C0urante commented on code in PR #15379: URL: https://github.com/apache/kafka/pull/15379#discussion_r1570960525
########## connect/transforms/src/main/java/org/apache/kafka/connect/transforms/field/SingleFieldPath.java: ########## @@ -0,0 +1,258 @@ +/* + * 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.kafka.connect.transforms.field; + +import org.apache.kafka.common.config.ConfigException; +import org.apache.kafka.connect.data.Field; +import org.apache.kafka.connect.data.Schema; +import org.apache.kafka.connect.data.Struct; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.List; +import java.util.Map; +import java.util.Objects; + +/** + * A SingleFieldPath is composed of one or more field names, known as path steps, + * to access values within a data object (either {@code Struct} or {@code Map<String, Object>}). + * + * <p>If the SMT requires accessing multiple fields on the same data object, use {@link MultiFieldPaths} instead. + * + * <p>The field path semantics are defined by the {@link FieldSyntaxVersion syntax version}. + * + * @see <a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-821%3A+Connect+Transforms+support+for+nested+structures";>KIP-821</a> + * @see FieldSyntaxVersion + * @see MultiFieldPaths + */ +public class SingleFieldPath { + // Invariants: + // - A field path can contain one or more steps + private static final char BACKTICK = '`'; + private static final char DOT = '.'; + private static final char BACKSLASH = '\\'; + + private final String originalPath; + private final FieldSyntaxVersion version; + private final List<String> steps; + + public SingleFieldPath(String pathText, FieldSyntaxVersion version) { + this.originalPath = Objects.requireNonNull(pathText, "Field path cannot be null"); + this.version = version; + switch (version) { + case V1: // backward compatibility + this.steps = Collections.singletonList(pathText); + break; + case V2: + this.steps = buildFieldPathV2(pathText); + break; + default: + throw new IllegalArgumentException("Unknown syntax version: " + version); + } + } + + private static List<String> buildFieldPathV2(String path) { + final List<String> steps = new ArrayList<>(); + // path character index to track backticks and dots and break path into steps + int idx = 0; + while (idx < path.length() && idx >= 0) { + if (path.charAt(idx) != BACKTICK) { + final int start = idx; + idx = path.indexOf(String.valueOf(DOT), idx); + if (idx >= 0) { // get path step and move forward + String field = path.substring(start, idx); + steps.add(field); + idx++; + } else { // add all + String field = path.substring(start); + steps.add(field); + } + } else { // has backtick + int backtickAt = idx; + idx++; + StringBuilder field = new StringBuilder(); + int start = idx; + while (true) { + // find closing backtick + idx = path.indexOf(String.valueOf(BACKTICK), idx); + if (idx == -1) { // if not found, then fail + failWhenIncompleteBacktickPair(path, backtickAt); + } + + // backtick escaped if right after backslash + boolean escaped = path.charAt(idx - 1) == BACKSLASH; + + if (idx >= path.length() - 1) { // at the end of path + if (escaped) { // but escaped, then fail + failWhenIncompleteBacktickPair(path, backtickAt); + } + field.append(path, start, idx); + // we've reached the end of the path, and the last character is the backtick + steps.add(field.toString()); + idx++; + break; + } + + if (path.charAt(idx + 1) != DOT) { // not followed by a dot + // this backtick isn't followed by a dot; include it in the field name, but continue + // looking for a matching backtick that is followed by a dot + idx++; + continue; + } + + if (escaped) { + // this backtick was escaped; include it in the field name, but continue + // looking for an unescaped matching backtick + field.append(path, start, idx - 1) + .append(BACKTICK); + + idx++; + start = idx; + continue; + } + + // we've found our matching backtick + field.append(path, start, idx); + steps.add(field.toString()); + idx += 2; // increment by two to include the backtick and the dot after it + break; + } + } + } + // add last step if last char is a dot + if (!path.isEmpty() && path.charAt(path.length() - 1) == DOT) + steps.add(""); + return Collections.unmodifiableList(steps); + } + + private static void failWhenIncompleteBacktickPair(String path, int backtickAt) { + throw new ConfigException("Incomplete backtick pair in path: [" + path + "]," + + " consider adding a backslash before backtick at position " + backtickAt + + " to escape it"); + } + + public String originalPath() { + return this.originalPath; + } + + + /** + * Access a {@code Field} at the current path within a schema {@code Schema} + * If field is not found, then {@code null} is returned. + */ + public Field fieldFrom(Schema schema) { + if (schema == null) return null; + + Schema current = schema; + for (String pathSegment : stepsWithoutLast()) { + final Field field = current.field(pathSegment); + if (field != null) { + current = field.schema(); + } else { + return null; + } + } + return current.field(lastStep()); + } + + /** + * Access a value at the current path within a schema-based {@code Struct} + * If object is not found, then {@code null} is returned. + */ + public Object valueFrom(Struct struct) { + if (struct == null) return null; + + Struct current = struct; + for (String pathSegment : stepsWithoutLast()) { + // Check to see if the field actually exists + if (current.schema().field(pathSegment) == null) { + return null; + } + current = current.getStruct(pathSegment); + } + + if (current.schema().field(lastStep()) != null) { + return current.get(lastStep()); + } else { + return null; + } + } + + List<String> stepsWithoutLast() { + return steps.subList(0, lastStepIndex()); + } + + /** + * Access a value at the current path within a schemaless {@code Map<String, Object>}. + * If object is not found, then {@code null} is returned. + */ + @SuppressWarnings("unchecked") + public Object valueFrom(Map<String, Object> map) { + if (map == null) return null; + + if (steps.size() == 1) { + return map.get(steps.get(0)); + } else { + Map<String, Object> current = map; + for (int i = 0; i < steps.size(); i++) { + if (current == null) { + return null; + } + if (i == lastStepIndex()) { + return current.get(steps.get(i)); + } else { + current = (Map<String, Object>) current.get(steps.get(i)); + } + } + } + return null; Review Comment: We can clean this up a bit: ```suggestion if (map == null) return null; Map<String, Object> current = map; for (String step : stepsWithoutLast()) { current = requireMapOrNull(current.get(step), "nested field access"); if (current == null) return null; } return current.get(lastStep()); ``` Using `requireMapOrNull` (statically imported from `org.apache.kafka.connect.transforms.util.Requirements`) makes this more type-safe, and leveraging `stepsWithoutLast` and `lastStep` helps simplify the logic. -- This is an automated message from the Apache Git Service. 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