ISSUE-7: S3ObjectSeeker

src/Seeker/S3ObjectSeeker.php

@@ -0,0 +1,141 @@
+<?php
+
+namespace Mingulay\Seeker;
+
+use Exception;
+use InvalidArgumentException;
+use Mingulay\SeekerInterface;
+
+class S3ObjectSeeker implements SeekerInterface {
+
+  /**
+   * The valid s3:// wrapper path to an S3 Object.
+   *
+   * @var string
+   */
+  protected $path;
+
+  /**
+   * The file pointer.
+   *
+   * @var false|resource
+   */
+  protected $stream;
+
+  /**
+   * The size of the file.
+   *
+   * @var int
+   */
+  protected $size;
+
+
+  /**
+   * Create a new S3ObjectSeeker object.
+   *
+   * @param string $path The  streamwrapper prefixed path to an S3 Object.
+   *
+   * @throws InvalidArgumentException if the path is not accessible.
+   */
+  public function __construct(string $path) {
+    $this->path = $path;
+    try {
+      $this->size = filesize($path);
+      if ($this->size === FALSE) {
+        throw new InvalidArgumentException(
+          "The provided S3 Object could not be opened"
+        );
+      }
+    } catch (Exception $e) {
+      throw new InvalidArgumentException(
+        "The provided S3 Object could not be opened: " . $e->getMessage()
+      );
+    }
+  }
+
+  /**
+   * Destructor function to ensure the file descriptor is closed.
+   */
+  public function __destruct() {
+    if ($this->stream) {
+      fclose($this->stream);
+    }
+  }
+
+  /**
+   * @inheritDoc
+   */
+  public function retrieveStart(int $length, int $offset = 0): ?string {
+    // Bail out if the parameters are invalid
+    if ($length <= 0 || $offset < 0 || ($offset + $length) > $this->size) {
+      return NULL;
+    }
+
+    try {
+      $context = stream_context_create(
+        [
+          's3' => [
+            'Range'    => "bytes=" . $offset . "-" . ($offset + $length - 1),
+            'seekable' => FALSE,
+          ],
+        ]
+      );
+
+      $this->stream = fopen($this->path, "r", FALSE, $context);
+      $data = '';
+      while (!feof( $this->stream)) {
+        $data .= fread($this->stream, 8192);
+      }
+      if (!$data or strlen($data)!= $length) {
+        return NULL;
+      }
+      return $data;
+    } catch (Exception $e) {
+      user_error("Caught exception: " . $e->getMessage(), E_USER_WARNING);
+      return NULL;
+    }
+  }
+
+  /**
+   * @inheritDoc
+   */
+  public function retrieveEnd(int $length, int $offset = 0): ?string {
+    if ($length <= 0 || ($offset + $length) > $this->size) {
+      return NULL;
+    }
+    // Make sure we can handle both positive and negative expressions of the offset, just in case.
+    $offset = abs($offset);
+
+    // Make sure we are not trying to seek past the start of the file.
+    if ($offset > $this->size) {
+      $offset = $this->size;
+    }
+
+    try {
+      $to = ($this->size - $offset - 1);
+      $from = $to - $length + 1;
+      $context = stream_context_create(
+        [
+          's3' => [
+            'Range'    => "bytes=" . $from
+              . "-" . $to,
+            'seekable' => FALSE,
+          ],
+        ]
+      );
+      $data = '';
+      $this->stream = fopen($this->path, "r", FALSE, $context);
+      while (!feof( $this->stream)) {
+        $data .= fread($this->stream, 8192);
+      }
+      // Be sure to close the stream resource when you're done with it
+      if (!$data || strlen($data)!= $length) {
+        return NULL;
+      }
+      return $data;
+    } catch (Exception $e) {
+      user_error("Caught exception: " . $e->getMessage(), E_USER_WARNING);
+      return NULL;
+    }
+  }
+}