Add support to migrate from gogs (#14342)

Add support to migrate gogs:

  *  issues
  *  comments
  *  labels
  *  milestones
  *  wiki


Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Andrew Thornton <art27@cantab.net>

modules/migrations/base/retry_downloader.go

@@ -0,0 +1,247 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package base
+
+import (
+	"context"
+	"time"
+)
+
+var (
+	_ Downloader = &RetryDownloader{}
+)
+
+// RetryDownloader retry the downloads
+type RetryDownloader struct {
+	Downloader
+	ctx        context.Context
+	RetryTimes int // the total execute times
+	RetryDelay int // time to delay seconds
+}
+
+// NewRetryDownloader creates a retry downloader
+func NewRetryDownloader(ctx context.Context, downloader Downloader, retryTimes, retryDelay int) *RetryDownloader {
+	return &RetryDownloader{
+		Downloader: downloader,
+		ctx:        ctx,
+		RetryTimes: retryTimes,
+		RetryDelay: retryDelay,
+	}
+}
+
+// SetContext set context
+func (d *RetryDownloader) SetContext(ctx context.Context) {
+	d.ctx = ctx
+	d.Downloader.SetContext(ctx)
+}
+
+// GetRepoInfo returns a repository information with retry
+func (d *RetryDownloader) GetRepoInfo() (*Repository, error) {
+	var (
+		times = d.RetryTimes
+		repo  *Repository
+		err   error
+	)
+	for ; times > 0; times-- {
+		if repo, err = d.Downloader.GetRepoInfo(); err == nil {
+			return repo, nil
+		}
+		if IsErrNotSupported(err) {
+			return nil, err
+		}
+		select {
+		case <-d.ctx.Done():
+			return nil, d.ctx.Err()
+		case <-time.After(time.Second * time.Duration(d.RetryDelay)):
+		}
+	}
+	return nil, err
+}
+
+// GetTopics returns a repository's topics with retry
+func (d *RetryDownloader) GetTopics() ([]string, error) {
+	var (
+		times  = d.RetryTimes
+		topics []string
+		err    error
+	)
+	for ; times > 0; times-- {
+		if topics, err = d.Downloader.GetTopics(); err == nil {
+			return topics, nil
+		}
+		if IsErrNotSupported(err) {
+			return nil, err
+		}
+		select {
+		case <-d.ctx.Done():
+			return nil, d.ctx.Err()
+		case <-time.After(time.Second * time.Duration(d.RetryDelay)):
+		}
+	}
+	return nil, err
+}
+
+// GetMilestones returns a repository's milestones with retry
+func (d *RetryDownloader) GetMilestones() ([]*Milestone, error) {
+	var (
+		times      = d.RetryTimes
+		milestones []*Milestone
+		err        error
+	)
+	for ; times > 0; times-- {
+		if milestones, err = d.Downloader.GetMilestones(); err == nil {
+			return milestones, nil
+		}
+		if IsErrNotSupported(err) {
+			return nil, err
+		}
+		select {
+		case <-d.ctx.Done():
+			return nil, d.ctx.Err()
+		case <-time.After(time.Second * time.Duration(d.RetryDelay)):
+		}
+	}
+	return nil, err
+}
+
+// GetReleases returns a repository's releases with retry
+func (d *RetryDownloader) GetReleases() ([]*Release, error) {
+	var (
+		times    = d.RetryTimes
+		releases []*Release
+		err      error
+	)
+	for ; times > 0; times-- {
+		if releases, err = d.Downloader.GetReleases(); err == nil {
+			return releases, nil
+		}
+		if IsErrNotSupported(err) {
+			return nil, err
+		}
+		select {
+		case <-d.ctx.Done():
+			return nil, d.ctx.Err()
+		case <-time.After(time.Second * time.Duration(d.RetryDelay)):
+		}
+	}
+	return nil, err
+}
+
+// GetLabels returns a repository's labels with retry
+func (d *RetryDownloader) GetLabels() ([]*Label, error) {
+	var (
+		times  = d.RetryTimes
+		labels []*Label
+		err    error
+	)
+	for ; times > 0; times-- {
+		if labels, err = d.Downloader.GetLabels(); err == nil {
+			return labels, nil
+		}
+		if IsErrNotSupported(err) {
+			return nil, err
+		}
+		select {
+		case <-d.ctx.Done():
+			return nil, d.ctx.Err()
+		case <-time.After(time.Second * time.Duration(d.RetryDelay)):
+		}
+	}
+	return nil, err
+}
+
+// GetIssues returns a repository's issues with retry
+func (d *RetryDownloader) GetIssues(page, perPage int) ([]*Issue, bool, error) {
+	var (
+		times  = d.RetryTimes
+		issues []*Issue
+		isEnd  bool
+		err    error
+	)
+	for ; times > 0; times-- {
+		if issues, isEnd, err = d.Downloader.GetIssues(page, perPage); err == nil {
+			return issues, isEnd, nil
+		}
+		if IsErrNotSupported(err) {
+			return nil, false, err
+		}
+		select {
+		case <-d.ctx.Done():
+			return nil, false, d.ctx.Err()
+		case <-time.After(time.Second * time.Duration(d.RetryDelay)):
+		}
+	}
+	return nil, false, err
+}
+
+// GetComments returns a repository's comments with retry
+func (d *RetryDownloader) GetComments(issueNumber int64) ([]*Comment, error) {
+	var (
+		times    = d.RetryTimes
+		comments []*Comment
+		err      error
+	)
+	for ; times > 0; times-- {
+		if comments, err = d.Downloader.GetComments(issueNumber); err == nil {
+			return comments, nil
+		}
+		if IsErrNotSupported(err) {
+			return nil, err
+		}
+		select {
+		case <-d.ctx.Done():
+			return nil, d.ctx.Err()
+		case <-time.After(time.Second * time.Duration(d.RetryDelay)):
+		}
+	}
+	return nil, err
+}
+
+// GetPullRequests returns a repository's pull requests with retry
+func (d *RetryDownloader) GetPullRequests(page, perPage int) ([]*PullRequest, bool, error) {
+	var (
+		times = d.RetryTimes
+		prs   []*PullRequest
+		err   error
+		isEnd bool
+	)
+	for ; times > 0; times-- {
+		if prs, isEnd, err = d.Downloader.GetPullRequests(page, perPage); err == nil {
+			return prs, isEnd, nil
+		}
+		if IsErrNotSupported(err) {
+			return nil, false, err
+		}
+		select {
+		case <-d.ctx.Done():
+			return nil, false, d.ctx.Err()
+		case <-time.After(time.Second * time.Duration(d.RetryDelay)):
+		}
+	}
+	return nil, false, err
+}
+
+// GetReviews returns pull requests reviews
+func (d *RetryDownloader) GetReviews(pullRequestNumber int64) ([]*Review, error) {
+	var (
+		times   = d.RetryTimes
+		reviews []*Review
+		err     error
+	)
+	for ; times > 0; times-- {
+		if reviews, err = d.Downloader.GetReviews(pullRequestNumber); err == nil {
+			return reviews, nil
+		}
+		if IsErrNotSupported(err) {
+			return nil, err
+		}
+		select {
+		case <-d.ctx.Done():
+			return nil, d.ctx.Err()
+		case <-time.After(time.Second * time.Duration(d.RetryDelay)):
+		}
+	}
+	return nil, err
+}