Index: src/__phutil_library_map__.php
===================================================================
--- src/__phutil_library_map__.php
+++ src/__phutil_library_map__.php
@@ -682,6 +682,7 @@
     'HarbormasterCapabilityManagePlans' => 'applications/harbormaster/capability/HarbormasterCapabilityManagePlans.php',
     'HarbormasterController' => 'applications/harbormaster/controller/HarbormasterController.php',
     'HarbormasterDAO' => 'applications/harbormaster/storage/HarbormasterDAO.php',
+    'HarbormasterHTTPRequestBuildStepImplementation' => 'applications/harbormaster/step/HarbormasterHTTPRequestBuildStepImplementation.php',
     'HarbormasterObject' => 'applications/harbormaster/storage/HarbormasterObject.php',
     'HarbormasterPHIDTypeBuild' => 'applications/harbormaster/phid/HarbormasterPHIDTypeBuild.php',
     'HarbormasterPHIDTypeBuildItem' => 'applications/harbormaster/phid/HarbormasterPHIDTypeBuildItem.php',
@@ -2979,6 +2980,7 @@
     'HarbormasterCapabilityManagePlans' => 'PhabricatorPolicyCapability',
     'HarbormasterController' => 'PhabricatorController',
     'HarbormasterDAO' => 'PhabricatorLiskDAO',
+    'HarbormasterHTTPRequestBuildStepImplementation' => 'VariableBuildStepImplementation',
     'HarbormasterObject' => 'HarbormasterDAO',
     'HarbormasterPHIDTypeBuild' => 'PhabricatorPHIDType',
     'HarbormasterPHIDTypeBuildItem' => 'PhabricatorPHIDType',
Index: src/applications/harbormaster/controller/HarbormasterBuildCancelController.php
===================================================================
--- src/applications/harbormaster/controller/HarbormasterBuildCancelController.php
+++ src/applications/harbormaster/controller/HarbormasterBuildCancelController.php
@@ -26,7 +26,7 @@
     $build_uri = $this->getApplicationURI('/build/'.$build->getID());
 
     if ($request->isDialogFormPost()) {
-      $build->setCancelRequested(true);
+      $build->setCancelRequested(1);
       $build->save();
 
       return id(new AphrontRedirectResponse())->setURI($build_uri);
Index: src/applications/harbormaster/step/HarbormasterHTTPRequestBuildStepImplementation.php
===================================================================
--- /dev/null
+++ src/applications/harbormaster/step/HarbormasterHTTPRequestBuildStepImplementation.php
@@ -0,0 +1,70 @@
+<?php
+
+final class HarbormasterHTTPRequestBuildStepImplementation
+  extends VariableBuildStepImplementation {
+
+  public function getName() {
+    return pht('Make HTTP Request');
+  }
+
+  public function getGenericDescription() {
+    return pht('Make an HTTP request.');
+  }
+
+  public function getDescription() {
+    $settings = $this->getSettings();
+
+    $uri = new PhutilURI($settings['uri']);
+    $domain = $uri->getDomain();
+    return pht('Make an HTTP request to %s', $domain);
+  }
+
+  public function execute(
+    HarbormasterBuild $build,
+    HarbormasterBuildStep $build_step) {
+
+    $settings = $this->getSettings();
+    $variables = $this->retrieveVariablesFromBuild($build);
+
+    $uri = $this->mergeVariables(
+      'vurisprintf',
+      $settings['uri'],
+      $variables);
+
+    $log_body = $build->createLog($build_step, $uri, 'http-body');
+    $start = $log_body->start();
+
+    list($status, $body, $headers) = id(new HTTPSFuture($uri))
+      ->setMethod('POST')
+      ->setTimeout(60)
+      ->resolve();
+
+    $log_body->append($body);
+    $log_body->finalize($start);
+
+    if ($status->getStatusCode() != 200) {
+      $build->setBuildStatus(HarbormasterBuild::STATUS_FAILED);
+    }
+  }
+
+  public function validateSettings() {
+    $settings = $this->getSettings();
+
+    if ($settings['uri'] === null || !is_string($settings['uri'])) {
+      return false;
+    }
+
+    return true;
+  }
+
+  public function getSettingDefinitions() {
+    return array(
+      'uri' => array(
+        'name' => 'URI',
+        'description' => pht('The URI to request.'),
+        'type' => BuildStepImplementation::SETTING_TYPE_STRING,
+      ),
+    );
+  }
+
+}
Index: src/applications/harbormaster/step/RemoteCommandBuildStepImplementation.php
===================================================================
--- src/applications/harbormaster/step/RemoteCommandBuildStepImplementation.php
+++ src/applications/harbormaster/step/RemoteCommandBuildStepImplementation.php
@@ -25,24 +25,12 @@
     HarbormasterBuildStep $build_step) {
 
     $settings = $this->getSettings();
-
-    $parameters = array();
-    $matches = array();
     $variables = $this->retrieveVariablesFromBuild($build);
-    $command = $settings['command'];
-    preg_match_all(
-      "/\\\$\\{(?P<name>[a-z\.]+)\\}/",
-      $command,
-      $matches);
-    foreach ($matches["name"] as $match) {
-      $parameters[] = idx($variables, $match, "");
-    }
-    $command = str_replace("%", "%%", $command);
-    $command = preg_replace("/\\\$\\{(?P<name>[a-z\.]+)\\}/", "%s", $command);
 
-    $command = vcsprintf(
-      $command,
-      $parameters);
+    $command = $this->mergeVariables(
+      'vcsprintf',
+      $settings['command'],
+      $variables);
 
     $future = null;
     if (empty($settings['sshkey'])) {
Index: src/applications/harbormaster/step/VariableBuildStepImplementation.php
===================================================================
--- src/applications/harbormaster/step/VariableBuildStepImplementation.php
+++ src/applications/harbormaster/step/VariableBuildStepImplementation.php
@@ -33,17 +33,42 @@
     return $results;
   }
 
-  public function mergeVariables(HarbormasterBuild $build, $string) {
-    $variables = $this->retrieveVariablesFromBuild($build);
-    foreach ($variables as $name => $value) {
-      if ($value === null) {
-        $value = '';
+
+  /**
+   * Convert a user-provided string with variables in it, like:
+   *
+   *   ls ${dirname}
+   *
+   * ...into a string with variables merged into it safely:
+   *
+   *   ls 'dir with spaces'
+   *
+   * @param string Name of a `vxsprintf` function, like @{function:vcsprintf}.
+   * @param string User-provided pattern string containing `${variables}`.
+   * @param dict   List of available replacement variables.
+   * @return string String with variables replaced safely into it.
+   */
+  protected function mergeVariables($function, $pattern, array $variables) {
+    $regexp = '/\\$\\{(?P<name>[a-z\\.]+)\\}/';
+
+    $matches = null;
+    preg_match_all($regexp, $pattern, $matches);
+
+    $argv = array();
+    foreach ($matches['name'] as $name) {
+      if (!array_key_exists($name, $variables)) {
+        throw new Exception(pht("No such variable '%s'!", $name));
       }
-      $string = str_replace('${'.$name.'}', $value, $string);
+      $argv[] = $variables[$name];
     }
-    return $string;
+
+    $pattern = str_replace('%', '%%', $pattern);
+    $pattern = preg_replace($regexp, '%s', $pattern);
+
+    return call_user_func($function, $pattern, $argv);
   }
 
+
   public function getAvailableVariables() {
     return array(
       'buildable.revision' =>
Index: src/applications/harbormaster/storage/build/HarbormasterBuild.php
===================================================================
--- src/applications/harbormaster/storage/build/HarbormasterBuild.php
+++ src/applications/harbormaster/storage/build/HarbormasterBuild.php
@@ -54,7 +54,7 @@
   public static function initializeNewBuild(PhabricatorUser $actor) {
     return id(new HarbormasterBuild())
       ->setBuildStatus(self::STATUS_INACTIVE)
-      ->setCancelRequested(false);
+      ->setCancelRequested(0);
   }
 
   public function getConfiguration() {
@@ -118,7 +118,7 @@
     $copy = id(new HarbormasterBuild())->load($this->getID());
     if ($copy->getCancelRequested()) {
       $this->setBuildStatus(HarbormasterBuild::STATUS_CANCELLED);
-      $this->setCancelRequested(false);
+      $this->setCancelRequested(0);
       $this->save();
       return true;
     }
Index: src/applications/harbormaster/storage/build/HarbormasterBuildLog.php
===================================================================
--- src/applications/harbormaster/storage/build/HarbormasterBuildLog.php
+++ src/applications/harbormaster/storage/build/HarbormasterBuildLog.php
@@ -28,7 +28,7 @@
       ->setBuildPHID($build->getPHID())
       ->setBuildStepPHID($build_step->getPHID())
       ->setDuration(null)
-      ->setLive(false);
+      ->setLive(0);
   }
 
   public function getConfiguration() {
@@ -70,7 +70,7 @@
       throw new Exception("Live logging has already started for this log.");
     }
 
-    $this->setLive(true);
+    $this->setLive(1);
     $this->save();
 
     return time();
@@ -150,7 +150,7 @@
     if ($start > 0) {
       $this->setDuration(time() - $start);
     }
-    $this->setLive(false);
+    $this->setLive(0);
     $this->save();
   }