[API] Add pagination to ListBranches (#14524)

* make PaginateUserSlice generic -> PaginateSlice

* Add pagination to ListBranches

* add skip, limit to Repository.GetBranches()

* Move routers/api/v1/utils/utils PaginateSlice -> modules/util/paginate.go

* repo_module.GetBranches paginate

* fix & rename & more logging

* better description

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: a1012112796 <1012112796@qq.com>

10 files changed, 172 insertions, 31 deletions

diff --git a/modules/context/repo.go b/modules/context/repo.go
index 13037f4625..bf149b8158 100644
--- a/modules/context/repo.go
+++ b/modules/context/repo.go
@@ -554,7 +554,7 @@ func RepoAssignment() func(http.Handler) http.Handler {
 			}
 			ctx.Data["Tags"] = tags
 
-			brs, err := ctx.Repo.GitRepo.GetBranches()
+			brs, _, err := ctx.Repo.GitRepo.GetBranches(0, 0)
 			if err != nil {
 				ctx.ServerError("GetBranches", err)
 				return
@@ -747,7 +747,7 @@ func RepoRefByType(refType RepoRefType) func(http.Handler) http.Handler {
 				refName = ctx.Repo.Repository.DefaultBranch
 				ctx.Repo.BranchName = refName
 				if !ctx.Repo.GitRepo.IsBranchExist(refName) {
-					brs, err := ctx.Repo.GitRepo.GetBranches()
+					brs, _, err := ctx.Repo.GitRepo.GetBranches(0, 0)
 					if err != nil {
 						ctx.ServerError("GetBranches", err)
 						return
diff --git a/modules/git/repo_branch.go b/modules/git/repo_branch.go
index 25438530f5..58781eb1c7 100644
--- a/modules/git/repo_branch.go
+++ b/modules/git/repo_branch.go
@@ -78,16 +78,17 @@ func (repo *Repository) GetBranch(branch string) (*Branch, error) {
 }
 
 // GetBranchesByPath returns a branch by it's path
-func GetBranchesByPath(path string) ([]*Branch, error) {
+// if limit = 0 it will not limit
+func GetBranchesByPath(path string, skip, limit int) ([]*Branch, int, error) {
 	gitRepo, err := OpenRepository(path)
 	if err != nil {
-		return nil, err
+		return nil, 0, err
 	}
 	defer gitRepo.Close()
 
-	brs, err := gitRepo.GetBranches()
+	brs, countAll, err := gitRepo.GetBranches(skip, limit)
 	if err != nil {
-		return nil, err
+		return nil, 0, err
 	}
 
 	branches := make([]*Branch, len(brs))
@@ -99,7 +100,7 @@ func GetBranchesByPath(path string) ([]*Branch, error) {
 		}
 	}
 
-	return branches, nil
+	return branches, countAll, nil
 }
 
 // DeleteBranchOptions Option(s) for delete branch
diff --git a/modules/git/repo_branch_gogit.go b/modules/git/repo_branch_gogit.go
index 65cb77a8b5..b00253f6ff 100644
--- a/modules/git/repo_branch_gogit.go
+++ b/modules/git/repo_branch_gogit.go
@@ -25,21 +25,32 @@ func (repo *Repository) IsBranchExist(name string) bool {
 	return reference.Type() != plumbing.InvalidReference
 }
 
-// GetBranches returns all branches of the repository.
-func (repo *Repository) GetBranches() ([]string, error) {
+// GetBranches returns branches from the repository, skipping skip initial branches and
+// returning at most limit branches, or all branches if limit is 0.
+func (repo *Repository) GetBranches(skip, limit int) ([]string, int, error) {
 	var branchNames []string
 
 	branches, err := repo.gogitRepo.Branches()
 	if err != nil {
-		return nil, err
+		return nil, 0, err
 	}
 
+	i := 0
+	count := 0
 	_ = branches.ForEach(func(branch *plumbing.Reference) error {
+		count++
+		if i < skip {
+			i++
+			return nil
+		} else if limit != 0 && count > skip+limit {
+			return nil
+		}
+
 		branchNames = append(branchNames, strings.TrimPrefix(branch.Name().String(), BranchPrefix))
 		return nil
 	})
 
 	// TODO: Sort?
 
-	return branchNames, nil
+	return branchNames, count, nil
 }
diff --git a/modules/git/repo_branch_nogogit.go b/modules/git/repo_branch_nogogit.go
index 5ec46d725e..0628a57285 100644
--- a/modules/git/repo_branch_nogogit.go
+++ b/modules/git/repo_branch_nogogit.go
@@ -21,14 +21,14 @@ func (repo *Repository) IsBranchExist(name string) bool {
 	return IsReferenceExist(repo.Path, BranchPrefix+name)
 }
 
-// GetBranches returns all branches of the repository.
-func (repo *Repository) GetBranches() ([]string, error) {
-	return callShowRef(repo.Path, BranchPrefix, "--heads")
+// GetBranches returns branches from the repository, skipping skip initial branches and
+// returning at most limit branches, or all branches if limit is 0.
+func (repo *Repository) GetBranches(skip, limit int) ([]string, int, error) {
+	return callShowRef(repo.Path, BranchPrefix, "--heads", skip, limit)
 }
 
-func callShowRef(repoPath, prefix, arg string) ([]string, error) {
-	var branchNames []string
-
+// callShowRef return refs, if limit = 0 it will not limit
+func callShowRef(repoPath, prefix, arg string, skip, limit int) (branchNames []string, countAll int, err error) {
 	stdoutReader, stdoutWriter := io.Pipe()
 	defer func() {
 		_ = stdoutReader.Close()
@@ -49,8 +49,21 @@ func callShowRef(repoPath, prefix, arg string) ([]string, error) {
 		}
 	}()
 
+	i := 0
 	bufReader := bufio.NewReader(stdoutReader)
-	for {
+	for i < skip {
+		_, isPrefix, err := bufReader.ReadLine()
+		if err == io.EOF {
+			return branchNames, i, nil
+		}
+		if err != nil {
+			return nil, 0, err
+		}
+		if !isPrefix {
+			i++
+		}
+	}
+	for limit == 0 || i < skip+limit {
 		// The output of show-ref is simply a list:
 		// <sha> SP <ref> LF
 		_, err := bufReader.ReadSlice(' ')
@@ -59,24 +72,39 @@ func callShowRef(repoPath, prefix, arg string) ([]string, error) {
 			_, err = bufReader.ReadSlice(' ')
 		}
 		if err == io.EOF {
-			return branchNames, nil
+			return branchNames, i, nil
 		}
 		if err != nil {
-			return nil, err
+			return nil, 0, err
 		}
 
 		branchName, err := bufReader.ReadString('\n')
 		if err == io.EOF {
 			// This shouldn't happen... but we'll tolerate it for the sake of peace
-			return branchNames, nil
+			return branchNames, i, nil
 		}
 		if err != nil {
-			return nil, err
+			return nil, i, err
 		}
 		branchName = strings.TrimPrefix(branchName, prefix)
 		if len(branchName) > 0 {
 			branchName = branchName[:len(branchName)-1]
 		}
 		branchNames = append(branchNames, branchName)
+		i++
+	}
+	// count all refs
+	for limit != 0 {
+		_, isPrefix, err := bufReader.ReadLine()
+		if err == io.EOF {
+			return branchNames, i, nil
+		}
+		if err != nil {
+			return nil, 0, err
+		}
+		if !isPrefix {
+			i++
+		}
 	}
+	return branchNames, i, nil
 }
diff --git a/modules/git/repo_branch_test.go b/modules/git/repo_branch_test.go
index 33d31aef68..05d5237e6a 100644
--- a/modules/git/repo_branch_test.go
+++ b/modules/git/repo_branch_test.go
@@ -17,11 +17,26 @@ func TestRepository_GetBranches(t *testing.T) {
 	assert.NoError(t, err)
 	defer bareRepo1.Close()
 
-	branches, err := bareRepo1.GetBranches()
+	branches, countAll, err := bareRepo1.GetBranches(0, 2)
+
+	assert.NoError(t, err)
+	assert.Len(t, branches, 2)
+	assert.EqualValues(t, 3, countAll)
+	assert.ElementsMatch(t, []string{"branch1", "branch2"}, branches)
+
+	branches, countAll, err = bareRepo1.GetBranches(0, 0)
 
 	assert.NoError(t, err)
 	assert.Len(t, branches, 3)
+	assert.EqualValues(t, 3, countAll)
 	assert.ElementsMatch(t, []string{"branch1", "branch2", "master"}, branches)
+
+	branches, countAll, err = bareRepo1.GetBranches(5, 1)
+
+	assert.NoError(t, err)
+	assert.Len(t, branches, 0)
+	assert.EqualValues(t, 3, countAll)
+	assert.ElementsMatch(t, []string{}, branches)
 }
 
 func BenchmarkRepository_GetBranches(b *testing.B) {
@@ -33,7 +48,7 @@ func BenchmarkRepository_GetBranches(b *testing.B) {
 	defer bareRepo1.Close()
 
 	for i := 0; i < b.N; i++ {
-		_, err := bareRepo1.GetBranches()
+		_, _, err := bareRepo1.GetBranches(0, 0)
 		if err != nil {
 			b.Fatal(err)
 		}
diff --git a/modules/git/repo_tag_nogogit.go b/modules/git/repo_tag_nogogit.go
index 83cbc58e34..b3fa5d6dc4 100644
--- a/modules/git/repo_tag_nogogit.go
+++ b/modules/git/repo_tag_nogogit.go
@@ -13,6 +13,7 @@ func (repo *Repository) IsTagExist(name string) bool {
 }
 
 // GetTags returns all tags of the repository.
-func (repo *Repository) GetTags() ([]string, error) {
-	return callShowRef(repo.Path, TagPrefix, "--tags")
+func (repo *Repository) GetTags() (tags []string, err error) {
+	tags, _, err = callShowRef(repo.Path, TagPrefix, "--tags", 0, 0)
+	return
 }
diff --git a/modules/repository/branch.go b/modules/repository/branch.go
index d369a200b0..275bae91e3 100644
--- a/modules/repository/branch.go
+++ b/modules/repository/branch.go
@@ -13,6 +13,9 @@ import (
 
 // GetBranch returns a branch by its name
 func GetBranch(repo *models.Repository, branch string) (*git.Branch, error) {
+	if len(branch) == 0 {
+		return nil, fmt.Errorf("GetBranch: empty string for branch")
+	}
 	gitRepo, err := git.OpenRepository(repo.RepoPath())
 	if err != nil {
 		return nil, err
@@ -22,9 +25,10 @@ func GetBranch(repo *models.Repository, branch string) (*git.Branch, error) {
 	return gitRepo.GetBranch(branch)
 }
 
-// GetBranches returns all the branches of a repository
-func GetBranches(repo *models.Repository) ([]*git.Branch, error) {
-	return git.GetBranchesByPath(repo.RepoPath())
+// GetBranches returns branches from the repository, skipping skip initial branches and
+// returning at most limit branches, or all branches if limit is 0.
+func GetBranches(repo *models.Repository, skip, limit int) ([]*git.Branch, int, error) {
+	return git.GetBranchesByPath(repo.RepoPath(), skip, limit)
 }
 
 // checkBranchName validates branch name with existing repository branches
@@ -35,7 +39,7 @@ func checkBranchName(repo *models.Repository, name string) error {
 	}
 	defer gitRepo.Close()
 
-	branches, err := GetBranches(repo)
+	branches, _, err := GetBranches(repo, 0, 0)
 	if err != nil {
 		return err
 	}
diff --git a/modules/repository/init.go b/modules/repository/init.go
index a100456e77..50cde4c0b9 100644
--- a/modules/repository/init.go
+++ b/modules/repository/init.go
@@ -239,7 +239,7 @@ func adoptRepository(ctx models.DBContext, repoPath string, u *models.User, repo
 
 		repo.DefaultBranch = strings.TrimPrefix(repo.DefaultBranch, git.BranchPrefix)
 	}
-	branches, _ := gitRepo.GetBranches()
+	branches, _, _ := gitRepo.GetBranches(0, 0)
 	found := false
 	hasDefault := false
 	hasMaster := false
diff --git a/modules/util/paginate.go b/modules/util/paginate.go
new file mode 100644
index 0000000000..2baa71664e
--- /dev/null
+++ b/modules/util/paginate.go
@@ -0,0 +1,34 @@
+// 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 util
+
+import "reflect"
+
+// PaginateSlice cut a slice as per pagination options
+// if page = 0 it do not paginate
+func PaginateSlice(list interface{}, page, pageSize int) interface{} {
+	if page <= 0 || pageSize <= 0 {
+		return list
+	}
+	if reflect.TypeOf(list).Kind() != reflect.Slice {
+		return list
+	}
+
+	listValue := reflect.ValueOf(list)
+
+	page--
+
+	if page*pageSize >= listValue.Len() {
+		return listValue.Slice(listValue.Len(), listValue.Len()).Interface()
+	}
+
+	listValue = listValue.Slice(page*pageSize, listValue.Len())
+
+	if listValue.Len() > pageSize {
+		return listValue.Slice(0, pageSize).Interface()
+	}
+
+	return listValue.Interface()
+}
diff --git a/modules/util/paginate_test.go b/modules/util/paginate_test.go
new file mode 100644
index 0000000000..d962e04c16
--- /dev/null
+++ b/modules/util/paginate_test.go
@@ -0,0 +1,47 @@
+// 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 util
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPaginateSlice(t *testing.T) {
+	stringSlice := []string{"a", "b", "c", "d", "e"}
+	result, ok := PaginateSlice(stringSlice, 1, 2).([]string)
+	assert.True(t, ok)
+	assert.EqualValues(t, []string{"a", "b"}, result)
+
+	result, ok = PaginateSlice(stringSlice, 100, 2).([]string)
+	assert.True(t, ok)
+	assert.EqualValues(t, []string{}, result)
+
+	result, ok = PaginateSlice(stringSlice, 3, 2).([]string)
+	assert.True(t, ok)
+	assert.EqualValues(t, []string{"e"}, result)
+
+	result, ok = PaginateSlice(stringSlice, 1, 0).([]string)
+	assert.True(t, ok)
+	assert.EqualValues(t, []string{"a", "b", "c", "d", "e"}, result)
+
+	result, ok = PaginateSlice(stringSlice, 1, -1).([]string)
+	assert.True(t, ok)
+	assert.EqualValues(t, []string{"a", "b", "c", "d", "e"}, result)
+
+	type Test struct {
+		Val int
+	}
+
+	var testVar = []*Test{{Val: 2}, {Val: 3}, {Val: 4}}
+	testVar, ok = PaginateSlice(testVar, 1, 50).([]*Test)
+	assert.True(t, ok)
+	assert.EqualValues(t, []*Test{{Val: 2}, {Val: 3}, {Val: 4}}, testVar)
+
+	testVar, ok = PaginateSlice(testVar, 2, 2).([]*Test)
+	assert.True(t, ok)
+	assert.EqualValues(t, []*Test{{Val: 4}}, testVar)
+}