vcs.go

Documentation: cmd/go/internal/modfetch/codehost

     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 codehost
     6  
     7  import (
     8  	"context"
     9  	"errors"
    10  	"fmt"
    11  	"internal/lazyregexp"
    12  	"io"
    13  	"io/fs"
    14  	"os"
    15  	"path/filepath"
    16  	"sort"
    17  	"strconv"
    18  	"strings"
    19  	"sync"
    20  	"time"
    21  
    22  	"cmd/go/internal/base"
    23  	"cmd/go/internal/lockedfile"
    24  	"cmd/go/internal/par"
    25  	"cmd/go/internal/str"
    26  )
    27  
    28  // A VCSError indicates an error using a version control system.
    29  // The implication of a VCSError is that we know definitively where
    30  // to get the code, but we can't access it due to the error.
    31  // The caller should report this error instead of continuing to probe
    32  // other possible module paths.
    33  //
    34  // TODO(golang.org/issue/31730): See if we can invert this. (Return a
    35  // distinguished error for “repo not found” and treat everything else
    36  // as terminal.)
    37  type VCSError struct {
    38  	Err error
    39  }
    40  
    41  func (e *VCSError) Error() string { return e.Err.Error() }
    42  
    43  func (e *VCSError) Unwrap() error { return e.Err }
    44  
    45  func vcsErrorf(format string, a ...any) error {
    46  	return &VCSError{Err: fmt.Errorf(format, a...)}
    47  }
    48  
    49  type vcsCacheKey struct {
    50  	vcs    string
    51  	remote string
    52  }
    53  
    54  func NewRepo(ctx context.Context, vcs, remote string) (Repo, error) {
    55  	return vcsRepoCache.Do(vcsCacheKey{vcs, remote}, func() (Repo, error) {
    56  		repo, err := newVCSRepo(ctx, vcs, remote)
    57  		if err != nil {
    58  			return nil, &VCSError{err}
    59  		}
    60  		return repo, nil
    61  	})
    62  }
    63  
    64  var vcsRepoCache par.ErrCache[vcsCacheKey, Repo]
    65  
    66  type vcsRepo struct {
    67  	mu lockedfile.Mutex // protects all commands, so we don't have to decide which are safe on a per-VCS basis
    68  
    69  	remote string
    70  	cmd    *vcsCmd
    71  	dir    string
    72  
    73  	tagsOnce sync.Once
    74  	tags     map[string]bool
    75  
    76  	branchesOnce sync.Once
    77  	branches     map[string]bool
    78  
    79  	fetchOnce sync.Once
    80  	fetchErr  error
    81  }
    82  
    83  func newVCSRepo(ctx context.Context, vcs, remote string) (Repo, error) {
    84  	if vcs == "git" {
    85  		return newGitRepo(ctx, remote, false)
    86  	}
    87  	cmd := vcsCmds[vcs]
    88  	if cmd == nil {
    89  		return nil, fmt.Errorf("unknown vcs: %s %s", vcs, remote)
    90  	}
    91  	if !strings.Contains(remote, "://") {
    92  		return nil, fmt.Errorf("invalid vcs remote: %s %s", vcs, remote)
    93  	}
    94  
    95  	r := &vcsRepo{remote: remote, cmd: cmd}
    96  	var err error
    97  	r.dir, r.mu.Path, err = WorkDir(ctx, vcsWorkDirType+vcs, r.remote)
    98  	if err != nil {
    99  		return nil, err
   100  	}
   101  
   102  	if cmd.init == nil {
   103  		return r, nil
   104  	}
   105  
   106  	unlock, err := r.mu.Lock()
   107  	if err != nil {
   108  		return nil, err
   109  	}
   110  	defer unlock()
   111  
   112  	if _, err := os.Stat(filepath.Join(r.dir, "."+vcs)); err != nil {
   113  		release, err := base.AcquireNet()
   114  		if err != nil {
   115  			return nil, err
   116  		}
   117  		_, err = Run(ctx, r.dir, cmd.init(r.remote))
   118  		release()
   119  
   120  		if err != nil {
   121  			os.RemoveAll(r.dir)
   122  			return nil, err
   123  		}
   124  	}
   125  	return r, nil
   126  }
   127  
   128  const vcsWorkDirType = "vcs1."
   129  
   130  type vcsCmd struct {
   131  	vcs           string                                                                              // vcs name "hg"
   132  	init          func(remote string) []string                                                        // cmd to init repo to track remote
   133  	tags          func(remote string) []string                                                        // cmd to list local tags
   134  	tagRE         *lazyregexp.Regexp                                                                  // regexp to extract tag names from output of tags cmd
   135  	branches      func(remote string) []string                                                        // cmd to list local branches
   136  	branchRE      *lazyregexp.Regexp                                                                  // regexp to extract branch names from output of tags cmd
   137  	badLocalRevRE *lazyregexp.Regexp                                                                  // regexp of names that must not be served out of local cache without doing fetch first
   138  	statLocal     func(rev, remote string) []string                                                   // cmd to stat local rev
   139  	parseStat     func(rev, out string) (*RevInfo, error)                                             // cmd to parse output of statLocal
   140  	fetch         []string                                                                            // cmd to fetch everything from remote
   141  	latest        string                                                                              // name of latest commit on remote (tip, HEAD, etc)
   142  	readFile      func(rev, file, remote string) []string                                             // cmd to read rev's file
   143  	readZip       func(rev, subdir, remote, target string) []string                                   // cmd to read rev's subdir as zip file
   144  	doReadZip     func(ctx context.Context, dst io.Writer, workDir, rev, subdir, remote string) error // arbitrary function to read rev's subdir as zip file
   145  }
   146  
   147  var re = lazyregexp.New
   148  
   149  var vcsCmds = map[string]*vcsCmd{
   150  	"hg": {
   151  		vcs: "hg",
   152  		init: func(remote string) []string {
   153  			return []string{"hg", "clone", "-U", "--", remote, "."}
   154  		},
   155  		tags: func(remote string) []string {
   156  			return []string{"hg", "tags", "-q"}
   157  		},
   158  		tagRE: re(`(?m)^[^\n]+$`),
   159  		branches: func(remote string) []string {
   160  			return []string{"hg", "branches", "-c", "-q"}
   161  		},
   162  		branchRE:      re(`(?m)^[^\n]+$`),
   163  		badLocalRevRE: re(`(?m)^(tip)$`),
   164  		statLocal: func(rev, remote string) []string {
   165  			return []string{"hg", "log", "-l1", "-r", rev, "--template", "{node} {date|hgdate} {tags}"}
   166  		},
   167  		parseStat: hgParseStat,
   168  		fetch:     []string{"hg", "pull", "-f"},
   169  		latest:    "tip",
   170  		readFile: func(rev, file, remote string) []string {
   171  			return []string{"hg", "cat", "-r", rev, file}
   172  		},
   173  		readZip: func(rev, subdir, remote, target string) []string {
   174  			pattern := []string{}
   175  			if subdir != "" {
   176  				pattern = []string{"-I", subdir + "/**"}
   177  			}
   178  			return str.StringList("hg", "archive", "-t", "zip", "--no-decode", "-r", rev, "--prefix=prefix/", pattern, "--", target)
   179  		},
   180  	},
   181  
   182  	"svn": {
   183  		vcs:  "svn",
   184  		init: nil, // no local checkout
   185  		tags: func(remote string) []string {
   186  			return []string{"svn", "list", "--", strings.TrimSuffix(remote, "/trunk") + "/tags"}
   187  		},
   188  		tagRE: re(`(?m)^(.*?)/?$`),
   189  		statLocal: func(rev, remote string) []string {
   190  			suffix := "@" + rev
   191  			if rev == "latest" {
   192  				suffix = ""
   193  			}
   194  			return []string{"svn", "log", "-l1", "--xml", "--", remote + suffix}
   195  		},
   196  		parseStat: svnParseStat,
   197  		latest:    "latest",
   198  		readFile: func(rev, file, remote string) []string {
   199  			return []string{"svn", "cat", "--", remote + "/" + file + "@" + rev}
   200  		},
   201  		doReadZip: svnReadZip,
   202  	},
   203  
   204  	"bzr": {
   205  		vcs: "bzr",
   206  		init: func(remote string) []string {
   207  			return []string{"bzr", "branch", "--use-existing-dir", "--", remote, "."}
   208  		},
   209  		fetch: []string{
   210  			"bzr", "pull", "--overwrite-tags",
   211  		},
   212  		tags: func(remote string) []string {
   213  			return []string{"bzr", "tags"}
   214  		},
   215  		tagRE:         re(`(?m)^\S+`),
   216  		badLocalRevRE: re(`^revno:-`),
   217  		statLocal: func(rev, remote string) []string {
   218  			return []string{"bzr", "log", "-l1", "--long", "--show-ids", "-r", rev}
   219  		},
   220  		parseStat: bzrParseStat,
   221  		latest:    "revno:-1",
   222  		readFile: func(rev, file, remote string) []string {
   223  			return []string{"bzr", "cat", "-r", rev, file}
   224  		},
   225  		readZip: func(rev, subdir, remote, target string) []string {
   226  			extra := []string{}
   227  			if subdir != "" {
   228  				extra = []string{"./" + subdir}
   229  			}
   230  			return str.StringList("bzr", "export", "--format=zip", "-r", rev, "--root=prefix/", "--", target, extra)
   231  		},
   232  	},
   233  
   234  	"fossil": {
   235  		vcs: "fossil",
   236  		init: func(remote string) []string {
   237  			return []string{"fossil", "clone", "--", remote, ".fossil"}
   238  		},
   239  		fetch: []string{"fossil", "pull", "-R", ".fossil"},
   240  		tags: func(remote string) []string {
   241  			return []string{"fossil", "tag", "-R", ".fossil", "list"}
   242  		},
   243  		tagRE: re(`XXXTODO`),
   244  		statLocal: func(rev, remote string) []string {
   245  			return []string{"fossil", "info", "-R", ".fossil", rev}
   246  		},
   247  		parseStat: fossilParseStat,
   248  		latest:    "trunk",
   249  		readFile: func(rev, file, remote string) []string {
   250  			return []string{"fossil", "cat", "-R", ".fossil", "-r", rev, file}
   251  		},
   252  		readZip: func(rev, subdir, remote, target string) []string {
   253  			extra := []string{}
   254  			if subdir != "" && !strings.ContainsAny(subdir, "*?[],") {
   255  				extra = []string{"--include", subdir}
   256  			}
   257  			// Note that vcsRepo.ReadZip below rewrites this command
   258  			// to run in a different directory, to work around a fossil bug.
   259  			return str.StringList("fossil", "zip", "-R", ".fossil", "--name", "prefix", extra, "--", rev, target)
   260  		},
   261  	},
   262  }
   263  
   264  func (r *vcsRepo) loadTags(ctx context.Context) {
   265  	out, err := Run(ctx, r.dir, r.cmd.tags(r.remote))
   266  	if err != nil {
   267  		return
   268  	}
   269  
   270  	// Run tag-listing command and extract tags.
   271  	r.tags = make(map[string]bool)
   272  	for _, tag := range r.cmd.tagRE.FindAllString(string(out), -1) {
   273  		if r.cmd.badLocalRevRE != nil && r.cmd.badLocalRevRE.MatchString(tag) {
   274  			continue
   275  		}
   276  		r.tags[tag] = true
   277  	}
   278  }
   279  
   280  func (r *vcsRepo) loadBranches(ctx context.Context) {
   281  	if r.cmd.branches == nil {
   282  		return
   283  	}
   284  
   285  	out, err := Run(ctx, r.dir, r.cmd.branches(r.remote))
   286  	if err != nil {
   287  		return
   288  	}
   289  
   290  	r.branches = make(map[string]bool)
   291  	for _, branch := range r.cmd.branchRE.FindAllString(string(out), -1) {
   292  		if r.cmd.badLocalRevRE != nil && r.cmd.badLocalRevRE.MatchString(branch) {
   293  			continue
   294  		}
   295  		r.branches[branch] = true
   296  	}
   297  }
   298  
   299  func (r *vcsRepo) CheckReuse(ctx context.Context, old *Origin, subdir string) error {
   300  	return fmt.Errorf("vcs %s: CheckReuse: %w", r.cmd.vcs, errors.ErrUnsupported)
   301  }
   302  
   303  func (r *vcsRepo) Tags(ctx context.Context, prefix string) (*Tags, error) {
   304  	unlock, err := r.mu.Lock()
   305  	if err != nil {
   306  		return nil, err
   307  	}
   308  	defer unlock()
   309  
   310  	r.tagsOnce.Do(func() { r.loadTags(ctx) })
   311  	tags := &Tags{
   312  		// None of the other VCS provide a reasonable way to compute TagSum
   313  		// without downloading the whole repo, so we only include VCS and URL
   314  		// in the Origin.
   315  		Origin: &Origin{
   316  			VCS: r.cmd.vcs,
   317  			URL: r.remote,
   318  		},
   319  		List: []Tag{},
   320  	}
   321  	for tag := range r.tags {
   322  		if strings.HasPrefix(tag, prefix) {
   323  			tags.List = append(tags.List, Tag{tag, ""})
   324  		}
   325  	}
   326  	sort.Slice(tags.List, func(i, j int) bool {
   327  		return tags.List[i].Name < tags.List[j].Name
   328  	})
   329  	return tags, nil
   330  }
   331  
   332  func (r *vcsRepo) Stat(ctx context.Context, rev string) (*RevInfo, error) {
   333  	unlock, err := r.mu.Lock()
   334  	if err != nil {
   335  		return nil, err
   336  	}
   337  	defer unlock()
   338  
   339  	if rev == "latest" {
   340  		rev = r.cmd.latest
   341  	}
   342  	r.branchesOnce.Do(func() { r.loadBranches(ctx) })
   343  	revOK := (r.cmd.badLocalRevRE == nil || !r.cmd.badLocalRevRE.MatchString(rev)) && !r.branches[rev]
   344  	if revOK {
   345  		if info, err := r.statLocal(ctx, rev); err == nil {
   346  			return info, nil
   347  		}
   348  	}
   349  
   350  	r.fetchOnce.Do(func() { r.fetch(ctx) })
   351  	if r.fetchErr != nil {
   352  		return nil, r.fetchErr
   353  	}
   354  	info, err := r.statLocal(ctx, rev)
   355  	if err != nil {
   356  		return nil, err
   357  	}
   358  	if !revOK {
   359  		info.Version = info.Name
   360  	}
   361  	return info, nil
   362  }
   363  
   364  func (r *vcsRepo) fetch(ctx context.Context) {
   365  	if len(r.cmd.fetch) > 0 {
   366  		release, err := base.AcquireNet()
   367  		if err != nil {
   368  			r.fetchErr = err
   369  			return
   370  		}
   371  		_, r.fetchErr = Run(ctx, r.dir, r.cmd.fetch)
   372  		release()
   373  	}
   374  }
   375  
   376  func (r *vcsRepo) statLocal(ctx context.Context, rev string) (*RevInfo, error) {
   377  	out, err := Run(ctx, r.dir, r.cmd.statLocal(rev, r.remote))
   378  	if err != nil {
   379  		return nil, &UnknownRevisionError{Rev: rev}
   380  	}
   381  	info, err := r.cmd.parseStat(rev, string(out))
   382  	if err != nil {
   383  		return nil, err
   384  	}
   385  	if info.Origin == nil {
   386  		info.Origin = new(Origin)
   387  	}
   388  	info.Origin.VCS = r.cmd.vcs
   389  	info.Origin.URL = r.remote
   390  	return info, nil
   391  }
   392  
   393  func (r *vcsRepo) Latest(ctx context.Context) (*RevInfo, error) {
   394  	return r.Stat(ctx, "latest")
   395  }
   396  
   397  func (r *vcsRepo) ReadFile(ctx context.Context, rev, file string, maxSize int64) ([]byte, error) {
   398  	if rev == "latest" {
   399  		rev = r.cmd.latest
   400  	}
   401  	_, err := r.Stat(ctx, rev) // download rev into local repo
   402  	if err != nil {
   403  		return nil, err
   404  	}
   405  
   406  	// r.Stat acquires r.mu, so lock after that.
   407  	unlock, err := r.mu.Lock()
   408  	if err != nil {
   409  		return nil, err
   410  	}
   411  	defer unlock()
   412  
   413  	out, err := Run(ctx, r.dir, r.cmd.readFile(rev, file, r.remote))
   414  	if err != nil {
   415  		return nil, fs.ErrNotExist
   416  	}
   417  	return out, nil
   418  }
   419  
   420  func (r *vcsRepo) RecentTag(ctx context.Context, rev, prefix string, allowed func(string) bool) (tag string, err error) {
   421  	// We don't technically need to lock here since we're returning an error
   422  	// unconditionally, but doing so anyway will help to avoid baking in
   423  	// lock-inversion bugs.
   424  	unlock, err := r.mu.Lock()
   425  	if err != nil {
   426  		return "", err
   427  	}
   428  	defer unlock()
   429  
   430  	return "", vcsErrorf("vcs %s: RecentTag: %w", r.cmd.vcs, errors.ErrUnsupported)
   431  }
   432  
   433  func (r *vcsRepo) DescendsFrom(ctx context.Context, rev, tag string) (bool, error) {
   434  	unlock, err := r.mu.Lock()
   435  	if err != nil {
   436  		return false, err
   437  	}
   438  	defer unlock()
   439  
   440  	return false, vcsErrorf("vcs %s: DescendsFrom: %w", r.cmd.vcs, errors.ErrUnsupported)
   441  }
   442  
   443  func (r *vcsRepo) ReadZip(ctx context.Context, rev, subdir string, maxSize int64) (zip io.ReadCloser, err error) {
   444  	if r.cmd.readZip == nil && r.cmd.doReadZip == nil {
   445  		return nil, vcsErrorf("vcs %s: ReadZip: %w", r.cmd.vcs, errors.ErrUnsupported)
   446  	}
   447  
   448  	unlock, err := r.mu.Lock()
   449  	if err != nil {
   450  		return nil, err
   451  	}
   452  	defer unlock()
   453  
   454  	if rev == "latest" {
   455  		rev = r.cmd.latest
   456  	}
   457  	f, err := os.CreateTemp("", "go-readzip-*.zip")
   458  	if err != nil {
   459  		return nil, err
   460  	}
   461  	if r.cmd.doReadZip != nil {
   462  		lw := &limitedWriter{
   463  			W:               f,
   464  			N:               maxSize,
   465  			ErrLimitReached: errors.New("ReadZip: encoded file exceeds allowed size"),
   466  		}
   467  		err = r.cmd.doReadZip(ctx, lw, r.dir, rev, subdir, r.remote)
   468  		if err == nil {
   469  			_, err = f.Seek(0, io.SeekStart)
   470  		}
   471  	} else if r.cmd.vcs == "fossil" {
   472  		// If you run
   473  		//	fossil zip -R .fossil --name prefix trunk /tmp/x.zip
   474  		// fossil fails with "unable to create directory /tmp" [sic].
   475  		// Change the command to run in /tmp instead,
   476  		// replacing the -R argument with an absolute path.
   477  		args := r.cmd.readZip(rev, subdir, r.remote, filepath.Base(f.Name()))
   478  		for i := range args {
   479  			if args[i] == ".fossil" {
   480  				args[i] = filepath.Join(r.dir, ".fossil")
   481  			}
   482  		}
   483  		_, err = Run(ctx, filepath.Dir(f.Name()), args)
   484  	} else {
   485  		_, err = Run(ctx, r.dir, r.cmd.readZip(rev, subdir, r.remote, f.Name()))
   486  	}
   487  	if err != nil {
   488  		f.Close()
   489  		os.Remove(f.Name())
   490  		return nil, err
   491  	}
   492  	return &deleteCloser{f}, nil
   493  }
   494  
   495  // deleteCloser is a file that gets deleted on Close.
   496  type deleteCloser struct {
   497  	*os.File
   498  }
   499  
   500  func (d *deleteCloser) Close() error {
   501  	defer os.Remove(d.File.Name())
   502  	return d.File.Close()
   503  }
   504  
   505  func hgParseStat(rev, out string) (*RevInfo, error) {
   506  	f := strings.Fields(out)
   507  	if len(f) < 3 {
   508  		return nil, vcsErrorf("unexpected response from hg log: %q", out)
   509  	}
   510  	hash := f[0]
   511  	version := rev
   512  	if strings.HasPrefix(hash, version) {
   513  		version = hash // extend to full hash
   514  	}
   515  	t, err := strconv.ParseInt(f[1], 10, 64)
   516  	if err != nil {
   517  		return nil, vcsErrorf("invalid time from hg log: %q", out)
   518  	}
   519  
   520  	var tags []string
   521  	for _, tag := range f[3:] {
   522  		if tag != "tip" {
   523  			tags = append(tags, tag)
   524  		}
   525  	}
   526  	sort.Strings(tags)
   527  
   528  	info := &RevInfo{
   529  		Origin: &Origin{
   530  			Hash: hash,
   531  		},
   532  		Name:    hash,
   533  		Short:   ShortenSHA1(hash),
   534  		Time:    time.Unix(t, 0).UTC(),
   535  		Version: version,
   536  		Tags:    tags,
   537  	}
   538  	return info, nil
   539  }
   540  
   541  func bzrParseStat(rev, out string) (*RevInfo, error) {
   542  	var revno int64
   543  	var tm time.Time
   544  	for _, line := range strings.Split(out, "\n") {
   545  		if line == "" || line[0] == ' ' || line[0] == '\t' {
   546  			// End of header, start of commit message.
   547  			break
   548  		}
   549  		if line[0] == '-' {
   550  			continue
   551  		}
   552  		before, after, found := strings.Cut(line, ":")
   553  		if !found {
   554  			// End of header, start of commit message.
   555  			break
   556  		}
   557  		key, val := before, strings.TrimSpace(after)
   558  		switch key {
   559  		case "revno":
   560  			if j := strings.Index(val, " "); j >= 0 {
   561  				val = val[:j]
   562  			}
   563  			i, err := strconv.ParseInt(val, 10, 64)
   564  			if err != nil {
   565  				return nil, vcsErrorf("unexpected revno from bzr log: %q", line)
   566  			}
   567  			revno = i
   568  		case "timestamp":
   569  			j := strings.Index(val, " ")
   570  			if j < 0 {
   571  				return nil, vcsErrorf("unexpected timestamp from bzr log: %q", line)
   572  			}
   573  			t, err := time.Parse("2006-01-02 15:04:05 -0700", val[j+1:])
   574  			if err != nil {
   575  				return nil, vcsErrorf("unexpected timestamp from bzr log: %q", line)
   576  			}
   577  			tm = t.UTC()
   578  		}
   579  	}
   580  	if revno == 0 || tm.IsZero() {
   581  		return nil, vcsErrorf("unexpected response from bzr log: %q", out)
   582  	}
   583  
   584  	info := &RevInfo{
   585  		Name:    strconv.FormatInt(revno, 10),
   586  		Short:   fmt.Sprintf("%012d", revno),
   587  		Time:    tm,
   588  		Version: rev,
   589  	}
   590  	return info, nil
   591  }
   592  
   593  func fossilParseStat(rev, out string) (*RevInfo, error) {
   594  	for _, line := range strings.Split(out, "\n") {
   595  		if strings.HasPrefix(line, "uuid:") || strings.HasPrefix(line, "hash:") {
   596  			f := strings.Fields(line)
   597  			if len(f) != 5 || len(f[1]) != 40 || f[4] != "UTC" {
   598  				return nil, vcsErrorf("unexpected response from fossil info: %q", line)
   599  			}
   600  			t, err := time.Parse(time.DateTime, f[2]+" "+f[3])
   601  			if err != nil {
   602  				return nil, vcsErrorf("unexpected response from fossil info: %q", line)
   603  			}
   604  			hash := f[1]
   605  			version := rev
   606  			if strings.HasPrefix(hash, version) {
   607  				version = hash // extend to full hash
   608  			}
   609  			info := &RevInfo{
   610  				Origin: &Origin{
   611  					Hash: hash,
   612  				},
   613  				Name:    hash,
   614  				Short:   ShortenSHA1(hash),
   615  				Time:    t,
   616  				Version: version,
   617  			}
   618  			return info, nil
   619  		}
   620  	}
   621  	return nil, vcsErrorf("unexpected response from fossil info: %q", out)
   622  }
   623  
   624  type limitedWriter struct {
   625  	W               io.Writer
   626  	N               int64
   627  	ErrLimitReached error
   628  }
   629  
   630  func (l *limitedWriter) Write(p []byte) (n int, err error) {
   631  	if l.N > 0 {
   632  		max := len(p)
   633  		if l.N < int64(max) {
   634  			max = int(l.N)
   635  		}
   636  		n, err = l.W.Write(p[:max])
   637  		l.N -= int64(n)
   638  		if err != nil || n >= len(p) {
   639  			return n, err
   640  		}
   641  	}
   642  
   643  	return n, l.ErrLimitReached
   644  }
   645
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