Support head operations (#232)

## Changes
Support head operations

## Tests
Generated SDK and run Files integration tests.

.codegen/impl.java.tmpl

@@ -33,9 +33,6 @@ class {{.PascalName}}Impl implements {{.PascalName}}Service {
     {{ template "api-call" . }}
     {{- else if .Response.ArrayValue -}} return apiClient.getCollection(path, null, {{template "type" .Response.ArrayValue}}.class, headers);
     {{- else if .Response.MapValue -}} return apiClient.getStringMap(path, {{ template "request-param" .}}, headers);
-    {{- else if .IsResponseByteStream -}}
-    InputStream response = {{ template "api-call" . }}
-    return new {{ .Response.PascalName }}().set{{.ResponseBodyField.PascalName}}(response);
     {{- else }}return {{ template "api-call" . }}
     {{- end}}
   }
@@ -46,7 +43,6 @@ class {{.PascalName}}Impl implements {{.PascalName}}Service {
 apiClient.{{.Verb}}(path
   {{- if .Request}}, {{ template "request-param" .}}{{end}}
   , {{ if not .Response -}}Void
-  {{- else if .IsResponseByteStream}}InputStream
   {{- else}}{{template "type" .Response}}{{- end -}}.class
   , headers);
 {{- end }}

.codegen/model.java.tmpl

@@ -10,6 +10,7 @@ import java.util.Collection;
 import java.util.Objects;
 
 import com.databricks.sdk.support.Generated;
+import com.databricks.sdk.support.Header;
 import com.databricks.sdk.support.QueryParam;
 import com.databricks.sdk.support.ToStringer;
 
@@ -29,7 +30,7 @@ public class {{.PascalName}} {
   /**
    {{.Comment "   * " 80}}
    */
-  {{if .IsJson}}@JsonProperty("{{.Name}}"){{end}}{{if .IsQuery}}@QueryParam("{{.Name}}"){{end}}
+  {{if .IsJson}}@JsonProperty("{{.Name}}"){{end}}{{if .IsQuery}}@QueryParam("{{.Name}}"){{end}}{{if .IsHeader}}@Header("{{.Name}}"){{end}}
   private {{template "type" .Entity }} {{.CamelName}}{{if .IsNameReserved}}Value{{end}};
   {{end}}
 

databricks-sdk-java/src/main/java/com/databricks/sdk/core/ApiClient.java

@@ -6,6 +6,7 @@
 import com.databricks.sdk.core.http.Response;
 import com.databricks.sdk.core.utils.SystemTimer;
 import com.databricks.sdk.core.utils.Timer;
+import com.databricks.sdk.support.Header;
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.DeserializationFeature;
@@ -14,6 +15,7 @@
 import com.fasterxml.jackson.databind.SerializationFeature;
 import java.io.IOException;
 import java.io.InputStream;
+import java.lang.reflect.Field;
 import java.util.*;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -131,6 +133,18 @@ protected <I, O> O withJavaType(
     }
   }
 
+  public <O> O HEAD(String path, Class<O> target, Map<String, String> headers) {
+    return HEAD(path, null, target, headers);
+  }
+
+  public <I, O> O HEAD(String path, I in, Class<O> target, Map<String, String> headers) {
+    try {
+      return execute(prepareRequest("HEAD", path, in, headers), target);
+    } catch (IOException e) {
+      throw new DatabricksException("IO error: " + e.getMessage(), e);
+    }
+  }
+
   public <O> O GET(String path, Class<O> target, Map<String, String> headers) {
     return GET(path, null, target, headers);
   }
@@ -212,7 +226,7 @@ private <T> T execute(Request in, Class<T> target) throws IOException {
     if (target == Void.class) {
       return null;
     }
-    return deserialize(out.getBody(), target);
+    return deserialize(out, target);
   }
 
   private Response getResponse(Request in) {
@@ -319,11 +333,18 @@ private String makeLogRecord(Request in, Response out) {
     return sb.toString();
   }
 
-  public <T> T deserialize(InputStream body, Class<T> target) throws IOException {
+  public <T> T deserialize(Response response, Class<T> target) throws IOException {
     if (target == InputStream.class) {
-      return (T) body;
+      return (T) response.getBody();
     }
-    return mapper.readValue(body, target);
+    T object;
+    try {
+      object = target.getDeclaredConstructor().newInstance();
+    } catch (Exception e) {
+      throw new DatabricksException("Unable to initialize an instance of type " + target.getName());
+    }
+    deserialize(response, object);
+    return object;
   }
 
   public <T> T deserialize(InputStream body, JavaType target) throws IOException {
@@ -333,6 +354,60 @@ public <T> T deserialize(InputStream body, JavaType target) throws IOException {
     return mapper.readValue(body, target);
   }
 
+  private <T> void fillInHeaders(T target, Response response) {
+    for (Field field : target.getClass().getDeclaredFields()) {
+      Header headerAnnotation = field.getAnnotation(Header.class);
+      if (headerAnnotation == null) {
+        continue;
+      }
+      String firstHeader = response.getFirstHeader(headerAnnotation.value());
+      if (firstHeader == null) {
+        continue;
+      }
+      try {
+        field.setAccessible(true);
+        if (field.getType() == String.class) {
+          field.set(target, firstHeader);
+        } else if (field.getType() == Long.class) {
+          field.set(target, Long.parseLong(firstHeader));
+        } else {
+          LOG.warn("Unsupported header type: " + field.getType());
+        }
+      } catch (IllegalAccessException e) {
+        throw new DatabricksException("Failed to unmarshal headers: " + e.getMessage(), e);
+      } finally {
+        field.setAccessible(false);
+      }
+    }
+  }
+
+  private <T> Optional<Field> getContentsField(T target) {
+    for (Field field : target.getClass().getDeclaredFields()) {
+      if (field.getName().equals("contents") && field.getType() == InputStream.class) {
+        return Optional.of(field);
+      }
+    }
+    return Optional.empty();
+  }
+
+  public <T> void deserialize(Response response, T object) throws IOException {
+    fillInHeaders(object, response);
+    Optional<Field> contentsField = getContentsField(object);
+    if (contentsField.isPresent()) {
+      Field field = contentsField.get();
+      try {
+        field.setAccessible(true);
+        field.set(object, response.getBody());
+      } catch (IllegalAccessException e) {
+        throw new DatabricksException("Failed to unmarshal headers: " + e.getMessage(), e);
+      } finally {
+        field.setAccessible(false);
+      }
+    } else if (response.getBody() != null) {
+      mapper.readerForUpdating(object).readValue(response.getBody());
+    }
+  }
+
   private String serialize(Object body) throws JsonProcessingException {
     if (body == null) {
       return null;

databricks-sdk-java/src/main/java/com/databricks/sdk/core/commons/CommonsHttpClient.java

@@ -122,6 +122,8 @@ private HttpUriRequest transformRequest(Request in) {
     switch (in.getMethod()) {
       case Request.GET:
         return new HttpGet(in.getUri());
+      case Request.HEAD:
+        return new HttpHead(in.getUri());
       case Request.DELETE:
         return new HttpDelete(in.getUri());
       case Request.POST:

databricks-sdk-java/src/main/java/com/databricks/sdk/core/http/Request.java

@@ -10,6 +10,7 @@
 
 public class Request {
   public static final String GET = "GET";
+  public static final String HEAD = "HEAD";
   public static final String DELETE = "DELETE";
   public static final String POST = "POST";
   public static final String PUT = "PUT";

databricks-sdk-java/src/main/java/com/databricks/sdk/support/Header.java

@@ -0,0 +1,13 @@
+package com.databricks.sdk.support;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/** Annotation to indicate that a field is a Header. */
+@Target({ElementType.FIELD})
+@Retention(RetentionPolicy.RUNTIME)
+public @interface Header {
+  String value();
+}

databricks-sdk-java/src/test/java/com/databricks/sdk/integration/FilesIT.java

@@ -44,7 +44,10 @@ private void writeFileAndReadFileInner(
 
     // Write the file to DBFS.
     workspace.files().upload(fileName, inputStream);
-
+    // TODO: Enable after SDK generated
+    // Check header deserialization
+    // GetMetadataResponse metadata = workspace.files().getMetadata(fileName);
+    // Assertions.assertEquals("application/octet-stream", metadata.getContentType());
     // Read the file back from DBFS.
     try (InputStream readContents = workspace.files().download(fileName).getContents()) {
       byte[] result = new byte[fileContents.length];