feat(gax): add StringHttpResponseParser

sdk-platform-java/gax-java/gax-httpjson/src/main/java/com/google/api/gax/httpjson/StringHttpResponseParser.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google LLC nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package com.google.api.gax.httpjson;
+
+import com.google.common.io.CharStreams;
+import com.google.protobuf.TypeRegistry;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.Reader;
+import java.nio.charset.StandardCharsets;
+import org.jspecify.annotations.NullMarked;
+
+/** An {@link HttpResponseParser} that reads the HTTP response body as a UTF-8 String. */
+@NullMarked
+class StringHttpResponseParser implements HttpResponseParser<String> {
+
+  private static final StringHttpResponseParser INSTANCE = new StringHttpResponseParser();
+
+  static StringHttpResponseParser create() {
+    return INSTANCE;
+  }
+
+  private StringHttpResponseParser() {}
+
+  @Override
+  public String parse(InputStream httpContent) {
+    try (Reader reader = new InputStreamReader(httpContent, StandardCharsets.UTF_8)) {
+      return CharStreams.toString(reader);
+    } catch (IOException e) {
+      throw new RestSerializationException("Failed to read response body as string", e);
+    }
+  }
+
+  @Override
+  public String parse(InputStream httpContent, TypeRegistry registry) {
+    return parse(httpContent);
+  }
+
+  @Override
+  public String parse(Reader httpContent, TypeRegistry registry) {
+    try {
+      return CharStreams.toString(httpContent);
+    } catch (IOException e) {
+      throw new RestSerializationException("Failed to read response body as string", e);
+    }
+  }
+
+  @Override
+  public String serialize(String response) {
+    return response;
+  }
+}

sdk-platform-java/gax-java/gax-httpjson/src/test/java/com/google/api/gax/httpjson/StringHttpResponseParserTest.java

@@ -0,0 +1,143 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google LLC nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package com.google.api.gax.httpjson;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import com.google.protobuf.TypeRegistry;
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.Reader;
+import java.io.StringReader;
+import java.nio.charset.StandardCharsets;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class StringHttpResponseParserTest {
+
+  private StringHttpResponseParser parser;
+
+  @BeforeEach
+  void setUp() {
+    parser = StringHttpResponseParser.create();
+  }
+
+  @Test
+  void parse_inputStream_returnsString() {
+    String expected = "Hello, world! \u4e16\u754c";
+    InputStream inputStream = new ByteArrayInputStream(expected.getBytes(StandardCharsets.UTF_8));
+
+    String result = parser.parse(inputStream);
+
+    assertThat(result).isEqualTo(expected);
+  }
+
+  @Test
+  void parse_inputStream_empty_returnsEmptyString() {
+    InputStream inputStream = new ByteArrayInputStream(new byte[0]);
+
+    String result = parser.parse(inputStream);
+
+    assertThat(result).isEmpty();
+  }
+
+  @Test
+  void parse_inputStream_withTypeRegistry_returnsString() {
+    String expected = "response content";
+    InputStream inputStream = new ByteArrayInputStream(expected.getBytes(StandardCharsets.UTF_8));
+
+    String result = parser.parse(inputStream, TypeRegistry.getEmptyTypeRegistry());
+
+    assertThat(result).isEqualTo(expected);
+  }
+
+  @Test
+  void parse_inputStream_ioException_throwsRestSerializationException() {
+    InputStream failingInputStream =
+        new InputStream() {
+          @Override
+          public int read() throws IOException {
+            throw new IOException("Simulated read failure");
+          }
+        };
+
+    RestSerializationException thrown =
+        assertThrows(RestSerializationException.class, () -> parser.parse(failingInputStream));
+    assertThat(thrown).hasCauseThat().isInstanceOf(IOException.class);
+  }
+
+  @Test
+  void parse_reader_returnsString() {
+    String expected = "Hello from Reader!";
+    Reader reader = new StringReader(expected);
+
+    String result = parser.parse(reader, TypeRegistry.getEmptyTypeRegistry());
+
+    assertThat(result).isEqualTo(expected);
+  }
+
+  @Test
+  void parse_reader_empty_returnsEmptyString() {
+    Reader reader = new StringReader("");
+
+    String result = parser.parse(reader, TypeRegistry.getEmptyTypeRegistry());
+
+    assertThat(result).isEmpty();
+  }
+
+  @Test
+  void parse_reader_ioException_throwsRestSerializationException() {
+    Reader failingReader =
+        new Reader() {
+          @Override
+          public int read(char[] cbuf, int off, int len) throws IOException {
+            throw new IOException("Simulated reader failure");
+          }
+
+          @Override
+          public void close() throws IOException {
+            // Intentionally empty for mock test
+          }
+        };
+
+    TypeRegistry emptyRegistry = TypeRegistry.getEmptyTypeRegistry();
+    RestSerializationException thrown =
+        assertThrows(
+            RestSerializationException.class, () -> parser.parse(failingReader, emptyRegistry));
+    assertThat(thrown).hasCauseThat().isInstanceOf(IOException.class);
+  }
+
+  @Test
+  void serialize_returnsInputString() {
+    assertThat(parser.serialize("hello")).isEqualTo("hello");
+  }
+}