api: Add a parser/editor for URL encoded query params

Author: jdcormie

api/src/main/java/io/grpc/QueryParams.java

@@ -0,0 +1,272 @@
+/*
+ * Copyright 2026 The gRPC 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 io.grpc;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import com.google.common.base.Splitter;
+import java.io.UnsupportedEncodingException;
+import java.net.URLDecoder;
+import java.net.URLEncoder;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Objects;
+import javax.annotation.Nullable;
+
+/**
+ * A parser and mutable container class for {@code application/x-www-form-urlencoded}-style URL
+ * parameters as conceived by <a href="https://datatracker.ietf.org/doc/html/rfc1866#section-8.2.1">
+ * RFC 1866 Section 8.2.1</a>.
+ *
+ * <p>For example, a URI like {@code "http://who?name=John+Doe&role=admin&role=user&active"} has:
+ *
+ * <ul>
+ *   <li>A key {@code "name"} with value {@code "John Doe"}
+ *   <li>A key {@code "role"} with value {@code "admin"}
+ *   <li>A second key named {@code "role"} with value {@code "user"}
+ *   <li>"Lone" key {@code "active"} without a value.
+ * </ul>
+ *
+ * <p>Instances are not safe for concurrent access by multiple threads.
+ */
+@Internal
+public final class QueryParams {
+
+  private static final String UTF_8 = "UTF-8";
+  private final List<Entry> entries = new ArrayList<>();
+
+  /** Creates a new, empty {@code QueryParameters} instance. */
+  public QueryParams() {}
+
+  /**
+   * Parses a raw query string into a {@code QueryParameters} instance.
+   *
+   * <p>The input is split on {@code '&'} and each parameter is parsed as either a key/value pair
+   * (if it contains an equals sign) or a "lone" key (if it does not).
+   *
+   * @param rawQuery the raw query component to parse, must not be null
+   * @return a new {@code QueryParameters} instance containing the parsed parameters
+   */
+  public static QueryParams parseRawQueryString(String rawQuery) {
+    checkNotNull(rawQuery, "rawQuery");
+    QueryParams params = new QueryParams();
+    if (!rawQuery.isEmpty()) {
+      for (String part : Splitter.on('&').split(rawQuery)) {
+        int equalsIndex = part.indexOf('=');
+        if (equalsIndex == -1) {
+          params.add(Entry.forRawLoneKey(part));
+        } else {
+          String rawKey = part.substring(0, equalsIndex);
+          String rawValue = part.substring(equalsIndex + 1);
+          params.add(Entry.forRawKeyValue(rawKey, rawValue));
+        }
+      }
+    }
+    return params;
+  }
+
+  /**
+   * Returns the last parameter in the parameters list having the specified key.
+   *
+   * @param key the key to search for (non-encoded)
+   * @return the matching {@link Entry}, or {@code null} if no match is found
+   */
+  @Nullable
+  public Entry getLast(String key) {
+    checkNotNull(key, "key");
+    for (int i = entries.size() - 1; i >= 0; --i) {
+      Entry entry = entries.get(i);
+      if (entry.getKey().equals(key)) {
+        return entry;
+      }
+    }
+    return null;
+  }
+
+  /**
+   * Appends 'entry' to the list of query parameters.
+   *
+   * @param entry the entry to add
+   */
+  public void add(Entry entry) {
+    entries.add(checkNotNull(entry, "entry"));
+  }
+
+  /**
+   * Removes all entries equal to the specified entry.
+   *
+   * <p>Two entries are considered equal if they have the same key and value *after* any URL
+   * decoding has been performed.
+   *
+   * @param entry the entry to remove, must not be null
+   * @return the number of entries removed
+   */
+  public int removeAll(Entry entry) {
+    checkNotNull(entry, "entry");
+    int removed = 0;
+    Iterator<Entry> it = entries.iterator();
+    while (it.hasNext()) {
+      if (it.next().equals(entry)) {
+        it.remove();
+        removed++;
+      }
+    }
+    return removed;
+  }
+
+  /**
+   * Returns the "raw" query string representation of these parameters, suitable for passing to the
+   * {@link io.grpc.Uri.Builder#setRawQuery} method.
+   *
+   * @return the raw query string
+   */
+  public String toRawQueryString() {
+    StringBuilder resultBuilder = new StringBuilder();
+    boolean first = true;
+    for (Entry entry : entries) {
+      if (!first) {
+        resultBuilder.append('&');
+      }
+      entry.appendToRawQueryStringBuilder(resultBuilder);
+      first = false;
+    }
+    return resultBuilder.toString();
+  }
+
+  /** Returns true if and only if there are zero entries in this collection. */
+  public boolean isEmpty() {
+    return entries.isEmpty();
+  }
+
+  @Override
+  public String toString() {
+    return toRawQueryString();
+  }
+
+  /** A single query parameter entry. */
+  public static final class Entry {
+    private final String rawKey;
+    @Nullable private final String rawValue;
+    private final String key;
+    @Nullable private final String value;
+
+    private Entry(String rawKey, @Nullable String rawValue, String key, @Nullable String value) {
+      this.rawKey = checkNotNull(rawKey, "rawKey");
+      this.rawValue = rawValue;
+      this.key = checkNotNull(key, "key");
+      this.value = value;
+    }
+
+    /**
+     * Returns the key.
+     *
+     * <p>Any characters that needed URL encoding have already been decoded.
+     */
+    public String getKey() {
+      return key;
+    }
+
+    /**
+     * Returns the value, or {@code null} if this is a "lone" key.
+     *
+     * <p>Any characters that needed URL encoding have already been decoded.
+     */
+    @Nullable
+    public String getValue() {
+      return value;
+    }
+
+    /**
+     * Creates a new key/value pair entry.
+     *
+     * <p>Both key and value can contain any character. They will be URL encoded for you later, if
+     * necessary.
+     */
+    public static Entry forKeyValue(String key, String value) {
+      checkNotNull(key, "key");
+      checkNotNull(value, "value");
+      return new Entry(encode(key), encode(value), key, value);
+    }
+
+    /**
+     * Creates a new query parameter with a "lone" key.
+     *
+     * <p>'key' can contain any character. It will be URL encoded for you later, as necessary.
+     *
+     * @param key the decoded key, must not be null
+     * @return a new {@code Entry}
+     */
+    public static Entry forLoneKey(String key) {
+      checkNotNull(key, "key");
+      return new Entry(encode(key), null, key, null);
+    }
+
+    static Entry forRawKeyValue(String rawKey, String rawValue) {
+      checkNotNull(rawKey, "rawKey");
+      checkNotNull(rawValue, "rawValue");
+      return new Entry(rawKey, rawValue, decode(rawKey), decode(rawValue));
+    }
+
+    static Entry forRawLoneKey(String rawKey) {
+      checkNotNull(rawKey, "rawKey");
+      return new Entry(rawKey, null, decode(rawKey), null);
+    }
+
+    void appendToRawQueryStringBuilder(StringBuilder sb) {
+      sb.append(rawKey);
+      if (rawValue != null) {
+        sb.append('=').append(rawValue);
+      }
+    }
+
+    @Override
+    public boolean equals(Object o) {
+      if (this == o) {
+        return true;
+      }
+      if (!(o instanceof Entry)) {
+        return false;
+      }
+      Entry entry = (Entry) o;
+      return Objects.equals(key, entry.key) && Objects.equals(value, entry.value);
+    }
+
+    @Override
+    public int hashCode() {
+      return Objects.hash(key, value);
+    }
+  }
+
+  private static String decode(String s) {
+    try {
+      // TODO: Use URLDecoder.decode(String, Charset) when available
+      return URLDecoder.decode(s, UTF_8);
+    } catch (UnsupportedEncodingException impossible) {
+      throw new AssertionError("UTF-8 is not supported", impossible);
+    }
+  }
+
+  private static String encode(String s) {
+    try {
+      // TODO: Use URLEncoder.encode(String, Charset) when available
+      return URLEncoder.encode(s, UTF_8);
+    } catch (UnsupportedEncodingException impossible) {
+      throw new AssertionError("UTF-8 is not supported", impossible);
+    }
+  }
+}