1 files changed, 448 insertions, 0 deletions
diff --git a/iris/backend.go b/iris/backend.go
new file mode 100644
index 0000000..787db96
--- /dev/null
+++ b/iris/backend.go
@@ -0,0 +1,448 @@
+package iris
+
+import (
+	"bytes"
+	"crypto/sha1"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/mail"
+	"net/textproto"
+	"os"
+	"os/exec"
+	"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.iris",
+	Description: "The iris message board",
+	Posting:     nntp.PostingPermitted,
+	Low:         1,
+}
+
+const DefaultWaitTime = 30 * time.Second
+const msgfile = ".iris.messages"
+
+// NewBackend builds an iris 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}
+	if err := b.refresh(); err != nil {
+		return nil, err
+	}
+
+	return b, nil
+}
+
+type backend struct {
+	logger   log.Logger
+	waitTime time.Duration
+	lastRead time.Time
+	messages []*nntp.Article
+}
+
+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.refresh(); err != nil {
+		return nil, err
+	}
+
+	return group, nil
+}
+
+func (b *backend) GetArticles(_ *nntp.Group, from, to int64) ([]nntpserver.NumberedArticle, error) {
+	if err := b.refresh(); err != nil {
+		return nil, err
+	}
+
+	numbered := make([]nntpserver.NumberedArticle, 0, len(b.messages))
+	for i, msg := range b.messages {
+		num := int64(i + 1)
+		if num >= from && num <= to {
+			numbered = append(numbered, nntpserver.NumberedArticle{
+				Num:     num,
+				Article: copyArticle(msg),
+			})
+		}
+	}
+
+	return numbered, nil
+}
+
+func (b *backend) GetArticle(_ *nntp.Group, messageID string) (*nntp.Article, error) {
+	if err := b.refresh(); err != nil {
+		return nil, err
+	}
+
+	for _, msg := range b.messages {
+		if msg.Header.Get("Message-Id") == messageID {
+			return msg, nil
+		}
+	}
+
+	num, err := strconv.Atoi(messageID)
+	if err == nil && num <= len(b.messages) {
+		return copyArticle(b.messages[num-1]), nil
+	}
+
+	return nil, nntpserver.ErrInvalidMessageID
+}
+
+func (b backend) Post(article *nntp.Article) error {
+	// iris replies are all made to a top-level post, there is no grandchild nesting.
+	//
+	// but NNTP supports this, so collapse the provided "References" header up to the OP.
+	parent := b.findOP(article.Header.Get("References"))
+	if parent != nil {
+		article.Header.Set("References", parent.MessageID())
+	}
+
+	msg, err := msgToIris(article)
+	if err != nil {
+		return err
+	}
+	return appendMessage(msg)
+}
+
+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 }
+
+func (b backend) findOP(ref string) *nntp.Article {
+	if ref == "" {
+		return nil
+	}
+	// all references should have the same OP so just take the first
+	msgID := strings.SplitN(ref, " ", 2)[0]
+
+	// traverse backwards expecting most reply activity concentrated late in the total history
+	for i := len(b.messages) - 1; i >= 0; i-- {
+		article := b.messages[i]
+		if article.MessageID() != msgID {
+			continue
+		}
+
+		gpID := article.Header.Get("References")
+		if gpID != "" {
+			return b.findOP(gpID)
+		}
+		return article
+	}
+
+	return nil
+}
+
+func (b *backend) refresh() error {
+	now := time.Now()
+	if b.lastRead.IsZero() || now.Sub(b.lastRead) > b.waitTime {
+		b.lastRead = now
+	} else {
+		return nil
+	}
+
+	binpath, err := exec.LookPath("iris")
+	if err != nil {
+		return err
+	}
+	cmd := exec.Command(binpath, "-d")
+	buf := &bytes.Buffer{}
+	cmd.Stdout = buf
+
+	if err := cmd.Run(); err != nil {
+		return err
+	}
+
+	msgs := irisDump{}
+	if err := json.NewDecoder(buf).Decode(&msgs); err != nil {
+		return err
+	}
+
+	b.messages, err = msgs.Articles()
+	if err != nil {
+		return err
+	}
+	group.High = int64(len(b.messages))
+	group.Count = int64(len(b.messages))
+	return nil
+}
+
+func copyArticle(article *nntp.Article) *nntp.Article {
+	out := *article
+	out.Body = bytes.NewBuffer(article.Body.(*bytes.Buffer).Bytes())
+	return &out
+}
+
+type irisMsg struct {
+	Hash      string  `json:"hash"`
+	EditHash  *string `json:"edit_hash"`
+	IsDeleted *bool   `json:"is_deleted"`
+	Data      struct {
+		Author    string  `json:"author"`
+		Parent    *string `json:"parent"`
+		Timestamp string  `json:"timestamp"`
+		Message   string  `json:"message"`
+	} `json:"data"`
+}
+
+func (m irisMsg) calcHash() (string, error) {
+	/*
+		Careful coding here to match ruby's hash calculation:
+		```
+		Base64.encode64(Digest::SHA1.digest(m["data"].to_json))
+		```
+
+		* have to use an encoder rather than json.Marshal so we can
+			turn off the default HTML escaping (ruby doesn't do this)
+		* strip trailing newline from JSON encoding output
+		* add a trailing newline to base64 encoded form
+	*/
+
+	b := &bytes.Buffer{}
+	enc := json.NewEncoder(b)
+	enc.SetEscapeHTML(false)
+	if err := enc.Encode(m.Data); err != nil {
+		return "", err
+	}
+
+	arr := sha1.Sum(bytes.TrimSuffix(b.Bytes(), []byte("\n")))
+	s := base64.StdEncoding.EncodeToString(arr[:])
+	if !strings.HasSuffix(s, "\n") {
+		s += "\n"
+	}
+	return s, nil
+}
+
+func msgToIris(article *nntp.Article) (*irisMsg, error) {
+	postTime := time.Now().UTC().Format(time.RFC3339)
+
+	body, err := io.ReadAll(article.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	var msg irisMsg
+	msg.Data.Author = irisAuthor(article.Header.Get("From"))
+	msg.Data.Timestamp = postTime
+	msg.Data.Message = string(body)
+	refs := article.Header.Get("References")
+	if refs != "" {
+		spl := strings.SplitN(refs, " ", 2)
+		ref := fromMsgID(spl[0])
+		msg.Data.Parent = &ref
+	}
+
+	hash, err := msg.calcHash()
+	if err != nil {
+		return nil, err
+	}
+	msg.Hash = hash
+
+	return &msg, nil
+}
+
+func irisAuthor(nntpAuthor string) string {
+	addr, err := mail.ParseAddress(nntpAuthor)
+	if err != nil {
+		return nntpAuthor
+	}
+
+	return addr.Address
+}
+
+type irisDump []irisMsg
+
+func (dump irisDump) Articles() ([]*nntp.Article, error) {
+	// calculate the article replacements due to edits
+	//
+	// note: this is only a single "hop", and because there can be edits-of-edits
+	// and edits-of-edits-of-edits, we must actually resolve replacements with a loop.
+	//
+	// we need to keep all the hops though because there could have been replies to
+	// the original or to any intermediate edits.
+	replacements := make(map[string]string)
+	for _, msg := range dump {
+		if msg.EditHash != nil {
+			replacements[*msg.EditHash] = msg.Hash
+		}
+	}
+
+	articles := make([]*nntp.Article, 0, len(dump)-len(replacements))
+
+	// index iris hashes -> nntp Articles for reference lookups
+	idx := make(map[string]*nntp.Article)
+
+	sort.SliceStable(dump, func(i, j int) bool {
+		return dump[i].Data.Timestamp < dump[j].Data.Timestamp
+	})
+
+outer:
+	for _, msg := range dump {
+		if _, ok := replacements[msg.Hash]; ok {
+			continue
+		}
+		if msg.EditHash != nil && *msg.EditHash == msg.Hash {
+			continue
+		}
+
+		msgID := msgIDFor(&msg)
+		ts, err := time.Parse(time.RFC3339, msg.Data.Timestamp)
+		if err != nil {
+			return nil, err
+		}
+
+		article := &nntp.Article{
+			Header: textproto.MIMEHeader{
+				"Message-Id": []string{msgID},
+				"From":       []string{msg.Data.Author},
+				"Newsgroups": []string{group.Name},
+				"Date":       []string{ts.Format(time.RFC1123Z)},
+			},
+		}
+
+		if msg.IsDeleted != nil && *msg.IsDeleted {
+			article.Header.Set("Subject", "**TOPIC DELETED BY AUTHOR**")
+			article.Body = &bytes.Buffer{}
+			article.Bytes = 0
+			article.Lines = 0
+		} else {
+			article.Body = bytes.NewBufferString(msg.Data.Message)
+			article.Bytes = len(msg.Data.Message)
+			article.Lines = strings.Count(msg.Data.Message, "\n")
+
+			if msg.Data.Parent == nil {
+				article.Header.Set("Subject", strings.SplitN(msg.Data.Message, "\n", 2)[0])
+			} else {
+				parentHash := *msg.Data.Parent
+				for {
+					if p, ok := replacements[parentHash]; ok {
+						if parentHash == p {
+							continue outer
+						}
+						parentHash = p
+					} else {
+						break
+					}
+				}
+				msg.Data.Parent = &parentHash
+				parent, ok := idx[parentHash]
+				if !ok {
+					continue
+				}
+				parentSubj := strings.TrimPrefix(parent.Header.Get("Subject"), "Re: ")
+				article.Header.Set("Subject", "Re: "+parentSubj)
+			}
+		}
+
+		if msg.Data.Parent != nil {
+			parent := idx[*msg.Data.Parent]
+			if parent == nil {
+				continue
+			}
+			parentRefs := parent.Header.Get("References")
+			if parentRefs != "" {
+				article.Header.Set("References", parentRefs)
+			} else {
+				article.Header.Set("References", parent.MessageID())
+			}
+		}
+
+		articles = append(articles, article)
+		idx[msg.Hash] = article
+	}
+
+	return articles, nil
+}
+
+func (id irisDump) MarshalJSON() ([]byte, error) {
+	buf := &bytes.Buffer{}
+	enc := json.NewEncoder(buf)
+	enc.SetEscapeHTML(false)
+
+	out := bytes.NewBufferString("[\n  ")
+
+	for i, msg := range id {
+		if err := enc.Encode(msg); err != nil {
+			return nil, err
+		}
+
+		if i > 0 {
+			_, _ = out.WriteString(",\n  ")
+		}
+		_, _ = out.Write(bytes.TrimSuffix(buf.Bytes(), []byte("\n")))
+		buf.Reset()
+	}
+	_, _ = out.WriteString("\n]")
+
+	return out.Bytes(), nil
+}
+
+func msgIDFor(msg *irisMsg) string {
+	return fmt.Sprintf("<%s.%s>",
+		strings.TrimSuffix(msg.Hash, "=\n"),
+		msg.Data.Author,
+	)
+}
+
+func fromMsgID(nntpID string) string {
+	hash, _, _ := strings.Cut(strings.TrimSuffix(strings.TrimPrefix(nntpID, "<"), ">"), ".")
+	return hash + "=\n"
+}
+
+func appendMessage(msg *irisMsg) error {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return err
+	}
+
+	msgFile, err := os.Open(path.Join(home, msgfile))
+	if err != nil {
+		return err
+	}
+
+	var msgs irisDump
+	if err := json.NewDecoder(msgFile).Decode(&msgs); err != nil {
+		_ = msgFile.Close()
+		return err
+	}
+	_ = msgFile.Close()
+	msgs = append(msgs, *msg)
+
+	msgFile, err = os.Create(path.Join(home, msgfile))
+	if err != nil {
+		return err
+	}
+	defer func() { _ = msgFile.Close() }()
+
+	out, err := msgs.MarshalJSON()
+	if err != nil {
+		return err
+	}
+	_, err = msgFile.Write(out)
+	return err
+}