[FAB-11334] Adds a function to purge a ledger's transient storage (#2769

)

This introduces a transientstore.Delete(ledgerID) routine to assist with the bookkeeping
while unjoining a peer from a channel.  Before removing the transient storage, the store
is marked as UNDER_DELETION in a system leveldb, providing an opportunity to recover from
a failed deletion at the next peer initialization.

Signed-off-by: Josh Kneubuhl <jkneubuh@us.ibm.com>

common/ledger/util/leveldbhelper/leveldb_helper.go

@@ -205,16 +205,25 @@ func (f *FileLock) Lock() error {
 		panic(fmt.Sprintf("Error creating dir if missing: %s", err))
 	}
 	dbOpts.ErrorIfMissing = !dirEmpty
-	f.db, err = leveldb.OpenFile(f.filePath, dbOpts)
+	db, err := leveldb.OpenFile(f.filePath, dbOpts)
 	if err != nil && err == syscall.EAGAIN {
 		return errors.Errorf("lock is already acquired on file %s", f.filePath)
 	}
 	if err != nil {
 		panic(fmt.Sprintf("Error acquiring lock on file %s: %s", f.filePath, err))
 	}
+
+	// only mutate the lock db reference AFTER validating that the lock was held.
+	f.db = db
+
 	return nil
 }
 
+// Determine if the lock is currently held open.
+func (f *FileLock) IsLocked() bool {
+	return f.db != nil
+}
+
 // Unlock releases a previously acquired lock. We achieve this by closing
 // the previously opened db. FileUnlock can be called multiple times.
 func (f *FileLock) Unlock() {

common/ledger/util/leveldbhelper/leveldb_helper_test.go

@@ -157,6 +157,33 @@ func TestFileLock(t *testing.T) {
 	require.NoError(t, os.RemoveAll(fileLockPath))
 }
 
+func TestFileLockLockUnlockLock(t *testing.T) {
+	// create an open lock
+	lockPath := testDBPath + "/fileLock"
+	lock := NewFileLock(lockPath)
+	require.Nil(t, lock.db)
+	require.Equal(t, lock.filePath, lockPath)
+	require.False(t, lock.IsLocked())
+
+	defer lock.Unlock()
+	defer os.RemoveAll(lockPath)
+
+	// lock
+	require.NoError(t, lock.Lock())
+	require.True(t, lock.IsLocked())
+
+	// lock
+	require.ErrorContains(t, lock.Lock(), "lock is already acquired")
+
+	// unlock
+	lock.Unlock()
+	require.False(t, lock.IsLocked())
+
+	// lock - this should not error
+	require.NoError(t, lock.Lock())
+	require.True(t, lock.IsLocked())
+}
+
 func TestCreateDBInEmptyDir(t *testing.T) {
 	require.NoError(t, os.RemoveAll(testDBPath), "")
 	require.NoError(t, os.MkdirAll(testDBPath, 0o775), "")