git-lfs/lfs/gitscanner_log.go
Chris Darroch 7fb982f946 lfs,git: use "git log -m" to collect stash diffs
When looking for recent objects to retain during a "git lfs prune",
we use "git log -m" to collect diffs of all stash commits, including
all the parents of the WIP merge commits from the reflog, where
index changes and untracked files are recorded for each stash.

This allows us to further simplify some of the changes from commit
404992801e194f50d5f3ea8dda56d5fc14671795 and avoid the need to
introduce a git.Show() function to use "git show"; it also lets
us iterate just twice, once over the reflog for refs/stash to get
the SHAs of the WIP merge commits, and then over all the individual
parent diffs output by "git log -m" for those merges.
2020-08-26 20:44:07 -07:00

328 lines
9.5 KiB
Go

package lfs
import (
"bufio"
"bytes"
"fmt"
"io"
"io/ioutil"
"regexp"
"strings"
"time"
"github.com/git-lfs/git-lfs/filepathfilter"
"github.com/git-lfs/git-lfs/git"
"github.com/git-lfs/git-lfs/subprocess"
"github.com/rubyist/tracerx"
)
// When scanning diffs e.g. parseLogOutputToPointers, which direction of diff to include
// data from, i.e. '+' or '-'. Depending on what you're scanning for either might be useful
type LogDiffDirection byte
const (
LogDiffAdditions = LogDiffDirection('+') // include '+' diffs
LogDiffDeletions = LogDiffDirection('-') // include '-' diffs
)
var (
// Arguments to append to a git log call which will limit the output to
// lfs changes and format the output suitable for parseLogOutput.. method(s)
logLfsSearchArgs = []string{
"-G", "oid sha256:", // only diffs which include an lfs file SHA change
"-p", // include diff so we can read the SHA
"-U12", // Make sure diff context is always big enough to support 10 extension lines to get whole pointer
`--format=lfs-commit-sha: %H %P`, // just a predictable commit header we can detect
}
)
type gitscannerResult struct {
Pointer *WrappedPointer
Err error
}
func scanUnpushed(cb GitScannerFoundPointer, remote string) error {
logArgs := []string{
"--branches", "--tags", // include all locally referenced commits
"--not"} // but exclude everything that comes after
if len(remote) == 0 {
logArgs = append(logArgs, "--remotes")
} else {
logArgs = append(logArgs, fmt.Sprintf("--remotes=%v", remote))
}
// Add standard search args to find lfs references
logArgs = append(logArgs, logLfsSearchArgs...)
cmd, err := git.Log(logArgs...)
if err != nil {
return err
}
parseScannerLogOutput(cb, LogDiffAdditions, cmd)
return nil
}
func scanStashed(cb GitScannerFoundPointer, s *GitScanner) error {
// Stashes are actually 2-3 commits, each containing one of:
// 1. Working copy (WIP) modified files
// 2. Index changes
// 3. Untracked files (but only if "git stash -u" was used)
// The first of these, the WIP commit, is a merge whose first parent
// is HEAD and whose other parent(s) are commits 2 and 3 above.
// We need to get the individual diff of each of these commits to
// ensure we have all of the LFS objects referenced by the stash,
// so a future "git stash pop" can restore them all.
// First we get the list of SHAs of the WIP merge commits from the
// reflog using "git log -g --format=%h refs/stash --". Because
// older Git versions (at least <=2.7) don't report merge parents in
// the reflog, we can't extract the parent SHAs from "Merge:" lines
// in the log; we can, however, use the "git log -m" option to force
// individual diffs of all the merge parents in a second step.
logArgs := []string{"-g", "--format=%h", "refs/stash", "--"}
cmd, err := git.Log(logArgs...)
if err != nil {
return err
}
scanner := bufio.NewScanner(cmd.Stdout)
var stashMergeShas []string
for scanner.Scan() {
stashMergeShas = append(stashMergeShas, strings.TrimSpace(scanner.Text()))
}
err = cmd.Wait()
if err != nil {
// Ignore this error, it really only happens when there's no refs/stash
return nil
}
// We can use the log parser if we provide the -m option to get
// merge diffs shown individually
logArgs = []string{"-m"}
// Add standard search args to find lfs references
logArgs = append(logArgs, logLfsSearchArgs...)
logArgs = append(logArgs, stashMergeShas...)
cmd, err = git.Log(logArgs...)
if err != nil {
return err
}
parseScannerLogOutput(cb, LogDiffAdditions, cmd)
return nil
}
func parseScannerLogOutput(cb GitScannerFoundPointer, direction LogDiffDirection, cmd *subprocess.BufferedCmd) {
ch := make(chan gitscannerResult, chanBufSize)
go func() {
scanner := newLogScanner(direction, cmd.Stdout)
for scanner.Scan() {
if p := scanner.Pointer(); p != nil {
ch <- gitscannerResult{Pointer: p}
}
}
stderr, _ := ioutil.ReadAll(cmd.Stderr)
err := cmd.Wait()
if err != nil {
ch <- gitscannerResult{Err: fmt.Errorf("error in git log: %v %v", err, string(stderr))}
}
close(ch)
}()
cmd.Stdin.Close()
for result := range ch {
cb(result.Pointer, result.Err)
}
}
// logPreviousVersions scans history for all previous versions of LFS pointers
// from 'since' up to (but not including) the final state at ref
func logPreviousSHAs(cb GitScannerFoundPointer, ref string, since time.Time) error {
logArgs := []string{
fmt.Sprintf("--since=%v", git.FormatGitDate(since)),
}
// Add standard search args to find lfs references
logArgs = append(logArgs, logLfsSearchArgs...)
// ending at ref
logArgs = append(logArgs, ref)
cmd, err := git.Log(logArgs...)
if err != nil {
return err
}
parseScannerLogOutput(cb, LogDiffDeletions, cmd)
return nil
}
func parseLogOutputToPointers(log io.Reader, dir LogDiffDirection,
includePaths, excludePaths []string, results chan *WrappedPointer) {
scanner := newLogScanner(dir, log)
if len(includePaths)+len(excludePaths) > 0 {
scanner.Filter = filepathfilter.New(includePaths, excludePaths)
}
for scanner.Scan() {
if p := scanner.Pointer(); p != nil {
results <- p
}
}
}
// logScanner parses log output formatted as per logLfsSearchArgs & returns
// pointers.
type logScanner struct {
// Filter will ensure file paths matching the include patterns, or not matchin
// the exclude patterns are skipped.
Filter *filepathfilter.Filter
s *bufio.Scanner
dir LogDiffDirection
pointer *WrappedPointer
pointerData *bytes.Buffer
currentFilename string
currentFileIncluded bool
commitHeaderRegex *regexp.Regexp
fileHeaderRegex *regexp.Regexp
fileMergeHeaderRegex *regexp.Regexp
pointerDataRegex *regexp.Regexp
}
// dir: whether to include results from + or - diffs
// r: a stream of output from git log with at least logLfsSearchArgs specified
func newLogScanner(dir LogDiffDirection, r io.Reader) *logScanner {
return &logScanner{
s: bufio.NewScanner(r),
dir: dir,
pointerData: &bytes.Buffer{},
currentFileIncluded: true,
// no need to compile these regexes on every `git-lfs` call, just ones that
// use the scanner.
commitHeaderRegex: regexp.MustCompile(fmt.Sprintf(`^lfs-commit-sha: (%s)(?: (%s))*`, git.ObjectIDRegex, git.ObjectIDRegex)),
fileHeaderRegex: regexp.MustCompile(`diff --git a\/(.+?)\s+b\/(.+)`),
fileMergeHeaderRegex: regexp.MustCompile(`diff --cc (.+)`),
pointerDataRegex: regexp.MustCompile(`^([\+\- ])(version https://git-lfs|oid sha256|size|ext-).*$`),
}
}
func (s *logScanner) Pointer() *WrappedPointer {
return s.pointer
}
func (s *logScanner) Err() error {
return s.s.Err()
}
func (s *logScanner) Scan() bool {
s.pointer = nil
p, canScan := s.scan()
s.pointer = p
return canScan
}
// Utility func used at several points below (keep in narrow scope)
func (s *logScanner) finishLastPointer() *WrappedPointer {
if s.pointerData.Len() == 0 || !s.currentFileIncluded {
return nil
}
p, err := DecodePointer(s.pointerData)
s.pointerData.Reset()
if err == nil {
return &WrappedPointer{Name: s.currentFilename, Pointer: p}
} else {
tracerx.Printf("Unable to parse pointer from log: %v", err)
return nil
}
}
// For each commit we'll get something like this:
/*
lfs-commit-sha: 60fde3d23553e10a55e2a32ed18c20f65edd91e7 e2eaf1c10b57da7b98eb5d722ec5912ddeb53ea1
diff --git a/1D_Noise.png b/1D_Noise.png
new file mode 100644
index 0000000..2622b4a
--- /dev/null
+++ b/1D_Noise.png
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:f5d84da40ab1f6aa28df2b2bf1ade2cdcd4397133f903c12b4106641b10e1ed6
+size 1289
*/
// There can be multiple diffs per commit (multiple binaries)
// Also when a binary is changed the diff will include a '-' line for the old SHA
func (s *logScanner) scan() (*WrappedPointer, bool) {
for s.s.Scan() {
line := s.s.Text()
if match := s.commitHeaderRegex.FindStringSubmatch(line); match != nil {
// Currently we're not pulling out commit groupings, but could if we wanted
// This just acts as a delimiter for finishing a multiline pointer
if p := s.finishLastPointer(); p != nil {
return p, true
}
} else if match := s.fileHeaderRegex.FindStringSubmatch(line); match != nil {
// Finding a regular file header
p := s.finishLastPointer()
// Pertinent file name depends on whether we're listening to additions or removals
if s.dir == LogDiffAdditions {
s.setFilename(match[2])
} else {
s.setFilename(match[1])
}
if p != nil {
return p, true
}
} else if match := s.fileMergeHeaderRegex.FindStringSubmatch(line); match != nil {
// Git merge file header is a little different, only one file
p := s.finishLastPointer()
s.setFilename(match[1])
if p != nil {
return p, true
}
} else if s.currentFileIncluded {
if match := s.pointerDataRegex.FindStringSubmatch(line); match != nil {
// An LFS pointer data line
// Include only the entirety of one side of the diff
// -U3 will ensure we always get all of it, even if only
// the SHA changed (version & size the same)
changeType := match[1][0]
// Always include unchanged context lines (normally just the version line)
if LogDiffDirection(changeType) == s.dir || changeType == ' ' {
// Must skip diff +/- marker
s.pointerData.WriteString(line[1:])
s.pointerData.WriteString("\n") // newline was stripped off by scanner
}
}
}
}
if p := s.finishLastPointer(); p != nil {
return p, true
}
return nil, false
}
func (s *logScanner) setFilename(name string) {
s.currentFilename = name
s.currentFileIncluded = s.Filter.Allows(name)
}