[release] Retry attaching release assets on 5xx server errors

Fixes #2197

features/release.feature

@@ -456,6 +456,33 @@ MARKDOWN
       Attaching 1 asset...\n
       """
 
+  Scenario: Retry attaching assets on 5xx errors
+    Given the GitHub API server:
+      """
+      attempt = 0
+      post('/repos/mislav/will_paginate/releases') {
+        status 201
+        json :html_url => "https://github.com/mislav/will_paginate/releases/v1.2.0",
+             :upload_url => "https://uploads.github.com/uploads/assets{?name,label}"
+      }
+      post('/uploads/assets', :host_name => 'uploads.github.com') {
+        attempt += 1
+        halt 400 unless request.body.read.to_s == "TARBALL"
+        halt 502 if attempt == 1
+        status 201
+      }
+      """
+    And a file named "hello-1.2.0.tar.gz" with:
+      """
+      TARBALL
+      """
+    When I successfully run `hub release create -m "hello" v1.2.0 -a hello-1.2.0.tar.gz`
+    Then the output should contain exactly:
+      """
+      https://github.com/mislav/will_paginate/releases/v1.2.0
+      Attaching 1 asset...\n
+      """
+
   Scenario: Create a release with some assets failing
     Given the GitHub API server:
       """

github/client.go

@@ -412,11 +412,28 @@ func (client *Client) UploadReleaseAssets(release *Release, assets []LocalAsset)
 		}
 		uploadPath := addQuery(uploadURL, params)
 
-		// TODO: retry failed assets
 		var res *simpleResponse
-		res, err = api.PostFile(uploadPath, asset.Contents, asset.Size)
-		if err = checkStatus(201, "uploading release asset", res, err); err != nil {
-			return
+		attempts := 0
+		maxAttempts := 3
+		body := asset.Contents
+		for {
+			res, err = api.PostFile(uploadPath, body, asset.Size)
+			if err == nil && res.StatusCode >= 500 && res.StatusCode < 600 && attempts < maxAttempts {
+				attempts++
+				time.Sleep(time.Second * time.Duration(attempts))
+				var f *os.File
+				f, err = os.Open(asset.Name)
+				if err != nil {
+					return
+				}
+				defer f.Close()
+				body = f
+				continue
+			}
+			if err = checkStatus(201, "uploading release asset", res, err); err != nil {
+				return
+			}
+			break
 		}
 
 		newAsset := ReleaseAsset{}