Add REST endpoint to get content of a file in a commit

It is already possible to get the content of a file from the HEAD
revision of a branch. Add the same functionality for arbitrary
commits.

Change-Id: Id8e48bb40b4f383997aa9b83440a57ab90e763ee
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

Documentation/rest-api-projects.txt

@@ -1025,6 +1025,30 @@ is returned that describes the commit.
   }
 ----
 
+[[get-content]]
+=== Get Content
+--
+'GET /projects/link:#project-name[\{project-name\}]/commits/link:#commit-id[\{commit-id\}]/files/link:rest-api-changes.html#file-id[\{file-id\}]/content'
+--
+
+Gets the content of a file from a certain commit.
+
+.Request
+----
+  GET /projects/work%2Fmy-project/commits/a8a477efffbbf3b44169bb9a1d3a334cbbd9aa96/files/gerrit-server%2Fsrc%2Fmain%2Fjava%2Fcom%2Fgoogle%2Fgerrit%2Fserver%2Fproject%2FRefControl.java/content HTTP/1.0
+----
+
+The content is returned as base64 encoded string.
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: text/plain;charset=UTF-8
+
+  Ly8gQ29weXJpZ2h0IChDKSAyMDEwIFRoZSBBbmRyb2lkIE9wZW4gU291cmNlIFByb2plY...
+----
+
 [[dashboard-endpoints]]
 == Dashboard Endpoints
 

gerrit-server/src/main/java/com/google/gerrit/server/project/FileResource.java

@@ -14,21 +14,33 @@
 
 package com.google.gerrit.server.project;
 
+import com.google.gerrit.extensions.restapi.RestResource;
 import com.google.gerrit.extensions.restapi.RestView;
-import com.google.gerrit.server.project.BranchResource;
+import com.google.gerrit.reviewdb.client.Project;
 import com.google.inject.TypeLiteral;
 
-public class FileResource extends BranchResource {
+public class FileResource implements RestResource {
   public static final TypeLiteral<RestView<FileResource>> FILE_KIND =
       new TypeLiteral<RestView<FileResource>>() {};
 
+  private final Project.NameKey project;
+  private final String rev;
   private final String path;
 
-  public FileResource(BranchResource rsrc, String path) {
-    super(rsrc.getControl(), rsrc.getBranchInfo());
+  public FileResource(Project.NameKey project, String rev, String path) {
+    this.project = project;
+    this.rev = rev;
     this.path = path;
   }
 
+  public Project.NameKey getProject() {
+    return project;
+  }
+
+  public String getRev() {
+    return rev;
+  }
+
   public String getPath() {
     return path;
   }

gerrit-server/src/main/java/com/google/gerrit/server/project/FilesCollection.java

@@ -40,7 +40,7 @@ public class FilesCollection implements
 
   @Override
   public FileResource parse(BranchResource parent, IdString id) {
-    return new FileResource(parent, id.get());
+    return new FileResource(parent.getNameKey(), parent.getRef(), id.get());
   }
 
   @Override

gerrit-server/src/main/java/com/google/gerrit/server/project/FilesInCommitCollection.java

@@ -0,0 +1,51 @@
+// Copyright (C) 2014 The Android Open Source Project
+//
+// 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 com.google.gerrit.server.project;
+
+import com.google.gerrit.extensions.registration.DynamicMap;
+import com.google.gerrit.extensions.restapi.ChildCollection;
+import com.google.gerrit.extensions.restapi.IdString;
+import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
+import com.google.gerrit.extensions.restapi.RestView;
+import com.google.inject.Inject;
+import com.google.inject.Singleton;
+
+@Singleton
+public class FilesInCommitCollection implements
+    ChildCollection<CommitResource, FileResource> {
+  private final DynamicMap<RestView<FileResource>> views;
+
+  @Inject
+  FilesInCommitCollection(DynamicMap<RestView<FileResource>> views) {
+    this.views = views;
+  }
+
+  @Override
+  public RestView<CommitResource> list() throws ResourceNotFoundException {
+    throw new ResourceNotFoundException();
+  }
+
+  @Override
+  public FileResource parse(CommitResource parent, IdString id)
+      throws ResourceNotFoundException {
+    return new FileResource(parent.getNameKey(), parent.getCommit().getName(),
+        id.get());
+  }
+
+  @Override
+  public DynamicMap<RestView<FileResource>> views() {
+    return views;
+  }
+}

gerrit-server/src/main/java/com/google/gerrit/server/project/GetContent.java

@@ -35,7 +35,7 @@ public class GetContent implements RestReadView<FileResource> {
   @Override
   public BinaryResult apply(FileResource rsrc)
       throws ResourceNotFoundException, IOException {
-    return getContent.get().apply(rsrc.getNameKey(), rsrc.getRef(),
+    return getContent.get().apply(rsrc.getProject(), rsrc.getRev(),
         rsrc.getPath());
   }
 }

gerrit-server/src/main/java/com/google/gerrit/server/project/Module.java

@@ -67,6 +67,7 @@ public class Module extends RestApiModule {
 
     child(PROJECT_KIND, "commits").to(CommitsCollection.class);
     get(COMMIT_KIND).to(GetCommit.class);
+    child(COMMIT_KIND, "files").to(FilesInCommitCollection.class);
 
     child(PROJECT_KIND, "dashboards").to(DashboardsCollection.class);
     get(DASHBOARD_KIND).to(GetDashboard.class);