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feat(gax): add getSingleHeader to HttpHeadersUtils (#14137)
The GAX HTTP/JSON stack stores response headers in a Map<String, Object> where values may be Strings, numbers, Iterables, etc., and header names may vary in casing depending on the HTTP version. This method provides case-insensitive lookup and safely extracts a single value in a typesafe way when it exists, returning null if not and throwing an exception if multiple values exist. This will be used in resumable upload support to retrieve protocol header values (e.g. X-Goog-Upload-URL, Location, and X-Goog-Upload-Status).
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‎sdk-platform-java/gax-java/gax-httpjson/src/main/java/com/google/api/gax/httpjson/HttpHeadersUtils.java‎

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@@ -34,6 +34,7 @@
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import com.google.api.client.util.FieldInfo;
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import com.google.api.core.InternalApi;
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import com.google.common.collect.ImmutableList;
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import com.google.common.collect.Iterables;
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import java.util.List;
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import java.util.Map;
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import org.jspecify.annotations.NullMarked;
@@ -52,6 +53,34 @@ public class HttpHeadersUtils {
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return null;
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}
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/**
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* Retrieves the single string value of a header by case-insensitive name from a headers map.
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*
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* @param headers the map of header names to header values
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* @param name the case-insensitive header name to look up
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* @return the single string value of the header, or {@code null} if not found
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* @throws IllegalArgumentException if multiple values are present for the header
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*/
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public static @Nullable String getSingleHeader(Map<String, Object> headers, String name) {
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return headers.entrySet().stream()
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.filter(entry -> name.equalsIgnoreCase(entry.getKey()))
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.findFirst()
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.map(entry -> extractSingleString(entry.getValue()))
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.orElse(null);
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}
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private static @Nullable String extractSingleString(@Nullable Object headerValue) {
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if (headerValue == null) {
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return null;
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}
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// HttpHeaders stores single-value headers as single-element Lists
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if (headerValue instanceof Iterable) {
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Object onlyElement = Iterables.getOnlyElement((Iterable<?>) headerValue, null);
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return onlyElement != null ? onlyElement.toString() : null;
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}
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return headerValue.toString();
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}
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public static HttpHeaders setHeaders(HttpHeaders headers, Map<String, String> headersMap) {
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for (Map.Entry<String, String> entry : headersMap.entrySet()) {
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setHeader(headers, entry.getKey(), entry.getValue());

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

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@@ -29,12 +29,16 @@
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*/
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package com.google.api.gax.httpjson;
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import static com.google.common.truth.Truth.assertThat;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertNull;
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import static org.junit.jupiter.api.Assertions.assertThrows;
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import com.google.api.client.http.HttpHeaders;
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import com.google.common.collect.ImmutableList;
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import com.google.common.collect.ImmutableMap;
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import java.util.Collections;
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import java.util.HashMap;
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import java.util.Map;
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import org.junit.jupiter.api.Test;
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@@ -130,4 +134,56 @@ void testGetUserAgentValue() {
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headersMap = ImmutableMap.of("Custom-Header", "CustomHeader", "accept", "Accept");
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assertNull(HttpHeadersUtils.getUserAgentValue(headersMap));
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}
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@Test
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void getSingleHeader_success() {
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Map<String, Object> headers =
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ImmutableMap.of(
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"X-Goog-Upload-URL",
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"https://test.googleapis.com/upload",
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"Location",
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ImmutableList.of("https://redirect.url"),
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"Content-Length",
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1024L);
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// Case-insensitive & exact lookup
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assertThat(HttpHeadersUtils.getSingleHeader(headers, "X-Goog-Upload-URL"))
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.isEqualTo("https://test.googleapis.com/upload");
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assertThat(HttpHeadersUtils.getSingleHeader(headers, "x-goog-upload-url"))
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.isEqualTo("https://test.googleapis.com/upload");
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// Single-element iterable
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assertThat(HttpHeadersUtils.getSingleHeader(headers, "location"))
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.isEqualTo("https://redirect.url");
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// Non-string object conversion
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assertThat(HttpHeadersUtils.getSingleHeader(headers, "content-length")).isEqualTo("1024");
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}
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@Test
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void getSingleHeader_multipleElements_throwsIllegalArgumentException() {
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Map<String, Object> headers =
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ImmutableMap.of(
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"Location", ImmutableList.of("https://redirect.url", "https://secondary.url"));
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assertThrows(
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IllegalArgumentException.class,
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() -> HttpHeadersUtils.getSingleHeader(headers, "location"));
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}
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@Test
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void getSingleHeader_missingOrEmpty_returnsNull() {
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Map<String, Object> headers = new HashMap<>();
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headers.put("Existing-Header", "value");
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headers.put("Null-Value-Header", null);
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headers.put("Empty-List-Header", Collections.emptyList());
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headers.put("Null-First-Header", Collections.singletonList(null));
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headers.put(null, "some-value");
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assertThat(HttpHeadersUtils.getSingleHeader(headers, "non-existent-header")).isNull();
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assertThat(HttpHeadersUtils.getSingleHeader(headers, "null-value-header")).isNull();
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assertThat(HttpHeadersUtils.getSingleHeader(headers, "empty-list-header")).isNull();
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assertThat(HttpHeadersUtils.getSingleHeader(headers, "null-first-header")).isNull();
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assertThat(HttpHeadersUtils.getSingleHeader(headers, "any-header")).isNull();
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}
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}

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