MagicCommitPaths.java
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.fs.s3a.commit;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import java.util.stream.IntStream;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.util.StringUtils;
import static org.apache.hadoop.fs.s3a.commit.CommitConstants.MAGIC_PATH_PREFIX;
import static org.apache.hadoop.util.Preconditions.checkArgument;
import static org.apache.hadoop.fs.s3a.commit.CommitConstants.BASE;
import static org.apache.hadoop.fs.s3a.commit.InternalCommitterConstants.E_NO_MAGIC_PATH_ELEMENT;
/**
* Operations on (magic) paths.
*/
public final class MagicCommitPaths {
private MagicCommitPaths() {
}
/**
* Take an absolute path, split it into a list of elements.
* If empty, the path is the root path.
* @param path input path
* @return a possibly empty list of elements.
* @throws IllegalArgumentException if the path is invalid -relative, empty...
*/
public static List<String> splitPathToElements(Path path) {
checkArgument(path.isAbsolute(), "path is relative");
String uriPath = path.toUri().getPath();
checkArgument(!uriPath.isEmpty(), "empty path");
if ("/".equals(uriPath)) {
// special case: empty list
return new ArrayList<>(0);
}
List<String> elements = new ArrayList<>();
int len = uriPath.length();
int firstElementChar = 1;
int endOfElement = uriPath.indexOf('/', firstElementChar);
while (endOfElement > 0) {
elements.add(uriPath.substring(firstElementChar, endOfElement));
firstElementChar = endOfElement + 1;
endOfElement = firstElementChar == len ? -1
: uriPath.indexOf('/', firstElementChar);
}
// expect a possible child element here
if (firstElementChar != len) {
elements.add(uriPath.substring(firstElementChar));
}
return elements;
}
/**
* Is a path in the magic tree?
* @param elements element list
* @return true if a path is considered magic
*/
public static boolean isMagicPath(List<String> elements) {
return elements.stream()
.anyMatch(element -> element.startsWith(MAGIC_PATH_PREFIX));
}
/**
* Does the list of magic elements contain a base path marker?
* @param elements element list, already stripped out
* from the magic tree.
* @return true if a path has a base directory
*/
public static boolean containsBasePath(List<String> elements) {
return elements.contains(BASE);
}
/**
* Get the index of the magic path element.
* @param elements full path element list
* @return the index.
* @throws IllegalArgumentException if there is no magic element
*/
public static int magicElementIndex(List<String> elements) {
Optional<Integer> index = IntStream.range(0, elements.size())
.filter(i -> elements.get(i).startsWith(MAGIC_PATH_PREFIX))
.boxed()
.findFirst();
if (index.isPresent()) {
return index.get();
} else {
throw new IllegalArgumentException(E_NO_MAGIC_PATH_ELEMENT);
}
}
/**
* Get the parent path elements of the magic path.
* The list may be immutable or may be a view of the underlying list.
* Both the parameter list and the returned list MUST NOT be modified.
* @param elements full path element list
* @return the parent elements; may be empty
*/
public static List<String> magicPathParents(List<String> elements) {
return elements.subList(0, magicElementIndex(elements));
}
/**
* Get the child path elements under the magic path.
* The list may be immutable or may be a view of the underlying list.
* Both the parameter list and the returned list MUST NOT be modified.
* @param elements full path element list
* @return the child elements; may be empty
*/
public static List<String> magicPathChildren(List<String> elements) {
int index = magicElementIndex(elements);
int len = elements.size();
if (index == len - 1) {
// empty index
return Collections.emptyList();
} else {
return elements.subList(index + 1, len);
}
}
/**
* Get any child path elements under any {@code __base} path,
* or an empty list if there is either: no {@code __base} path element,
* or no child entries under it.
* The list may be immutable or may be a view of the underlying list.
* Both the parameter list and the returned list MUST NOT be modified.
* @param elements full path element list
* @return the child elements; may be empty
*/
public static List<String> basePathChildren(List<String> elements) {
int index = elements.indexOf(BASE);
if (index < 0) {
return Collections.emptyList();
}
int len = elements.size();
if (index == len - 1) {
// empty index
return Collections.emptyList();
} else {
return elements.subList(index + 1, len);
}
}
/**
* Take a list of elements and create an S3 key by joining them
* with "/" between each one.
* @param elements path elements
* @return a path which can be used in the AWS API
*/
public static String elementsToKey(List<String> elements) {
return StringUtils.join("/", elements);
}
/**
* Get the filename of a path: the last element.
* @param elements element list.
* @return the filename; the last element.
*/
public static String filename(List<String> elements) {
return lastElement(elements);
}
/**
* Last element of a (non-empty) list.
* @param strings strings in
* @return the last one.
*/
public static String lastElement(List<String> strings) {
checkArgument(!strings.isEmpty(), "empty list");
return strings.get(strings.size() - 1);
}
/**
* Calculates the final destination of a file.
* This is the parent of any "MAGIC PATH" element, and the filename
* of the path. That is: all intermediate child path elements are discarded.
* Why so? paths under the magic path include job attempt and task attempt
* subdirectories, which need to be skipped.
*
* If there is a {@code __base} directory in the children, then it becomes
* a base for unflattened paths, that is: all its children are pulled into
* the final destination.
* @param elements element list.
* @return the path
*/
public static List<String> finalDestination(List<String> elements) {
if (isMagicPath(elements)) {
List<String> destDir = magicPathParents(elements);
List<String> children = magicPathChildren(elements);
checkArgument(!children.isEmpty(), "No path found under the prefix " +
MAGIC_PATH_PREFIX);
ArrayList<String> dest = new ArrayList<>(destDir);
if (containsBasePath(children)) {
// there's a base marker in the path
List<String> baseChildren = basePathChildren(children);
checkArgument(!baseChildren.isEmpty(),
"No path found under " + BASE);
dest.addAll(baseChildren);
} else {
dest.add(filename(children));
}
return dest;
} else {
return elements;
}
}
}