Adding GCE metadata lib.

Fixes googleapis#8

src/Compute/Metadata.php

@@ -0,0 +1,98 @@
+<?php
+
+/**
+ * Copyright 2015 Google Inc.
+ *
+ * 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.
+ */
+namespace Google\Cloud\Compute;
+
+use Google\Cloud\Compute\Metadata\Readers\StreamReader;
+
+/**
+ * A library for accessing the GCE metadata.
+ *
+ * You can get the GCE metadata values very easily like:
+ *
+ * use Google\Cloud\Compute\Metadata;
+ *
+ * $metadata = new Metadata();
+ * $project_id = $metadata->getProjectId();
+ *
+ * $val = $metadata->getProjectMetadata($key);
+ */
+class Metadata
+{
+    /**
+     * The metadata reader.
+     */
+    private $reader;
+
+    /**
+     * The project id.
+     */
+    private $projectId;
+
+    /**
+     * We use StreamReader for the default implementation for fetching the URL.
+     */
+    public function __construct()
+    {
+        $this->reader = new StreamReader();
+    }
+
+    /**
+     * A method to replace the reader implementation.
+     */
+    public function setReader($reader)
+    {
+        $this->reader = $reader;
+    }
+
+    /**
+     * This method retrieves a single metadata value for a given path.
+     */
+    public function get($path)
+    {
+        return $this->reader->read($path);
+    }
+
+    /**
+     * This method detects the project id and returns it.
+     */
+    public function getProjectId()
+    {
+        if (! isset($this->projectId)) {
+            $this->projectId = $this->reader->read('project/project-id');
+        }
+        return $this->projectId;
+    }
+
+    /**
+     * This method fetches the project custom metadta and returns it.
+     */
+    public function getProjectMetadata($key)
+    {
+        $path = 'project/attributes/'.$key;
+        return $this->get($path);
+    }
+
+    /**
+     * This method fetches the instance custom metadta and returns it.
+     */
+    public function getInstanceMetadata($key)
+    {
+        $path = 'instance/attributes/'.$key;
+        return $this->get($path);
+    }
+}

src/Compute/Metadata/Readers/StreamReader.php

@@ -0,0 +1,85 @@
+<?php
+
+/**
+ * Copyright 2015 Google Inc.
+ *
+ * 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.
+ */
+namespace Google\Cloud\Compute\Metadata\Readers;
+
+/**
+ * A class only reading the metadata URL with an appropriate header.
+ *
+ * This class makes it easy to test the MetadataStream class.
+ */
+class StreamReader
+{
+    /**
+     * The base PATH for the metadata.
+     */
+    const BASE_URL = 'http://169.254.169.254/computeMetadata/v1/';
+
+    /**
+     * The default host name for metadata.
+     */
+    const HOST = 'metadata.google.internal';
+
+    /**
+     * The header whose presence indicates GCE presence.
+     */
+    const FLAVOR_HEADER = 'Metadata-Flavor: Google';
+
+    /**
+     * A common context for this reader.
+     */
+    private $context;
+
+    /**
+     * We create the common context in the constructor.
+     */
+    public function __construct()
+    {
+        $options = array(
+            'http' => array(
+                'method' => 'GET',
+                'header' => self::FLAVOR_HEADER,
+            ),
+        );
+        $this->context = stream_context_create($options);
+    }
+
+    /**
+     * A method to read the metadata value for a given path.
+     */
+    public function read($path)
+    {
+        $url = self::BASE_URL.$path;
+        return file_get_contents($url, false, $this->context);
+    }
+
+    /**
+     * A method to detect whether it's running on Compute Engine or not.
+     */
+    public function onGCE()
+    {
+        // We use the hostname for failing faster on non-gce environment.
+        $url = 'http://'.self::HOST;
+        $result = file_get_contents($url, false, $this->context);
+        if ($result != false
+            && array_key_exists('Metadata-Flavor', $http_response_header)
+            && $http_response_header['Metadata-Flavor'] == 'Google') {
+            return true;
+        }
+        return false;
+    }
+}

tests/ComputeMetadataTest.php

@@ -0,0 +1,74 @@
+<?php
+
+/**
+ * Copyright 2015 Google Inc.
+ *
+ * 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.
+ */
+namespace Google\Cloud\tests;
+
+use Google\Cloud\Compute\Metadata;
+
+class ComputeMetadataTest extends \PHPUnit_Framework_TestCase
+{
+    protected $mock;
+    protected $metadata;
+
+    public function setUp()
+    {
+        $this->metadata = new Metadata();
+        $this->mock = $this->getMockBuilder(
+            '\Google\Cloud\Compute\Metadata\Readers\StreamReader')
+            ->setMethods(array('read'))
+            ->getmock();
+        $this->metadata->setReader($this->mock);
+    }
+
+    public function testProjectMetadata()
+    {
+        $expected_path = 'project/attributes/mykey';
+        $expected_val = 'myval';
+        $this->mock->expects($this->once())
+            ->method('read')
+            ->with($this->equalTo($expected_path))
+            ->willReturn($expected_val);
+        $val = $this->metadata->getProjectMetadata('mykey');
+        $this->assertEquals($expected_val, $val);
+    }
+
+    public function testInstanceMetadata()
+    {
+        $expected_path = 'instance/attributes/mykey';
+        $expected_val = 'myval';
+        $this->mock->expects($this->once())
+            ->method('read')
+            ->with($this->equalTo($expected_path))
+            ->willReturn($expected_val);
+        $val = $this->metadata->getInstanceMetadata('mykey');
+        $this->assertEquals($expected_val, $val);
+    }
+
+    public function testGetProjectIdCached()
+    {
+        $expected_path = 'project/project-id';
+        $expected_val = 'my-project';
+        $this->mock->expects($this->once())
+            ->method('read')
+            ->with($this->equalTo($expected_path))
+            ->willReturn($expected_val);
+        $project_id = $this->metadata->getProjectId();
+        $this->assertEquals($expected_val, $project_id);
+        // Ensure this value is cached thus we `read` only once.
+        $project_id = $this->metadata->getProjectId();
+    }
+}