Source file src/cmd/go/internal/modfetch/coderepo.go

Documentation: cmd/go/internal/modfetch

     1  // Copyright 2018 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package modfetch
     6  
     7  import (
     8  	"archive/zip"
     9  	"bytes"
    10  	"context"
    11  	"errors"
    12  	"fmt"
    13  	"io"
    14  	"io/fs"
    15  	"os"
    16  	"path"
    17  	"path/filepath"
    18  	"sort"
    19  	"strings"
    20  	"time"
    21  
    22  	"cmd/go/internal/gover"
    23  	"cmd/go/internal/modfetch/codehost"
    24  
    25  	"golang.org/x/mod/modfile"
    26  	"golang.org/x/mod/module"
    27  	"golang.org/x/mod/semver"
    28  	modzip "golang.org/x/mod/zip"
    29  )
    30  
    31  // A codeRepo implements modfetch.Repo using an underlying codehost.Repo.
    32  type codeRepo struct {
    33  	modPath string
    34  
    35  	// code is the repository containing this module.
    36  	code codehost.Repo
    37  	// codeRoot is the import path at the root of code.
    38  	codeRoot string
    39  	// codeDir is the directory (relative to root) at which we expect to find the module.
    40  	// If pathMajor is non-empty and codeRoot is not the full modPath,
    41  	// then we look in both codeDir and codeDir/pathMajor[1:].
    42  	codeDir string
    43  
    44  	// pathMajor is the suffix of modPath that indicates its major version,
    45  	// or the empty string if modPath is at major version 0 or 1.
    46  	//
    47  	// pathMajor is typically of the form "/vN", but possibly ".vN", or
    48  	// ".vN-unstable" for modules resolved using gopkg.in.
    49  	pathMajor string
    50  	// pathPrefix is the prefix of modPath that excludes pathMajor.
    51  	// It is used only for logging.
    52  	pathPrefix string
    53  
    54  	// pseudoMajor is the major version prefix to require when generating
    55  	// pseudo-versions for this module, derived from the module path. pseudoMajor
    56  	// is empty if the module path does not include a version suffix (that is,
    57  	// accepts either v0 or v1).
    58  	pseudoMajor string
    59  }
    60  
    61  // newCodeRepo returns a Repo that reads the source code for the module with the
    62  // given path, from the repo stored in code, with the root of the repo
    63  // containing the path given by codeRoot.
    64  func newCodeRepo(code codehost.Repo, codeRoot, path string) (Repo, error) {
    65  	if !hasPathPrefix(path, codeRoot) {
    66  		return nil, fmt.Errorf("mismatched repo: found %s for %s", codeRoot, path)
    67  	}
    68  	pathPrefix, pathMajor, ok := module.SplitPathVersion(path)
    69  	if !ok {
    70  		return nil, fmt.Errorf("invalid module path %q", path)
    71  	}
    72  	if codeRoot == path {
    73  		pathPrefix = path
    74  	}
    75  	pseudoMajor := module.PathMajorPrefix(pathMajor)
    76  
    77  	// Compute codeDir = bar, the subdirectory within the repo
    78  	// corresponding to the module root.
    79  	//
    80  	// At this point we might have:
    81  	//	path = github.com/rsc/foo/bar/v2
    82  	//	codeRoot = github.com/rsc/foo
    83  	//	pathPrefix = github.com/rsc/foo/bar
    84  	//	pathMajor = /v2
    85  	//	pseudoMajor = v2
    86  	//
    87  	// which gives
    88  	//	codeDir = bar
    89  	//
    90  	// We know that pathPrefix is a prefix of path, and codeRoot is a prefix of
    91  	// path, but codeRoot may or may not be a prefix of pathPrefix, because
    92  	// codeRoot may be the entire path (in which case codeDir should be empty).
    93  	// That occurs in two situations.
    94  	//
    95  	// One is when a go-import meta tag resolves the complete module path,
    96  	// including the pathMajor suffix:
    97  	//	path = nanomsg.org/go/mangos/v2
    98  	//	codeRoot = nanomsg.org/go/mangos/v2
    99  	//	pathPrefix = nanomsg.org/go/mangos
   100  	//	pathMajor = /v2
   101  	//	pseudoMajor = v2
   102  	//
   103  	// The other is similar: for gopkg.in only, the major version is encoded
   104  	// with a dot rather than a slash, and thus can't be in a subdirectory.
   105  	//	path = gopkg.in/yaml.v2
   106  	//	codeRoot = gopkg.in/yaml.v2
   107  	//	pathPrefix = gopkg.in/yaml
   108  	//	pathMajor = .v2
   109  	//	pseudoMajor = v2
   110  	//
   111  	codeDir := ""
   112  	if codeRoot != path {
   113  		if !hasPathPrefix(pathPrefix, codeRoot) {
   114  			return nil, fmt.Errorf("repository rooted at %s cannot contain module %s", codeRoot, path)
   115  		}
   116  		codeDir = strings.Trim(pathPrefix[len(codeRoot):], "/")
   117  	}
   118  
   119  	r := &codeRepo{
   120  		modPath:     path,
   121  		code:        code,
   122  		codeRoot:    codeRoot,
   123  		codeDir:     codeDir,
   124  		pathPrefix:  pathPrefix,
   125  		pathMajor:   pathMajor,
   126  		pseudoMajor: pseudoMajor,
   127  	}
   128  
   129  	return r, nil
   130  }
   131  
   132  func (r *codeRepo) ModulePath() string {
   133  	return r.modPath
   134  }
   135  
   136  func (r *codeRepo) CheckReuse(ctx context.Context, old *codehost.Origin) error {
   137  	return r.code.CheckReuse(ctx, old, r.codeDir)
   138  }
   139  
   140  func (r *codeRepo) Versions(ctx context.Context, prefix string) (*Versions, error) {
   141  	// Special case: gopkg.in/macaroon-bakery.v2-unstable
   142  	// does not use the v2 tags (those are for macaroon-bakery.v2).
   143  	// It has no possible tags at all.
   144  	if strings.HasPrefix(r.modPath, "gopkg.in/") && strings.HasSuffix(r.modPath, "-unstable") {
   145  		return &Versions{}, nil
   146  	}
   147  
   148  	p := prefix
   149  	if r.codeDir != "" {
   150  		p = r.codeDir + "/" + p
   151  	}
   152  	tags, err := r.code.Tags(ctx, p)
   153  	if err != nil {
   154  		return nil, &module.ModuleError{
   155  			Path: r.modPath,
   156  			Err:  err,
   157  		}
   158  	}
   159  	if tags.Origin != nil {
   160  		tags.Origin.Subdir = r.codeDir
   161  	}
   162  
   163  	var list, incompatible []string
   164  	for _, tag := range tags.List {
   165  		if !strings.HasPrefix(tag.Name, p) {
   166  			continue
   167  		}
   168  		v := tag.Name
   169  		if r.codeDir != "" {
   170  			v = v[len(r.codeDir)+1:]
   171  		}
   172  		// Note: ./codehost/codehost.go's isOriginTag knows about these conditions too.
   173  		// If these are relaxed, isOriginTag will need to be relaxed as well.
   174  		if v == "" || v != semver.Canonical(v) {
   175  			// Ignore non-canonical tags: Stat rewrites those to canonical
   176  			// pseudo-versions. Note that we compare against semver.Canonical here
   177  			// instead of module.CanonicalVersion: revToRev strips "+incompatible"
   178  			// suffixes before looking up tags, so a tag like "v2.0.0+incompatible"
   179  			// would not resolve at all. (The Go version string "v2.0.0+incompatible"
   180  			// refers to the "v2.0.0" version tag, which we handle below.)
   181  			continue
   182  		}
   183  		if module.IsPseudoVersion(v) {
   184  			// Ignore tags that look like pseudo-versions: Stat rewrites those
   185  			// unambiguously to the underlying commit, and tagToVersion drops them.
   186  			continue
   187  		}
   188  
   189  		if err := module.CheckPathMajor(v, r.pathMajor); err != nil {
   190  			if r.codeDir == "" && r.pathMajor == "" && semver.Major(v) > "v1" {
   191  				incompatible = append(incompatible, v)
   192  			}
   193  			continue
   194  		}
   195  
   196  		list = append(list, v)
   197  	}
   198  	semver.Sort(list)
   199  	semver.Sort(incompatible)
   200  
   201  	return r.appendIncompatibleVersions(ctx, tags.Origin, list, incompatible)
   202  }
   203  
   204  // appendIncompatibleVersions appends "+incompatible" versions to list if
   205  // appropriate, returning the final list.
   206  //
   207  // The incompatible list contains candidate versions without the '+incompatible'
   208  // prefix.
   209  //
   210  // Both list and incompatible must be sorted in semantic order.
   211  func (r *codeRepo) appendIncompatibleVersions(ctx context.Context, origin *codehost.Origin, list, incompatible []string) (*Versions, error) {
   212  	versions := &Versions{
   213  		Origin: origin,
   214  		List:   list,
   215  	}
   216  	if len(incompatible) == 0 || r.pathMajor != "" {
   217  		// No +incompatible versions are possible, so no need to check them.
   218  		return versions, nil
   219  	}
   220  
   221  	versionHasGoMod := func(v string) (bool, error) {
   222  		_, err := r.code.ReadFile(ctx, v, "go.mod", codehost.MaxGoMod)
   223  		if err == nil {
   224  			return true, nil
   225  		}
   226  		if !os.IsNotExist(err) {
   227  			return false, &module.ModuleError{
   228  				Path: r.modPath,
   229  				Err:  err,
   230  			}
   231  		}
   232  		return false, nil
   233  	}
   234  
   235  	if len(list) > 0 {
   236  		ok, err := versionHasGoMod(list[len(list)-1])
   237  		if err != nil {
   238  			return nil, err
   239  		}
   240  		if ok {
   241  			// The latest compatible version has a go.mod file, so assume that all
   242  			// subsequent versions do as well, and do not include any +incompatible
   243  			// versions. Even if we are wrong, the author clearly intends module
   244  			// consumers to be on the v0/v1 line instead of a higher +incompatible
   245  			// version. (See https://golang.org/issue/34189.)
   246  			//
   247  			// We know of at least two examples where this behavior is desired
   248  			// (github.com/russross/blackfriday@v2.0.0 and
   249  			// github.com/libp2p/go-libp2p@v6.0.23), and (as of 2019-10-29) have no
   250  			// concrete examples for which it is undesired.
   251  			return versions, nil
   252  		}
   253  	}
   254  
   255  	var (
   256  		lastMajor         string
   257  		lastMajorHasGoMod bool
   258  	)
   259  	for i, v := range incompatible {
   260  		major := semver.Major(v)
   261  
   262  		if major != lastMajor {
   263  			rem := incompatible[i:]
   264  			j := sort.Search(len(rem), func(j int) bool {
   265  				return semver.Major(rem[j]) != major
   266  			})
   267  			latestAtMajor := rem[j-1]
   268  
   269  			var err error
   270  			lastMajor = major
   271  			lastMajorHasGoMod, err = versionHasGoMod(latestAtMajor)
   272  			if err != nil {
   273  				return nil, err
   274  			}
   275  		}
   276  
   277  		if lastMajorHasGoMod {
   278  			// The latest release of this major version has a go.mod file, so it is
   279  			// not allowed as +incompatible. It would be confusing to include some
   280  			// minor versions of this major version as +incompatible but require
   281  			// semantic import versioning for others, so drop all +incompatible
   282  			// versions for this major version.
   283  			//
   284  			// If we're wrong about a minor version in the middle, users will still be
   285  			// able to 'go get' specific tags for that version explicitly — they just
   286  			// won't appear in 'go list' or as the results for queries with inequality
   287  			// bounds.
   288  			continue
   289  		}
   290  		versions.List = append(versions.List, v+"+incompatible")
   291  	}
   292  
   293  	return versions, nil
   294  }
   295  
   296  func (r *codeRepo) Stat(ctx context.Context, rev string) (*RevInfo, error) {
   297  	if rev == "latest" {
   298  		return r.Latest(ctx)
   299  	}
   300  	codeRev := r.revToRev(rev)
   301  	info, err := r.code.Stat(ctx, codeRev)
   302  	if err != nil {
   303  		// Note: info may be non-nil to supply Origin for caching error.
   304  		var revInfo *RevInfo
   305  		if info != nil {
   306  			revInfo = &RevInfo{
   307  				Origin:  info.Origin,
   308  				Version: rev,
   309  			}
   310  		}
   311  		return revInfo, &module.ModuleError{
   312  			Path: r.modPath,
   313  			Err: &module.InvalidVersionError{
   314  				Version: rev,
   315  				Err:     err,
   316  			},
   317  		}
   318  	}
   319  	return r.convert(ctx, info, rev)
   320  }
   321  
   322  func (r *codeRepo) Latest(ctx context.Context) (*RevInfo, error) {
   323  	info, err := r.code.Latest(ctx)
   324  	if err != nil {
   325  		if info != nil {
   326  			return &RevInfo{Origin: info.Origin}, err
   327  		}
   328  		return nil, err
   329  	}
   330  	return r.convert(ctx, info, "")
   331  }
   332  
   333  // convert converts a version as reported by the code host to a version as
   334  // interpreted by the module system.
   335  //
   336  // If statVers is a valid module version, it is used for the Version field.
   337  // Otherwise, the Version is derived from the passed-in info and recent tags.
   338  func (r *codeRepo) convert(ctx context.Context, info *codehost.RevInfo, statVers string) (revInfo *RevInfo, err error) {
   339  	defer func() {
   340  		if info.Origin == nil {
   341  			return
   342  		}
   343  		if revInfo == nil {
   344  			revInfo = new(RevInfo)
   345  		} else if revInfo.Origin != nil {
   346  			panic("internal error: RevInfo Origin unexpectedly already populated")
   347  		}
   348  
   349  		origin := *info.Origin
   350  		revInfo.Origin = &origin
   351  		origin.Subdir = r.codeDir
   352  
   353  		v := revInfo.Version
   354  		if module.IsPseudoVersion(v) && (v != statVers || !strings.HasPrefix(v, "v0.0.0-")) {
   355  			// Add tags that are relevant to pseudo-version calculation to origin.
   356  			prefix := r.codeDir
   357  			if prefix != "" {
   358  				prefix += "/"
   359  			}
   360  			if r.pathMajor != "" { // "/v2" or "/.v2"
   361  				prefix += r.pathMajor[1:] + "." // += "v2."
   362  			}
   363  			tags, tagsErr := r.code.Tags(ctx, prefix)
   364  			if tagsErr != nil {
   365  				revInfo.Origin = nil
   366  				if err == nil {
   367  					err = tagsErr
   368  				}
   369  			} else {
   370  				origin.TagPrefix = tags.Origin.TagPrefix
   371  				origin.TagSum = tags.Origin.TagSum
   372  			}
   373  		}
   374  	}()
   375  
   376  	// If this is a plain tag (no dir/ prefix)
   377  	// and the module path is unversioned,
   378  	// and if the underlying file tree has no go.mod,
   379  	// then allow using the tag with a +incompatible suffix.
   380  	//
   381  	// (If the version is +incompatible, then the go.mod file must not exist:
   382  	// +incompatible is not an ongoing opt-out from semantic import versioning.)
   383  	incompatibleOk := map[string]bool{}
   384  	canUseIncompatible := func(v string) bool {
   385  		if r.codeDir != "" || r.pathMajor != "" {
   386  			// A non-empty codeDir indicates a module within a subdirectory,
   387  			// which necessarily has a go.mod file indicating the module boundary.
   388  			// A non-empty pathMajor indicates a module path with a major-version
   389  			// suffix, which must match.
   390  			return false
   391  		}
   392  
   393  		ok, seen := incompatibleOk[""]
   394  		if !seen {
   395  			_, errGoMod := r.code.ReadFile(ctx, info.Name, "go.mod", codehost.MaxGoMod)
   396  			ok = (errGoMod != nil)
   397  			incompatibleOk[""] = ok
   398  		}
   399  		if !ok {
   400  			// A go.mod file exists at the repo root.
   401  			return false
   402  		}
   403  
   404  		// Per https://go.dev/issue/51324, previous versions of the 'go' command
   405  		// didn't always check for go.mod files in subdirectories, so if the user
   406  		// requests a +incompatible version explicitly, we should continue to allow
   407  		// it. Otherwise, if vN/go.mod exists, expect that release tags for that
   408  		// major version are intended for the vN module.
   409  		if v != "" && !strings.HasSuffix(statVers, "+incompatible") {
   410  			major := semver.Major(v)
   411  			ok, seen = incompatibleOk[major]
   412  			if !seen {
   413  				_, errGoModSub := r.code.ReadFile(ctx, info.Name, path.Join(major, "go.mod"), codehost.MaxGoMod)
   414  				ok = (errGoModSub != nil)
   415  				incompatibleOk[major] = ok
   416  			}
   417  			if !ok {
   418  				return false
   419  			}
   420  		}
   421  
   422  		return true
   423  	}
   424  
   425  	// checkCanonical verifies that the canonical version v is compatible with the
   426  	// module path represented by r, adding a "+incompatible" suffix if needed.
   427  	//
   428  	// If statVers is also canonical, checkCanonical also verifies that v is
   429  	// either statVers or statVers with the added "+incompatible" suffix.
   430  	checkCanonical := func(v string) (*RevInfo, error) {
   431  		// If r.codeDir is non-empty, then the go.mod file must exist: the module
   432  		// author — not the module consumer, — gets to decide how to carve up the repo
   433  		// into modules.
   434  		//
   435  		// Conversely, if the go.mod file exists, the module author — not the module
   436  		// consumer — gets to determine the module's path
   437  		//
   438  		// r.findDir verifies both of these conditions. Execute it now so that
   439  		// r.Stat will correctly return a notExistError if the go.mod location or
   440  		// declared module path doesn't match.
   441  		_, _, _, err := r.findDir(ctx, v)
   442  		if err != nil {
   443  			// TODO: It would be nice to return an error like "not a module".
   444  			// Right now we return "missing go.mod", which is a little confusing.
   445  			return nil, &module.ModuleError{
   446  				Path: r.modPath,
   447  				Err: &module.InvalidVersionError{
   448  					Version: v,
   449  					Err:     notExistError{err: err},
   450  				},
   451  			}
   452  		}
   453  
   454  		invalidf := func(format string, args ...any) error {
   455  			return &module.ModuleError{
   456  				Path: r.modPath,
   457  				Err: &module.InvalidVersionError{
   458  					Version: v,
   459  					Err:     fmt.Errorf(format, args...),
   460  				},
   461  			}
   462  		}
   463  
   464  		// Add the +incompatible suffix if needed or requested explicitly, and
   465  		// verify that its presence or absence is appropriate for this version
   466  		// (which depends on whether it has an explicit go.mod file).
   467  
   468  		if v == strings.TrimSuffix(statVers, "+incompatible") {
   469  			v = statVers
   470  		}
   471  		base := strings.TrimSuffix(v, "+incompatible")
   472  		var errIncompatible error
   473  		if !module.MatchPathMajor(base, r.pathMajor) {
   474  			if canUseIncompatible(base) {
   475  				v = base + "+incompatible"
   476  			} else {
   477  				if r.pathMajor != "" {
   478  					errIncompatible = invalidf("module path includes a major version suffix, so major version must match")
   479  				} else {
   480  					errIncompatible = invalidf("module contains a go.mod file, so module path must match major version (%q)", path.Join(r.pathPrefix, semver.Major(v)))
   481  				}
   482  			}
   483  		} else if strings.HasSuffix(v, "+incompatible") {
   484  			errIncompatible = invalidf("+incompatible suffix not allowed: major version %s is compatible", semver.Major(v))
   485  		}
   486  
   487  		if statVers != "" && statVers == module.CanonicalVersion(statVers) {
   488  			// Since the caller-requested version is canonical, it would be very
   489  			// confusing to resolve it to anything but itself, possibly with a
   490  			// "+incompatible" suffix. Error out explicitly.
   491  			if statBase := strings.TrimSuffix(statVers, "+incompatible"); statBase != base {
   492  				return nil, &module.ModuleError{
   493  					Path: r.modPath,
   494  					Err: &module.InvalidVersionError{
   495  						Version: statVers,
   496  						Err:     fmt.Errorf("resolves to version %v (%s is not a tag)", v, statBase),
   497  					},
   498  				}
   499  			}
   500  		}
   501  
   502  		if errIncompatible != nil {
   503  			return nil, errIncompatible
   504  		}
   505  
   506  		return &RevInfo{
   507  			Name:    info.Name,
   508  			Short:   info.Short,
   509  			Time:    info.Time,
   510  			Version: v,
   511  		}, nil
   512  	}
   513  
   514  	// Determine version.
   515  
   516  	if module.IsPseudoVersion(statVers) {
   517  		// Validate the go.mod location and major version before
   518  		// we check for an ancestor tagged with the pseudo-version base.
   519  		//
   520  		// We can rule out an invalid subdirectory or major version with only
   521  		// shallow commit information, but checking the pseudo-version base may
   522  		// require downloading a (potentially more expensive) full history.
   523  		revInfo, err = checkCanonical(statVers)
   524  		if err != nil {
   525  			return revInfo, err
   526  		}
   527  		if err := r.validatePseudoVersion(ctx, info, statVers); err != nil {
   528  			return nil, err
   529  		}
   530  		return revInfo, nil
   531  	}
   532  
   533  	// statVers is not a pseudo-version, so we need to either resolve it to a
   534  	// canonical version or verify that it is already a canonical tag
   535  	// (not a branch).
   536  
   537  	// Derive or verify a version from a code repo tag.
   538  	// Tag must have a prefix matching codeDir.
   539  	tagPrefix := ""
   540  	if r.codeDir != "" {
   541  		tagPrefix = r.codeDir + "/"
   542  	}
   543  
   544  	isRetracted, err := r.retractedVersions(ctx)
   545  	if err != nil {
   546  		isRetracted = func(string) bool { return false }
   547  	}
   548  
   549  	// tagToVersion returns the version obtained by trimming tagPrefix from tag.
   550  	// If the tag is invalid, retracted, or a pseudo-version, tagToVersion returns
   551  	// an empty version.
   552  	tagToVersion := func(tag string) (v string, tagIsCanonical bool) {
   553  		if !strings.HasPrefix(tag, tagPrefix) {
   554  			return "", false
   555  		}
   556  		trimmed := tag[len(tagPrefix):]
   557  		// Tags that look like pseudo-versions would be confusing. Ignore them.
   558  		if module.IsPseudoVersion(tag) {
   559  			return "", false
   560  		}
   561  
   562  		v = semver.Canonical(trimmed) // Not module.Canonical: we don't want to pick up an explicit "+incompatible" suffix from the tag.
   563  		if v == "" || !strings.HasPrefix(trimmed, v) {
   564  			return "", false // Invalid or incomplete version (just vX or vX.Y).
   565  		}
   566  		if v == trimmed {
   567  			tagIsCanonical = true
   568  		}
   569  		return v, tagIsCanonical
   570  	}
   571  
   572  	// If the VCS gave us a valid version, use that.
   573  	if v, tagIsCanonical := tagToVersion(info.Version); tagIsCanonical {
   574  		if info, err := checkCanonical(v); err == nil {
   575  			return info, err
   576  		}
   577  	}
   578  
   579  	// Look through the tags on the revision for either a usable canonical version
   580  	// or an appropriate base for a pseudo-version.
   581  	var (
   582  		highestCanonical string
   583  		pseudoBase       string
   584  	)
   585  	for _, pathTag := range info.Tags {
   586  		v, tagIsCanonical := tagToVersion(pathTag)
   587  		if statVers != "" && semver.Compare(v, statVers) == 0 {
   588  			// The tag is equivalent to the version requested by the user.
   589  			if tagIsCanonical {
   590  				// This tag is the canonical form of the requested version,
   591  				// not some other form with extra build metadata.
   592  				// Use this tag so that the resolved version will match exactly.
   593  				// (If it isn't actually allowed, we'll error out in checkCanonical.)
   594  				return checkCanonical(v)
   595  			} else {
   596  				// The user explicitly requested something equivalent to this tag. We
   597  				// can't use the version from the tag directly: since the tag is not
   598  				// canonical, it could be ambiguous. For example, tags v0.0.1+a and
   599  				// v0.0.1+b might both exist and refer to different revisions.
   600  				//
   601  				// The tag is otherwise valid for the module, so we can at least use it as
   602  				// the base of an unambiguous pseudo-version.
   603  				//
   604  				// If multiple tags match, tagToVersion will canonicalize them to the same
   605  				// base version.
   606  				pseudoBase = v
   607  			}
   608  		}
   609  		// Save the highest non-retracted canonical tag for the revision.
   610  		// If we don't find a better match, we'll use it as the canonical version.
   611  		if tagIsCanonical && semver.Compare(highestCanonical, v) < 0 && !isRetracted(v) {
   612  			if module.MatchPathMajor(v, r.pathMajor) || canUseIncompatible(v) {
   613  				highestCanonical = v
   614  			}
   615  		}
   616  	}
   617  
   618  	// If we found a valid canonical tag for the revision, return it.
   619  	// Even if we found a good pseudo-version base, a canonical version is better.
   620  	if highestCanonical != "" {
   621  		return checkCanonical(highestCanonical)
   622  	}
   623  
   624  	// Find the highest tagged version in the revision's history, subject to
   625  	// major version and +incompatible constraints. Use that version as the
   626  	// pseudo-version base so that the pseudo-version sorts higher. Ignore
   627  	// retracted versions.
   628  	tagAllowed := func(tag string) bool {
   629  		v, _ := tagToVersion(tag)
   630  		if v == "" {
   631  			return false
   632  		}
   633  		if !module.MatchPathMajor(v, r.pathMajor) && !canUseIncompatible(v) {
   634  			return false
   635  		}
   636  		return !isRetracted(v)
   637  	}
   638  	if pseudoBase == "" {
   639  		tag, err := r.code.RecentTag(ctx, info.Name, tagPrefix, tagAllowed)
   640  		if err != nil && !errors.Is(err, errors.ErrUnsupported) {
   641  			return nil, err
   642  		}
   643  		if tag != "" {
   644  			pseudoBase, _ = tagToVersion(tag)
   645  		}
   646  	}
   647  
   648  	return checkCanonical(module.PseudoVersion(r.pseudoMajor, pseudoBase, info.Time, info.Short))
   649  }
   650  
   651  // validatePseudoVersion checks that version has a major version compatible with
   652  // r.modPath and encodes a base version and commit metadata that agrees with
   653  // info.
   654  //
   655  // Note that verifying a nontrivial base version in particular may be somewhat
   656  // expensive: in order to do so, r.code.DescendsFrom will need to fetch at least
   657  // enough of the commit history to find a path between version and its base.
   658  // Fortunately, many pseudo-versions — such as those for untagged repositories —
   659  // have trivial bases!
   660  func (r *codeRepo) validatePseudoVersion(ctx context.Context, info *codehost.RevInfo, version string) (err error) {
   661  	defer func() {
   662  		if err != nil {
   663  			if _, ok := err.(*module.ModuleError); !ok {
   664  				if _, ok := err.(*module.InvalidVersionError); !ok {
   665  					err = &module.InvalidVersionError{Version: version, Pseudo: true, Err: err}
   666  				}
   667  				err = &module.ModuleError{Path: r.modPath, Err: err}
   668  			}
   669  		}
   670  	}()
   671  
   672  	rev, err := module.PseudoVersionRev(version)
   673  	if err != nil {
   674  		return err
   675  	}
   676  	if rev != info.Short {
   677  		switch {
   678  		case strings.HasPrefix(rev, info.Short):
   679  			return fmt.Errorf("revision is longer than canonical (expected %s)", info.Short)
   680  		case strings.HasPrefix(info.Short, rev):
   681  			return fmt.Errorf("revision is shorter than canonical (expected %s)", info.Short)
   682  		default:
   683  			return fmt.Errorf("does not match short name of revision (expected %s)", info.Short)
   684  		}
   685  	}
   686  
   687  	t, err := module.PseudoVersionTime(version)
   688  	if err != nil {
   689  		return err
   690  	}
   691  	if !t.Equal(info.Time.Truncate(time.Second)) {
   692  		return fmt.Errorf("does not match version-control timestamp (expected %s)", info.Time.UTC().Format(module.PseudoVersionTimestampFormat))
   693  	}
   694  
   695  	tagPrefix := ""
   696  	if r.codeDir != "" {
   697  		tagPrefix = r.codeDir + "/"
   698  	}
   699  
   700  	// A pseudo-version should have a precedence just above its parent revisions,
   701  	// and no higher. Otherwise, it would be possible for library authors to "pin"
   702  	// dependency versions (and bypass the usual minimum version selection) by
   703  	// naming an extremely high pseudo-version rather than an accurate one.
   704  	//
   705  	// Moreover, if we allow a pseudo-version to use any arbitrary pre-release
   706  	// tag, we end up with infinitely many possible names for each commit. Each
   707  	// name consumes resources in the module cache and proxies, so we want to
   708  	// restrict them to a finite set under control of the module author.
   709  	//
   710  	// We address both of these issues by requiring the tag upon which the
   711  	// pseudo-version is based to refer to some ancestor of the revision. We
   712  	// prefer the highest such tag when constructing a new pseudo-version, but do
   713  	// not enforce that property when resolving existing pseudo-versions: we don't
   714  	// know when the parent tags were added, and the highest-tagged parent may not
   715  	// have existed when the pseudo-version was first resolved.
   716  	base, err := module.PseudoVersionBase(strings.TrimSuffix(version, "+incompatible"))
   717  	if err != nil {
   718  		return err
   719  	}
   720  	if base == "" {
   721  		if r.pseudoMajor == "" && semver.Major(version) == "v1" {
   722  			return fmt.Errorf("major version without preceding tag must be v0, not v1")
   723  		}
   724  		return nil
   725  	} else {
   726  		for _, tag := range info.Tags {
   727  			versionOnly := strings.TrimPrefix(tag, tagPrefix)
   728  			if versionOnly == base {
   729  				// The base version is canonical, so if the version from the tag is
   730  				// literally equal (not just equivalent), then the tag is canonical too.
   731  				//
   732  				// We allow pseudo-versions to be derived from non-canonical tags on the
   733  				// same commit, so that tags like "v1.1.0+some-metadata" resolve as
   734  				// close as possible to the canonical version ("v1.1.0") while still
   735  				// enforcing a total ordering ("v1.1.1-0.[…]" with a unique suffix).
   736  				//
   737  				// However, canonical tags already have a total ordering, so there is no
   738  				// reason not to use the canonical tag directly, and we know that the
   739  				// canonical tag must already exist because the pseudo-version is
   740  				// derived from it. In that case, referring to the revision by a
   741  				// pseudo-version derived from its own canonical tag is just confusing.
   742  				return fmt.Errorf("tag (%s) found on revision %s is already canonical, so should not be replaced with a pseudo-version derived from that tag", tag, rev)
   743  			}
   744  		}
   745  	}
   746  
   747  	tags, err := r.code.Tags(ctx, tagPrefix+base)
   748  	if err != nil {
   749  		return err
   750  	}
   751  
   752  	var lastTag string // Prefer to log some real tag rather than a canonically-equivalent base.
   753  	ancestorFound := false
   754  	for _, tag := range tags.List {
   755  		versionOnly := strings.TrimPrefix(tag.Name, tagPrefix)
   756  		if semver.Compare(versionOnly, base) == 0 {
   757  			lastTag = tag.Name
   758  			ancestorFound, err = r.code.DescendsFrom(ctx, info.Name, tag.Name)
   759  			if ancestorFound {
   760  				break
   761  			}
   762  		}
   763  	}
   764  
   765  	if lastTag == "" {
   766  		return fmt.Errorf("preceding tag (%s) not found", base)
   767  	}
   768  
   769  	if !ancestorFound {
   770  		if err != nil {
   771  			return err
   772  		}
   773  		rev, err := module.PseudoVersionRev(version)
   774  		if err != nil {
   775  			return fmt.Errorf("not a descendent of preceding tag (%s)", lastTag)
   776  		}
   777  		return fmt.Errorf("revision %s is not a descendent of preceding tag (%s)", rev, lastTag)
   778  	}
   779  	return nil
   780  }
   781  
   782  func (r *codeRepo) revToRev(rev string) string {
   783  	if semver.IsValid(rev) {
   784  		if module.IsPseudoVersion(rev) {
   785  			r, _ := module.PseudoVersionRev(rev)
   786  			return r
   787  		}
   788  		if semver.Build(rev) == "+incompatible" {
   789  			rev = rev[:len(rev)-len("+incompatible")]
   790  		}
   791  		if r.codeDir == "" {
   792  			return rev
   793  		}
   794  		return r.codeDir + "/" + rev
   795  	}
   796  	return rev
   797  }
   798  
   799  func (r *codeRepo) versionToRev(version string) (rev string, err error) {
   800  	if !semver.IsValid(version) {
   801  		return "", &module.ModuleError{
   802  			Path: r.modPath,
   803  			Err: &module.InvalidVersionError{
   804  				Version: version,
   805  				Err:     errors.New("syntax error"),
   806  			},
   807  		}
   808  	}
   809  	return r.revToRev(version), nil
   810  }
   811  
   812  // findDir locates the directory within the repo containing the module.
   813  //
   814  // If r.pathMajor is non-empty, this can be either r.codeDir or — if a go.mod
   815  // file exists — r.codeDir/r.pathMajor[1:].
   816  func (r *codeRepo) findDir(ctx context.Context, version string) (rev, dir string, gomod []byte, err error) {
   817  	rev, err = r.versionToRev(version)
   818  	if err != nil {
   819  		return "", "", nil, err
   820  	}
   821  
   822  	// Load info about go.mod but delay consideration
   823  	// (except I/O error) until we rule out v2/go.mod.
   824  	file1 := path.Join(r.codeDir, "go.mod")
   825  	gomod1, err1 := r.code.ReadFile(ctx, rev, file1, codehost.MaxGoMod)
   826  	if err1 != nil && !os.IsNotExist(err1) {
   827  		return "", "", nil, fmt.Errorf("reading %s/%s at revision %s: %v", r.codeRoot, file1, rev, err1)
   828  	}
   829  	mpath1 := modfile.ModulePath(gomod1)
   830  	found1 := err1 == nil && (isMajor(mpath1, r.pathMajor) || r.canReplaceMismatchedVersionDueToBug(mpath1))
   831  
   832  	var file2 string
   833  	if r.pathMajor != "" && r.codeRoot != r.modPath && !strings.HasPrefix(r.pathMajor, ".") {
   834  		// Suppose pathMajor is "/v2".
   835  		// Either go.mod should claim v2 and v2/go.mod should not exist,
   836  		// or v2/go.mod should exist and claim v2. Not both.
   837  		// Note that we don't check the full path, just the major suffix,
   838  		// because of replacement modules. This might be a fork of
   839  		// the real module, found at a different path, usable only in
   840  		// a replace directive.
   841  		dir2 := path.Join(r.codeDir, r.pathMajor[1:])
   842  		file2 = path.Join(dir2, "go.mod")
   843  		gomod2, err2 := r.code.ReadFile(ctx, rev, file2, codehost.MaxGoMod)
   844  		if err2 != nil && !os.IsNotExist(err2) {
   845  			return "", "", nil, fmt.Errorf("reading %s/%s at revision %s: %v", r.codeRoot, file2, rev, err2)
   846  		}
   847  		mpath2 := modfile.ModulePath(gomod2)
   848  		found2 := err2 == nil && isMajor(mpath2, r.pathMajor)
   849  
   850  		if found1 && found2 {
   851  			return "", "", nil, fmt.Errorf("%s/%s and ...%s/go.mod both have ...%s module paths at revision %s", r.pathPrefix, file1, r.pathMajor, r.pathMajor, rev)
   852  		}
   853  		if found2 {
   854  			return rev, dir2, gomod2, nil
   855  		}
   856  		if err2 == nil {
   857  			if mpath2 == "" {
   858  				return "", "", nil, fmt.Errorf("%s/%s is missing module path at revision %s", r.codeRoot, file2, rev)
   859  			}
   860  			return "", "", nil, fmt.Errorf("%s/%s has non-...%s module path %q at revision %s", r.codeRoot, file2, r.pathMajor, mpath2, rev)
   861  		}
   862  	}
   863  
   864  	// Not v2/go.mod, so it's either go.mod or nothing. Which is it?
   865  	if found1 {
   866  		// Explicit go.mod with matching major version ok.
   867  		return rev, r.codeDir, gomod1, nil
   868  	}
   869  	if err1 == nil {
   870  		// Explicit go.mod with non-matching major version disallowed.
   871  		suffix := ""
   872  		if file2 != "" {
   873  			suffix = fmt.Sprintf(" (and ...%s/go.mod does not exist)", r.pathMajor)
   874  		}
   875  		if mpath1 == "" {
   876  			return "", "", nil, fmt.Errorf("%s is missing module path%s at revision %s", file1, suffix, rev)
   877  		}
   878  		if r.pathMajor != "" { // ".v1", ".v2" for gopkg.in
   879  			return "", "", nil, fmt.Errorf("%s has non-...%s module path %q%s at revision %s", file1, r.pathMajor, mpath1, suffix, rev)
   880  		}
   881  		if _, _, ok := module.SplitPathVersion(mpath1); !ok {
   882  			return "", "", nil, fmt.Errorf("%s has malformed module path %q%s at revision %s", file1, mpath1, suffix, rev)
   883  		}
   884  		return "", "", nil, fmt.Errorf("%s has post-%s module path %q%s at revision %s", file1, semver.Major(version), mpath1, suffix, rev)
   885  	}
   886  
   887  	if r.codeDir == "" && (r.pathMajor == "" || strings.HasPrefix(r.pathMajor, ".")) {
   888  		// Implicit go.mod at root of repo OK for v0/v1 and for gopkg.in.
   889  		return rev, "", nil, nil
   890  	}
   891  
   892  	// Implicit go.mod below root of repo or at v2+ disallowed.
   893  	// Be clear about possibility of using either location for v2+.
   894  	if file2 != "" {
   895  		return "", "", nil, fmt.Errorf("missing %s/go.mod and ...%s/go.mod at revision %s", r.pathPrefix, r.pathMajor, rev)
   896  	}
   897  	return "", "", nil, fmt.Errorf("missing %s/go.mod at revision %s", r.pathPrefix, rev)
   898  }
   899  
   900  // isMajor reports whether the versions allowed for mpath are compatible with
   901  // the major version(s) implied by pathMajor, or false if mpath has an invalid
   902  // version suffix.
   903  func isMajor(mpath, pathMajor string) bool {
   904  	if mpath == "" {
   905  		// If we don't have a path, we don't know what version(s) it is compatible with.
   906  		return false
   907  	}
   908  	_, mpathMajor, ok := module.SplitPathVersion(mpath)
   909  	if !ok {
   910  		// An invalid module path is not compatible with any version.
   911  		return false
   912  	}
   913  	if pathMajor == "" {
   914  		// All of the valid versions for a gopkg.in module that requires major
   915  		// version v0 or v1 are compatible with the "v0 or v1" implied by an empty
   916  		// pathMajor.
   917  		switch module.PathMajorPrefix(mpathMajor) {
   918  		case "", "v0", "v1":
   919  			return true
   920  		default:
   921  			return false
   922  		}
   923  	}
   924  	if mpathMajor == "" {
   925  		// Even if pathMajor is ".v0" or ".v1", we can't be sure that a module
   926  		// without a suffix is tagged appropriately. Besides, we don't expect clones
   927  		// of non-gopkg.in modules to have gopkg.in paths, so a non-empty,
   928  		// non-gopkg.in mpath is probably the wrong module for any such pathMajor
   929  		// anyway.
   930  		return false
   931  	}
   932  	// If both pathMajor and mpathMajor are non-empty, then we only care that they
   933  	// have the same major-version validation rules. A clone fetched via a /v2
   934  	// path might replace a module with path gopkg.in/foo.v2-unstable, and that's
   935  	// ok.
   936  	return pathMajor[1:] == mpathMajor[1:]
   937  }
   938  
   939  // canReplaceMismatchedVersionDueToBug reports whether versions of r
   940  // could replace versions of mpath with otherwise-mismatched major versions
   941  // due to a historical bug in the Go command (golang.org/issue/34254).
   942  func (r *codeRepo) canReplaceMismatchedVersionDueToBug(mpath string) bool {
   943  	// The bug caused us to erroneously accept unversioned paths as replacements
   944  	// for versioned gopkg.in paths.
   945  	unversioned := r.pathMajor == ""
   946  	replacingGopkgIn := strings.HasPrefix(mpath, "gopkg.in/")
   947  	return unversioned && replacingGopkgIn
   948  }
   949  
   950  func (r *codeRepo) GoMod(ctx context.Context, version string) (data []byte, err error) {
   951  	if version != module.CanonicalVersion(version) {
   952  		return nil, fmt.Errorf("version %s is not canonical", version)
   953  	}
   954  
   955  	if module.IsPseudoVersion(version) {
   956  		// findDir ignores the metadata encoded in a pseudo-version,
   957  		// only using the revision at the end.
   958  		// Invoke Stat to verify the metadata explicitly so we don't return
   959  		// a bogus file for an invalid version.
   960  		_, err := r.Stat(ctx, version)
   961  		if err != nil {
   962  			return nil, err
   963  		}
   964  	}
   965  
   966  	rev, dir, gomod, err := r.findDir(ctx, version)
   967  	if err != nil {
   968  		return nil, err
   969  	}
   970  	if gomod != nil {
   971  		return gomod, nil
   972  	}
   973  	data, err = r.code.ReadFile(ctx, rev, path.Join(dir, "go.mod"), codehost.MaxGoMod)
   974  	if err != nil {
   975  		if os.IsNotExist(err) {
   976  			return LegacyGoMod(r.modPath), nil
   977  		}
   978  		return nil, err
   979  	}
   980  	return data, nil
   981  }
   982  
   983  // LegacyGoMod generates a fake go.mod file for a module that doesn't have one.
   984  // The go.mod file contains a module directive and nothing else: no go version,
   985  // no requirements.
   986  //
   987  // We used to try to build a go.mod reflecting pre-existing
   988  // package management metadata files, but the conversion
   989  // was inherently imperfect (because those files don't have
   990  // exactly the same semantics as go.mod) and, when done
   991  // for dependencies in the middle of a build, impossible to
   992  // correct. So we stopped.
   993  func LegacyGoMod(modPath string) []byte {
   994  	return fmt.Appendf(nil, "module %s\n", modfile.AutoQuote(modPath))
   995  }
   996  
   997  func (r *codeRepo) modPrefix(rev string) string {
   998  	return r.modPath + "@" + rev
   999  }
  1000  
  1001  func (r *codeRepo) retractedVersions(ctx context.Context) (func(string) bool, error) {
  1002  	vs, err := r.Versions(ctx, "")
  1003  	if err != nil {
  1004  		return nil, err
  1005  	}
  1006  	versions := vs.List
  1007  
  1008  	for i, v := range versions {
  1009  		if strings.HasSuffix(v, "+incompatible") {
  1010  			// We're looking for the latest release tag that may list retractions in a
  1011  			// go.mod file. +incompatible versions necessarily do not, and they start
  1012  			// at major version 2 — which is higher than any version that could
  1013  			// validly contain a go.mod file.
  1014  			versions = versions[:i]
  1015  			break
  1016  		}
  1017  	}
  1018  	if len(versions) == 0 {
  1019  		return func(string) bool { return false }, nil
  1020  	}
  1021  
  1022  	var highest string
  1023  	for i := len(versions) - 1; i >= 0; i-- {
  1024  		v := versions[i]
  1025  		if semver.Prerelease(v) == "" {
  1026  			highest = v
  1027  			break
  1028  		}
  1029  	}
  1030  	if highest == "" {
  1031  		highest = versions[len(versions)-1]
  1032  	}
  1033  
  1034  	data, err := r.GoMod(ctx, highest)
  1035  	if err != nil {
  1036  		return nil, err
  1037  	}
  1038  	f, err := modfile.ParseLax("go.mod", data, nil)
  1039  	if err != nil {
  1040  		return nil, err
  1041  	}
  1042  	retractions := make([]modfile.VersionInterval, 0, len(f.Retract))
  1043  	for _, r := range f.Retract {
  1044  		retractions = append(retractions, r.VersionInterval)
  1045  	}
  1046  
  1047  	return func(v string) bool {
  1048  		for _, r := range retractions {
  1049  			if semver.Compare(r.Low, v) <= 0 && semver.Compare(v, r.High) <= 0 {
  1050  				return true
  1051  			}
  1052  		}
  1053  		return false
  1054  	}, nil
  1055  }
  1056  
  1057  func (r *codeRepo) Zip(ctx context.Context, dst io.Writer, version string) error {
  1058  	if version != module.CanonicalVersion(version) {
  1059  		return fmt.Errorf("version %s is not canonical", version)
  1060  	}
  1061  
  1062  	if module.IsPseudoVersion(version) {
  1063  		// findDir ignores the metadata encoded in a pseudo-version,
  1064  		// only using the revision at the end.
  1065  		// Invoke Stat to verify the metadata explicitly so we don't return
  1066  		// a bogus file for an invalid version.
  1067  		_, err := r.Stat(ctx, version)
  1068  		if err != nil {
  1069  			return err
  1070  		}
  1071  	}
  1072  
  1073  	rev, subdir, _, err := r.findDir(ctx, version)
  1074  	if err != nil {
  1075  		return err
  1076  	}
  1077  
  1078  	if gomod, err := r.code.ReadFile(ctx, rev, filepath.Join(subdir, "go.mod"), codehost.MaxGoMod); err == nil {
  1079  		goVers := gover.GoModLookup(gomod, "go")
  1080  		if gover.Compare(goVers, gover.Local()) > 0 {
  1081  			return &gover.TooNewError{What: r.ModulePath() + "@" + version, GoVersion: goVers}
  1082  		}
  1083  	} else if !errors.Is(err, fs.ErrNotExist) {
  1084  		return err
  1085  	}
  1086  
  1087  	dl, err := r.code.ReadZip(ctx, rev, subdir, codehost.MaxZipFile)
  1088  	if err != nil {
  1089  		return err
  1090  	}
  1091  	defer dl.Close()
  1092  	subdir = strings.Trim(subdir, "/")
  1093  
  1094  	// Spool to local file.
  1095  	f, err := os.CreateTemp("", "go-codehost-")
  1096  	if err != nil {
  1097  		dl.Close()
  1098  		return err
  1099  	}
  1100  	defer os.Remove(f.Name())
  1101  	defer f.Close()
  1102  	maxSize := int64(codehost.MaxZipFile)
  1103  	lr := &io.LimitedReader{R: dl, N: maxSize + 1}
  1104  	if _, err := io.Copy(f, lr); err != nil {
  1105  		dl.Close()
  1106  		return err
  1107  	}
  1108  	dl.Close()
  1109  	if lr.N <= 0 {
  1110  		return fmt.Errorf("downloaded zip file too large")
  1111  	}
  1112  	size := (maxSize + 1) - lr.N
  1113  	if _, err := f.Seek(0, 0); err != nil {
  1114  		return err
  1115  	}
  1116  
  1117  	// Translate from zip file we have to zip file we want.
  1118  	zr, err := zip.NewReader(f, size)
  1119  	if err != nil {
  1120  		return err
  1121  	}
  1122  
  1123  	var files []modzip.File
  1124  	if subdir != "" {
  1125  		subdir += "/"
  1126  	}
  1127  	haveLICENSE := false
  1128  	topPrefix := ""
  1129  	for _, zf := range zr.File {
  1130  		if topPrefix == "" {
  1131  			i := strings.Index(zf.Name, "/")
  1132  			if i < 0 {
  1133  				return fmt.Errorf("missing top-level directory prefix")
  1134  			}
  1135  			topPrefix = zf.Name[:i+1]
  1136  		}
  1137  		var name string
  1138  		var found bool
  1139  		if name, found = strings.CutPrefix(zf.Name, topPrefix); !found {
  1140  			return fmt.Errorf("zip file contains more than one top-level directory")
  1141  		}
  1142  
  1143  		if name, found = strings.CutPrefix(name, subdir); !found {
  1144  			continue
  1145  		}
  1146  
  1147  		if name == "" || strings.HasSuffix(name, "/") {
  1148  			continue
  1149  		}
  1150  		files = append(files, zipFile{name: name, f: zf})
  1151  		if name == "LICENSE" {
  1152  			haveLICENSE = true
  1153  		}
  1154  	}
  1155  
  1156  	if !haveLICENSE && subdir != "" {
  1157  		data, err := r.code.ReadFile(ctx, rev, "LICENSE", codehost.MaxLICENSE)
  1158  		if err == nil {
  1159  			files = append(files, dataFile{name: "LICENSE", data: data})
  1160  		}
  1161  	}
  1162  
  1163  	return modzip.Create(dst, module.Version{Path: r.modPath, Version: version}, files)
  1164  }
  1165  
  1166  type zipFile struct {
  1167  	name string
  1168  	f    *zip.File
  1169  }
  1170  
  1171  func (f zipFile) Path() string                 { return f.name }
  1172  func (f zipFile) Lstat() (fs.FileInfo, error)  { return f.f.FileInfo(), nil }
  1173  func (f zipFile) Open() (io.ReadCloser, error) { return f.f.Open() }
  1174  
  1175  type dataFile struct {
  1176  	name string
  1177  	data []byte
  1178  }
  1179  
  1180  func (f dataFile) Path() string                { return f.name }
  1181  func (f dataFile) Lstat() (fs.FileInfo, error) { return dataFileInfo{f}, nil }
  1182  func (f dataFile) Open() (io.ReadCloser, error) {
  1183  	return io.NopCloser(bytes.NewReader(f.data)), nil
  1184  }
  1185  
  1186  type dataFileInfo struct {
  1187  	f dataFile
  1188  }
  1189  
  1190  func (fi dataFileInfo) Name() string       { return path.Base(fi.f.name) }
  1191  func (fi dataFileInfo) Size() int64        { return int64(len(fi.f.data)) }
  1192  func (fi dataFileInfo) Mode() fs.FileMode  { return 0644 }
  1193  func (fi dataFileInfo) ModTime() time.Time { return time.Time{} }
  1194  func (fi dataFileInfo) IsDir() bool        { return false }
  1195  func (fi dataFileInfo) Sys() any           { return nil }
  1196  
  1197  func (fi dataFileInfo) String() string {
  1198  	return fs.FormatFileInfo(fi)
  1199  }
  1200  
  1201  // hasPathPrefix reports whether the path s begins with the
  1202  // elements in prefix.
  1203  func hasPathPrefix(s, prefix string) bool {
  1204  	switch {
  1205  	default:
  1206  		return false
  1207  	case len(s) == len(prefix):
  1208  		return s == prefix
  1209  	case len(s) > len(prefix):
  1210  		if prefix != "" && prefix[len(prefix)-1] == '/' {
  1211  			return strings.HasPrefix(s, prefix)
  1212  		}
  1213  		return s[len(prefix)] == '/' && s[:len(prefix)] == prefix
  1214  	}
  1215  }
  1216  

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