Myo C++ Header files. Who wants to write a node binding for this?

README.md

The state of Myo bindings in Node.js

... any takers? Comment on this gist! The discussion all started from a Tweet:

Who's going to be the first to write a wrapper for the @thalmic #myo C++ library? Latest headers: https://gist.github.com/indexzero/60d1224f0082f0d16f14

As pointed out by @c4milo there are a number of libraries that exist, but from first glance they all have deficiencies:

• https://github.com/HektorW/myo-node: Only works on Windows
• https://github.com/KamalAman/Myo-Node-Red: I don't even understand how this works
• https://github.com/logotype/MyoJS: Just HTTP communcation with another Daemon
• https://github.com/stolksdorf/myo.js: Just HTTP communcation with another Daemon
• https://github.com/logotype/myodaemon: Only works on OSX

So because all of these libraries have deficiencies, I'd like to outline some ways one could approach this problem

1. Write a direct wrapper to the libmyo C++ library (see header file in this gist): The advantages here is that it is cross platform (because node and node-gyp) and it would be easy to stay in-sync with the Thalmic Myo C++ SDK when they release updates. The downside is that it would only work on the platforms where the Thalmic Myo C++ SDK can compile, so it might not work on ARM, or other hardware platforms.
2. Communicate directly over Bluetooth with the Myo prototcol: The advantage here is working anywhere that node runs with no external C++ code (except for perhaps whatever we need for Bluetooth). The disadvantage is that it would be tightly coupled to the firmware versions where we had figured out the protocol since that could change in any SDK release.

libmyo.h

// Copyright (C) 2013-2014 Thalmic Labs Inc.
// Distributed under the Myo SDK license agreement. See LICENSE.txt for details.
#ifndef MYO_LIBMYO_H
#define MYO_LIBMYO_H

#include <stdint.h>

#include "libmyo/detail/visibility.h"

#ifdef __cplusplus
extern "C" {
#endif

/// @file libmyo.h
/// libmyo C API declarations.

typedef void* libmyo_hub_t;

/// \defgroup errors Error Handling
/// @{

/// Function result codes.
/// All libmyo functions that can fail return a value of this type.
typedef enum {
    libmyo_success,
    libmyo_error,
    libmyo_error_invalid_argument,
    libmyo_error_runtime
} libmyo_result_t;

/// Opaque handle to detailed error information.
typedef void* libmyo_error_details_t;

/// Return a null-terminated string with a detailed error message.
LIBMYO_EXPORT
const char* libmyo_error_cstring(libmyo_error_details_t);

/// Returns the kind of error that occurred.
LIBMYO_EXPORT
libmyo_result_t libmyo_error_kind(libmyo_error_details_t);

/// Free the resources allocated by an error object.
LIBMYO_EXPORT
void libmyo_free_error_details(libmyo_error_details_t);

/// @}

/// @defgroup libmyo_hub Hub instance
/// @{

/// Initialize a connection to the hub.
/// \a application_identifier must follow a reverse domain name format (ex. com.domainname.appname). Application
/// identifiers can be formed from the set of alphanumeric ASCII characters (a-z, A-Z, 0-9). The hyphen (-) and
/// underscore (_) characters are permitted if they are not adjacent to a period (.) character (i.e. not at the start or
/// end of each segment), but are not permitted in the top-level domain. Application identifiers must have three or more
/// segments. For example, if a company's domain is example.com and the application is named hello-world, one could use
/// "com.example.hello-world" as a valid application identifier. \a application_identifier can be NULL or empty.
/// @returns libmyo_success if the connection is successfully established, otherwise:
///  - libmyo_error_runtime if a connection could not be established
///  - libmyo_error_invalid_argument if \a out_hub is NULL
///  - libmyo_error_invalid_argument if \a application_identifier is longer than 255 characters
///  - libmyo_error_invalid_argument if \a application_identifier is not in the proper reverse domain name format
LIBMYO_EXPORT
libmyo_result_t libmyo_init_hub(libmyo_hub_t* out_hub, const char* application_identifier,
                                libmyo_error_details_t* out_error);

/// Free the resources allocated to a hub.
/// @returns libmyo_success if shutdown is successful, otherwise:
///  - libmyo_error_invalid_argument if \a hub is NULL
///  - libmyo_error if \a hub is not a valid hub
LIBMYO_EXPORT
libmyo_result_t libmyo_shutdown_hub(libmyo_hub_t hub, libmyo_error_details_t* out_error);

// Locking policies.
typedef enum {
    libmyo_locking_policy_none,    ///< Pose events are always sent.
    libmyo_locking_policy_standard ///< Pose events are not sent while a Myo is locked.
} libmyo_locking_policy_t;

/// Set the locking policy for Myos connected to the hub.
/// @returns libmyo_success if the locking policy is successfully set, otherwise
///  - libmyo_error_invalid_argument if \a hub is NULL
///  - libmyo_error if \a hub is not a valid hub
LIBMYO_EXPORT
libmyo_result_t libmyo_set_locking_policy(libmyo_hub_t hub, libmyo_locking_policy_t locking_policy,
                                          libmyo_error_details_t* out_error);

/// @}

/// @defgroup libmyo_myo Myo instances
/// @{

/// Opaque type corresponding to a known Myo device.
typedef void* libmyo_myo_t;

/// Types of vibration
typedef enum {
    libmyo_vibration_short,
    libmyo_vibration_medium,
    libmyo_vibration_long
} libmyo_vibration_type_t;

/// Vibrate the given myo.
/// Can be called when a Myo is paired.
/// @returns libmyo_success if the Myo successfully vibrated, otherwise
///  - libmyo_error_invalid_argument if \a myo is NULL
LIBMYO_EXPORT
libmyo_result_t libmyo_vibrate(libmyo_myo_t myo, libmyo_vibration_type_t type, libmyo_error_details_t* out_error);

/// Request the RSSI for a given myo.
/// Can be called when a Myo is paired. A libmyo_event_rssi event will likely be generated with the value of the RSSI.
/// @returns libmyo_success if the Myo successfully got the RSSI, otherwise
///  - libmyo_error_invalid_argument if \a myo is NULL
LIBMYO_EXPORT
libmyo_result_t libmyo_request_rssi(libmyo_myo_t myo, libmyo_error_details_t* out_error);

/// EMG streaming modes.
typedef enum {
    libmyo_stream_emg_disabled, ///< Do not send EMG data.
    libmyo_stream_emg_enabled   ///< Send EMG data.
} libmyo_stream_emg_t;

/// Set whether or not to stream EMG data for a given myo.
/// Can be called when a Myo is paired.
/// @returns libmyo_success if the EMG mode was set successfully, otherwise
///  - libmyo_error_invalid_argument if \a myo is NULL
LIBMYO_EXPORT
libmyo_result_t libmyo_set_stream_emg(libmyo_myo_t myo, libmyo_stream_emg_t emg, libmyo_error_details_t* out_error);

/// @}

/// @defgroup libmyo_poses Pose recognition.
/// @{

/// Supported poses.
typedef enum {
    libmyo_pose_rest           = 0, ///< Rest pose.
    libmyo_pose_fist           = 1, ///< User is making a fist.
    libmyo_pose_wave_in        = 2, ///< User has an open palm rotated towards the posterior of their wrist.
    libmyo_pose_wave_out       = 3, ///< User has an open palm rotated towards the anterior of their wrist.
    libmyo_pose_fingers_spread = 4, ///< User has an open palm with their fingers spread away from each other.
    libmyo_pose_double_tap     = 5, ///< User tapped their thumb and middle finger together twice in succession.

    libmyo_num_poses,               ///< Number of poses supported; not a valid pose.

    libmyo_pose_unknown = 0xffff    ///< Unknown pose.
} libmyo_pose_t;

/// @}

/// @defgroup libmyo_locking Myo locking mechanism

/// Valid unlock types.
typedef enum {
    libmyo_unlock_timed = 0, ///< Unlock for a fixed period of time.
    libmyo_unlock_hold  = 1, ///< Unlock until explicitly told to re-lock.
} libmyo_unlock_type_t;

/// Unlock the given Myo.
/// Can be called when a Myo is paired. A libmyo_event_unlocked event will be generated if the Myo was locked.
/// @returns libmyo_success if the Myo was successfully unlocked, otherwise
///  - libmyo_error_invalid_argument if \a myo is NULL
LIBMYO_EXPORT
libmyo_result_t libmyo_myo_unlock(libmyo_myo_t myo, libmyo_unlock_type_t type, libmyo_error_details_t* out_error);

/// Lock the given Myo immediately.
/// Can be called when a Myo is paired. A libmyo_event_locked event will be generated if the Myo was unlocked.
/// @returns libmyo_success if the Myo was successfully locked, otherwise
///  - libmyo_error_invalid_argument if \a myo is NULL
LIBMYO_EXPORT
libmyo_result_t libmyo_myo_lock(libmyo_myo_t myo, libmyo_error_details_t* out_error);

/// User action types.
typedef enum {
    libmyo_user_action_single = 0, ///< User did a single, discrete action, such as pausing a video.
} libmyo_user_action_type_t;

/// Notify the given Myo that a user action was recognized.
/// Can be called when a Myo is paired. Will cause Myo to vibrate.
/// @returns libmyo_success if the Myo was successfully notified, otherwise
///  - libmyo_error_invalid_argument if \a myo is NULL
LIBMYO_EXPORT
libmyo_result_t libmyo_myo_notify_user_action(libmyo_myo_t myo, libmyo_user_action_type_t type,
                                              libmyo_error_details_t* out_error);

/// @}

/// @defgroup libmyo_events Event Handling
/// @{

/// Types of events.
typedef enum {
    libmyo_event_paired,           ///< Successfully paired with a Myo.
    libmyo_event_unpaired,         ///< Successfully unpaired from a Myo.
    libmyo_event_connected,        ///< A Myo has successfully connected.
    libmyo_event_disconnected,     ///< A Myo has been disconnected.
    libmyo_event_arm_synced,       ///< A Myo has recognized that the sync gesture has been successfully performed.
    libmyo_event_arm_unsynced,     ///< A Myo has been moved or removed from the arm.
    libmyo_event_orientation,      ///< Orientation data has been received.
    libmyo_event_pose,             ///< A change in pose has been detected. @see libmyo_pose_t.
    libmyo_event_rssi,             ///< An RSSI value has been received.
    libmyo_event_unlocked,         ///< A Myo has become unlocked.
    libmyo_event_locked,           ///< A Myo has become locked.
    libmyo_event_emg,              ///< EMG data has been received.
} libmyo_event_type_t;

/// Information about an event.
typedef const void* libmyo_event_t;

/// Retrieve the type of an event.
LIBMYO_EXPORT
uint32_t libmyo_event_get_type(libmyo_event_t event);

/// Retrieve the timestamp of an event.
/// @see libmyo_now() for details on timestamps.
LIBMYO_EXPORT
uint64_t libmyo_event_get_timestamp(libmyo_event_t event);

/// Retrieve the Myo associated with an event.
LIBMYO_EXPORT
libmyo_myo_t libmyo_event_get_myo(libmyo_event_t event);

/// Components of version.
typedef enum {
    libmyo_version_major,        ///< Major version.
    libmyo_version_minor,        ///< Minor version.
    libmyo_version_patch,        ///< Patch version.
    libmyo_version_hardware_rev, ///< Hardware revision.
} libmyo_version_component_t;

/// Hardware revisions.
typedef enum {
    libmyo_hardware_rev_c = 1, ///< Alpha units
    libmyo_hardware_rev_d = 2, ///< Consumer units
} libmyo_hardware_rev_t;

/// Retrieve the Myo armband's firmware version from this event.
/// Valid for libmyo_event_paired and libmyo_event_connected events.
LIBMYO_EXPORT
unsigned int libmyo_event_get_firmware_version(libmyo_event_t event, libmyo_version_component_t);

/// Enumeration identifying a right arm or left arm. @see libmyo_event_get_arm().
typedef enum {
    libmyo_arm_right, ///< Myo is on the right arm.
    libmyo_arm_left, ///< Myo is on the left arm.
    libmyo_arm_unknown, ///< Unknown arm.
} libmyo_arm_t;

/// Retrieve the arm associated with an event.
/// Valid for libmyo_event_arm_synced events only.
LIBMYO_EXPORT
libmyo_arm_t libmyo_event_get_arm(libmyo_event_t event);

/// Possible directions for Myo's +x axis relative to a user's arm.
typedef enum {
    libmyo_x_direction_toward_wrist, ///< Myo's +x axis is pointing toward the user's wrist.
    libmyo_x_direction_toward_elbow, ///< Myo's +x axis is pointing toward the user's elbow.
    libmyo_x_direction_unknown, ///< Unknown +x axis direction.
} libmyo_x_direction_t;

/// Retrieve the x-direction associated with an event.
/// The x-direction specifies which way Myo's +x axis is pointing relative to the user's arm.
/// Valid for libmyo_event_arm_synced events only.
LIBMYO_EXPORT
libmyo_x_direction_t libmyo_event_get_x_direction(libmyo_event_t event);

/// Index into orientation data, which is provided as a quaternion.
/// Orientation data is returned as a unit quaternion of floats, represented as `w + x * i + y * j + z * k`.
typedef enum {
    libmyo_orientation_x = 0, ///< First component of the quaternion's vector part
    libmyo_orientation_y = 1, ///< Second component of the quaternion's vector part
    libmyo_orientation_z = 2, ///< Third component of the quaternion's vector part
    libmyo_orientation_w = 3, ///< Scalar component of the quaternion.
} libmyo_orientation_index;

/// Retrieve orientation data associated with an event.
/// Valid for libmyo_event_orientation events only.
/// @see libmyo_orientation_index
LIBMYO_EXPORT
float libmyo_event_get_orientation(libmyo_event_t event, libmyo_orientation_index index);

/// Retrieve raw accelerometer data associated with an event in units of g.
/// Valid for libmyo_event_orientation events only.
/// Requires `index < 3`.
LIBMYO_EXPORT
float libmyo_event_get_accelerometer(libmyo_event_t event, unsigned int index);

/// Retrieve raw gyroscope data associated with an event in units of deg/s.
/// Valid for libmyo_event_orientation events only.
/// Requires `index < 3`.
LIBMYO_EXPORT
float libmyo_event_get_gyroscope(libmyo_event_t event, unsigned int index);

/// Retrieve the pose associated with an event.
/// Valid for libmyo_event_pose events only.
LIBMYO_EXPORT
libmyo_pose_t libmyo_event_get_pose(libmyo_event_t event);

/// Retreive the RSSI associated with an event.
/// Valid for libmyo_event_rssi events only.
LIBMYO_EXPORT
int8_t libmyo_event_get_rssi(libmyo_event_t event);

/// Retrieve an EMG data point associated with an event.
/// Valid for libmyo_event_emg events only.
/// @a sensor must be smaller than 8.
LIBMYO_EXPORT
int8_t libmyo_event_get_emg(libmyo_event_t event, unsigned int sensor);

/// Return type for event handlers.
typedef enum {
    libmyo_handler_continue, ///< Continue processing events
    libmyo_handler_stop,     ///< Stop processing events
} libmyo_handler_result_t;

/// Callback function type to handle events as they occur from libmyo_run().
typedef libmyo_handler_result_t (*libmyo_handler_t)(void* user_data, libmyo_event_t event);

/// Process events and call the provided callback as they occur.
/// Runs for up to approximately \a duration_ms milliseconds or until a called handler returns libmyo_handler_stop.
/// @returns libmyo_success after a successful run, otherwise
///  - libmyo_error_invalid_argument if \a hub is NULL
///  - libmyo_error_invalid_argument if \a handler is NULL
LIBMYO_EXPORT
libmyo_result_t libmyo_run(libmyo_hub_t hub, unsigned int duration_ms, libmyo_handler_t handler, void* user_data,
                           libmyo_error_details_t* out_error);

/// @}

#ifdef __cplusplus
} // extern "C"
#endif

#endif // MYO_LIBMYO_H

I'm going to dig into https://github.com/dzhu/myo-raw soon, which might make 2 viable.

I've started a little project to expose the Myo socket events as Observables. Since the socket can also accept commands, back-talk has to be preserved, which means composing Subjects (bidirectional pairs of [Observer, Observable]) instead of only Observables. Doing it this way is (theoretically) slower than uni-directional communication, but it gives us a sweet API: https://github.com/trxcllnt/RxJS-Myo