Plexum-fabric-channel-plugin/internal/attachments/attachments.go

// Package attachments downloads Fabric attachment files referenced in
// inbound messages into a temp dir so the agent can read them via the
// exec tool (cat / file / etc.).
//
// Plexum's notifications/plexum/channel/inbound payload doesn't yet
// have a structured "media" field (host-side work), so we surface the
// downloaded paths by appending a markdown footer to the message text:
//
//	hello, please review the attached file
//
//	Attachments:
//	  - /tmp/plexum-fabric/<msg-id>/proposal.md (text/markdown, 3142 bytes)
//
// Agent then uses the exec tool to read whichever paths it cares about.
package attachments

import (
	"context"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"
	"time"
)

// DownloadResult tracks one downloaded file.
type DownloadResult struct {
	LocalPath string
	Name      string
	MimeType  string
	Size      int64
}

// Downloader fetches attachments using a per-call guild token.
type Downloader struct {
	HTTP    *http.Client
	BaseDir string // e.g. /tmp/plexum-fabric
}

// New constructs a Downloader. baseDir defaults to /tmp/plexum-fabric.
func New(baseDir string) *Downloader {
	if baseDir == "" {
		baseDir = filepath.Join(os.TempDir(), "plexum-fabric")
	}
	return &Downloader{
		HTTP:    &http.Client{Timeout: 30 * time.Second},
		BaseDir: baseDir,
	}
}

// FetchAll downloads every attachment for messageID; returns the
// successful results. Per-attachment errors are accumulated as nil
// entries' "err" field skipped — caller may log via supplied logger.
// Files land under <BaseDir>/<messageID>/<filename>.
func (d *Downloader) FetchAll(ctx context.Context, guildToken, messageID string, urls []AttachmentRef) []DownloadResult {
	if len(urls) == 0 {
		return nil
	}
	dir := filepath.Join(d.BaseDir, sanitizeID(messageID))
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return nil
	}
	var out []DownloadResult
	for i, ref := range urls {
		if ref.URL == "" {
			continue
		}
		name := ref.Name
		if name == "" {
			name = fmt.Sprintf("attachment-%d", i)
		}
		name = sanitizeFilename(name)
		dst := filepath.Join(dir, name)
		size, err := d.fetchOne(ctx, guildToken, ref.URL, dst)
		if err != nil {
			continue
		}
		out = append(out, DownloadResult{
			LocalPath: dst, Name: name, MimeType: ref.MimeType, Size: size,
		})
	}
	return out
}

// fetchOne downloads ref.URL into dst with auth. Returns bytes written.
func (d *Downloader) fetchOne(ctx context.Context, guildToken, src, dst string) (int64, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, src, nil)
	if err != nil {
		return 0, err
	}
	if guildToken != "" {
		req.Header.Set("authorization", "Bearer "+guildToken)
	}
	resp, err := d.HTTP.Do(req)
	if err != nil {
		return 0, err
	}
	defer resp.Body.Close()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return 0, fmt.Errorf("attachments: %s -> %d", src, resp.StatusCode)
	}
	f, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o600)
	if err != nil {
		return 0, err
	}
	defer f.Close()
	return io.Copy(f, resp.Body)
}

// AttachmentRef is the minimum the downloader needs per file.
type AttachmentRef struct {
	URL      string
	Name     string
	MimeType string
}

// AppendFooter returns body with a markdown footer listing the
// downloaded attachments (in agent-friendly form). Empty list →
// body unchanged.
func AppendFooter(body string, files []DownloadResult) string {
	if len(files) == 0 {
		return body
	}
	var sb strings.Builder
	sb.WriteString(body)
	if !strings.HasSuffix(body, "\n") {
		sb.WriteByte('\n')
	}
	sb.WriteString("\nAttachments:\n")
	for _, f := range files {
		fmt.Fprintf(&sb, "  - %s (%s, %d bytes)\n", f.LocalPath, dispMime(f.MimeType), f.Size)
	}
	return sb.String()
}

// ---- helpers ----

func sanitizeFilename(name string) string {
	// Strip path separators; collapse weird chars. Keep ext.
	name = filepath.Base(name)
	if name == "" || name == "." || name == "/" {
		return "attachment.bin"
	}
	// Reject query strings if any leaked in via name=url.
	if i := strings.IndexAny(name, "?#"); i > 0 {
		name = name[:i]
	}
	if u, err := url.QueryUnescape(name); err == nil {
		name = u
	}
	// Drop any leading dots so we don't end up writing hidden files.
	name = strings.TrimLeft(name, ".")
	if name == "" {
		return "attachment.bin"
	}
	return name
}

func sanitizeID(s string) string {
	// Allow [a-zA-Z0-9_-]; replace anything else with '_'.
	var sb strings.Builder
	sb.Grow(len(s))
	for _, r := range s {
		switch {
		case r >= '0' && r <= '9', r >= 'a' && r <= 'z', r >= 'A' && r <= 'Z', r == '-', r == '_':
			sb.WriteRune(r)
		default:
			sb.WriteByte('_')
		}
	}
	if sb.Len() == 0 {
		return "msg"
	}
	return sb.String()
}

func dispMime(m string) string {
	if m == "" {
		return "application/octet-stream"
	}
	return m
}