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/*
* Copyright (c) 2019, 2024 Oracle and/or its affiliates.
*
* Licensed 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 io.helidon.config;
import java.util.HashMap;
import java.util.Map;
import java.util.regex.Pattern;
import static java.util.Collections.unmodifiableMap;
/**
* Provides environment variables that include aliases enabling setting or overriding configuration with keys that are
* unlikely to be legal as environment variables.
*
* The
* MP config specification describes the environment variables {@code ConfigSource} as follows:
*
* Some operating systems allow only alphabetic characters or an underscore, _, in environment variables. Other
* characters such as ., /, etc may be disallowed. In order to set a value for a config property that has a name
* containing such disallowed characters from an environment variable, the following rules are used.
*
* This ConfigSource searches 3 environment variables for a given property name (e.g. com.ACME.size):
*
* 1. Exact match (i.e. com.ACME.size)
* 2. Replace the character that is neither alphanumeric nor _ with _ (i.e. com_ACME_size)
* 3. Replace the character that is neither alphanumeric nor _ with _ and convert to upper case (i.e. COM_ACME_SIZE)
*
* The first environment variable that is found is returned by this ConfigSource.
*
*
* The spec assumes the mapping takes place during search, where the desired key is known, but Helidon merges
* {@code ConfigSource}s instead; therefore this implementation produces additional KV pairs with aliases
* for any variable that can meaningfully be mapped. See {@link #shouldAlias(String)} for the mapping criteria.
*
* Since Helidon supports many configuration keys that contain {@code '-'} (e.g. {@code "server.executor-service.max-pool-size"}),
* an additional mapping is required to produce a matching alias. Given that it must map from legal environment variable names
* and reduce the chances of inadvertent mappings, a verbose mapping is used: {@code "_dash_"} substrings (upper and lower case)
* are first replaced by {@code '-'}. See {@link #expand()} for the aliases produced.
*/
public final class EnvironmentVariables {
private static final Pattern DASH_PATTERN = Pattern.compile("_dash_|_DASH_");
private static final String UNDERSCORE = "_";
private static final String DOUBLE_UNDERSCORE = "__";
private static final String DASH = "-";
private static final char UNDERSCORE_CHAR = '_';
private static final char DOT_CHAR = '.';
/**
* Tests whether aliases should be created for the given environment variable name.
*
* To provide a meaningful alias, the name must meet all of the following criteria:
*
* - does not begin or end with a {@code '_'} character
* - does not contain {@code "__"}
* - contains one or more {@code '_'} characters
*
*
* @param name The environment variable name.
* @return {@code true} if aliases should be created.
*/
public static boolean shouldAlias(final String name) {
final int length = name.length();
return length > 2
&& name.charAt(0) != UNDERSCORE_CHAR
&& name.charAt(length - 1) != UNDERSCORE_CHAR
&& name.contains(UNDERSCORE)
&& !name.contains(DOUBLE_UNDERSCORE);
}
/**
* Returns the environment variables and their aliases.
*
* The following mappings are applied to any environment variable name for which {@link #shouldAlias(String)} returns
* {@code true}:
*
* - Replace {@code "_dash_"} by {@code '-'}, e.g. {@code "SERVER_EXECUTOR_dash_SERVICE_MAX_dash_POOL_dash_SIZE"} becomes
* {@code "SERVER_EXECUTOR-SERVICE_MAX-POOL-SIZE"}.
* - Replace {@code '_'} by {@code '.'} and add as a alias, e.g. {@code "com_ACME_size"} becomes {@code "com.ACME.size"}
* and {@code "SERVER_EXECUTOR-SERVICE_MAX-POOL-SIZE"} becomes {@code "SERVER.EXECUTOR-SERVICE.MAX-POOL-SIZE"}. This mapping
* is added primarily to support mixed case config keys such as {@code "app.someCamelCaseKey"}.
* - Convert the result of step 2 to lowercase and add as a alias, e.g. {@code "com.ACME.size"} becomes
* {@code "com.acme.size"} and {@code "SERVER.EXECUTOR-SERVICE.MAX-POOL-SIZE"} becomes
* {@code "server.executor-service.max-pool-size"}.
*
*
*
* @return An unmodifiable copy of {@link System#getenv()} including aliases.
*/
public static Map expand() {
return expand(PropertiesFilter.create(System.getProperties()).filter(System.getenv()));
}
/**
* Returns the environment variables and their aliases.
*
* The following mappings are applied to any environment variable name for which {@link #shouldAlias(String)} returns
* {@code true}:
*
* - Replace {@code "_dash_"} by {@code '-'}, e.g. {@code "SERVER_EXECUTOR_dash_SERVICE_MAX_dash_POOL_dash_SIZE"} becomes
* {@code "SERVER_EXECUTOR-SERVICE_MAX-POOL-SIZE"}.
* - Replace {@code '_'} by {@code '.'} and add as an alias, e.g. {@code "com_ACME_size"} becomes {@code "com.ACME.size"}
* and {@code "SERVER_EXECUTOR-SERVICE_MAX-POOL-SIZE"} becomes {@code "SERVER.EXECUTOR-SERVICE.MAX-POOL-SIZE"}. This mapping
* is added primarily to support mixed case config keys such as {@code "app.someCamelCaseKey"}.
* - Convert the result of step 2 to lowercase and add as an alias, e.g. {@code "com.ACME.size"} becomes
* {@code "com.acme.size"} and {@code "SERVER.EXECUTOR-SERVICE.MAX-POOL-SIZE"} becomes
* {@code "server.executor-service.max-pool-size"}.
*
*
*
* @param env The environment variables.
* @return An unmodifiable copy of {@code env} with aliases added.
*/
public static Map expand(final Map env) {
final Map result = new HashMap<>(env.size());
env.forEach((name, value) -> {
result.put(name, value);
if (shouldAlias(name)) {
String alias = DASH_PATTERN.matcher(name).replaceAll(DASH);
alias = alias.replace(UNDERSCORE_CHAR, DOT_CHAR);
result.put(alias, value);
result.put(alias.toLowerCase(), value);
}
});
return unmodifiableMap(result);
}
private EnvironmentVariables() {
}
}