Function readGitHead

source code/utils/git/gitFilesystem.ts:151–185

(
  gitDir: string,
)

 * this by trimming after slicing past "ref:".
 */
export async function readGitHead(
  gitDir: string,
): Promise<
  { type: 'branch'; name: string } | { type: 'detached'; sha: string } | null
> {
  try {
    const content = (await readFile(join(gitDir, 'HEAD'), 'utf-8')).trim()
    if (content.startsWith('ref:')) {
      const ref = content.slice('ref:'.length).trim()
      if (ref.startsWith('refs/heads/')) {
        const name = ref.slice('refs/heads/'.length)
        // Reject path traversal and argument injection from a tampered HEAD.
        if (!isSafeRefName(name)) {
          return null
        }
        return { type: 'branch', name }
      }
      // Unusual symref (not a local branch) — resolve to SHA
      if (!isSafeRefName(ref)) {
        return null
      }
      const sha = await resolveRef(gitDir, ref)
      return sha ? { type: 'detached', sha } : { type: 'detached', sha: '' }
    }
    // Raw SHA (detached HEAD). Validate: an attacker-controlled HEAD file
    // could contain shell metacharacters that flow into downstream shell
    // contexts.
    if (!isValidGitSha(content)) {
      return null
    }
    return { type: 'detached', sha: content }
  } catch {
    return null
  }
}

// ---------------------------------------------------------------------------
// resolveRef — resolve loose/packed refs to SHAs