Send commands from webcamPrivate API to the webcam via V4L2 ioctls

chrome/browser/extensions/api/webcam_private/webcam_private_api.cc

Index: chrome/browser/extensions/api/webcam_private/webcam_private_api.cc
diff --git a/chrome/browser/extensions/api/webcam_private/webcam_private_api.cc b/chrome/browser/extensions/api/webcam_private/webcam_private_api.cc
index f956ba4a11d4f056906d3fec1168d3f802cca9c6..a0259d2f84bdade987d3ce588030a24883fb5cb2 100644
--- a/chrome/browser/extensions/api/webcam_private/webcam_private_api.cc
+++ b/chrome/browser/extensions/api/webcam_private/webcam_private_api.cc
@@ -4,8 +4,106 @@
 
 #include "chrome/browser/extensions/api/webcam_private/webcam_private_api.h"
 
+#include <fcntl.h>
+#include <linux/videodev2.h>
+#include <stdio.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include "base/files/scoped_file.h"
+#include "base/posix/eintr_wrapper.h"
 #include "chrome/common/extensions/api/webcam_private.h"
 
+namespace content {
+class BrowserContext;
+} // namespace content
+
+namespace {
+
+enum WebcamParameter {
+  WEBCAM_PAN,
+  WEBCAM_TILT,
+  WEBCAM_ZOOM,
+};
+
+const int kDefaultZoom = 100;

[vrk (LEFT CHROMIUM), 2014/04/17 23:16:56]

You should make this a static local constant in the function, since that's the
only place it's used.

[Zachary Kuznia, 2014/04/18 22:44:15]

Done.

+
+base::ScopedFD OpenWebcam(const std::string& extension_id,
+                          content::BrowserContext* browser_context,
+                          const std::string& webcam_id) {
+  // TODO(zork): Get device_id from content::MediaStreamManager

[vrk (LEFT CHROMIUM), 2014/04/17 23:16:56]

nit: period at end of sentence

[Zachary Kuznia, 2014/04/18 22:44:15]

Done.

+  std::string device_id = "/dev/video0";

[vrk (LEFT CHROMIUM), 2014/04/17 23:16:56]

Hmmm... this feels wrong to me. I know you're planning to fix this later,
though, so I defer to tommi@ on what's the best way to query the default device.
If tommi's OK with this, fine with me too.

[Zachary Kuznia, 2014/04/18 22:44:15]

I'll be sending out a follow-up CL for review as soon as this one lands.  If the
follow up CL hasn't landed by the time this code would be in use, then I'll be
disabling the whole API.

+
+  return base::ScopedFD(HANDLE_EINTR(open(device_id.c_str(), 0)));
+}
+
+void SetWebcamParameter(int fd, WebcamParameter param, int value) {

[vrk (LEFT CHROMIUM), 2014/04/17 23:16:56]

The WebcamParameter enum seems superfluous. I'd split this method up a little
differently, like:

  SetWebcamParameter(int fd, int control_id, int control_value) {
    struct v4l2_control v4l2_ctrl = {control_id, control_value};
    HANDLE_EINTR(ioctl(fd, VIDIOC_S_CTRL, &v4l2_ctrl);
  }

Then in the callsite, you can have:
  if (params->config.pan)
    SetWebcamParameter(fd.get(), V4L2_CID_PAN_ABSOLUTE, *(params->config.pan));

WDYT? I'd suggest collapsing all the {Set,Get,Reset}Parameter methods in this
manner. (You could probably get rid of the Reset method, actually.)

[Zachary Kuznia, 2014/04/18 22:44:15]

Done.

+  struct v4l2_control v4l2_ctrl;
+  switch (param) {
+    case WEBCAM_PAN:
+      v4l2_ctrl.id = V4L2_CID_PAN_ABSOLUTE;
+      break;
+
+    case WEBCAM_TILT:
+      v4l2_ctrl.id = V4L2_CID_TILT_ABSOLUTE;
+      break;
+
+    case WEBCAM_ZOOM:
+      v4l2_ctrl.id = V4L2_CID_ZOOM_ABSOLUTE;
+      break;
+  }
+
+  v4l2_ctrl.value = value;
+  HANDLE_EINTR(ioctl(fd, VIDIOC_S_CTRL, &v4l2_ctrl));
+}
+
+bool GetWebcamParameter(int fd, WebcamParameter param, int* value) {
+  struct v4l2_control v4l2_ctrl;
+  switch (param) {
+    case WEBCAM_PAN:
+      v4l2_ctrl.id = V4L2_CID_PAN_ABSOLUTE;
+      break;
+    case WEBCAM_TILT:
+      v4l2_ctrl.id = V4L2_CID_TILT_ABSOLUTE;
+      break;
+    case WEBCAM_ZOOM:
+      v4l2_ctrl.id = V4L2_CID_ZOOM_ABSOLUTE;
+      break;
+  }
+
+  if (HANDLE_EINTR(ioctl(fd, VIDIOC_G_CTRL, &v4l2_ctrl)))
+    return false;
+
+  *value = v4l2_ctrl.value;
+  return true;
+}
+
+void ResetWebcamParameter(int fd, WebcamParameter param) {
+  switch (param) {
+    case WEBCAM_PAN: {
+        struct v4l2_control v4l2_ctrl;
+        v4l2_ctrl.id = V4L2_CID_PAN_RESET;
+        ioctl(fd, VIDIOC_S_CTRL, &v4l2_ctrl);
+      }
+      break;
+
+    case WEBCAM_TILT: {
+        struct v4l2_control v4l2_ctrl;
+        v4l2_ctrl.id = V4L2_CID_TILT_RESET;
+        ioctl(fd, VIDIOC_S_CTRL, &v4l2_ctrl);
+      }
+      break;
+
+    case WEBCAM_ZOOM:
+      SetWebcamParameter(fd, WEBCAM_ZOOM, kDefaultZoom);
+      break;
+  }
+
+}
+
+const char kUnknownWebcam[] = "Unknown webcam id";
+} // namespace
+
 namespace extensions {
 
 WebcamPrivateSetFunction::WebcamPrivateSetFunction() {
@@ -20,7 +118,21 @@ bool WebcamPrivateSetFunction::RunImpl() {
       api::webcam_private::Set::Params::Create(*args_));
   EXTENSION_FUNCTION_VALIDATE(params.get());
 
-  // TODO(zork): Send the value to the webcam.
+  base::ScopedFD fd =
+      OpenWebcam(extension_id(), browser_context(), params->webcam_id);
+  if (!fd.is_valid()) {
+    SetError(kUnknownWebcam);
+    return false;
+  }
+
+  if (params->config.pan)
+    SetWebcamParameter(fd.get(), WEBCAM_PAN, *(params->config.pan));
+
+  if (params->config.tilt)
+    SetWebcamParameter(fd.get(), WEBCAM_TILT, *(params->config.tilt));
+
+  if (params->config.zoom)
+    SetWebcamParameter(fd.get(), WEBCAM_ZOOM, *(params->config.zoom));
 
   return true;
 }
@@ -37,9 +149,30 @@ bool WebcamPrivateGetFunction::RunImpl() {
       api::webcam_private::Get::Params::Create(*args_));
   EXTENSION_FUNCTION_VALIDATE(params.get());
 
-  // TODO(zork): Get the value from the webcam.
+  base::ScopedFD fd =
+      OpenWebcam(extension_id(), browser_context(), params->webcam_id);
+  if (!fd.is_valid()) {
+    SetError(kUnknownWebcam);
+    return false;
+  }
+
+  api::webcam_private::WebcamConfiguration result;
+
+  int pan;
+  if (GetWebcamParameter(fd.get(), WEBCAM_PAN, &pan))
+    result.pan.reset(new double(pan));
 
-  return false;
+  int tilt;
+  if (GetWebcamParameter(fd.get(), WEBCAM_TILT, &tilt))
+    result.tilt.reset(new double(tilt));
+
+  int zoom;
+  if (GetWebcamParameter(fd.get(), WEBCAM_ZOOM, &zoom))
+    result.zoom.reset(new double(zoom));
+
+  SetResult(result.ToValue().release());
+
+  return true;
 }
 
 WebcamPrivateResetFunction::WebcamPrivateResetFunction() {
@@ -54,7 +187,21 @@ bool WebcamPrivateResetFunction::RunImpl() {
       api::webcam_private::Reset::Params::Create(*args_));
   EXTENSION_FUNCTION_VALIDATE(params.get());
 
-  // TODO(zork): Reset the webcam state.
+  base::ScopedFD fd =
+      OpenWebcam(extension_id(), browser_context(), params->webcam_id);
+  if (!fd.is_valid()) {
+    SetError(kUnknownWebcam);
+    return false;
+  }
+
+  if (params->config.pan)
+    ResetWebcamParameter(fd.get(), WEBCAM_PAN);
+
+  if (params->config.tilt)
+    ResetWebcamParameter(fd.get(), WEBCAM_TILT);
+
+  if (params->config.zoom)
+    ResetWebcamParameter(fd.get(), WEBCAM_ZOOM);
 
   return true;
 }