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Fix link parsing for non-trivial cases #2128

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Fix link parsing for non-trivial cases #2128

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de1927a
Fix link parsing for non-trivial cases
Mar 20, 2024
a6fcbda
Fix indentation
Mar 20, 2024
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269 changes: 193 additions & 76 deletions src/main/java/org/springframework/hateoas/Link.java
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Original file line number Diff line number Diff line change
Expand Up @@ -23,31 +23,30 @@
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.springframework.lang.NonNull;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.springframework.util.StringUtils;

/**
* Value object for links.
*
* @author Oliver Gierke
* @author Greg Turnquist
* @author Jens Schauder
* @author Viliam Durina
*/
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonIgnoreProperties(value = { "templated", "template" }, ignoreUnknown = true)
public class Link implements Serializable {

private static final long serialVersionUID = -9037755944661782121L;
private static final Pattern URI_AND_ATTRIBUTES_PATTERN = Pattern.compile("<(.*)>;(.*)");

public static final String ATOM_NAMESPACE = "http://www.w3.org/2005/Atom";

Expand Down Expand Up @@ -241,7 +240,7 @@ public Link andAffordances(List<Affordance> affordances) {
}

/**
* Creats a new {@link Link} with the given {@link Affordance}s.
* Creates a new {@link Link} with the given {@link Affordance}s.
*
* @param affordances must not be {@literal null}.
* @return will never be {@literal null}.
Expand Down Expand Up @@ -384,77 +383,162 @@ public URI toUri() {
}

/**
* Factory method to easily create {@link Link} instances from RFC-8288 compatible {@link String} representations of a
* link.
* Internal method to parse and consume one link from input string.
*
* @param element an RFC-8288 compatible representation of a link.
* @throws IllegalArgumentException if a {@link String} was given that does not adhere to RFC-8288.
* @throws IllegalArgumentException if no {@code rel} attribute could be found.
* @return
* @param input The input string
* @param pos Position to start from. It must be a 1-element array. The element will be
* mutated to point to the first non-consumed character (either ',' or the end of input).
* @return a non-null Link
*/
public static Link valueOf(String element) {

if (!StringUtils.hasText(element)) {
throw new IllegalArgumentException(String.format("Given link header %s is not RFC-8288 compliant!", element));
@NonNull
static Link valueOfInt(@NonNull String input, @NonNull int[] pos) {
assert pos.length == 1;
int l = input.length();
while (pos[0] < l && Character.isWhitespace(input.charAt(pos[0]))) {
pos[0]++;
}

Matcher matcher = URI_AND_ATTRIBUTES_PATTERN.matcher(element);

if (matcher.find()) {

Map<String, String> attributes = getAttributeMap(matcher.group(2));

if (!attributes.containsKey("rel")) {
throw new IllegalArgumentException("Link does not provide a rel attribute!");
if (input.charAt(pos[0]) != '<') {
throw new IllegalArgumentException("Expecting '<' at index " + pos[0]);
}
pos[0]++;
int urlEnd = input.indexOf('>', pos[0]);
if (urlEnd < 0) {
throw new IllegalArgumentException("Missing closing '>' at index " + input.length());
}
String url = input.substring(pos[0], urlEnd);
pos[0] = urlEnd + 1;

// parse parameters
Map<String, String> params = new HashMap<>();
enum State { INITIAL, IN_KEY, BEFORE_VALUE, IN_VALUE };
State state = State.INITIAL;
StringBuilder
key = new StringBuilder(),
value = new StringBuilder();

outer:
while (pos[0] <= l) {
boolean eoi = pos[0] == l; // EOI - end of input
char ch = eoi ? 0 : input.charAt(pos[0]);
switch (state) {
// searching for the initial `;`
case INITIAL:
if (Character.isWhitespace(ch)) {
pos[0]++;
}
else if (ch == ';') {
state = State.IN_KEY;
pos[0]++;
}
else {
// if there's something else, it's the end of this link
break outer;
}
break;

// consuming the key up to `=`
case IN_KEY:
if (ch == '=') {
state = State.BEFORE_VALUE;
}
// value isn't mandatory, so param separator, link separator, or end of input all create a new param
else if (ch == ';' || ch == ',' || eoi) {
if (!key.isEmpty()) {
params.put(key.toString().trim(), "");
key.setLength(0);
}
} else {
key.append(ch);
}
pos[0]++;
break;

case BEFORE_VALUE:
if (Character.isWhitespace(ch)) {
pos[0]++;
}
else if (ch == '"' || ch == '\'') {
consumeQuotedString(input, value, pos);
params.putIfAbsent(key.toString().trim(), value.toString());
key.setLength(0);
value.setLength(0);
state = State.INITIAL;
} else {
state = State.IN_VALUE;
}
break;

case IN_VALUE:
if (ch == ';' || ch == ',' || eoi) {
params.putIfAbsent(key.toString().trim(), value.toString().trim());
key.setLength(0);
value.setLength(0);
state = State.INITIAL;
} else {
value.append(ch);
pos[0]++;
}
break;

default:
throw new AssertionError();
}
}

LinkRelation rel = LinkRelation.of(attributes.get("rel"));
String href = matcher.group(1);
String hrefLang = attributes.get("hreflang");
String media = attributes.get("media");
String title = attributes.get("title");
String type = attributes.get("type");
String deprecation = attributes.get("deprecation");
String profile = attributes.get("profile");
String name = attributes.get("name");

return new Link(rel, href, hrefLang, media, title, type, deprecation, profile, name, templateOrNull(href),
Collections.emptyList());

} else {
throw new IllegalArgumentException(String.format("Given link header %s is not RFC-8288 compliant!", element));
String sRel = params.get("rel");
if (!StringUtils.hasText(sRel)) {
throw new IllegalArgumentException("Missing 'rel' attribute at index " + pos[0]);
}
LinkRelation rel = LinkRelation.of(sRel);
String hrefLang = params.get("hreflang");
String media = params.get("media");
String title = params.get("title");
String type = params.get("type");
String deprecation = params.get("deprecation");
String profile = params.get("profile");
String name = params.get("name");

return new Link(rel, url, hrefLang, media, title, type, deprecation, profile, name, templateOrNull(url),
Collections.emptyList());
}

/**
* Consume a quoted string from `input`, adding its contents to `target`. The starting position should be at
* starting quote. After consuming, the ending position will be just after the last final quote.
*/
private static void consumeQuotedString(String input, StringBuilder target, int[] pos) {
int l = input.length();
char quotingChar = input.charAt(pos[0]);
assert quotingChar == '"' || quotingChar == '\'';
// skip quoting char
pos[0]++;
for (; pos[0] < l; pos[0]++) {
char ch = input.charAt(pos[0]);
if (ch == quotingChar) {
pos[0]++; // consume the final quote
return;
}
if (ch == '\\') {
ch = input.charAt(++pos[0]);
}
target.append(ch);
}
throw new IllegalArgumentException("Missing final quote at index " + pos[0]);
}

/**
* Parses the links attributes from the given source {@link String}.
* Factory method to easily create {@link Link} instances from RFC-8288 compatible {@link String} representations of a
* link.
*
* @param source
* @return
* @param element an RFC-8288 compatible representation of a link.
* @throws IllegalArgumentException if a {@link String} was given that does not adhere to RFC-8288.
* @throws IllegalArgumentException if no {@code rel} attribute could be found.
* @return The parsed link
* @deprecated Use {@link Links#parse(String)} instead. This method parses only the first link from a list of links.
*/
private static Map<String, String> getAttributeMap(String source) {

if (!StringUtils.hasText(source)) {
return Collections.emptyMap();
}

String[] parts = source.split(";");
Map<String, String> attributes = new HashMap<>();

for (String part : parts) {

int delimiter = part.indexOf('=');

String key = part.substring(0, delimiter).trim();
String value = part.substring(delimiter + 1).trim();

// Potentially unquote value
value = value.startsWith("\"") ? value.substring(1, value.length() - 1) : value;

attributes.put(key, value);
}

return attributes;
@Deprecated
public static Link valueOf(String element) {
return valueOfInt(element, new int[]{0});
}

/**
Expand All @@ -471,7 +555,7 @@ public Link withHref(String href) {
}

/**
* Create a new {@link Link} by copying all attributes and applying the new {@literal hrefleng}.
* Create a new {@link Link} by copying all attributes and applying the new {@literal hreflang}.
*
* @param hreflang can be {@literal null}
* @return will never be {@literal null}.
Expand Down Expand Up @@ -659,38 +743,71 @@ public int hashCode() {
*/
@Override
public String toString() {

String linkString = String.format("<%s>;rel=\"%s\"", href, rel.value());
StringBuilder result = new StringBuilder(64);
result.append('<')
// We only url-encode the `>`. We expect other special chars to already be escaped. `;` and `,` need not
// be escaped within the URL
.append(href.replace(">", "%3e"))
.append(">;rel=");
quoteParamValue(rel.value(), result);

if (hreflang != null) {
linkString += ";hreflang=\"" + hreflang + "\"";
result.append(";hreflang=");
quoteParamValue(hreflang, result);
}

if (media != null) {
linkString += ";media=\"" + media + "\"";
result.append(";media=");
quoteParamValue(media, result);
}

if (title != null) {
linkString += ";title=\"" + title + "\"";
result.append(";title=");
quoteParamValue(title, result);
}

if (type != null) {
linkString += ";type=\"" + type + "\"";
result.append(";type=");
quoteParamValue(type, result);
}

if (deprecation != null) {
linkString += ";deprecation=\"" + deprecation + "\"";
result.append(";deprecation=");
quoteParamValue(deprecation, result);
}

if (profile != null) {
linkString += ";profile=\"" + profile + "\"";
result.append(";profile=");
quoteParamValue(profile, result);
}

if (name != null) {
linkString += ";name=\"" + name + "\"";
result.append(";name=");
quoteParamValue(name, result);
}

return linkString;
return result.toString();
}

/**
* Quotes the given string `s` and appends the result to the `target`. This method appends the start quote, the
* escaped text, and the end quote.
*
* @param s Text to quote
* @param target StringBuilder to append to
*/
private void quoteParamValue(String s, StringBuilder target) {
// we reserve extra 6 chars: two for the start and end quote, 2 is a reserve for potential escaped chars
target.ensureCapacity(target.length() + s.length() + 2);
target.append('"');
for (int i = 0, l = s.length(); i < l; i++) {
char ch = s.charAt(i);
if (ch == '"' || ch == '\\') {
target.append('\\');
}
target.append(ch);
}
target.append('"');
}

@Nullable
Expand Down