1 files changed, 361 insertions, 0 deletions
diff --git a/internal/rosa/mirror.go b/internal/rosa/mirror.go
new file mode 100644
index 00000000..3f7822e5
--- /dev/null
+++ b/internal/rosa/mirror.go
@@ -0,0 +1,361 @@
+package rosa
+
+import (
+	"compress/gzip"
+	"context"
+	"crypto/ed25519"
+	"crypto/sha512"
+	"errors"
+	"io"
+	"io/fs"
+	"net/http"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"unique"
+
+	"hakurei.app/internal/pkg"
+	"hakurei.app/message"
+)
+
+// Remote is an authenticated cache mirror.
+type Remote struct {
+	// Mirror URL.
+	url *url.URL
+	// Trusted public key.
+	pub ed25519.PublicKey
+	// For requests to the mirror.
+	c *http.Client
+}
+
+// NewRemote returns a populated [Remote]
+func NewRemote(base string, pub ed25519.PublicKey, c *http.Client) (Remote, error) {
+	u, err := url.Parse(base)
+	return Remote{u, pub, c}, err
+}
+
+// get makes a [http.MethodGet] request and returns the response, or nil if
+// the response StatusCode is [http.StatusNotFound].
+func (r Remote) get(ctx context.Context, elem ...string) (*http.Response, error) {
+	if r.url == nil || len(r.pub) != ed25519.PublicKeySize || r.c == nil {
+		return nil, os.ErrInvalid
+	}
+
+	req, err := http.NewRequestWithContext(
+		ctx,
+		http.MethodGet,
+		r.url.JoinPath(elem...).String(),
+		nil,
+	)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("User-Agent", "Rosa/1.1")
+
+	var resp *http.Response
+	if resp, err = r.c.Do(req); err != nil {
+		return nil, err
+	}
+
+	switch resp.StatusCode {
+	case http.StatusOK:
+		return resp, nil
+
+	case http.StatusNotFound:
+		return nil, resp.Body.Close()
+
+	default:
+		_ = resp.Body.Close()
+		return nil, pkg.ResponseStatusError(resp.StatusCode)
+	}
+}
+
+const (
+	// dirArtifact holds signed artifact outcome checksums.
+	dirArtifact = "artifact"
+	// dirOutcome holds outcome archives by their checksum.
+	dirOutcome = "outcome"
+	// dirStatus holds signed status files.
+	dirStatus = "status"
+)
+
+// An OutcomeBadSizeError describes a mirror outcome with unexpected size.
+type OutcomeBadSizeError struct {
+	Ident unique.Handle[pkg.ID]
+	Size  int64
+}
+
+func (e OutcomeBadSizeError) Error() string {
+	if e.Size < 0 {
+		return "remote did not return outcome size for " +
+			pkg.Encode(e.Ident.Value())
+	}
+	return "outcome size " + strconv.FormatInt(e.Size, 10) +
+		" invalid for " + pkg.Encode(e.Ident.Value())
+}
+
+// An OutcomeAuthError describes a mirror outcome with invalid signature.
+type OutcomeAuthError unique.Handle[pkg.ID]
+
+func (e OutcomeAuthError) Error() string {
+	return "invalid outcome signature for " +
+		pkg.Encode(unique.Handle[pkg.ID](e).Value())
+}
+
+// Artifact fetches and authenticates an outcome.
+func (r Remote) Artifact(
+	ctx context.Context,
+	id unique.Handle[pkg.ID],
+) (*pkg.Checksum, error) {
+	if len(r.pub) != ed25519.PublicKeySize || r.c == nil {
+		return nil, os.ErrInvalid
+	}
+
+	resp, err := r.get(ctx, dirArtifact, pkg.Encode(id.Value()))
+	if err != nil || resp == nil {
+		return nil, err
+	}
+
+	var buf [ed25519.SignatureSize + 2*len(pkg.Checksum{})]byte
+	if resp.ContentLength != int64(len(buf)) {
+		_ = resp.Body.Close()
+		return nil, OutcomeBadSizeError{id, resp.ContentLength}
+	}
+	if _, err = io.ReadFull(resp.Body, buf[:]); err != nil {
+		return nil, errors.Join(err, resp.Body.Close())
+	} else if err = resp.Body.Close(); err != nil {
+		return nil, err
+	}
+
+	if !ed25519.Verify(
+		r.pub,
+		buf[ed25519.SignatureSize:],
+		buf[:ed25519.SignatureSize],
+	) {
+		return nil, OutcomeAuthError(id)
+	} else if unique.Make((pkg.ID)(buf[ed25519.SignatureSize:])) != id {
+		return nil, OutcomeAuthError(id)
+	}
+	return (*pkg.Checksum)(buf[ed25519.SignatureSize+len(pkg.Checksum{}):]), nil
+}
+
+// Checksum returns an artifact satisfying checksum.
+func (r Remote) Checksum(checksum unique.Handle[pkg.Checksum]) pkg.Artifact {
+	return pkg.NewArchive(pkg.NewHTTPGet(
+		r.c,
+		r.url.JoinPath(dirOutcome, pkg.Encode(checksum.Value())).String(),
+		checksum.Value(),
+	))
+}
+
+// A StatusBadSizeError describes a mirror status with unexpected size.
+type StatusBadSizeError unique.Handle[pkg.ID]
+
+func (e StatusBadSizeError) Error() string {
+	return "status payload too short for " +
+		pkg.Encode(unique.Handle[pkg.ID](e).Value())
+}
+
+// A StatusAuthError describes a mirror status with invalid signature.
+type StatusAuthError unique.Handle[pkg.ID]
+
+func (e StatusAuthError) Error() string {
+	return "invalid status signature for " +
+		pkg.Encode(unique.Handle[pkg.ID](e).Value())
+}
+
+// Status authenticates the checksum of a status file and returns its
+// corresponding measured reader.
+func (r Remote) Status(
+	ctx *pkg.RContext,
+	id unique.Handle[pkg.ID],
+) (io.ReadCloser, error) {
+	resp, err := r.get(ctx.Unwrap(), dirStatus, pkg.Encode(id.Value()))
+	if err != nil || resp == nil {
+		return nil, err
+	}
+
+	var buf [ed25519.SignatureSize + 2*len(pkg.Checksum{})]byte
+	if _, err = io.ReadFull(resp.Body, buf[:]); err != nil {
+		if errors.Is(err, io.ErrUnexpectedEOF) {
+			err = StatusBadSizeError(id)
+		}
+		return nil, err
+	}
+
+	if !ed25519.Verify(
+		r.pub,
+		buf[ed25519.SignatureSize:],
+		buf[:ed25519.SignatureSize],
+	) {
+		_ = resp.Body.Close()
+		return nil, StatusAuthError(id)
+	} else if unique.Make((pkg.ID)(buf[ed25519.SignatureSize:])) != id {
+		return nil, StatusAuthError(id)
+	}
+	return ctx.NewMeasuredReader(
+		resp.Body,
+		unique.Make((pkg.Checksum)(buf[ed25519.SignatureSize+len(pkg.Checksum{}):])),
+	), nil
+}
+
+// NewMirror returns an [http.Handler] for servicing mirror requests.
+func NewMirror(
+	msg message.Msg,
+	base *os.Root,
+	key ed25519.PrivateKey,
+) http.Handler {
+	const identName = "ident"
+	var mux http.ServeMux
+
+	mux.HandleFunc("/"+dirArtifact+"/{"+identName+"}", func(
+		w http.ResponseWriter,
+		req *http.Request,
+	) {
+		var buf [2 * len(pkg.Checksum{})]byte
+		if err := pkg.Decode(
+			(*pkg.Checksum)(buf[:len(pkg.Checksum{})]),
+			req.PathValue(identName),
+		); err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+
+		ids := pkg.Encode((pkg.Checksum)(buf[:len(pkg.Checksum{})]))
+		if linkname, err := base.Readlink(filepath.Join(
+			"identifier",
+			ids,
+		)); err != nil {
+			if errors.Is(err, os.ErrNotExist) {
+				w.WriteHeader(http.StatusNotFound)
+				return
+			}
+			msg.GetLogger().Println(err)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		} else if err = pkg.Decode(
+			(*pkg.Checksum)(buf[len(pkg.Checksum{}):]),
+			filepath.Base(linkname),
+		); err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+		msg.Verbosef("serving artifact %s", ids)
+
+		w.Header().Set(
+			"Content-Length",
+			strconv.Itoa(ed25519.SignatureSize+len(buf)),
+		)
+		if _, err := w.Write(append(
+			ed25519.Sign(key, buf[:]),
+			buf[:]...,
+		)); err != nil {
+			msg.Verbose(err)
+		}
+	})
+
+	mux.HandleFunc("/"+dirOutcome+"/{"+identName+"}", func(
+		w http.ResponseWriter,
+		req *http.Request,
+	) {
+		if !strings.Contains(req.Header.Get("Accept-Encoding"), "gzip") {
+			w.WriteHeader(http.StatusNotAcceptable)
+			return
+		}
+
+		var buf pkg.Checksum
+		if err := pkg.Decode(
+			&buf,
+			req.PathValue(identName),
+		); err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+
+		checksums := pkg.Encode(buf)
+		rel := filepath.Join("checksum", checksums)
+		if _, err := base.Lstat(rel); err != nil {
+			if errors.Is(err, os.ErrNotExist) {
+				w.WriteHeader(http.StatusNotFound)
+				return
+			}
+			msg.GetLogger().Println(err)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+		msg.Verbosef("serving outcome %s", pkg.Encode(buf))
+
+		fsys, err := fs.Sub(base.FS(), rel)
+		if err != nil {
+			msg.GetLogger().Println(err)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+
+		var gw *gzip.Writer
+		if gw, err = gzip.NewWriterLevel(w, gzip.BestCompression); err != nil {
+			msg.GetLogger().Println(err)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+		w.Header().Set("Content-Encoding", "gzip")
+		if err = pkg.Write(fsys, ".", gw); err != nil {
+			msg.Verbose(err)
+		}
+		if err = gw.Close(); err != nil {
+			msg.GetLogger().Println(err)
+		}
+	})
+
+	mux.HandleFunc("/"+dirStatus+"/{"+identName+"}", func(
+		w http.ResponseWriter,
+		req *http.Request,
+	) {
+		var buf [2 * len(pkg.Checksum{})]byte
+		if err := pkg.Decode(
+			(*pkg.Checksum)(buf[:len(pkg.Checksum{})]),
+			req.PathValue(identName),
+		); err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+
+		ids := pkg.Encode((pkg.Checksum)(buf[:len(pkg.Checksum{})]))
+		f, err := base.Open(filepath.Join(
+			"status",
+			ids,
+		))
+		if err != nil {
+			if errors.Is(err, os.ErrNotExist) {
+				w.WriteHeader(http.StatusNotFound)
+				return
+			}
+			msg.GetLogger().Println(err)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+		msg.Verbosef("serving status %s", ids)
+
+		h := sha512.New384()
+		if _, err = io.Copy(h, f); err != nil {
+			_ = f.Close()
+			msg.Verbose(err)
+			w.WriteHeader(http.StatusInternalServerError)
+		}
+		h.Sum(buf[len(pkg.Checksum{}):len(pkg.Checksum{})])
+		if _, err = w.Write(append(ed25519.Sign(key, buf[:]), buf[:]...)); err != nil {
+			msg.Verbose(err)
+			return
+		} else if _, err = f.Seek(0, io.SeekStart); err != nil {
+			msg.GetLogger().Println(err)
+			return
+		} else if _, err = io.Copy(w, f); err != nil {
+			msg.Verbose(err)
+			return
+		}
+	})
+
+	return &mux
+}