refactor: move packages to internal/

1 files changed, 546 insertions, 0 deletions

diff --git a/internal/gitdiff/file_header.go b/internal/gitdiff/file_header.go
new file mode 100644
index 0000000..7ae4bc9
--- /dev/null
+++ b/internal/gitdiff/file_header.go
@@ -0,0 +1,546 @@
+package gitdiff
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const (
+	devNull = "/dev/null"
+)
+
+// ParseNextFileHeader finds and parses the next file header in the stream. If
+// a header is found, it returns a file and all input before the header. It
+// returns nil if no headers are found before the end of the input.
+func (p *parser) ParseNextFileHeader() (*File, string, error) {
+	var preamble strings.Builder
+	var file *File
+	for {
+		// check for disconnected fragment headers (corrupt patch)
+		frag, err := p.ParseTextFragmentHeader()
+		if err != nil {
+			// not a valid header, nothing to worry about
+			goto NextLine
+		}
+		if frag != nil {
+			return nil, "", p.Errorf(-1, "patch fragment without file header: %s", frag.Header())
+		}
+
+		// check for a git-generated patch
+		file, err = p.ParseGitFileHeader()
+		if err != nil {
+			return nil, "", err
+		}
+		if file != nil {
+			return file, preamble.String(), nil
+		}
+
+		// check for a "traditional" patch
+		file, err = p.ParseTraditionalFileHeader()
+		if err != nil {
+			return nil, "", err
+		}
+		if file != nil {
+			return file, preamble.String(), nil
+		}
+
+	NextLine:
+		preamble.WriteString(p.Line(0))
+		if err := p.Next(); err != nil {
+			if err == io.EOF {
+				break
+			}
+			return nil, "", err
+		}
+	}
+	return nil, preamble.String(), nil
+}
+
+func (p *parser) ParseGitFileHeader() (*File, error) {
+	const prefix = "diff --git "
+
+	if !strings.HasPrefix(p.Line(0), prefix) {
+		return nil, nil
+	}
+	header := p.Line(0)[len(prefix):]
+
+	defaultName, err := parseGitHeaderName(header)
+	if err != nil {
+		return nil, p.Errorf(0, "git file header: %v", err)
+	}
+
+	f := &File{}
+	for {
+		end, err := parseGitHeaderData(f, p.Line(1), defaultName)
+		if err != nil {
+			return nil, p.Errorf(1, "git file header: %v", err)
+		}
+
+		if err := p.Next(); err != nil {
+			if err == io.EOF {
+				break
+			}
+			return nil, err
+		}
+
+		if end {
+			break
+		}
+	}
+
+	if f.OldName == "" && f.NewName == "" {
+		if defaultName == "" {
+			return nil, p.Errorf(0, "git file header: missing filename information")
+		}
+		f.OldName = defaultName
+		f.NewName = defaultName
+	}
+
+	if (f.NewName == "" && !f.IsDelete) || (f.OldName == "" && !f.IsNew) {
+		return nil, p.Errorf(0, "git file header: missing filename information")
+	}
+
+	return f, nil
+}
+
+func (p *parser) ParseTraditionalFileHeader() (*File, error) {
+	const shortestValidFragHeader = "@@ -1 +1 @@\n"
+	const (
+		oldPrefix = "--- "
+		newPrefix = "+++ "
+	)
+
+	oldLine, newLine := p.Line(0), p.Line(1)
+
+	if !strings.HasPrefix(oldLine, oldPrefix) || !strings.HasPrefix(newLine, newPrefix) {
+		return nil, nil
+	}
+	// heuristic: only a file header if followed by a (probable) fragment header
+	if len(p.Line(2)) < len(shortestValidFragHeader) || !strings.HasPrefix(p.Line(2), "@@ -") {
+		return nil, nil
+	}
+
+	// advance past the first two lines so parser is after the header
+	// no EOF check needed because we know there are >=3 valid lines
+	if err := p.Next(); err != nil {
+		return nil, err
+	}
+	if err := p.Next(); err != nil {
+		return nil, err
+	}
+
+	oldName, _, err := parseName(oldLine[len(oldPrefix):], '\t', 0)
+	if err != nil {
+		return nil, p.Errorf(0, "file header: %v", err)
+	}
+
+	newName, _, err := parseName(newLine[len(newPrefix):], '\t', 0)
+	if err != nil {
+		return nil, p.Errorf(1, "file header: %v", err)
+	}
+
+	f := &File{}
+	switch {
+	case oldName == devNull || hasEpochTimestamp(oldLine):
+		f.IsNew = true
+		f.NewName = newName
+	case newName == devNull || hasEpochTimestamp(newLine):
+		f.IsDelete = true
+		f.OldName = oldName
+	default:
+		// if old name is a prefix of new name, use that instead
+		// this avoids picking variants like "file.bak" or "file~"
+		if strings.HasPrefix(newName, oldName) {
+			f.OldName = oldName
+			f.NewName = oldName
+		} else {
+			f.OldName = newName
+			f.NewName = newName
+		}
+	}
+
+	return f, nil
+}
+
+// parseGitHeaderName extracts a default file name from the Git file header
+// line. This is required for mode-only changes and creation/deletion of empty
+// files. Other types of patch include the file name(s) in the header data.
+// If the names in the header do not match because the patch is a rename,
+// return an empty default name.
+func parseGitHeaderName(header string) (string, error) {
+	header = strings.TrimSuffix(header, "\n")
+	if len(header) == 0 {
+		return "", nil
+	}
+
+	var err error
+	var first, second string
+
+	// there are 4 cases to account for:
+	//
+	//   1) unquoted unquoted
+	//   2) unquoted "quoted"
+	//   3) "quoted" unquoted
+	//   4) "quoted" "quoted"
+	//
+	quote := strings.IndexByte(header, '"')
+	switch {
+	case quote < 0:
+		// case 1
+		first = header
+
+	case quote > 0:
+		// case 2
+		first = header[:quote-1]
+		if !isSpace(header[quote-1]) {
+			return "", fmt.Errorf("missing separator")
+		}
+
+		second, _, err = parseQuotedName(header[quote:])
+		if err != nil {
+			return "", err
+		}
+
+	case quote == 0:
+		// case 3 or case 4
+		var n int
+		first, n, err = parseQuotedName(header)
+		if err != nil {
+			return "", err
+		}
+
+		// git accepts multiple spaces after a quoted name, but not after an
+		// unquoted name, since the name might end with one or more spaces
+		for n < len(header) && isSpace(header[n]) {
+			n++
+		}
+		if n == len(header) {
+			return "", nil
+		}
+
+		if header[n] == '"' {
+			second, _, err = parseQuotedName(header[n:])
+			if err != nil {
+				return "", err
+			}
+		} else {
+			second = header[n:]
+		}
+	}
+
+	first = trimTreePrefix(first, 1)
+	if second != "" {
+		if first == trimTreePrefix(second, 1) {
+			return first, nil
+		}
+		return "", nil
+	}
+
+	// at this point, both names are unquoted (case 1)
+	// since names may contain spaces, we can't use a known separator
+	// instead, look for a split that produces two equal names
+
+	for i := 0; i < len(first)-1; i++ {
+		if !isSpace(first[i]) {
+			continue
+		}
+		second = trimTreePrefix(first[i+1:], 1)
+		if name := first[:i]; name == second {
+			return name, nil
+		}
+	}
+	return "", nil
+}
+
+// parseGitHeaderData parses a single line of metadata from a Git file header.
+// It returns true when header parsing is complete; in that case, line was the
+// first line of non-header content.
+func parseGitHeaderData(f *File, line, defaultName string) (end bool, err error) {
+	if len(line) > 0 && line[len(line)-1] == '\n' {
+		line = line[:len(line)-1]
+	}
+
+	for _, hdr := range []struct {
+		prefix string
+		end    bool
+		parse  func(*File, string, string) error
+	}{
+		{"@@ -", true, nil},
+		{"--- ", false, parseGitHeaderOldName},
+		{"+++ ", false, parseGitHeaderNewName},
+		{"old mode ", false, parseGitHeaderOldMode},
+		{"new mode ", false, parseGitHeaderNewMode},
+		{"deleted file mode ", false, parseGitHeaderDeletedMode},
+		{"new file mode ", false, parseGitHeaderCreatedMode},
+		{"copy from ", false, parseGitHeaderCopyFrom},
+		{"copy to ", false, parseGitHeaderCopyTo},
+		{"rename old ", false, parseGitHeaderRenameFrom},
+		{"rename new ", false, parseGitHeaderRenameTo},
+		{"rename from ", false, parseGitHeaderRenameFrom},
+		{"rename to ", false, parseGitHeaderRenameTo},
+		{"similarity index ", false, parseGitHeaderScore},
+		{"dissimilarity index ", false, parseGitHeaderScore},
+		{"index ", false, parseGitHeaderIndex},
+	} {
+		if strings.HasPrefix(line, hdr.prefix) {
+			if hdr.parse != nil {
+				err = hdr.parse(f, line[len(hdr.prefix):], defaultName)
+			}
+			return hdr.end, err
+		}
+	}
+
+	// unknown line indicates the end of the header
+	// this usually happens if the diff is empty
+	return true, nil
+}
+
+func parseGitHeaderOldName(f *File, line, defaultName string) error {
+	name, _, err := parseName(line, '\t', 1)
+	if err != nil {
+		return err
+	}
+	if f.OldName == "" && !f.IsNew {
+		f.OldName = name
+		return nil
+	}
+	return verifyGitHeaderName(name, f.OldName, f.IsNew, "old")
+}
+
+func parseGitHeaderNewName(f *File, line, defaultName string) error {
+	name, _, err := parseName(line, '\t', 1)
+	if err != nil {
+		return err
+	}
+	if f.NewName == "" && !f.IsDelete {
+		f.NewName = name
+		return nil
+	}
+	return verifyGitHeaderName(name, f.NewName, f.IsDelete, "new")
+}
+
+func parseGitHeaderOldMode(f *File, line, defaultName string) (err error) {
+	f.OldMode, err = parseMode(strings.TrimSpace(line))
+	return
+}
+
+func parseGitHeaderNewMode(f *File, line, defaultName string) (err error) {
+	f.NewMode, err = parseMode(strings.TrimSpace(line))
+	return
+}
+
+func parseGitHeaderDeletedMode(f *File, line, defaultName string) error {
+	f.IsDelete = true
+	f.OldName = defaultName
+	return parseGitHeaderOldMode(f, line, defaultName)
+}
+
+func parseGitHeaderCreatedMode(f *File, line, defaultName string) error {
+	f.IsNew = true
+	f.NewName = defaultName
+	return parseGitHeaderNewMode(f, line, defaultName)
+}
+
+func parseGitHeaderCopyFrom(f *File, line, defaultName string) (err error) {
+	f.IsCopy = true
+	f.OldName, _, err = parseName(line, 0, 0)
+	return
+}
+
+func parseGitHeaderCopyTo(f *File, line, defaultName string) (err error) {
+	f.IsCopy = true
+	f.NewName, _, err = parseName(line, 0, 0)
+	return
+}
+
+func parseGitHeaderRenameFrom(f *File, line, defaultName string) (err error) {
+	f.IsRename = true
+	f.OldName, _, err = parseName(line, 0, 0)
+	return
+}
+
+func parseGitHeaderRenameTo(f *File, line, defaultName string) (err error) {
+	f.IsRename = true
+	f.NewName, _, err = parseName(line, 0, 0)
+	return
+}
+
+func parseGitHeaderScore(f *File, line, defaultName string) error {
+	score, err := strconv.ParseInt(strings.TrimSuffix(line, "%"), 10, 32)
+	if err != nil {
+		nerr := err.(*strconv.NumError)
+		return fmt.Errorf("invalid score line: %v", nerr.Err)
+	}
+	if score <= 100 {
+		f.Score = int(score)
+	}
+	return nil
+}
+
+func parseGitHeaderIndex(f *File, line, defaultName string) error {
+	const sep = ".."
+
+	// note that git stops parsing if the OIDs are too long to be valid
+	// checking this requires knowing if the repository uses SHA1 or SHA256
+	// hashes, which we don't know, so we just skip that check
+
+	parts := strings.SplitN(line, " ", 2)
+	oids := strings.SplitN(parts[0], sep, 2)
+
+	if len(oids) < 2 {
+		return fmt.Errorf("invalid index line: missing %q", sep)
+	}
+	f.OldOIDPrefix, f.NewOIDPrefix = oids[0], oids[1]
+
+	if len(parts) > 1 {
+		return parseGitHeaderOldMode(f, parts[1], defaultName)
+	}
+	return nil
+}
+
+func parseMode(s string) (os.FileMode, error) {
+	mode, err := strconv.ParseInt(s, 8, 32)
+	if err != nil {
+		nerr := err.(*strconv.NumError)
+		return os.FileMode(0), fmt.Errorf("invalid mode line: %v", nerr.Err)
+	}
+	return os.FileMode(mode), nil
+}
+
+// parseName extracts a file name from the start of a string and returns the
+// name and the index of the first character after the name. If the name is
+// unquoted and term is non-zero, parsing stops at the first occurrence of
+// term.
+//
+// If the name is exactly "/dev/null", no further processing occurs. Otherwise,
+// if dropPrefix is greater than zero, that number of prefix components
+// separated by forward slashes are dropped from the name and any duplicate
+// slashes are collapsed.
+func parseName(s string, term byte, dropPrefix int) (name string, n int, err error) {
+	if len(s) > 0 && s[0] == '"' {
+		name, n, err = parseQuotedName(s)
+	} else {
+		name, n, err = parseUnquotedName(s, term)
+	}
+	if err != nil {
+		return "", 0, err
+	}
+	if name == devNull {
+		return name, n, nil
+	}
+	return cleanName(name, dropPrefix), n, nil
+}
+
+func parseQuotedName(s string) (name string, n int, err error) {
+	for n = 1; n < len(s); n++ {
+		if s[n] == '"' && s[n-1] != '\\' {
+			n++
+			break
+		}
+	}
+	if n == 2 {
+		return "", 0, fmt.Errorf("missing name")
+	}
+	if name, err = strconv.Unquote(s[:n]); err != nil {
+		return "", 0, err
+	}
+	return name, n, err
+}
+
+func parseUnquotedName(s string, term byte) (name string, n int, err error) {
+	for n = 0; n < len(s); n++ {
+		if s[n] == '\n' {
+			break
+		}
+		if term > 0 && s[n] == term {
+			break
+		}
+	}
+	if n == 0 {
+		return "", 0, fmt.Errorf("missing name")
+	}
+	return s[:n], n, nil
+}
+
+// verifyGitHeaderName checks a parsed name against state set by previous lines
+func verifyGitHeaderName(parsed, existing string, isNull bool, side string) error {
+	if existing != "" {
+		if isNull {
+			return fmt.Errorf("expected %s, but filename is set to %s", devNull, existing)
+		}
+		if existing != parsed {
+			return fmt.Errorf("inconsistent %s filename", side)
+		}
+	}
+	if isNull && parsed != devNull {
+		return fmt.Errorf("expected %s", devNull)
+	}
+	return nil
+}
+
+// cleanName removes double slashes and drops prefix segments.
+func cleanName(name string, drop int) string {
+	var b strings.Builder
+	for i := 0; i < len(name); i++ {
+		if name[i] == '/' {
+			if i < len(name)-1 && name[i+1] == '/' {
+				continue
+			}
+			if drop > 0 {
+				drop--
+				b.Reset()
+				continue
+			}
+		}
+		b.WriteByte(name[i])
+	}
+	return b.String()
+}
+
+// trimTreePrefix removes up to n leading directory components from name.
+func trimTreePrefix(name string, n int) string {
+	i := 0
+	for ; i < len(name) && n > 0; i++ {
+		if name[i] == '/' {
+			n--
+		}
+	}
+	return name[i:]
+}
+
+// hasEpochTimestamp returns true if the string ends with a POSIX-formatted
+// timestamp for the UNIX epoch after a tab character. According to git, this
+// is used by GNU diff to mark creations and deletions.
+func hasEpochTimestamp(s string) bool {
+	const posixTimeLayout = "2006-01-02 15:04:05.9 -0700"
+
+	start := strings.IndexRune(s, '\t')
+	if start < 0 {
+		return false
+	}
+
+	ts := strings.TrimSuffix(s[start+1:], "\n")
+
+	// a valid timestamp can have optional ':' in zone specifier
+	// remove that if it exists so we have a single format
+	if len(ts) >= 3 && ts[len(ts)-3] == ':' {
+		ts = ts[:len(ts)-3] + ts[len(ts)-2:]
+	}
+
+	t, err := time.Parse(posixTimeLayout, ts)
+	if err != nil {
+		return false
+	}
+	if !t.Equal(time.Unix(0, 0)) {
+		return false
+	}
+	return true
+}
+
+func isSpace(c byte) bool {
+	return c == ' ' || c == '\t' || c == '\n'
+}