[GH-61]: Show code block previews of Gitlab permalinks

plugin.json

@@ -88,6 +88,12 @@
                 "help_text": "(Optional) Allow the plugin to work with private repositories.",
                 "placeholder": "",
                 "default": null
+            },
+            {
+                "key": "EnableCodePreview",
+                "display_name": "Enable Code Previews",
+                "type": "bool",
+                "help_text": "(Optional) Allow the plugin to expand permalinks to GitLab files with an actual preview of the linked file."
             }
         ]
     }

server/configuration.go

@@ -33,6 +33,7 @@ type configuration struct {
 	EncryptionKey               string `json:"encryptionkey"`
 	GitlabGroup                 string `json:"gitlabgroup"`
 	EnablePrivateRepo           bool   `json:"enableprivaterepo"`
+	EnableCodePreview           bool   `json:"enablecodepreview"`
 	UsePreregisteredApplication bool   `json:"usepreregisteredapplication"`
 }
 

server/gitlab/api.go

@@ -18,7 +18,7 @@ const (
 
 // NewGroupHook creates a webhook associated with a GitLab group
 func (g *gitlab) NewGroupHook(ctx context.Context, user *UserInfo, groupName string, webhookOptions *AddWebhookOptions) (*WebhookInfo, error) {
-	client, err := g.gitlabConnect(*user.Token)
+	client, err := g.GitlabConnect(*user.Token)
 	if err != nil {
 		return nil, err
 	}
@@ -63,7 +63,7 @@ func (g *gitlab) NewGroupHook(ctx context.Context, user *UserInfo, groupName str
 
 // NewProjectHook creates a webhook associated with a GitLab project
 func (g *gitlab) NewProjectHook(ctx context.Context, user *UserInfo, projectID interface{}, webhookOptions *AddWebhookOptions) (*WebhookInfo, error) {
-	client, err := g.gitlabConnect(*user.Token)
+	client, err := g.GitlabConnect(*user.Token)
 	if err != nil {
 		return nil, err
 	}
@@ -99,7 +99,7 @@ func (g *gitlab) NewProjectHook(ctx context.Context, user *UserInfo, projectID i
 
 // GetGroupHooks gathers all the group level hooks for a GitLab group.
 func (g *gitlab) GetGroupHooks(ctx context.Context, user *UserInfo, owner string) ([]*WebhookInfo, error) {
-	client, err := g.gitlabConnect(*user.Token)
+	client, err := g.GitlabConnect(*user.Token)
 	if err != nil {
 		return nil, err
 	}
@@ -206,7 +206,7 @@ func getGroupHookInfo(hook *internGitlab.GroupHook) *WebhookInfo {
 
 // GetProjectHooks gathers all the project level hooks from a single GitLab project.
 func (g *gitlab) GetProjectHooks(ctx context.Context, user *UserInfo, owner string, repo string) ([]*WebhookInfo, error) {
-	client, err := g.gitlabConnect(*user.Token)
+	client, err := g.GitlabConnect(*user.Token)
 	if err != nil {
 		return nil, err
 	}
@@ -227,7 +227,7 @@ func (g *gitlab) GetProjectHooks(ctx context.Context, user *UserInfo, owner stri
 }
 
 func (g *gitlab) GetProject(ctx context.Context, user *UserInfo, owner, repo string) (*internGitlab.Project, error) {
-	client, err := g.gitlabConnect(*user.Token)
+	client, err := g.GitlabConnect(*user.Token)
 	if err != nil {
 		return nil, err
 	}
@@ -247,7 +247,7 @@ func (g *gitlab) GetProject(ctx context.Context, user *UserInfo, owner, repo str
 }
 
 func (g *gitlab) GetReviews(ctx context.Context, user *UserInfo) ([]*internGitlab.MergeRequest, error) {
-	client, err := g.gitlabConnect(*user.Token)
+	client, err := g.GitlabConnect(*user.Token)
 	if err != nil {
 		return nil, err
 	}
@@ -279,7 +279,7 @@ func (g *gitlab) GetReviews(ctx context.Context, user *UserInfo) ([]*internGitla
 }
 
 func (g *gitlab) GetYourPrs(ctx context.Context, user *UserInfo) ([]*internGitlab.MergeRequest, error) {
-	client, err := g.gitlabConnect(*user.Token)
+	client, err := g.GitlabConnect(*user.Token)
 	if err != nil {
 		return nil, err
 	}
@@ -318,7 +318,7 @@ func (g *gitlab) GetYourPrs(ctx context.Context, user *UserInfo) ([]*internGitla
 }
 
 func (g *gitlab) GetYourAssignments(ctx context.Context, user *UserInfo) ([]*internGitlab.Issue, error) {
-	client, err := g.gitlabConnect(*user.Token)
+	client, err := g.GitlabConnect(*user.Token)
 	if err != nil {
 		return nil, err
 	}
@@ -357,7 +357,7 @@ func (g *gitlab) GetYourAssignments(ctx context.Context, user *UserInfo) ([]*int
 }
 
 func (g *gitlab) GetUnreads(ctx context.Context, user *UserInfo) ([]*internGitlab.Todo, error) {
-	client, err := g.gitlabConnect(*user.Token)
+	client, err := g.GitlabConnect(*user.Token)
 	if err != nil {
 		return nil, err
 	}
@@ -390,7 +390,7 @@ func (g *gitlab) ResolveNamespaceAndProject(
 	allowPrivate bool,
 ) (owner string, repo string, err error) {
 	// Initialize client
-	client, err := g.gitlabConnect(*userInfo.Token)
+	client, err := g.GitlabConnect(*userInfo.Token)
 	if err != nil {
 		return "", "", err
 	}

server/gitlab/gitlab.go

@@ -21,6 +21,7 @@ var (
 
 // Gitlab is a client to call GitLab api see New() to build one
 type Gitlab interface {
+	GitlabConnect(token oauth2.Token) (*internGitlab.Client, error)
 	GetCurrentUser(ctx context.Context, userID string, token oauth2.Token) (*UserInfo, error)
 	GetUserDetails(ctx context.Context, user *UserInfo) (*internGitlab.User, error)
 	GetProject(ctx context.Context, user *UserInfo, owner, repo string) (*internGitlab.Project, error)
@@ -73,7 +74,7 @@ func New(gitlabURL string, gitlabGroup string, checkGroup func(projectNameWithGr
 	return &gitlab{gitlabURL: gitlabURL, gitlabGroup: gitlabGroup, checkGroup: checkGroup}
 }
 
-func (g *gitlab) gitlabConnect(token oauth2.Token) (*internGitlab.Client, error) {
+func (g *gitlab) GitlabConnect(token oauth2.Token) (*internGitlab.Client, error) {
 	if g.gitlabURL == "" || strings.EqualFold(g.gitlabURL, Gitlabdotcom) {
 		return internGitlab.NewOAuthClient(token.AccessToken)
 	}

server/gitlab/user.go

@@ -27,7 +27,7 @@ type UserSettings struct {
 }
 
 func (g *gitlab) GetCurrentUser(ctx context.Context, userID string, token oauth2.Token) (*UserInfo, error) {
-	client, err := g.gitlabConnect(token)
+	client, err := g.GitlabConnect(token)
 	if err != nil {
 		return nil, err
 	}
@@ -55,7 +55,7 @@ func (g *gitlab) GetCurrentUser(ctx context.Context, userID string, token oauth2
 }
 
 func (g *gitlab) GetUserDetails(ctx context.Context, user *UserInfo) (*internGitlab.User, error) {
-	client, err := g.gitlabConnect(*user.Token)
+	client, err := g.GitlabConnect(*user.Token)
 	if err != nil {
 		return nil, err
 	}

server/main.go

@@ -5,5 +5,5 @@ import (
 )
 
 func main() {
-	plugin.ClientMain(&Plugin{})
+	plugin.ClientMain(NewPlugin())
 }

server/permalinks.go

@@ -0,0 +1,165 @@
+package main
+
+import (
+	"context"
+	"encoding/base64"
+	"fmt"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/xanzy/go-gitlab"
+)
+
+// maxPermalinkReplacements sets the maximum limit to the number of
+// permalink replacements that can be performed on a single message.
+const maxPermalinkReplacements = 10
+
+const permalinkReqTimeout = 5 * time.Second
+
+// maxPreviewLines sets the maximum number of preview lines that will be shown
+// while replacing a permalink.
+const maxPreviewLines = 10
+
+// permalinkLineContext shows the number of lines before and after to show
+// if the link points to a single line.
+const permalinkLineContext = 3
+
+// replacement holds necessary info to replace GitLab permalinks
+// in messages with a code preview block.
+type replacement struct {
+	index         int    // Index of the permalink in the string
+	word          string // The permalink
+	permalinkData permalinkInfo
+}
+
+type permalinkInfo struct { // Holds the necessary metadata of a permalink
+	haswww string
+	commit string
+	user   string
+	repo   string
+	path   string
+	line   string
+}
+
+// getPermalinkReplacements returns the permalink replacements that need to be performed
+// on a message. The returned slice is sorted by the index in ascending order.
+func (p *Plugin) getPermalinkReplacements(msg string) []replacement {
+	// Find the permalinks from the msg using a regex
+	matches := gitlabPermalinkRegex.FindAllStringSubmatch(msg, -1)
+	indices := gitlabPermalinkRegex.FindAllStringIndex(msg, -1)
+	var replacements []replacement
+	for i, m := range matches {
+		// Have a limit on the number of replacements to do
+		if i > maxPermalinkReplacements {
+			break
+		}
+		word := m[0]
+		index := indices[i][0]
+		r := replacement{
+			index: index,
+			word:  word,
+		}
+		// Ignore if the word is inside a link
+		if isInsideLink(msg, index) {
+			continue
+		}
+		// Populate the permalinkInfo with the extracted groups of the regex
+		for j, name := range gitlabPermalinkRegex.SubexpNames() {
+			if j == 0 {
+				continue
+			}
+			switch name {
+			case "haswww":
+				r.permalinkData.haswww = m[j]
+			case "user":
+				r.permalinkData.user = m[j]
+			case "repo":
+				r.permalinkData.repo = m[j]
+			case "commit":
+				r.permalinkData.commit = m[j]
+			case "path":
+				r.permalinkData.path = m[j]
+			case "line":
+				r.permalinkData.line = m[j]
+			}
+		}
+		replacements = append(replacements, r)
+	}
+	return replacements
+}
+
+// processReplacement processes a single replacement and stores the resulting markdown at the given index of the given array. Multiple goroutines are executing this function but all the goroutines concurrently modify unique indices of the given array, and concurrently modifying unique slice elements is not racy.
+func (p *Plugin) processReplacement(r replacement, glClient *gitlab.Client, wg *sync.WaitGroup, markdownForPermalink []string, index int) {
+	defer wg.Done()
+
+	// Get the file contents
+	opts := gitlab.GetFileOptions{
+		Ref: &r.permalinkData.commit,
+	}
+	projectPath := fmt.Sprintf("%s/%s", r.permalinkData.user, r.permalinkData.repo)
+	_, cancel := context.WithTimeout(context.Background(), permalinkReqTimeout)
+	file, _, err := glClient.RepositoryFiles.GetFile(projectPath, r.permalinkData.path, &opts)
+	defer cancel()
+	if err != nil {
+		p.API.LogDebug("Error while fetching file contents", "error", err.Error(), "path", r.permalinkData.path)
+		return
+	}
+	// If this is not a file, ignore.
+	if file == nil {
+		p.API.LogWarn("Permalink is not a file", "file", r.permalinkData.path)
+		return
+	}
+
+	decoded, err := base64.StdEncoding.DecodeString(file.Content)
+	if err != nil {
+		p.API.LogDebug("Error while decoding file contents", "error", err.Error(), "path", r.permalinkData.path)
+		return
+	}
+	// Get the required lines.
+	start, end := getLineNumbers(r.permalinkData.line)
+	// Bad anchor tag, ignore.
+	if start == -1 || end == -1 {
+		return
+	}
+
+	isTruncated := false
+	if end-start > maxPreviewLines {
+		end = start + maxPreviewLines
+		isTruncated = true
+	}
+
+	lines, err := filterLines(string(decoded), start, end)
+	if err != nil {
+		p.API.LogDebug("Error while filtering lines", "error", err.Error(), "path", r.permalinkData.path)
+	}
+
+	if lines == "" {
+		p.API.LogDebug("Line numbers out of range. Skipping.", "file", r.permalinkData.path, "start", start, "end", end)
+		return
+	}
+
+	markdownForPermalink[index] = getCodeMarkdown(r.permalinkData.user, r.permalinkData.repo, r.permalinkData.path, r.word, lines, isTruncated)
+}
+
+// makeReplacements performs the given replacements on the msg and returns
+// the new msg. The replacements slice needs to be sorted by the index in ascending order.
+// Ref: mattermost plugin github (/~https://github.com/mattermost/mattermost-plugin-github/blob/fcc50523c17c2670cb595a8038864a8a7f7fd1e5/server/plugin/permalinks.go#L90)
+func (p *Plugin) makeReplacements(msg string, replacements []replacement, glClient *gitlab.Client) string {
+	// Iterating the slice in reverse to preserve the replacement indices.
+	wg := new(sync.WaitGroup)
+	markdownForPermalink := make([]string, len(replacements))
+	for i := len(replacements) - 1; i >= 0; i-- {
+		wg.Add(1)
+		go p.processReplacement(replacements[i], glClient, wg, markdownForPermalink, i)
+	}
+	wg.Wait()
+	for i := len(replacements) - 1; i >= 0; i-- {
+		r := replacements[i]
+		if markdownForPermalink[i] != "" {
+			// Replace word in msg starting from r.index only once.
+			msg = msg[:r.index] + strings.Replace(msg[r.index:], r.word, markdownForPermalink[i], 1)
+		}
+	}
+	return msg
+}