changeset: Look in packed-refs if ref file not found.

changeset/commit.go

@@ -17,6 +17,7 @@ limitations under the License.
 package changeset
 
 import (
+	"bufio"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -28,6 +29,10 @@ import (
 const (
 	commitIDFile      = "HEAD"
 	koDataPathEnvName = "KO_DATA_PATH"
+	// packedRefsFile is a file containing a list of refs, used to compact the
+	// list of refs instead of storing them on the filesystem directly.
+	// See https://git-scm.com/docs/git-pack-refs
+	packedRefsFile = "packed-refs"
 )
 
 var commitIDRE = regexp.MustCompile(`^[a-f0-9]{40}$`)
@@ -41,9 +46,27 @@ func Get() (string, error) {
 	}
 	commitID := strings.TrimSpace(string(data))
 	if rID := strings.TrimPrefix(commitID, "ref: "); rID != commitID {
+		// First try to read from the direct ref file - e.g. refs/heads/main
 		data, err := readFileFromKoData(rID)
 		if err != nil {
-			return "", err
+			if !os.IsNotExist(err) {
+				return "", err
+			}
+
+			// Ref file didn't exist - it might be contained in the packed-refs
+			// file.
+			var pferr error
+			data, pferr = findPackedRef(rID)
+			// Only return the sub-error if the packed-refs file exists, otherwise
+			// just let the original error return (e.g. treat it as if we didn't
+			// even attempt the operation). This is primarily to keep the error
+			// messages clean.
+			if pferr != nil {
+				if os.IsNotExist(pferr) {
+					return "", err
+				}
+				return "", pferr
+			}
 		}
 		commitID = strings.TrimSpace(string(data))
 	}
@@ -58,9 +81,49 @@ func Get() (string, error) {
 // to be wrapped into the container from /kodata by ko. If it fails, returns
 // the error it gets.
 func readFileFromKoData(filename string) ([]byte, error) {
+	f, err := koDataFile(filename)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	return ioutil.ReadAll(f)
+}
+
+// readFileFromKoData tries to open the file with given name under KO_DATA_PATH.
+// The file is expected to be wrapped into the container from /kodata by ko.
+// If it fails, returns the error it gets.
+func koDataFile(filename string) (*os.File, error) {
 	koDataPath := os.Getenv(koDataPathEnvName)
 	if koDataPath == "" {
 		return nil, fmt.Errorf("%q does not exist or is empty", koDataPathEnvName)
 	}
-	return ioutil.ReadFile(filepath.Join(koDataPath, filename))
+	return os.Open(filepath.Join(koDataPath, filename))
+}
+
+// findPackedRef searches the packed-ref file for ref values.
+// This can happen if the # of refs in a repo grows too much - git will try
+// and condense them into a file.
+// See https://git-scm.com/docs/git-pack-refs
+func findPackedRef(ref string) ([]byte, error) {
+	f, err := koDataFile(packedRefsFile)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		// We only care about lines with `<commit> <ref>` pairs.
+		// Why this might happen:
+		// 1. Lines starting with ^ refer to unpeeled tag SHAs
+		// 	  (e.g. the commits pointed to by annotated tags)
+		s := strings.Split(scanner.Text(), " ")
+		if len(s) != 2 {
+			continue
+		}
+		if ref == s[1] {
+			return []byte(s[0]), nil
+		}
+	}
+	return nil, fmt.Errorf("%q ref not found in packed-refs", ref)
 }

changeset/commit_test.go

@@ -70,6 +70,15 @@ func TestReadFile(t *testing.T) {
 		koDataPath: "testdata/nonexisting",
 		wantErr:    true,
 		err:        errors.New("open testdata/nonexisting/HEAD: no such file or directory"),
+	}, {
+		name:       "packed-ref",
+		koDataPath: "testdata/packed-refs",
+		want:       testCommitID,
+	}, {
+		name:       "no refs with packed-ref",
+		koDataPath: "testdata/noncommited-packed-refs",
+		wantErr:    true,
+		err:        fmt.Errorf("%q ref not found in packed-refs", nonCommittedHeadRef),
 	}}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {

changeset/testdata/noncommited-packed-refs/HEAD

@@ -0,0 +1 @@
+ref: refs/heads/non_committed_branch

changeset/testdata/packed-refs/HEAD

@@ -0,0 +1 @@
+ref: refs/heads/foo

changeset/testdata/packed-refs/packed-refs

@@ -0,0 +1,4 @@
+a2d1bdfe929516d7da141aef68631a7ee6941b2d refs/tags/bar
+^51be315ed160e68627a3bc51a244ec77e470c667
+a2d1bdfe929516d7da141aef68631a7ee6941b2d refs/tags/baz
+a2d1bdfe929516d7da141aef68631a7ee6941b2d refs/heads/foo