docs: publish Tend Compose continuity evidence

Export the reviewed allowlisted snapshot from private source commit 07c1655921f21ee5e4fc4d85639d199e8867b17d. This records the Docker Compose activation, schema-compatible rollback, and stateful migration resource findings from Observatory Preview 19 dogfooding. AI-Assisted: OpenAI Codex Signed-off-by: Cole Speelman <crspeelman@gmail.com>
2026-08-18 21:42:33 -04:00
commit bf56dbce0f
83 changed files with 8555 additions and 0 deletions
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+
+// Package transport implements Tend's bounded, versioned deployment stream.
+package transport
+
+import (
+	"bufio"
+	"bytes"
+	"crypto/sha256"
+	"encoding/binary"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"regexp"
+	"strings"
+)
+
+const (
+	Protocol         = "tend-receive-v1"
+	MaxArtifactBytes = 512 << 20
+	maxHeaderBytes   = 64 << 10
+	maxArtifactName  = 128
+)
+
+var (
+	servicePattern  = regexp.MustCompile(`^[a-z][a-z0-9-]{1,62}$`)
+	artifactPattern = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._-]{0,127}$`)
+)
+
+type Header struct {
+	Protocol       string `json:"protocol"`
+	Service        string `json:"service"`
+	ArtifactName   string `json:"artifact_name"`
+	Size           int64  `json:"size"`
+	SHA256         string `json:"sha256"`
+	ApprovedSHA256 string `json:"approved_sha256"`
+	Activate       bool   `json:"activate"`
+}
+
+func (h Header) Validate(maxBytes int64) error {
+	if h.Protocol != Protocol {
+		return errors.New("unsupported receive protocol")
+	}
+	if !servicePattern.MatchString(h.Service) {
+		return errors.New("invalid service name")
+	}
+	if len(h.ArtifactName) > maxArtifactName || !artifactPattern.MatchString(h.ArtifactName) {
+		return errors.New("invalid artifact name")
+	}
+	if h.Size <= 0 || h.Size > maxBytes {
+		return errors.New("artifact size exceeds policy")
+	}
+	if h.SHA256 != h.ApprovedSHA256 || len(h.SHA256) != 64 || strings.ToLower(h.SHA256) != h.SHA256 {
+		return errors.New("artifact digest was not explicitly approved")
+	}
+	if _, err := hex.DecodeString(h.SHA256); err != nil {
+		return errors.New("artifact digest is not hexadecimal")
+	}
+	return nil
+}
+
+func Prefix(header Header) ([]byte, error) {
+	if err := header.Validate(MaxArtifactBytes); err != nil {
+		return nil, err
+	}
+	body, err := json.Marshal(header)
+	if err != nil {
+		return nil, err
+	}
+	if len(body) > maxHeaderBytes {
+		return nil, errors.New("receive header exceeds limit")
+	}
+	prefix := make([]byte, 4+len(body))
+	binary.BigEndian.PutUint32(prefix[:4], uint32(len(body)))
+	copy(prefix[4:], body)
+	return prefix, nil
+}
+
+func ReadHeader(reader *bufio.Reader) (Header, error) {
+	var size [4]byte
+	if _, err := io.ReadFull(reader, size[:]); err != nil {
+		return Header{}, fmt.Errorf("read receive header length: %w", err)
+	}
+	length := binary.BigEndian.Uint32(size[:])
+	if length == 0 || length > maxHeaderBytes {
+		return Header{}, errors.New("receive header length is invalid")
+	}
+	body := make([]byte, length)
+	if _, err := io.ReadFull(reader, body); err != nil {
+		return Header{}, fmt.Errorf("read receive header: %w", err)
+	}
+	decoder := json.NewDecoder(bytes.NewReader(body))
+	decoder.DisallowUnknownFields()
+	var header Header
+	if err := decoder.Decode(&header); err != nil {
+		return Header{}, fmt.Errorf("decode receive header: %w", err)
+	}
+	var trailing any
+	if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
+		return Header{}, errors.New("receive header contains trailing data")
+	}
+	return header, nil
+}
+
+func CopyArtifact(destination io.Writer, reader *bufio.Reader, header Header, maxBytes int64) error {
+	if err := header.Validate(maxBytes); err != nil {
+		return err
+	}
+	hash := sha256.New()
+	written, err := io.CopyN(io.MultiWriter(destination, hash), reader, header.Size)
+	if err != nil || written != header.Size {
+		return errors.New("artifact stream ended before declared size")
+	}
+	if _, err = reader.ReadByte(); !errors.Is(err, io.EOF) {
+		return errors.New("artifact stream contains trailing bytes")
+	}
+	if hex.EncodeToString(hash.Sum(nil)) != header.SHA256 {
+		return errors.New("artifact stream digest does not match")
+	}
+	return nil
+}