClient = &http.Client{
+				Transport: &http.Transport{
+					Proxy: http.ProxyURL(u),
+					Dial:  dialTimeout,
+				},
+			}
+			return
+		}
+	}
+
+	httpClient = &http.Client{
+		Timeout: httpTimeout,
+	}
+}
+
 func CreatePostAsUser(post *model.Post, siteURL string) (*model.Post, *model.AppError) {
 	// Check that channel has not been deleted
 	var channel *model.Channel
@@ -484,14 +509,15 @@ func GetFileInfosForPost(postId string, readFromMaster bool) ([]*model.FileInfo,
 func GetOpenGraphMetadata(url string) *opengraph.OpenGraph {
 	og := opengraph.NewOpenGraph()
 
-	res, err := c.Get(url)
+	res, err := httpClient.Get(url)
 	if err != nil {
+		l4g.Error(err.Error())
 		return og
 	}
 	defer CloseBody(res)
 
 	if err := og.ProcessHTML(res.Body); err != nil {
-		return og
+		l4g.Error(err.Error())
 	}
 
 	return og