AddFileWithHash rejects hashes that are not multihashes (closes #129)

AddFileWithHash took any non-empty bytes as a hash, so the builder could
write a manifest that mfer refuses to load. It now decodes the hash with
go-multihash and also requires a digest of at least 32 bytes, the SHA-256
length the reader's decoding-cost limit assumes: a valid but shorter
multihash, such as an empty identity hash or SHA-1, still makes a
manifest of one-character paths too costly to load. Test fixtures that
used 34 zero bytes, which is not a valid multihash, now use a SHA-256
multihash.

Model: opus-5-5

Dockerfile

@@ -75,5 +75,7 @@ RUN version="${VERSION:-$(git describe --tags --always)}"; \
 RUN ldd /mfer 2>&1 | grep -q 'not a dynamic executable'
 
 FROM scratch
+# scratch has no CA certificates; fetch needs them to verify HTTPS servers.
+COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
 COPY --from=builder /mfer /mfer
 ENTRYPOINT ["/mfer"]

FORMAT.md

@@ -49,7 +49,9 @@ The `innerMessage` field is compressed with
 enforce a decompression size limit to prevent decompression bombs. The reference
 implementation limits decompressed size to 256 MB. It writes zstd frames with a
 window of at most 8 MiB, the largest window the zstd format recommends decoders
-support, and refuses frames that ask for a larger one.
+support, and refuses frames that ask for a larger one. It also refuses an inner
+message whose file entries, hashes, timestamps and MIME types, counted at 160,
+112, 64 and 16 bytes each, add up to more than 8 times its size.
 
 ## Inner Message (`MFFile`)
 

go.mod

@@ -12,13 +12,13 @@ require (
 	github.com/pterm/pterm v0.12.35
 	github.com/spf13/afero v1.8.0
 	github.com/stretchr/testify v1.8.1
-	github.com/urfave/cli/v2 v2.23.6
+	github.com/urfave/cli/v2 v2.27.7
 	google.golang.org/protobuf v1.28.1
 )
 
 require (
 	github.com/atomicgo/cursor v0.0.1 // indirect
-	github.com/cpuguy83/go-md2man/v2 v2.0.2 // indirect
+	github.com/cpuguy83/go-md2man/v2 v2.0.7 // indirect
 	github.com/fatih/color v1.7.0 // indirect
 	github.com/gookit/color v1.4.2 // indirect
 	github.com/klauspost/cpuid/v2 v2.0.9 // indirect
@@ -34,7 +34,7 @@ require (
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
 	github.com/spaolacci/murmur3 v1.1.0 // indirect
 	github.com/xo/terminfo v0.0.0-20210125001918-ca9a967f8778 // indirect
-	github.com/xrash/smetrics v0.0.0-20201216005158-039620a65673 // indirect
+	github.com/xrash/smetrics v0.0.0-20240521201337-686a1a2994c1 // indirect
 	golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e // indirect
 	golang.org/x/sys v0.1.0 // indirect
 	golang.org/x/term v0.0.0-20210927222741-03fcf44c2211 // indirect

go.sum

@@ -61,8 +61,8 @@ github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDk
 github.com/cncf/udpa/go v0.0.0-20191209042840-269d4d468f6f/go.mod h1:M8M6+tZqaGXZJjfX53e64911xZQV5JYwmTeXPW+k8Sc=
 github.com/cncf/udpa/go v0.0.0-20200629203442-efcf912fb354/go.mod h1:WmhPx2Nbnhtbo57+VJT5O0JRkEi1Wbu0z5j0R8u5Hbk=
 github.com/cncf/udpa/go v0.0.0-20201120205902-5459f2c99403/go.mod h1:WmhPx2Nbnhtbo57+VJT5O0JRkEi1Wbu0z5j0R8u5Hbk=
-github.com/cpuguy83/go-md2man/v2 v2.0.2 h1:p1EgwI/C7NhT0JmVkwCD2ZBK8j4aeHQX2pMHHBfMQ6w=
-github.com/cpuguy83/go-md2man/v2 v2.0.2/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46tRHOmNcaadrF8o=
+github.com/cpuguy83/go-md2man/v2 v2.0.7 h1:zbFlGlXEAKlwXpmvle3d8Oe3YnkKIK4xSRTd3sHPnBo=
+github.com/cpuguy83/go-md2man/v2 v2.0.7/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -231,12 +231,12 @@ github.com/tj/go-buffer v1.1.0/go.mod h1:iyiJpfFcR2B9sXu7KvjbT9fpM4mOelRSDTbntVj
 github.com/tj/go-elastic v0.0.0-20171221160941-36157cbbebc2/go.mod h1:WjeM0Oo1eNAjXGDx2yma7uG2XoyRZTq1uv3M/o7imD0=
 github.com/tj/go-kinesis v0.0.0-20171128231115-08b17f58cb1b/go.mod h1:/yhzCV0xPfx6jb1bBgRFjl5lytqVqZXEaeqWP8lTEao=
 github.com/tj/go-spin v1.1.0/go.mod h1:Mg1mzmePZm4dva8Qz60H2lHwmJ2loum4VIrLgVnKwh4=
-github.com/urfave/cli/v2 v2.23.6 h1:iWmtKD+prGo1nKUtLO0Wg4z9esfBM4rAV4QRLQiEmJ4=
-github.com/urfave/cli/v2 v2.23.6/go.mod h1:GHupkWPMM0M/sj1a2b4wUrWBPzazNrIjouW6fmdJLxc=
+github.com/urfave/cli/v2 v2.27.7 h1:bH59vdhbjLv3LAvIu6gd0usJHgoTTPhCFib8qqOwXYU=
+github.com/urfave/cli/v2 v2.27.7/go.mod h1:CyNAG/xg+iAOg0N4MPGZqVmv2rCoP267496AOXUZjA4=
 github.com/xo/terminfo v0.0.0-20210125001918-ca9a967f8778 h1:QldyIu/L63oPpyvQmHgvgickp1Yw510KJOqX7H24mg8=
 github.com/xo/terminfo v0.0.0-20210125001918-ca9a967f8778/go.mod h1:2MuV+tbUrU1zIOPMxZ5EncGwgmMJsa+9ucAQZXxsObs=
-github.com/xrash/smetrics v0.0.0-20201216005158-039620a65673 h1:bAn7/zixMGCfxrRTfdpNzjtPYqr8smhKouy9mxVdGPU=
-github.com/xrash/smetrics v0.0.0-20201216005158-039620a65673/go.mod h1:N3UwUGtsrSj3ccvlPHLoLsHnpR27oXr4ZE984MbSER8=
+github.com/xrash/smetrics v0.0.0-20240521201337-686a1a2994c1 h1:gEOO8jv9F4OT7lGCjxCBTO/36wtF6j2nSip77qHd4x4=
+github.com/xrash/smetrics v0.0.0-20240521201337-686a1a2994c1/go.mod h1:Ohn+xnUBiLI6FVj/9LpzZWtj1/D6lUovWYBkxHVV3aM=
 github.com/yuin/goldmark v1.1.25/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.1.32/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=

internal/cli/check.go

@@ -298,7 +298,11 @@ func (mfa *CLIApp) checkManifestOperation(ctx *cli.Context) error {
 	log.Infof("checking manifest %s with base %s", manifestPath, basePath)
 
 	// Create checker
-	chk, err := mfer.NewChecker(manifestPath, basePath, mfa.Fs)
+	chk, err := mfer.NewChecker(&mfer.CheckerOptions{
+		ManifestPath: manifestPath,
+		BasePath:     basePath,
+		Fs:           mfa.Fs,
+	})
 	if err != nil {
 		return fmt.Errorf("failed to load manifest: %w", err)
 	}

internal/cli/entry_test.go

@@ -8,6 +8,8 @@ import (
 	"io"
 	"math/rand"
 	"os"
+	"slices"
+	"strings"
 	"sync"
 	"testing"
 
@@ -30,6 +32,7 @@ const (
 	testFlagBase    = "--base"
 	testFlagNoExtra = "--no-extra-files"
 	testFlagVersion = "--version"
+	testFlagVerbose = "--verbose"
 )
 
 var errSimulatedWrite = errors.New("simulated write failure")
@@ -42,20 +45,32 @@ var errSimulatedWrite = errors.New("simulated write failure")
 var runMu sync.Mutex
 
 // runCLI invokes RunWithOptions while holding runMu so parallel tests
-// capture their own output. Before releasing the lock it points the
-// process-global logger at io.Discard: other tests log outside the lock
-// (manifest loads, scans), and those lines must not land in this run's
-// buffers once it has returned and its test is reading them.
+// capture their own output, and returns its exit code.
 func runCLI(opts *RunOptions) int {
+	exitCode, _ := runCLIWithLevel(opts)
+
+	return exitCode
+}
+
+// runCLIWithLevel is runCLI that also returns the log level the run left
+// set, read while runMu still keeps other runs from changing it. Each run
+// starts at the default level, as a new process does. Before releasing the
+// lock it points the process-global logger at io.Discard: other tests log
+// outside the lock (manifest loads, scans), and those lines must not land in
+// this run's buffers once it has returned and its test is reading them.
+func runCLIWithLevel(opts *RunOptions) (int, log.Level) {
 	runMu.Lock()
 	defer runMu.Unlock()
 
+	log.SetLevel(log.InfoLevel)
+
 	exitCode := RunWithOptions(opts)
+	level := log.GetLevel()
 
 	log.SetOutput(io.Discard, io.Discard)
 	log.Init()
 
-	return exitCode
+	return exitCode, level
 }
 
 func TestMain(m *testing.M) {
@@ -235,6 +250,90 @@ func TestRootVerbosityFlags(t *testing.T) {
 	})
 }
 
+// commandsTakingVerbose returns the command lines -v can follow: the root and
+// the generate, check, freshen and fetch subcommands.
+func commandsTakingVerbose() [][]string {
+	return [][]string{
+		{testApp},
+		{testApp, cmdGenerate},
+		{testApp, cmdCheck},
+		{testApp, cmdFreshen},
+		{testApp, cmdFetch},
+	}
+}
+
+// TestVerboseCount asserts that one -v or --verbose gives verbose output and
+// two -v give debug output (issue #125). urfave/cli before v2.25.5 counted a
+// flag given by its alias twice, so one -v gave debug output.
+func TestVerboseCount(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		flags []string
+		want  log.Level
+	}{
+		{[]string{"-v"}, log.VerboseLevel},
+		{[]string{testFlagVerbose}, log.VerboseLevel},
+		{[]string{"-v", "-v"}, log.DebugLevel},
+	}
+
+	for _, command := range commandsTakingVerbose() {
+		for _, tc := range cases {
+			args := slices.Concat(command, tc.flags)
+
+			t.Run(strings.Join(args, " "), func(t *testing.T) {
+				t.Parallel()
+
+				_, level := runCLIWithLevel(testOpts(args, afero.NewMemMapFs()))
+				assert.Equal(t, tc.want, level)
+			})
+		}
+	}
+}
+
+// TestCombinedShortVerboseRefused asserts that -vv is refused (issue #125):
+// single-letter flags do not combine, so the -v help text says -v -v.
+func TestCombinedShortVerboseRefused(t *testing.T) {
+	t.Parallel()
+
+	for _, command := range commandsTakingVerbose() {
+		args := slices.Concat(command, []string{"-vv"})
+
+		t.Run(strings.Join(args, " "), func(t *testing.T) {
+			t.Parallel()
+
+			opts := testOpts(args, afero.NewMemMapFs())
+			exitCode, level := runCLIWithLevel(opts)
+
+			assert.Equal(t, 1, exitCode)
+			assert.Contains(t, testStderr(t, opts), "flag provided but not defined: -vv")
+			assert.Equal(t, log.InfoLevel, level)
+		})
+	}
+}
+
+// TestShortAndLongVerboseRefused asserts that -v and --verbose given together
+// are refused (issue #125): urfave/cli v2 refuses a flag given under two of its
+// names, and one flag with an alias keeps help and parsing simple.
+func TestShortAndLongVerboseRefused(t *testing.T) {
+	t.Parallel()
+
+	for _, command := range commandsTakingVerbose() {
+		args := slices.Concat(command, []string{"-v", testFlagVerbose})
+
+		t.Run(strings.Join(args, " "), func(t *testing.T) {
+			t.Parallel()
+
+			opts := testOpts(args, afero.NewMemMapFs())
+			exitCode, level := runCLIWithLevel(opts)
+
+			assert.Equal(t, 1, exitCode)
+			assert.Contains(t, testStderr(t, opts), "Cannot use two forms of the same flag")
+			assert.Equal(t, log.InfoLevel, level)
+		})
+	}
+}
+
 func TestHelpCommand(t *testing.T) {
 	t.Parallel()
 
@@ -405,7 +504,10 @@ func TestGenerateExcludesDotfilesByDefault(t *testing.T) {
 	assert.True(t, exists)
 
 	// Verify manifest only has 1 file (the non-dotfile)
-	manifest, err := mfer.NewManifestFromFile(fs, testMF)
+	manifest, err := mfer.NewManifestFromFile(&mfer.ManifestFromFileOptions{
+		Path: testMF,
+		Fs:   fs,
+	})
 	require.NoError(t, err)
 	assert.Len(t, manifest.Files(), 1)
 	assert.Equal(t, "file1.txt", manifest.Files()[0].GetPath())
@@ -429,7 +531,10 @@ func TestGenerateWithIncludeDotfiles(t *testing.T) {
 	require.Equal(t, 0, exitCode)
 
 	// Verify manifest has 2 files (including dotfile)
-	manifest, err := mfer.NewManifestFromFile(fs, testMF)
+	manifest, err := mfer.NewManifestFromFile(&mfer.ManifestFromFileOptions{
+		Path: testMF,
+		Fs:   fs,
+	})
 	require.NoError(t, err)
 	assert.Len(t, manifest.Files(), 2)
 }

internal/cli/errmsg_test.go

@@ -61,7 +61,11 @@ func unsignedChecker(t *testing.T) *mfer.Checker {
 	require.NoError(t, s.ToManifest(context.Background(), &buf, nil))
 	require.NoError(t, afero.WriteFile(fs, "/d/index.mf", buf.Bytes(), 0o644))
 
-	chk, err := mfer.NewChecker("/d/index.mf", "/d", fs)
+	chk, err := mfer.NewChecker(&mfer.CheckerOptions{
+		ManifestPath: "/d/index.mf",
+		BasePath:     "/d",
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 	require.False(t, chk.IsSigned())
 
@@ -167,7 +171,11 @@ func signedChecker(t *testing.T) *mfer.Checker {
 	fs := afero.NewMemMapFs()
 	require.NoError(t, afero.WriteFile(fs, "/index.mf", buf.Bytes(), 0o644))
 
-	chk, err := mfer.NewChecker("/index.mf", "/", fs)
+	chk, err := mfer.NewChecker(&mfer.CheckerOptions{
+		ManifestPath: "/index.mf",
+		BasePath:     "/",
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 	require.True(t, chk.IsSigned())
 

internal/cli/freshen.go

@@ -445,7 +445,10 @@ func (mfa *CLIApp) loadExistingEntries(
 	log.Infof("loading manifest from %s", manifestPath)
 
 	// Load existing manifest
-	manifest, err := mfer.NewManifestFromFile(mfa.Fs, manifestPath)
+	manifest, err := mfer.NewManifestFromFile(&mfer.ManifestFromFileOptions{
+		Path: manifestPath,
+		Fs:   mfa.Fs,
+	})
 	if err != nil {
 		return nil, fmt.Errorf("failed to load manifest: %w", err)
 	}

internal/cli/freshen_test.go

@@ -58,7 +58,10 @@ func TestFreshenUnchanged(t *testing.T) {
 	setupFreshenDir(t, fs)
 
 	// Parse manifest to verify
-	manifest, err := mfer.NewManifestFromFile(fs, "/testdir/.index.mf")
+	manifest, err := mfer.NewManifestFromFile(&mfer.ManifestFromFileOptions{
+		Path: "/testdir/.index.mf",
+		Fs:   fs,
+	})
 	require.NoError(t, err)
 	assert.Len(t, manifest.Files(), 2)
 }
@@ -70,7 +73,10 @@ func TestFreshenWithChanges(t *testing.T) {
 	setupFreshenDir(t, fs)
 
 	// Verify initial manifest has 2 files
-	manifest, err := mfer.NewManifestFromFile(fs, "/testdir/.index.mf")
+	manifest, err := mfer.NewManifestFromFile(&mfer.ManifestFromFileOptions{
+		Path: "/testdir/.index.mf",
+		Fs:   fs,
+	})
 	require.NoError(t, err)
 	assert.Len(t, manifest.Files(), 2)
 

internal/cli/mfer.go

@@ -17,6 +17,7 @@ import (
 const (
 	cmdGenerate = "generate"
 	cmdCheck    = "check"
+	cmdFreshen  = "freshen"
 	cmdExport   = "export"
 	cmdFetch    = "fetch"
 	cmdVersion  = "version"
@@ -118,7 +119,7 @@ func commonFlags() []cli.Flag {
 		&cli.BoolFlag{
 			Name:    "verbose",
 			Aliases: []string{"v"},
-			Usage:   "Increase verbosity (-v for verbose, -vv for debug)",
+			Usage:   "Increase verbosity (-v for verbose, -v -v for debug)",
 			Count:   new(int),
 		},
 		&cli.BoolFlag{
@@ -131,9 +132,10 @@ func commonFlags() []cli.Flag {
 
 func (mfa *CLIApp) generateCommand() *cli.Command {
 	return &cli.Command{
-		Name:    cmdGenerate,
-		Aliases: []string{"gen"},
-		Usage:   "Generate manifest file",
+		Name:      cmdGenerate,
+		Aliases:   []string{"gen"},
+		Usage:     "Generate manifest file",
+		ArgsUsage: "[path ...]",
 		Action: func(c *cli.Context) error {
 			mfa.setVerbosity(c)
 			mfa.printBanner()
@@ -227,7 +229,7 @@ func (mfa *CLIApp) checkCommand() *cli.Command {
 
 func (mfa *CLIApp) freshenCommand() *cli.Command {
 	return &cli.Command{
-		Name:      "freshen",
+		Name:      cmdFreshen,
 		Usage:     "Update manifest with changed, new, and removed files",
 		ArgsUsage: manifestArgsUsage,
 		Action: func(c *cli.Context) error {
@@ -324,8 +326,9 @@ func (mfa *CLIApp) listCommand() *cli.Command {
 
 func (mfa *CLIApp) fetchCommand() *cli.Command {
 	return &cli.Command{
-		Name:  cmdFetch,
-		Usage: "fetch manifest and referenced files",
+		Name:      cmdFetch,
+		Usage:     "fetch manifest and referenced files",
+		ArgsUsage: "URL",
 		Action: func(c *cli.Context) error {
 			mfa.setVerbosity(c)
 			mfa.printBanner()

mfer/builder.go

@@ -35,7 +35,8 @@ var (
 	errPathDotDot       = errors.New("contains '..' segment")
 	errSizeMismatch     = errors.New("size mismatch")
 	errNegativeSize     = errors.New("size cannot be negative")
-	errEmptyHash        = errors.New("hash cannot be nil or empty")
+	errHashNotMultihash = errors.New("hash is not a valid multihash")
+	errHashTooShort     = errors.New("hash digest is too short")
 )
 
 // ValidatePath checks that a file path conforms to manifest path invariants:
@@ -228,7 +229,8 @@ func (b *Builder) FileCount() int {
 
 // AddFileWithHash adds a file entry with a pre-computed hash.
 // This is useful when the hash is already known (e.g., from an existing manifest).
-// Returns an error if path is empty, size is negative, or hash is nil/empty.
+// Returns an error if path is invalid, size is negative, or hash is not a
+// multihash with a digest of at least 32 bytes, as long as SHA-256's.
 func (b *Builder) AddFileWithHash(
 	path RelFilePath,
 	size FileSize,
@@ -244,8 +246,19 @@ func (b *Builder) AddFileWithHash(
 		return errNegativeSize
 	}
 
-	if len(hash) == 0 {
-		return errEmptyHash
+	decoded, err := multihash.Decode(hash)
+	if err != nil {
+		return fmt.Errorf("%w: %w", errHashNotMultihash, err)
+	}
+
+	// The reader's limit on decoding cost (maxDecodedGrowth) assumes every
+	// hash is at least as long as a SHA-256 multihash, so a manifest of
+	// shorter ones could fail to load.
+	if len(decoded.Digest) < sha256.Size {
+		return fmt.Errorf(
+			"%w: %d bytes, at least %d needed",
+			errHashTooShort, len(decoded.Digest), sha256.Size,
+		)
 	}
 
 	entry := &MFFilePath{

mfer/builder_test.go

@@ -4,11 +4,15 @@ package mfer
 import (
 	"bytes"
 	"context"
+	"crypto/sha256"
 	"fmt"
+	"path/filepath"
 	"strings"
 	"testing"
 	"time"
 
+	"github.com/multiformats/go-multihash"
+	"github.com/spf13/afero"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -42,9 +46,10 @@ func TestBuilderAddFileWithHash(t *testing.T) {
 	t.Parallel()
 
 	b := NewBuilder()
-	hash := make([]byte, 34) // SHA256 multihash is 34 bytes
+	hash, err := multihash.Encode(make([]byte, sha256.Size), multihash.SHA2_256)
+	require.NoError(t, err)
 
-	err := b.AddFileWithHash("test.txt", 100, ModTime(time.Now()), hash)
+	err = b.AddFileWithHash("test.txt", 100, ModTime(time.Now()), hash)
 	require.NoError(t, err)
 	assert.Equal(t, 1, b.FileCount())
 }
@@ -52,12 +57,14 @@ func TestBuilderAddFileWithHash(t *testing.T) {
 func TestBuilderAddFileWithHashValidation(t *testing.T) {
 	t.Parallel()
 
+	sha256Hash, err := multihash.Encode(make([]byte, sha256.Size), multihash.SHA2_256)
+	require.NoError(t, err)
+
 	t.Run("empty path", func(t *testing.T) {
 		t.Parallel()
 
 		b := NewBuilder()
-		hash := make([]byte, 34)
-		err := b.AddFileWithHash("", 100, ModTime(time.Now()), hash)
+		err := b.AddFileWithHash("", 100, ModTime(time.Now()), sha256Hash)
 		require.Error(t, err)
 		assert.Contains(t, err.Error(), "path")
 	})
@@ -66,41 +73,53 @@ func TestBuilderAddFileWithHashValidation(t *testing.T) {
 		t.Parallel()
 
 		b := NewBuilder()
-		hash := make([]byte, 34)
-		err := b.AddFileWithHash("test.txt", -1, ModTime(time.Now()), hash)
+		err := b.AddFileWithHash("test.txt", -1, ModTime(time.Now()), sha256Hash)
 		require.Error(t, err)
 		assert.Contains(t, err.Error(), "size")
 	})
 
-	t.Run("nil hash", func(t *testing.T) {
-		t.Parallel()
-
-		b := NewBuilder()
-		err := b.AddFileWithHash("test.txt", 100, ModTime(time.Now()), nil)
-		require.Error(t, err)
-		assert.Contains(t, err.Error(), "hash")
-	})
-
-	t.Run("empty hash", func(t *testing.T) {
-		t.Parallel()
-
-		b := NewBuilder()
-		err := b.AddFileWithHash("test.txt", 100, ModTime(time.Now()), []byte{})
-		require.Error(t, err)
-		assert.Contains(t, err.Error(), "hash")
-	})
-
 	t.Run("valid inputs", func(t *testing.T) {
 		t.Parallel()
 
 		b := NewBuilder()
-		hash := make([]byte, 34)
-		err := b.AddFileWithHash("test.txt", 100, ModTime(time.Now()), hash)
+		err := b.AddFileWithHash("test.txt", 100, ModTime(time.Now()), sha256Hash)
 		require.NoError(t, err)
 		assert.Equal(t, 1, b.FileCount())
 	})
 }
 
+func TestBuilderAddFileWithHashRejectsBadHashes(t *testing.T) {
+	t.Parallel()
+
+	sha1Hash, err := multihash.Encode(make([]byte, 20), multihash.SHA1)
+	require.NoError(t, err)
+
+	tests := []struct {
+		name string
+		hash Multihash
+		want error
+	}{
+		{"nil hash", nil, errHashNotMultihash},
+		{"empty hash", []byte{}, errHashNotMultihash},
+		{"one-byte hash", []byte{0x12}, errHashNotMultihash},
+		// A SHA-256 code and 32-byte length, then only two bytes of digest.
+		{"malformed multihash", []byte{0x12, 0x20, 0x01, 0x02}, errHashNotMultihash},
+		// A valid multihash, but its 20-byte SHA-1 digest is too short.
+		{"SHA-1 multihash", sha1Hash, errHashTooShort},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			b := NewBuilder()
+			err := b.AddFileWithHash("test.txt", 100, ModTime(time.Now()), tt.hash)
+			require.ErrorIs(t, err, tt.want)
+			assert.Equal(t, 0, b.FileCount())
+		})
+	}
+}
+
 func TestBuilderBuild(t *testing.T) {
 	t.Parallel()
 
@@ -356,7 +375,8 @@ func TestBuilderBuildRoundTrip(t *testing.T) {
 func TestBuilderBuildRoundTripLargeManifest(t *testing.T) {
 	t.Parallel()
 
-	hash := make([]byte, 34) // multihash: 2-byte prefix + 32-byte SHA-256
+	hash, err := multihash.Encode(make([]byte, sha256.Size), multihash.SHA2_256)
+	require.NoError(t, err)
 
 	b := NewBuilder()
 
@@ -397,6 +417,29 @@ func TestNewManifestFromReaderTruncated(t *testing.T) {
 	assert.Error(t, err)
 }
 
+func TestNewManifestFromFileRequiresPath(t *testing.T) {
+	t.Parallel()
+
+	_, err := NewManifestFromFile(nil)
+	require.ErrorIs(t, err, errManifestPathEmpty)
+
+	_, err = NewManifestFromFile(&ManifestFromFileOptions{Fs: afero.NewMemMapFs()})
+	require.ErrorIs(t, err, errManifestPathEmpty)
+}
+
+func TestNewManifestFromFileNilFsUsesOsFs(t *testing.T) {
+	t.Parallel()
+
+	path := filepath.Join(t.TempDir(), "index.mf")
+	createTestManifest(t, afero.NewOsFs(), path, map[string][]byte{
+		testFileName: []byte("hello"),
+	})
+
+	m, err := NewManifestFromFile(&ManifestFromFileOptions{Path: path})
+	require.NoError(t, err)
+	assert.Len(t, m.Files(), 1)
+}
+
 func TestManifestString(t *testing.T) {
 	t.Parallel()
 

mfer/checker.go

@@ -14,7 +14,11 @@ import (
 	"github.com/spf13/afero"
 )
 
-var errNoSigningPubKey = errors.New("manifest has no signing public key")
+var (
+	errNoSigningPubKey   = errors.New("manifest has no signing public key")
+	errManifestPathEmpty = errors.New("manifest path cannot be empty")
+	errBasePathEmpty     = errors.New("base path cannot be empty")
+)
 
 // Result represents the outcome of checking a single file.
 type Result struct {
@@ -82,20 +86,42 @@ type Checker struct {
 	signingPubKey []byte
 }
 
-// NewChecker creates a new Checker for the given manifest, base path, and filesystem.
-// The basePath is the directory relative to which manifest paths are resolved.
-// If fs is nil, the real filesystem (OsFs) is used.
-func NewChecker(manifestPath string, basePath string, fs afero.Fs) (*Checker, error) {
+// CheckerOptions configures a Checker.
+type CheckerOptions struct {
+	// ManifestPath is the manifest file to check against (required).
+	ManifestPath string
+	// BasePath is the directory relative to which manifest paths are
+	// resolved (required).
+	BasePath string
+	// Fs is the filesystem to use, defaults to OsFs if nil.
+	Fs afero.Fs
+}
+
+// NewChecker creates a new Checker with the given options. It returns an
+// error if opts is nil or either path is empty.
+func NewChecker(opts *CheckerOptions) (*Checker, error) {
+	if opts == nil || opts.ManifestPath == "" {
+		return nil, errManifestPathEmpty
+	}
+
+	if opts.BasePath == "" {
+		return nil, errBasePathEmpty
+	}
+
+	fs := opts.Fs
 	if fs == nil {
 		fs = afero.NewOsFs()
 	}
 
-	m, err := NewManifestFromFile(fs, manifestPath)
+	m, err := NewManifestFromFile(&ManifestFromFileOptions{
+		Path: opts.ManifestPath,
+		Fs:   fs,
+	})
 	if err != nil {
 		return nil, err
 	}
 
-	abs, err := filepath.Abs(basePath)
+	abs, err := filepath.Abs(opts.BasePath)
 	if err != nil {
 		return nil, err
 	}
@@ -108,7 +134,7 @@ func NewChecker(manifestPath string, basePath string, fs afero.Fs) (*Checker, er
 	}
 
 	// Compute manifest's relative path from basePath for exclusion in FindExtraFiles
-	absManifest, err := filepath.Abs(manifestPath)
+	absManifest, err := filepath.Abs(opts.ManifestPath)
 	if err != nil {
 		return nil, err
 	}

mfer/checker_test.go

@@ -5,6 +5,8 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"os"
+	"path/filepath"
 	"testing"
 	"time"
 
@@ -14,9 +16,11 @@ import (
 )
 
 const (
-	testFile1      = "file1.txt"
-	testFile2      = "file2.txt"
-	testExistsFile = "exists.txt"
+	testFile1        = "file1.txt"
+	testFile2        = "file2.txt"
+	testExistsFile   = "exists.txt"
+	testManifestPath = "/manifest.mf"
+	testDataDir      = "/data"
 )
 
 func TestStatusString(t *testing.T) {
@@ -66,15 +70,13 @@ func createTestManifest(
 }
 
 // createFilesOnDisk creates the given files on the filesystem under
-// /data.
+// testDataDir.
 func createFilesOnDisk(t *testing.T, fs afero.Fs, files map[string][]byte) {
 	t.Helper()
 
-	basePath := "/data"
-
 	for path, content := range files {
-		fullPath := basePath + "/" + path
-		require.NoError(t, fs.MkdirAll(basePath, 0o755))
+		fullPath := testDataDir + "/" + path
+		require.NoError(t, fs.MkdirAll(testDataDir, 0o755))
 		require.NoError(t, afero.WriteFile(fs, fullPath, content, 0o644))
 	}
 }
@@ -90,9 +92,13 @@ func TestNewChecker(t *testing.T) {
 			testFile1: []byte("hello"),
 			testFile2: []byte("world"),
 		}
-		createTestManifest(t, fs, "/manifest.mf", files)
+		createTestManifest(t, fs, testManifestPath, files)
 
-		chk, err := NewChecker("/manifest.mf", "/", fs)
+		chk, err := NewChecker(&CheckerOptions{
+			ManifestPath: testManifestPath,
+			BasePath:     "/",
+			Fs:           fs,
+		})
 		require.NoError(t, err)
 		assert.NotNil(t, chk)
 		assert.Equal(t, FileCount(2), chk.FileCount())
@@ -102,7 +108,11 @@ func TestNewChecker(t *testing.T) {
 		t.Parallel()
 
 		fs := afero.NewMemMapFs()
-		_, err := NewChecker("/nonexistent.mf", "/", fs)
+		_, err := NewChecker(&CheckerOptions{
+			ManifestPath: "/nonexistent.mf",
+			BasePath:     "/",
+			Fs:           fs,
+		})
 		assert.Error(t, err)
 	})
 
@@ -111,11 +121,73 @@ func TestNewChecker(t *testing.T) {
 
 		fs := afero.NewMemMapFs()
 		require.NoError(t, afero.WriteFile(fs, "/bad.mf", []byte("not a manifest"), 0o644))
-		_, err := NewChecker("/bad.mf", "/", fs)
+		_, err := NewChecker(&CheckerOptions{
+			ManifestPath: "/bad.mf",
+			BasePath:     "/",
+			Fs:           fs,
+		})
 		assert.Error(t, err)
 	})
 }
 
+func TestNewCheckerRequiredPaths(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name string
+		opts *CheckerOptions
+		want string
+		is   error
+	}{
+		{
+			name: "nil options",
+			opts: nil,
+			want: "manifest path cannot be empty",
+			is:   errManifestPathEmpty,
+		},
+		{
+			name: "empty manifest path",
+			opts: &CheckerOptions{BasePath: testDataDir},
+			want: "manifest path cannot be empty",
+			is:   errManifestPathEmpty,
+		},
+		{
+			name: "empty base path",
+			opts: &CheckerOptions{ManifestPath: testManifestPath},
+			want: "base path cannot be empty",
+			is:   errBasePathEmpty,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			chk, err := NewChecker(tc.opts)
+			require.ErrorIs(t, err, tc.is)
+			require.EqualError(t, err, tc.want)
+			assert.Nil(t, chk)
+		})
+	}
+}
+
+func TestNewCheckerNilFsUsesOsFs(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	manifestPath := filepath.Join(dir, "index.mf")
+	content := []byte("hello")
+	createTestManifest(t, afero.NewOsFs(), manifestPath, map[string][]byte{
+		testFile1: content,
+	})
+	require.NoError(t, os.WriteFile(filepath.Join(dir, testFile1), content, 0o600))
+
+	chk, err := NewChecker(&CheckerOptions{ManifestPath: manifestPath, BasePath: dir})
+	require.NoError(t, err)
+
+	results := make(chan Result, 1)
+	require.NoError(t, chk.Check(context.Background(), results, nil))
+	assert.Equal(t, StatusOK, (<-results).Status)
+}
+
 func TestCheckerFileCountAndTotalBytes(t *testing.T) {
 	t.Parallel()
 
@@ -125,9 +197,13 @@ func TestCheckerFileCountAndTotalBytes(t *testing.T) {
 		"medium.txt": []byte("hello world"),
 		"large.txt":  bytes.Repeat([]byte("x"), 1000),
 	}
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 
-	chk, err := NewChecker("/manifest.mf", "/", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     "/",
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	assert.Equal(t, FileCount(3), chk.FileCount())
@@ -142,10 +218,14 @@ func TestCheckAllFilesOK(t *testing.T) {
 		testFile1: []byte("content one"),
 		testFile2: []byte("content two"),
 	}
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 	createFilesOnDisk(t, fs, files)
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 10)
@@ -172,13 +252,17 @@ func TestCheckMissingFile(t *testing.T) {
 		testExistsFile: []byte("I exist"),
 		"missing.txt":  []byte("I don't exist on disk"),
 	}
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 	// Only create one file
 	createFilesOnDisk(t, fs, map[string][]byte{
 		testExistsFile: []byte("I exist"),
 	})
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 10)
@@ -211,13 +295,17 @@ func TestCheckSizeMismatch(t *testing.T) {
 	files := map[string][]byte{
 		testFileName: []byte("original content"),
 	}
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 	// Create file with different size
 	createFilesOnDisk(t, fs, map[string][]byte{
 		testFileName: []byte("short"),
 	})
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 10)
@@ -237,7 +325,7 @@ func TestCheckHashMismatch(t *testing.T) {
 	files := map[string][]byte{
 		testFileName: originalContent,
 	}
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 	// Create file with same size but different content
 	differentContent := []byte("different contnt") // same length (16 bytes) but different
 	require.Len(t, differentContent, len(originalContent), "test requires same length")
@@ -245,7 +333,11 @@ func TestCheckHashMismatch(t *testing.T) {
 		testFileName: differentContent,
 	})
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 10)
@@ -265,10 +357,14 @@ func TestCheckWithProgress(t *testing.T) {
 		testFile1: bytes.Repeat([]byte("a"), 100),
 		testFile2: bytes.Repeat([]byte("b"), 200),
 	}
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 	createFilesOnDisk(t, fs, files)
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 10)
@@ -305,10 +401,14 @@ func TestCheckContextCancellation(t *testing.T) {
 		files[string(rune('a'+i%26))+".txt"] = bytes.Repeat([]byte("x"), 1000)
 	}
 
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 	createFilesOnDisk(t, fs, files)
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	ctx, cancel := context.WithCancel(context.Background())
@@ -327,7 +427,7 @@ func TestFindExtraFiles(t *testing.T) {
 	manifestFiles := map[string][]byte{
 		testFile1: []byte("in manifest"),
 	}
-	createTestManifest(t, fs, "/manifest.mf", manifestFiles)
+	createTestManifest(t, fs, testManifestPath, manifestFiles)
 
 	// Disk has file1 and file2
 	createFilesOnDisk(t, fs, map[string][]byte{
@@ -335,7 +435,11 @@ func TestFindExtraFiles(t *testing.T) {
 		testFile2: []byte("extra file"),
 	})
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 10)
@@ -368,10 +472,14 @@ func TestFindExtraFilesSkipsManifestAndDotfiles(t *testing.T) {
 	require.NoError(t, afero.WriteFile(fs, "/data/.hidden", []byte("hidden"), 0o644))
 	require.NoError(t, afero.WriteFile(fs, "/data/.config/settings", []byte("cfg"), 0o644))
 	// Create a real extra file
-	require.NoError(t, fs.MkdirAll("/data", 0o755))
+	require.NoError(t, fs.MkdirAll(testDataDir, 0o755))
 	require.NoError(t, afero.WriteFile(fs, "/data/extra.txt", []byte("extra"), 0o644))
 
-	chk, err := NewChecker("/data/.index.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: "/data/.index.mf",
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 10)
@@ -400,10 +508,14 @@ func TestFindExtraFilesContextCancellation(t *testing.T) {
 
 	fs := afero.NewMemMapFs()
 	files := map[string][]byte{testFileName: []byte("data")}
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 	createFilesOnDisk(t, fs, files)
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	ctx, cancel := context.WithCancel(context.Background())
@@ -419,10 +531,14 @@ func TestCheckNilChannels(t *testing.T) {
 
 	fs := afero.NewMemMapFs()
 	files := map[string][]byte{testFileName: []byte("data")}
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 	createFilesOnDisk(t, fs, files)
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	// Should not panic with nil channels
@@ -435,10 +551,14 @@ func TestFindExtraFilesNilChannel(t *testing.T) {
 
 	fs := afero.NewMemMapFs()
 	files := map[string][]byte{testFileName: []byte("data")}
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 	createFilesOnDisk(t, fs, files)
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	// Should not panic with nil channel
@@ -455,7 +575,7 @@ func TestCheckSubdirectories(t *testing.T) {
 		"dir1/dir2/file2.txt":     []byte("content2"),
 		"dir1/dir2/dir3/deep.txt": []byte("deep content"),
 	}
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 
 	// Create files with full directory structure
 	for path, content := range files {
@@ -465,7 +585,11 @@ func TestCheckSubdirectories(t *testing.T) {
 		require.NoError(t, afero.WriteFile(fs, fullPath, content, 0o644))
 	}
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 10)
@@ -493,13 +617,17 @@ func TestCheckMissingFileDetectedWithoutFallback(t *testing.T) {
 		testExistsFile: []byte("here"),
 		"missing.txt":  []byte("not on disk"),
 	}
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 	// Only create one file on disk
 	createFilesOnDisk(t, fs, map[string][]byte{
 		testExistsFile: []byte("here"),
 	})
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 10)
@@ -537,7 +665,11 @@ func TestFindExtraFilesSkipsDotfiles(t *testing.T) {
 	require.NoError(t,
 		afero.WriteFile(fs, "/data/.git/config", []byte("git config"), 0o644))
 
-	chk, err := NewChecker("/data/.index.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: "/data/.index.mf",
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 10)
@@ -566,7 +698,11 @@ func TestFindExtraFilesSkipsManifestFile(t *testing.T) {
 	createTestManifest(t, fs, "/data/index.mf", files)
 	createFilesOnDisk(t, fs, files)
 
-	chk, err := NewChecker("/data/index.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: "/data/index.mf",
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 10)
@@ -587,9 +723,13 @@ func TestCheckEmptyManifest(t *testing.T) {
 
 	fs := afero.NewMemMapFs()
 	// Create manifest with no files
-	createTestManifest(t, fs, "/manifest.mf", map[string][]byte{})
+	createTestManifest(t, fs, testManifestPath, map[string][]byte{})
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	assert.Equal(t, FileCount(0), chk.FileCount())
@@ -621,10 +761,14 @@ func TestCheckProgressRateLimited(t *testing.T) {
 		files[name] = []byte("content")
 	}
 
-	createTestManifest(t, fs, "/manifest.mf", files)
+	createTestManifest(t, fs, testManifestPath, files)
 	createFilesOnDisk(t, fs, files)
 
-	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	chk, err := NewChecker(&CheckerOptions{
+		ManifestPath: testManifestPath,
+		BasePath:     testDataDir,
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 
 	results := make(chan Result, 200)

mfer/constants.go

@@ -17,4 +17,28 @@ const (
 
 	// uuidLength is the length in bytes of a binary UUID.
 	uuidLength = 16
+
+	// Numbers in mf.proto of MFFile.files and of the MFFilePath fields
+	// that decoding sets aside a fixed amount of memory for.
+	filesFieldNumber    = 101
+	hashesFieldNumber   = 3
+	mimeTypeFieldNumber = 301
+	mtimeFieldNumber    = 302
+	ctimeFieldNumber    = 303
+
+	// Bytes decoding sets aside for each file entry, hash, timestamp and
+	// MIME type, however short its encoding. checkDecodedSize refuses an
+	// inner message for which these add up to more than maxDecodedGrowth
+	// times its size.
+	decodedFileEntrySize = 160
+	decodedHashSize      = 112
+	decodedTimestampSize = 64
+	decodedMIMETypeSize  = 16
+
+	// Each file entry mfer writes holds a path of at least one byte, a
+	// multihash at least as long as SHA-256's 34 bytes (AddFileWithHash
+	// refuses shorter ones) and a modification time: at least 47 bytes,
+	// counted at 336. So its manifests add up to at most about 7.15 times
+	// their size, and this limit is about 12% above that.
+	maxDecodedGrowth = 8
 )

mfer/deserialize.go

@@ -11,6 +11,7 @@ import (
 	"github.com/google/uuid"
 	"github.com/klauspost/compress/zstd"
 	"github.com/spf13/afero"
+	"google.golang.org/protobuf/encoding/protowire"
 	"google.golang.org/protobuf/proto"
 	"sneak.berlin/go/mfer/internal/bork"
 	"sneak.berlin/go/mfer/internal/log"
@@ -27,6 +28,8 @@ var (
 	errUUIDMismatch         = errors.New("outer and inner UUID mismatch")
 	errInvalidFileFormat    = errors.New("invalid file format")
 	errInvalidManifestPath  = errors.New("manifest contains invalid path")
+	errDecodedTooLarge      = errors.New(
+		"manifest would take too much memory to decode")
 )
 
 // validateUUID checks that the byte slice is a valid UUID (16 bytes, parseable).
@@ -154,6 +157,85 @@ func (m *manifest) decompressInner() ([]byte, error) {
 	return dat, nil
 }
 
+// checkDecodedSize refuses an encoded inner message whose file entries,
+// hashes, timestamps and MIME types would take more than maxDecodedGrowth
+// times its size to decode. Decoding sets aside a fixed amount for each,
+// however short its encoding, so a message of empty ones would take about
+// 50 times its size.
+func checkDecodedSize(inner []byte) error {
+	limit := maxDecodedGrowth * int64(len(inner))
+
+	var decoded int64
+
+	add := func(size int64) error {
+		decoded += size
+		if decoded > limit {
+			return errDecodedTooLarge
+		}
+
+		return nil
+	}
+
+	return forEachBytesField(inner, func(num protowire.Number, entry []byte) error {
+		if num != filesFieldNumber {
+			return nil
+		}
+
+		err := add(decodedFileEntrySize)
+		if err != nil {
+			return err
+		}
+
+		return forEachBytesField(entry, func(num protowire.Number, _ []byte) error {
+			if num == hashesFieldNumber {
+				return add(decodedHashSize)
+			}
+
+			if num == mtimeFieldNumber || num == ctimeFieldNumber {
+				return add(decodedTimestampSize)
+			}
+
+			if num == mimeTypeFieldNumber {
+				return add(decodedMIMETypeSize)
+			}
+
+			return nil
+		})
+	})
+}
+
+// forEachBytesField calls fn with the number and value of each
+// length-delimited field in the encoded message msg, and fails if msg is
+// malformed.
+func forEachBytesField(
+	msg []byte, fn func(num protowire.Number, value []byte) error,
+) error {
+	for len(msg) > 0 {
+		num, wireType, tagLen := protowire.ConsumeTag(msg)
+		if tagLen < 0 {
+			return protowire.ParseError(tagLen)
+		}
+
+		valueLen := protowire.ConsumeFieldValue(num, wireType, msg[tagLen:])
+		if valueLen < 0 {
+			return protowire.ParseError(valueLen)
+		}
+
+		if wireType == protowire.BytesType {
+			value, _ := protowire.ConsumeBytes(msg[tagLen:])
+
+			err := fn(num, value)
+			if err != nil {
+				return err
+			}
+		}
+
+		msg = msg[tagLen+valueLen:]
+	}
+
+	return nil
+}
+
 func (m *manifest) deserializeInner() error {
 	err := m.validateOuterHeader()
 	if err != nil {
@@ -177,10 +259,16 @@ func (m *manifest) deserializeInner() error {
 		return bork.ErrFileTruncated
 	}
 
+	err = checkDecodedSize(dat)
+	if err != nil {
+		return fmt.Errorf("deserialize: unmarshal inner: %w", err)
+	}
+
 	// Deserialize inner message
 	m.pbInner = new(MFFile)
 
-	err = proto.Unmarshal(dat, m.pbInner)
+	// Unknown fields would cost memory; mfer never writes a loaded manifest out.
+	err = proto.UnmarshalOptions{DiscardUnknown: true}.Unmarshal(dat, m.pbInner)
 	if err != nil {
 		return fmt.Errorf("deserialize: unmarshal inner: %w", err)
 	}
@@ -249,7 +337,8 @@ func NewManifestFromReader(input io.Reader) (*manifest, error) {
 	// deserialize outer:
 	m.pbOuter = new(MFFileOuter)
 
-	err = proto.Unmarshal(dat, m.pbOuter)
+	// Unknown fields would cost memory; mfer never writes a loaded manifest out.
+	err = proto.UnmarshalOptions{DiscardUnknown: true}.Unmarshal(dat, m.pbOuter)
 	if err != nil {
 		return nil, err
 	}
@@ -263,16 +352,29 @@ func NewManifestFromReader(input io.Reader) (*manifest, error) {
 	return m, nil
 }
 
-// NewManifestFromFile reads a manifest from a file path using the given filesystem.
-// If fs is nil, the real filesystem (OsFs) is used.
+// ManifestFromFileOptions configures NewManifestFromFile.
+type ManifestFromFileOptions struct {
+	// Path is the manifest file to read (required).
+	Path string
+	// Fs is the filesystem to use, defaults to OsFs if nil.
+	Fs afero.Fs
+}
+
+// NewManifestFromFile reads a manifest from a file. It returns an error if
+// opts is nil or its path is empty.
 //
 //nolint:revive // unexported-return: exporting manifest is owner question 13
-func NewManifestFromFile(fs afero.Fs, path string) (*manifest, error) {
+func NewManifestFromFile(opts *ManifestFromFileOptions) (*manifest, error) {
+	if opts == nil || opts.Path == "" {
+		return nil, errManifestPathEmpty
+	}
+
+	fs := opts.Fs
 	if fs == nil {
 		fs = afero.NewOsFs()
 	}
 
-	f, err := fs.Open(path)
+	f, err := fs.Open(opts.Path)
 	if err != nil {
 		return nil, err
 	}

mfer/deserialize_fuzz_test.go

@@ -54,9 +54,15 @@ func FuzzNewManifestFromReader(f *testing.F) {
 		}
 
 		// It also keeps a few copies of its input. Buffers grow by
-		// copying, so reaching those sizes allocates a few times them in
-		// total: sixteen times the input and the decompressed data leaves
-		// room for that.
+		// copying, so reaching those sizes allocates up to about six times
+		// them in total. Decoding the decompressed data takes up to
+		// maxDecodedGrowth times its size for file entries, hashes,
+		// timestamps and MIME types, and drops fields it does not know.
+		// The strings and bytes it copies out of it, such as many one-byte
+		// values in one hash, take up to about five times more under the
+		// race detector, which pads every small copy to 16 bytes, and about
+		// half that without it. Twenty times the input and the
+		// decompressed data leaves room for all of that.
 		//
 		// The decoder also sets aside a new buffer of one to two times the
 		// window for each frame that asks for a larger window than the
@@ -71,8 +77,9 @@ func FuzzNewManifestFromReader(f *testing.F) {
 		// fails if the decoder accepts windows of twice zstdWindowSize; the
 		// seed whose two frames together exceed MaxDecompressedSize fails
 		// if the decoder decodes them in full instead of stopping at the
-		// declared size.
-		limit := 16*(uint64(len(data))+decompressed) + 24*zstdWindowSize
+		// declared size; the seeds of empty file entries and of a file
+		// entry of empty hashes fail if the parser decodes them.
+		limit := 20*(uint64(len(data))+decompressed) + 24*zstdWindowSize
 
 		allocated := after.TotalAlloc - before.TotalAlloc
 		if allocated > limit {

mfer/deserialize_path_test.go

@@ -6,10 +6,14 @@ import (
 	"context"
 	"crypto/sha256"
 	"fmt"
+	"strconv"
+	"strings"
 	"testing"
+	"time"
 
 	"github.com/google/uuid"
 	"github.com/klauspost/compress/zstd"
+	"github.com/multiformats/go-multihash"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"google.golang.org/protobuf/encoding/protowire"
@@ -114,10 +118,119 @@ func TestDeserializeRejectsInvalidEntryPaths(t *testing.T) {
 	}
 }
 
+// Entries of a path, an empty hash, an empty MIME type and empty modification
+// and change times are counted at 416 bytes each (160 + 112 + 16 + 64 + 64)
+// and take 16 bytes plus the path to encode. A 35-character path makes that
+// 51 bytes, about 8.2 times: refused, and leaving any one of the five
+// uncounted, even the MIME type, brings it under 8. A 37-character path makes
+// it 53 bytes, about 7.8 times: loaded.
+func TestDeserializeRefusesEntriesThatDecodeTooLarge(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		pathLen int
+		refused bool
+	}{
+		{35, true},
+		{37, false},
+	}
+
+	for _, tt := range tests {
+		t.Run(strconv.Itoa(tt.pathLen), func(t *testing.T) {
+			t.Parallel()
+
+			entry := protowire.AppendTag(nil, 1, protowire.BytesType) // MFFilePath.path
+			entry = protowire.AppendString(entry, strings.Repeat("a", tt.pathLen))
+			entry = protowire.AppendTag(entry, 3, protowire.BytesType) // MFFilePath.hashes
+			entry = protowire.AppendBytes(entry, nil)
+			entry = protowire.AppendTag(entry, 301, protowire.BytesType) // MFFilePath.mimeType
+			entry = protowire.AppendBytes(entry, nil)
+			entry = protowire.AppendTag(entry, 302, protowire.BytesType) // MFFilePath.mtime
+			entry = protowire.AppendBytes(entry, nil)
+			entry = protowire.AppendTag(entry, 303, protowire.BytesType) // MFFilePath.ctime
+			entry = protowire.AppendBytes(entry, nil)
+
+			id := uuid.New()
+			inner := protowire.AppendTag(nil, 102, protowire.BytesType) // MFFile.uuid
+			inner = protowire.AppendBytes(inner, id[:])
+
+			for range 1000 {
+				inner = protowire.AppendTag(inner, 101, protowire.BytesType) // MFFile.files
+				inner = protowire.AppendBytes(inner, entry)
+			}
+
+			_, err := NewManifestFromReader(bytes.NewReader(wrapInner(t, id, inner)))
+			if tt.refused {
+				require.ErrorIs(t, err, errDecodedTooLarge)
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
+}
+
+// Fields the decoder does not know are dropped, in the outer message, the inner
+// message and a file entry, so that they take no memory once loaded.
+func TestDeserializeDropsUnknownFields(t *testing.T) {
+	t.Parallel()
+
+	unknown := protowire.AppendTag(nil, 99, protowire.BytesType) // in no message
+	unknown = protowire.AppendBytes(unknown, []byte("not known"))
+
+	entry := protowire.AppendTag(nil, 1, protowire.BytesType) // MFFilePath.path
+	entry = protowire.AppendString(entry, "a")
+	entry = append(entry, unknown...)
+
+	id := uuid.New()
+	inner := protowire.AppendTag(nil, 101, protowire.BytesType) // MFFile.files
+	inner = protowire.AppendBytes(inner, entry)
+	inner = protowire.AppendTag(inner, 102, protowire.BytesType) // MFFile.uuid
+	inner = protowire.AppendBytes(inner, id[:])
+	inner = append(inner, unknown...)
+
+	data := wrapInner(t, id, inner)
+	data = append(data, unknown...) // the outer message ends the file
+
+	m, err := NewManifestFromReader(bytes.NewReader(data))
+	require.NoError(t, err)
+	require.Len(t, m.Files(), 1)
+	assert.Empty(t, m.pbOuter.ProtoReflect().GetUnknown())
+	assert.Empty(t, m.pbInner.ProtoReflect().GetUnknown())
+	assert.Empty(t, m.Files()[0].ProtoReflect().GetUnknown())
+}
+
+// Many empty files with names of at most three characters and modification
+// times at the epoch make about the densest manifest mfer writes: it takes
+// about 7 times its size to decode, and still loads. A signature would not
+// change the inner message, so none is added.
+func TestDeserializeLoadsDensestManifest(t *testing.T) {
+	t.Parallel()
+
+	hash, err := multihash.Encode(make([]byte, sha256.Size), multihash.SHA2_256)
+	require.NoError(t, err)
+
+	b := NewBuilder()
+	b.SetIncludeTimestamps(true)
+
+	const files = 10000
+	for i := range files {
+		name := RelFilePath(strconv.FormatInt(int64(i), 36))
+		require.NoError(t, b.AddFileWithHash(name, 0, ModTime(time.Unix(0, 0)), hash))
+	}
+
+	var buf bytes.Buffer
+	require.NoError(t, b.Build(context.Background(), &buf))
+
+	m, err := NewManifestFromReader(&buf)
+	require.NoError(t, err)
+	assert.Len(t, m.Files(), files)
+}
+
 func TestDeserializeValidManifestRoundTrips(t *testing.T) {
 	t.Parallel()
 
-	hash := make([]byte, 34) // multihash: 2-byte prefix + 32-byte SHA-256
+	hash, err := multihash.Encode(make([]byte, sha256.Size), multihash.SHA2_256)
+	require.NoError(t, err)
 
 	b := NewBuilder()
 	require.NoError(t, b.AddFileWithHash("dir/file.txt", 123, ModTime{}, hash))

mfer/testdata/fuzz/FuzzNewManifestFromReader/empty-file-entries

@@ -0,0 +1,2 @@
+go test fuzz v1
+[]byte("ZNAVSRFG\xa8\x06\x01\xb0\x06\x01\xb8\x06\xff\xff\xff\x03\xc2\x06 {\x16\xbdu\xa0\xa2\x11\xfcH\xef*\x1b7\r\x99\xefb\x04\x02g\n\xa9\xf3B5\xe5p\x96\x8c\x8c\xac\x0e\xca\x06\x10\x03Q\xb2\xd0\x19`F\xc1\xb1\xc0Z\xf4x\xf4g^\xba\f\xa1\x06(\xb5/\xfd\x04h\x04\x01\x00d\x01\xb2\x06\x10\x03Q\xb2\xd0\x19`F\xc1\xb1\xc0Z\xf4x\xf4g^\xaa\x06\x00\x01T\x13\x024\xce\xff\rL\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15L\x00\x00\x00\x01T\x00\x044\xfd\xff\x15M\x00\x00\x00\x01T\x00\x044\xfc\xff\x153\xea\a\xb4")

mfer/testdata/fuzz/FuzzNewManifestFromReader/file-entry-of-empty-hashes

@@ -0,0 +1,2 @@
+go test fuzz v1
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