1 files changed, 319 insertions, 0 deletions
diff --git a/slog/backend.go b/slog/backend.go
new file mode 100644
index 0000000..613601c
--- /dev/null
+++ b/slog/backend.go
@@ -0,0 +1,319 @@
+package slog
+
+import (
+	"bytes"
+	"crypto/rand"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"io"
+	"io/fs"
+	"net/textproto"
+	"os"
+	"path"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/dustin/go-nntp"
+	nntpserver "github.com/dustin/go-nntp/server"
+	"github.com/go-kit/log"
+	"github.com/go-kit/log/level"
+)
+
+var group = &nntp.Group{
+	Name:        "ctrl-c.slog",
+	Description: "The slog local blogging platform",
+	Posting:     nntp.PostingPermitted,
+	Low:         1,
+}
+
+const DefaultWaitTime = 30 * time.Second
+
+// NewBackend builds a slog nntp backend.
+//
+// The provided waitTime may be <= 0, in which case DefaultWaitTime will be used.
+func NewBackend(logger log.Logger, waitTime time.Duration) (nntpserver.Backend, error) {
+	if waitTime <= 0 {
+		waitTime = DefaultWaitTime
+	}
+
+	b := &backend{logger: logger, waitTime: waitTime, index: make([]indexEntry, 0)}
+	if err := b.refreshIndex(); err != nil {
+		return nil, err
+	}
+	return b, nil
+}
+
+type backend struct {
+	logger   log.Logger
+	waitTime time.Duration
+	lastRead time.Time
+	index    []indexEntry
+}
+
+func (b backend) debug(keyvals ...any) error { return level.Debug(b.logger).Log(keyvals...) }
+func (b backend) info(keyvals ...any) error  { return level.Info(b.logger).Log(keyvals...) }
+func (b backend) warn(keyvals ...any) error  { return level.Warn(b.logger).Log(keyvals...) }
+func (b backend) err(keyvals ...any) error   { return level.Error(b.logger).Log(keyvals...) }
+
+func (b backend) ListGroups(max int) ([]*nntp.Group, error) {
+	return []*nntp.Group{group}, nil
+}
+
+func (b *backend) GetGroup(name string) (*nntp.Group, error) {
+	if name != group.Name {
+		return nil, nntpserver.ErrNoSuchGroup
+	}
+	if err := b.refreshIndex(); err != nil {
+		return nil, err
+	}
+
+	return group, nil
+}
+
+func (b *backend) GetArticles(_ *nntp.Group, from, to int64) ([]nntpserver.NumberedArticle, error) {
+	if err := b.refreshIndex(); err != nil {
+		return nil, err
+	}
+
+	numbered := make([]nntpserver.NumberedArticle, 0, len(b.index))
+	for i := range b.index {
+		entry := b.index[i]
+		num := int64(i + 1)
+		if num >= from && num <= to {
+			article, err := makeArticle(entry)
+			if err != nil {
+				return nil, err
+			}
+
+			numbered = append(numbered, nntpserver.NumberedArticle{
+				Num:     num,
+				Article: article,
+			})
+		}
+	}
+
+	return numbered, nil
+}
+
+func (b *backend) GetArticle(_ *nntp.Group, messageID string) (*nntp.Article, error) {
+	if err := b.refreshIndex(); err != nil {
+		return nil, err
+	}
+
+	for i := range b.index {
+		entry := b.index[i]
+		if entry.messageID() == messageID {
+			return makeArticle(entry)
+		}
+	}
+
+	num, err := strconv.Atoi(messageID)
+	if err == nil && num <= len(b.index) {
+		return makeArticle(b.index[num-1])
+	}
+
+	return nil, nntpserver.ErrInvalidMessageID
+}
+
+func (b backend) Post(article *nntp.Article) error {
+	indexFile, err := os.Open(path.Join(os.Getenv("HOME"), ".slog", "index"))
+	if err != nil {
+		return err
+	}
+
+	entries, err := parseIndexFile(indexFile)
+	if err != nil {
+		return err
+	}
+
+	postID, err := newPostID()
+	if err != nil {
+		return err
+	}
+
+	entries = append(entries, indexEntry{
+		id: postID,
+		ts: time.Now(),
+		title: article.Header.Get("Subject"),
+	})
+
+	file, err := os.Create(path.Join(os.Getenv("HOME"), ".slog", "posts", postID))
+	if err != nil {
+		return err
+	}
+	defer func() { _ = file.Close() }()
+
+	_, err = io.Copy(file, article.Body)
+	if err != nil {
+		return err
+	}
+
+	return writeIndexFile(entries)
+}
+
+func (b backend) Authorized() bool                                     { return true }
+func (b backend) AllowPost() bool                                      { return true }
+func (b backend) Authenticate(_, _ string) (nntpserver.Backend, error) { return nil, nil }
+
+type indexEntry struct {
+	id     string
+	ts     time.Time
+	title  string
+	user   string
+	author string
+}
+
+const indexTimeFmt = "2006-01-02 15:04:05.999999"
+
+func (ie *indexEntry) UnmarshalJSON(b []byte) error {
+	var tgt struct {
+		Timestamp string
+		Id        string
+		Title     string
+	}
+	if err := json.Unmarshal(b, &tgt); err != nil {
+		return err
+	}
+
+	ts, err := time.Parse(indexTimeFmt, tgt.Timestamp)
+	if err != nil {
+		return err
+	}
+
+	ie.id = tgt.Id
+	ie.ts = ts
+	ie.title = tgt.Title
+	return nil
+}
+
+func (ie *indexEntry) MarshalJSON() ([]byte, error) {
+	return json.Marshal(map[string]any{
+		"id":        ie.id,
+		"timestamp": ie.ts.Format(indexTimeFmt),
+		"title":     ie.title,
+	})
+}
+
+func (ie indexEntry) messageID() string {
+	return fmt.Sprintf("<%s.%s>", ie.id, ie.author)
+}
+
+func (b *backend) refreshIndex() error {
+	now := time.Now()
+	if b.lastRead.IsZero() || now.Sub(b.lastRead) > b.waitTime {
+		b.lastRead = now
+	} else {
+		return nil
+	}
+
+	fsys := os.DirFS("/home")
+	indices, err := fs.Glob(fsys, "*/.slog/index")
+	if err != nil {
+		return err
+	}
+
+	b.index = b.index[:0]
+	for _, index := range indices {
+		username := strings.SplitN(index, "/", 2)[0]
+
+		file, err := fsys.Open(index)
+		if err != nil {
+			_ = b.warn(
+				"msg", "error opening index file",
+				"user", username,
+				"err", err,
+			)
+			continue
+		}
+
+		items, err := parseIndexFile(file)
+		if err != nil {
+			_ = b.warn(
+				"msg", "error parsing index file",
+				"user", username,
+				"err", err,
+			)
+			continue
+		}
+		for i := range items {
+			items[i].user = username
+			items[i].author = username + "@ctrl-c.club"
+		}
+		b.index = append(b.index, items...)
+	}
+
+	sort.Slice(b.index, func(i, j int) bool {
+		return b.index[i].ts.Before(b.index[j].ts)
+	})
+
+	group.High = int64(len(b.index))
+	group.Count = group.High
+
+	return nil
+}
+
+func myIndexPath() string {
+	return path.Join(os.Getenv("HOME"), ".slog", "index")
+}
+
+func parseIndexFile(file fs.File) ([]indexEntry, error) {
+	defer func() { _ = file.Close() }()
+
+	var entries []indexEntry
+	if err := json.NewDecoder(file).Decode(&entries); err != nil {
+		return nil, err
+	}
+	return entries, nil
+}
+
+func writeIndexFile(entries []indexEntry) error {
+	file, err := os.Create(myIndexPath())
+	if err != nil {
+		return err
+	}
+	defer func() { _ = file.Close() }()
+
+	return json.NewEncoder(file).Encode(entries)
+}
+
+func makeArticle(entry indexEntry) (*nntp.Article, error) {
+	f, err := os.Open(fmt.Sprintf("/home/%s/.slog/posts/%s", entry.user, entry.id))
+	if err != nil {
+		return nil, err
+	}
+	defer func() { _ = f.Close() }()
+
+	body := &bytes.Buffer{}
+	size, err := io.Copy(body, f)
+	if err != nil {
+		return nil, err
+	}
+	lines := bytes.Count(body.Bytes(), []byte{'\n'})
+
+	article := &nntp.Article{
+		Header: textproto.MIMEHeader{
+			"Message-Id": []string{entry.messageID()},
+			"From":       []string{entry.author},
+			"Newsgroups": []string{group.Name},
+			"Date":       []string{entry.ts.Format(time.RFC1123Z)},
+			"Subject":    []string{entry.title},
+		},
+		Body:  body,
+		Bytes: int(size),
+		Lines: lines,
+	}
+
+	return article, nil
+}
+
+func newPostID() (string, error) {
+	buf := make([]byte, 5)
+	_, err := rand.Read(buf)
+	if err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(buf), nil
+}