[CPS] Relocate CrossProjectRoutingResolver (#136129)

Move CrossProjectRoutingResolver to the same search.crossproject package
as the other cross-project index classes.

Author: prwhelan

server/src/main/java/org/elasticsearch/search/crossproject/CrossProjectRoutingResolver.java

@@ -0,0 +1,220 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+package org.elasticsearch.search.crossproject;
+
+import org.elasticsearch.ElasticsearchStatusException;
+
+import java.util.List;
+import java.util.Set;
+import java.util.function.Predicate;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+import static org.elasticsearch.rest.RestStatus.BAD_REQUEST;
+
+/**
+ * Tech Preview.
+ * Resolves a single entry _alias for a cross-project request specifying a project_routing.
+ * We currently only support a single entry routing containing either a specific name, a prefix, a suffix, or a match-all (*).
+ */
+public class CrossProjectRoutingResolver {
+    private static final String ALIAS = "_alias:";
+    private static final String ORIGIN = "_origin";
+    private static final int ALIAS_LENGTH = ALIAS.length();
+    private static final String ALIAS_MATCH_ALL = ALIAS + "*";
+    private static final String ALIAS_MATCH_ORIGIN = ALIAS + ORIGIN;
+
+    /**
+     * Initially, we only support the "*" wildcard.
+     * https://www.elastic.co/docs/reference/query-languages/query-dsl/query-dsl-query-string-query
+     */
+    private static final Set<Character> UNSUPPORTED_CHARACTERS = Set.of(
+        '+',
+        '-',
+        '=',
+        '&',
+        '|',
+        '>',
+        '<',
+        '!',
+        '(',
+        ')',
+        '{',
+        '}',
+        '[',
+        ']',
+        '^',
+        '"',
+        '~',
+        '?',
+        ':',
+        '\\',
+        '/'
+    );
+
+    /**
+     * @param projectRouting the project_routing specified in the request object.
+     * @param originProject the project alias where this function is being called.
+     * @param candidateProjects the list of project aliases for the active request. This list must *NOT* contain the originProject entry.
+     * @return the filtered list of projects matching the projectRouting, or an empty list if none are found.
+     * @throws ElasticsearchStatusException if the projectRouting is null, empty, does not start with "_alias:", contains more than one
+     *                                      entry, or contains an '*' in the middle of a string.
+     */
+    public List<ProjectRoutingInfo> resolve(
+        String projectRouting,
+        ProjectRoutingInfo originProject,
+        List<ProjectRoutingInfo> candidateProjects
+    ) {
+        assert originProject.projectAlias().equalsIgnoreCase(ORIGIN) == false : "origin project alias must not be " + ORIGIN;
+
+        var candidateProjectStream = candidateProjects.stream().peek(candidateProject -> {
+            assert candidateProject.projectAlias().equalsIgnoreCase(ORIGIN) == false : "project alias must not be " + ORIGIN;
+        }).filter(candidateProject -> {
+            assert candidateProject.equals(originProject) == false : "origin project must not be in the candidateProjects list";
+            return candidateProject.equals(originProject) == false; // assertions are disabled in prod, instead we should filter this out
+        });
+
+        if (ALIAS_MATCH_ORIGIN.equalsIgnoreCase(projectRouting)) {
+            return List.of(originProject);
+        }
+
+        if (projectRouting == null || projectRouting.isEmpty() || ALIAS_MATCH_ALL.equalsIgnoreCase(projectRouting)) {
+            return Stream.concat(Stream.of(originProject), candidateProjectStream).toList();
+        }
+
+        validateProjectRouting(projectRouting);
+
+        var matchesSpecifiedRoute = createRoutingEntryFilter(projectRouting);
+        return Stream.concat(Stream.of(originProject), candidateProjectStream).filter(matchesSpecifiedRoute).toList();
+    }
+
+    private static void validateProjectRouting(String projectRouting) {
+        var startsWithAlias = startsWithIgnoreCase(ALIAS, projectRouting);
+        if (startsWithAlias && projectRouting.length() == ALIAS_LENGTH) {
+            throw new ElasticsearchStatusException("project_routing expression [{}] cannot be empty", BAD_REQUEST, projectRouting);
+        }
+        if ((startsWithAlias == false) && projectRouting.contains(":")) {
+            throw new ElasticsearchStatusException(
+                "Unsupported tag [{}] in project_routing expression [{}]. Supported tags [_alias].",
+                BAD_REQUEST,
+                projectRouting.substring(0, projectRouting.indexOf(":")),
+                projectRouting
+            );
+        }
+        if (startsWithAlias == false) {
+            throw new ElasticsearchStatusException(
+                "project_routing [{}] must start with the prefix [_alias:]",
+                BAD_REQUEST,
+                projectRouting
+            );
+        }
+    }
+
+    private static Predicate<ProjectRoutingInfo> createRoutingEntryFilter(String projectRouting) {
+        // we're using index pointers and directly accessing the internal character array rather than using higher abstraction
+        // methods like String.split or creating multiple substrings. we don't expect a lot of linked projects or long project routing
+        // expressions, but this is expected to run on every search request so we're opting to avoid creating multiple objects.
+        // plus we plan to replace this all soon anyway...
+        var matchPrefix = projectRouting.charAt(projectRouting.length() - 1) == '*';
+        var matchSuffix = projectRouting.charAt(ALIAS_LENGTH) == '*';
+
+        int foundAsterix = -1;
+        int startIndex = matchSuffix ? ALIAS_LENGTH + 1 : ALIAS_LENGTH;
+        int endIndex = matchPrefix ? projectRouting.length() - 1 : projectRouting.length();
+
+        for (int i = startIndex; i < endIndex; ++i) {
+            var nextChar = projectRouting.charAt(i);
+
+            // verify that there are no whitespaces, unsupported characters,
+            // or more complex asterisk expressions (*pro*_2 is unsupported, pro*_2, pro*, and *project_2 are all supported)
+            if (Character.isWhitespace(nextChar)
+                || UNSUPPORTED_CHARACTERS.contains(nextChar)
+                || (nextChar == '*' && (foundAsterix >= 0 || matchPrefix || matchSuffix))) {
+                throw new ElasticsearchStatusException(
+                    "Unsupported project_routing expression [{}]. "
+                        + "Tech Preview only supports project routing via a single project alias or wildcard alias expression",
+                    BAD_REQUEST,
+                    projectRouting.substring(ALIAS_LENGTH)
+                );
+            }
+
+            if (nextChar == '*') {
+                foundAsterix = i;
+            }
+        }
+
+        if (foundAsterix >= 0) {
+            var prefix = projectRouting.substring(startIndex, foundAsterix);
+            var suffix = projectRouting.substring(foundAsterix + 1, endIndex);
+            return possibleRoute -> startsWithIgnoreCase(prefix, possibleRoute.projectAlias())
+                && endsWithIgnoreCase(suffix, possibleRoute.projectAlias());
+        }
+
+        var routingEntry = projectRouting.substring(startIndex, endIndex);
+        if (matchPrefix && matchSuffix) {
+            return possibleRoute -> containsIgnoreCase(routingEntry, possibleRoute.projectAlias());
+        } else if (matchPrefix) {
+            return possibleRoute -> startsWithIgnoreCase(routingEntry, possibleRoute.projectAlias());
+        } else if (matchSuffix) {
+            return possibleRoute -> endsWithIgnoreCase(routingEntry, possibleRoute.projectAlias());
+        } else {
+            return possibleRoute -> possibleRoute.projectAlias().equalsIgnoreCase(routingEntry);
+        }
+    }
+
+    private static boolean startsWithIgnoreCase(String prefix, String str) {
+        if (prefix == null || str == null) {
+            return false;
+        }
+        if (str.startsWith(prefix)) {
+            return true;
+        }
+        if (str.length() < prefix.length()) {
+            return false;
+        }
+        if (str.length() == prefix.length() && str.equalsIgnoreCase(prefix)) {
+            return true;
+        }
+        return str.substring(0, prefix.length()).equalsIgnoreCase(prefix);
+    }
+
+    private static boolean endsWithIgnoreCase(String suffix, String str) {
+        if (suffix == null || str == null) {
+            return false;
+        }
+        if (str.endsWith(suffix)) {
+            return true;
+        }
+        if (str.length() < suffix.length()) {
+            return false;
+        }
+        if (str.length() == suffix.length() && str.equalsIgnoreCase(suffix)) {
+            return true;
+        }
+        return str.substring(str.length() - suffix.length()).equalsIgnoreCase(suffix);
+    }
+
+    private static boolean containsIgnoreCase(String substring, String str) {
+        if (substring == null || str == null) {
+            return false;
+        }
+        if (str.contains(substring)) {
+            return true;
+        }
+        if (str.length() < substring.length()) {
+            return false;
+        }
+        if (str.length() == substring.length() && str.equalsIgnoreCase(substring)) {
+            return true;
+        }
+        var substringLength = substring.length();
+        return IntStream.range(0, str.length() - substringLength).anyMatch(i -> str.regionMatches(true, i, substring, 0, substringLength));
+    }
+}