#32 - Add headerAddIfAbsent() helper method

Author: rbygrave

client/src/main/java/io/avaje/http/client/DHttpClientRequest.java

@@ -105,6 +105,14 @@ public HttpClientRequest requestTimeout(Duration requestTimeout) {
     return this;
   }
 
+  @Override
+  public HttpClientRequest headerAddIfAbsent(String name, Object value) {
+    if (headers == null || !headers.containsKey(name)) {
+      header(name, value);
+    }
+    return this;
+  }
+
   @Override
   public HttpClientRequest header(String name, String value) {
     if (headers == null) {
@@ -131,6 +139,9 @@ public HttpClientRequest header(Map<String, ?> headers) {
 
   @Override
   public List<String> header(String name) {
+    if (headers == null) {
+      return Collections.emptyList();
+    }
     final List<String> values = headers.get(name);
     return values == null ? Collections.emptyList() : values;
   }

client/src/main/java/io/avaje/http/client/HttpClientRequest.java

@@ -90,6 +90,15 @@ public interface HttpClientRequest {
    */
   HttpClientRequest requestTimeout(Duration requestTimeout);
 
+  /**
+   * Add the header to the request but only if there is no existing value for the given header.
+   *
+   * @param name  The header name
+   * @param value The header value
+   * @return The request being built
+   */
+  HttpClientRequest headerAddIfAbsent(String name, Object value);
+
   /**
    * Add the header to the request.
    *

client/src/test/java/io/avaje/http/client/HelloControllerTest.java

@@ -432,6 +432,35 @@ void asString_readInvalidResponse() {
     assertThat(errorMap.get("email")).isEqualTo("must be a well-formed email address");
   }
 
+  @Test
+  void headers_get_whenEmpty() {
+    final HttpClientRequest request = clientContext.request();
+
+    List<String> headers = request.header("x-client-id");
+    if (headers.isEmpty()) {
+      request.header("x-client-id", "42");
+    }
+    assertThat(request.header("x-client-id")).containsExactly("42");
+  }
+
+  @Test
+  void headers_headerAddIfAbsent_whenEmpty() {
+    final HttpClientRequest request = clientContext.request();
+    assertThat(request.header("x-client-id")).isEmpty();
+
+    request.headerAddIfAbsent("x-client-id", "42");
+    assertThat(request.header("x-client-id")).containsExactly("42");
+  }
+
+  @Test
+  void headers_headerAddIfAbsent_whenAlreadySet() {
+    final HttpClientRequest request = clientContext.request();
+    request.header("x-client-id", "someValue");
+
+    request.headerAddIfAbsent("x-client-id", "42");
+    assertThat(request.header("x-client-id")).containsExactly("someValue");
+  }
+
   @Test
   void headers() {
     final HttpClientRequest request = clientContext.request();