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Expressions.java
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/*
* Copyright 2012-2023 The Feign Authors
*
* 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 feign.template;
import feign.Param.Expander;
import feign.Util;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Optional;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public final class Expressions {
private static final int MAX_EXPRESSION_LENGTH = 10000;
private static final String PATH_STYLE_OPERATOR = ";";
/**
* Literals may be present and preceded the expression.
*
* The expression part must start with a '{' and end with a '}'. The contents of the expression
* may start with an RFC Operator or the operators reserved by the rfc: Level 2 Operators: '+' and
* '#' Level 3 Operators: '.' and '/' and ';' and '?' and '&' Reserved Operators: '=' and ',' and
* '!' and '@' and '|'
*
* The RFC specifies that '{' or '}' or '(' or ')' or'$' is are illegal characters. Feign does not
* honor this portion of the RFC Expressions allow '$' characters for Collection expansions, and
* all other characters are legal as a regular expression may be passed as a Value Modifier in
* Feign
*
* This is not a complete implementation of the rfc
*
* <a href="https://www.rfc-editor.org/rfc/rfc6570#section-2.2">RFC 6570 Expressions</a>
*/
static final Pattern EXPRESSION_PATTERN =
Pattern.compile("^(\\{([+#./;?&=,!@|]?)(.+)\\})$");
// Partially From:
// https://stackoverflow.com/questions/29494608/regex-for-uri-templates-rfc-6570-wanted -- I
// suspect much of the codebase could be refactored around the example regex there
/**
* A pattern for matching possible variable names.
*
* This pattern accepts characters allowed in RFC 6570 Section 2.3 It also allows the characters
* feign has allowed in the past "[]-$"
*
* The RFC specifies that a variable name followed by a ':' should be a max-length specification.
* Feign deviates from the rfc in that the ':' value modifier is used to mark a regular
* expression.
*
*/
private static final Pattern VARIABLE_LIST_PATTERN = Pattern.compile(
"(([\\w-\\[\\]$]|%[0-9A-Fa-f]{2})(\\.?([\\w-\\[\\]$]|%[0-9A-Fa-f]{2}))*(:.*|\\*)?)(,(([\\w-\\[\\]$]|%[0-9A-Fa-f]{2})(\\.?([\\w-\\[\\]$]|%[0-9A-Fa-f]{2}))*(:.*|\\*)?))*");
public static Expression create(final String value) {
/* remove the start and end braces */
final String expression = stripBraces(value);
if (expression == null || expression.isEmpty()) {
throw new IllegalArgumentException("an expression is required.");
}
/* Check if the expression is too long */
if (expression.length() > MAX_EXPRESSION_LENGTH) {
throw new IllegalArgumentException(
"expression is too long. Max length: " + MAX_EXPRESSION_LENGTH);
}
/* create a new regular expression matcher for the expression */
String variableName = null;
String variablePattern = null;
String operator = null;
Matcher matcher = EXPRESSION_PATTERN.matcher(value);
if (matcher.matches()) {
/* grab the operator */
operator = matcher.group(2).trim();
/* we have a valid variable expression, extract the name from the first group */
variableName = matcher.group(3).trim();
if (variableName.contains(":")) {
/* split on the colon and ensure the size of parts array must be 2 */
String[] parts = variableName.split(":", 2);
variableName = parts[0];
variablePattern = parts[1];
}
/* look for nested expressions */
if (variableName.contains("{")) {
/* nested, literal */
return null;
}
}
/* check for an operator */
if (PATH_STYLE_OPERATOR.equalsIgnoreCase(operator)) {
return new PathStyleExpression(variableName, variablePattern);
}
/* default to simple */
return SimpleExpression.isSimpleExpression(value)
? new SimpleExpression(variableName, variablePattern)
: null; // Return null if it can't be validated as a Simple Expression -- Probably a Literal
}
private static String stripBraces(String expression) {
if (expression == null) {
return null;
}
if (expression.startsWith("{") && expression.endsWith("}")) {
return expression.substring(1, expression.length() - 1);
}
return expression;
}
/**
* Expression that adheres to Simple String Expansion as outlined in <a
* href="https://tools.ietf.org/html/rfc6570#section-3.2.2>Simple String Expansion (Level 1)</a>
*/
static class SimpleExpression extends Expression {
private static final String DEFAULT_SEPARATOR = ",";
protected String separator = DEFAULT_SEPARATOR;
private boolean nameRequired = false;
SimpleExpression(String name, String pattern) {
super(name, pattern);
}
SimpleExpression(String name, String pattern, String separator, boolean nameRequired) {
this(name, pattern);
this.separator = separator;
this.nameRequired = nameRequired;
}
protected String encode(Object value) {
return UriUtils.encode(value.toString(), Util.UTF_8);
}
@SuppressWarnings("unchecked")
@Override
protected String expand(Object variable, boolean encode) {
StringBuilder expanded = new StringBuilder();
if (Iterable.class.isAssignableFrom(variable.getClass())) {
expanded.append(this.expandIterable((Iterable<?>) variable));
} else if (Map.class.isAssignableFrom(variable.getClass())) {
expanded.append(this.expandMap((Map<String, ?>) variable));
} else if (Optional.class.isAssignableFrom(variable.getClass())) {
Optional<?> optional = (Optional) variable;
if (optional.isPresent()) {
expanded.append(this.expand(optional.get(), encode));
} else {
if (!this.nameRequired) {
return null;
}
expanded.append(this.encode(this.getName()))
.append("=");
}
} else {
if (this.nameRequired) {
expanded.append(this.encode(this.getName()))
.append("=");
}
expanded.append((encode) ? encode(variable) : variable);
}
/* return the string value of the variable */
String result = expanded.toString();
if (!this.matches(result)) {
throw new IllegalArgumentException("Value " + expanded
+ " does not match the expression pattern: " + this.getPattern());
}
return result;
}
protected String expandIterable(Iterable<?> values) {
StringBuilder result = new StringBuilder();
for (Object value : values) {
if (value == null) {
/* skip */
continue;
}
/* expand the value */
String expanded = this.encode(value);
if (expanded.isEmpty()) {
/* always append the separator */
result.append(this.separator);
} else {
if (result.length() != 0) {
if (!result.toString().equalsIgnoreCase(this.separator)) {
result.append(this.separator);
}
}
if (this.nameRequired) {
result.append(this.encode(this.getName()))
.append("=");
}
result.append(expanded);
}
}
/* return the expanded value */
return result.toString();
}
protected String expandMap(Map<String, ?> values) {
StringBuilder result = new StringBuilder();
for (Entry<String, ?> entry : values.entrySet()) {
StringBuilder expanded = new StringBuilder();
String name = this.encode(entry.getKey());
String value = this.encode(entry.getValue().toString());
expanded.append(name)
.append("=");
if (!value.isEmpty()) {
expanded.append(value);
}
if (result.length() != 0) {
result.append(this.separator);
}
result.append(expanded);
}
return result.toString();
}
protected static boolean isSimpleExpression(String expressionCandidate) {
final Matcher matcher = EXPRESSION_PATTERN.matcher(expressionCandidate);
return matcher.matches()
&& matcher.group(2).isEmpty() // Simple Expressions do not support any special operators
&& VARIABLE_LIST_PATTERN.matcher(matcher.group(3)).matches();
}
}
public static class PathStyleExpression extends SimpleExpression implements Expander {
public PathStyleExpression(String name, String pattern) {
super(name, pattern, ";", true);
}
@Override
protected String expand(Object variable, boolean encode) {
return this.separator + super.expand(variable, encode);
}
@Override
public String expand(Object value) {
return this.expand(value, true);
}
@Override
public String getValue() {
if (this.getPattern() != null) {
return "{" + this.separator + this.getName() + ":" + this.getName() + "}";
}
return "{" + this.separator + this.getName() + "}";
}
}
}