mavnative.c

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/*
    Native mavlink glue for python.
    Author: kevinh@geeksville.com
*/

#undef NDEBUG

#include <Python.h>
#include <structmember.h>

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <assert.h>
#include <stddef.h>
#include <setjmp.h>

#if PY_MAJOR_VERSION >= 3
// In python3 it only has longs, not 32 bit ints
#define PyInt_AsLong PyLong_AsLong
#define PyInt_FromLong PyLong_FromLong

// We returns strings for byte arreays in python2, but bytes objects in python3
#define PyByteString_FromString PyBytes_FromString
#define PyByteString_FromStringAndSize PyBytes_FromStringAndSize
#define PyByteString_ConcatAndDel PyBytes_ConcatAndDel
#else
#define PyByteString_FromString PyString_FromString
#define PyByteString_FromStringAndSize PyString_FromStringAndSize
#define PyByteString_ConcatAndDel PyString_ConcatAndDel
#endif

#include "mavlink_defaults.h"

#define MAVLINK_USE_CONVENIENCE_FUNCTIONS

#include <mavlink_types.h>

// Mavlink send support
// Not currently used, but keeps mavlink_helpers send code happy
static mavlink_system_t mavlink_system = {42,11,};
static void comm_send_ch(mavlink_channel_t chan, uint8_t c) {
    // Sending not supported yet in native code
    assert(0);
}

#define MAVLINK_ASSERT(x) assert(x)

// static mavlink_message_t last_msg;

/*
  default message crc function. You can override this per-system to
  put this data in a different memory segment
*/
#define MAVLINK_MESSAGE_CRC(msgid) py_message_info[msgid].crc_extra

/* Enable this option to check the length of each message.
 This allows invalid messages to be caught much sooner. Use if the transmission
 medium is prone to missing (or extra) characters (e.g. a radio that fades in
 and out). Only use if the channel will only contain messages types listed in
 the headers.
*/

#define MAVLINK_MESSAGE_LENGTH(msgid) py_message_info[msgid].len

// #include <mavlink.h>

#define TRUE 1
#define FALSE 0

typedef struct {
        PyObject                *name;               // name of this field
        mavlink_message_type_t  type;                // type of this field
        unsigned int            array_length;        // if non-zero, field is an array
        unsigned int            wire_offset;         // offset of each field in the payload
} py_field_info_t;

// note that in this structure the order of fields is the order
// in the XML file, not necessary the wire order
typedef struct {
    PyObject            *id;                                          // The int id for this msg
    PyObject            *name;                                        // name of the message
    unsigned            len;                                          // the raw message length of this message - not including headers & CRC
    uint8_t             crc_extra;                                    // the CRC extra for this message
    unsigned            num_fields;                                   // how many fields in this message
    PyObject            *fieldnames;                                  // fieldnames in the correct order expected by user (not wire order)
    py_field_info_t     fields[MAVLINK_MAX_FIELDS];                   // field information
} py_message_info_t;

static py_message_info_t py_message_info[256];
static uint8_t           info_inited = FALSE; // We only do the init once (assuming only one dialect in use)

#include <protocol.h>

typedef struct {
    mavlink_message_t   msg;
    int                 numBytes;
    uint8_t             bytes[MAVLINK_MAX_PACKET_LEN];
} py_message_t;

typedef struct {
    PyObject_HEAD

    PyObject            *MAVLinkMessage;
    mavlink_status_t    mav_status;
    py_message_t        msg;
} NativeConnection;

// #define MAVNATIVE_DEBUG
#ifdef MAVNATIVE_DEBUG
#  define mavdebug    printf
#else
#  define mavdebug(x...)
#endif


// My exception type
static PyObject *MAVNativeError;

static jmp_buf python_entry;

#define PYTHON_ENTRY if(!setjmp(python_entry)) {
#define PYTHON_EXIT  } else { return NULL; }   // Used for routines thar return ptrs
#define PYTHON_EXIT_INT  } else { return -1; } // Used for routines that return ints


MAVLINK_HELPER uint8_t py_mavlink_parse_char(uint8_t c, py_message_t* pymsg, mavlink_status_t* status)
{
    mavlink_message_t *rxmsg = &pymsg->msg;

    int bufferIndex = 0;

    status->msg_received = 0;

    switch (status->parse_state)
    {
    case MAVLINK_PARSE_STATE_UNINIT:
    case MAVLINK_PARSE_STATE_IDLE:
        if (c == MAVLINK_STX)
        {
            status->parse_state = MAVLINK_PARSE_STATE_GOT_STX;
            rxmsg->len = 0;
            pymsg->numBytes = 0;
            rxmsg->magic = c;
            mavlink_start_checksum(rxmsg);
            pymsg->bytes[pymsg->numBytes++] = c;
        }
        break;

    case MAVLINK_PARSE_STATE_GOT_STX:
            if (status->msg_received 
/* Support shorter buffers than the
   default maximum packet size */
#if (MAVLINK_MAX_PAYLOAD_LEN < 255)
                || c > MAVLINK_MAX_PAYLOAD_LEN
#endif
                )
        {
            status->buffer_overrun++;
            status->parse_error++;
            status->msg_received = 0;
            status->parse_state = MAVLINK_PARSE_STATE_IDLE;
        }
        else
        {
            // NOT counting STX, LENGTH, SEQ, SYSID, COMPID, MSGID, CRC1 and CRC2
            rxmsg->len = c;
            status->packet_idx = 0;
            mavlink_update_checksum(rxmsg, c);
            pymsg->bytes[pymsg->numBytes++] = c;
            status->parse_state = MAVLINK_PARSE_STATE_GOT_LENGTH;
        }
        break;

    case MAVLINK_PARSE_STATE_GOT_LENGTH:
        rxmsg->seq = c;
        mavlink_update_checksum(rxmsg, c);
        pymsg->bytes[pymsg->numBytes++] = c;
        status->parse_state = MAVLINK_PARSE_STATE_GOT_SEQ;
        break;

    case MAVLINK_PARSE_STATE_GOT_SEQ:
        rxmsg->sysid = c;
        mavlink_update_checksum(rxmsg, c);
        pymsg->bytes[pymsg->numBytes++] = c;
        status->parse_state = MAVLINK_PARSE_STATE_GOT_SYSID;
        break;

    case MAVLINK_PARSE_STATE_GOT_SYSID:
        rxmsg->compid = c;
        mavlink_update_checksum(rxmsg, c);
        pymsg->bytes[pymsg->numBytes++] = c;
        status->parse_state = MAVLINK_PARSE_STATE_GOT_COMPID;
        break;

    case MAVLINK_PARSE_STATE_GOT_COMPID:
#ifdef MAVLINK_CHECK_MESSAGE_LENGTH
            if (rxmsg->len != MAVLINK_MESSAGE_LENGTH(c))
        {
            status->parse_error++;
            status->parse_state = MAVLINK_PARSE_STATE_IDLE;
            break;
        }
#endif
        rxmsg->msgid = c;
        mavlink_update_checksum(rxmsg, c);
        pymsg->bytes[pymsg->numBytes++] = c;
        if (rxmsg->len == 0)
        {
            status->parse_state = MAVLINK_PARSE_STATE_GOT_PAYLOAD;
        }
        else
        {
            status->parse_state = MAVLINK_PARSE_STATE_GOT_MSGID;
        }
        break;

    case MAVLINK_PARSE_STATE_GOT_MSGID:
        _MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx++] = (char)c;
        mavlink_update_checksum(rxmsg, c);
        pymsg->bytes[pymsg->numBytes++] = c;
        if (status->packet_idx == rxmsg->len)
        {
            status->parse_state = MAVLINK_PARSE_STATE_GOT_PAYLOAD;
        }
        break;

    case MAVLINK_PARSE_STATE_GOT_PAYLOAD:
#if MAVLINK_CRC_EXTRA
        mavlink_update_checksum(rxmsg, MAVLINK_MESSAGE_CRC(rxmsg->msgid));
#endif
        pymsg->bytes[pymsg->numBytes++] = c;
        if (c != (rxmsg->checksum & 0xFF)) {
            // Check first checksum byte
            status->parse_error++;
            status->msg_received = 0;
            status->parse_state = MAVLINK_PARSE_STATE_IDLE;
            if (c == MAVLINK_STX)
            {
                status->parse_state = MAVLINK_PARSE_STATE_GOT_STX;
                rxmsg->len = 0;
                mavlink_start_checksum(rxmsg);
            }
        }
        else
        {
            status->parse_state = MAVLINK_PARSE_STATE_GOT_CRC1;
            _MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx] = (char)c;
        }
        break;

    case MAVLINK_PARSE_STATE_GOT_CRC1:
        pymsg->bytes[pymsg->numBytes++] = c;
        if (c != (rxmsg->checksum >> 8)) {
            // Check second checksum byte
            status->parse_error++;
            status->msg_received = 0;
            status->parse_state = MAVLINK_PARSE_STATE_IDLE;
            if (c == MAVLINK_STX)
            {
                status->parse_state = MAVLINK_PARSE_STATE_GOT_STX;
                rxmsg->len = 0;
                mavlink_start_checksum(rxmsg);
            }
        }
        else
        {
            // Successfully got message
            status->msg_received = 1;
            status->parse_state = MAVLINK_PARSE_STATE_IDLE;
            _MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx+1] = (char)c;
        }
        break;

    case MAVLINK_PARSE_STATE_GOT_BAD_CRC1:  // not used, just to fix compiler warning
        break;
    }

    bufferIndex++;
    // If a message has been sucessfully decoded, check index
    if (status->msg_received == 1)
    {
        //while(status->current_seq != rxmsg->seq)
        //{
        //  status->packet_rx_drop_count++;
        //               status->current_seq++;
        //}
        status->current_rx_seq = rxmsg->seq;
        // Initial condition: If no packet has been received so far, drop count is undefined
        if (status->packet_rx_success_count == 0) status->packet_rx_drop_count = 0;
        // Count this packet as received
        status->packet_rx_success_count++;
    }

    return status->msg_received;
}


// Raise a python exception
static void set_pyerror(const char *msg) {
    PyErr_SetString(MAVNativeError,  msg);
}

// Pass assertion failures back to python (if we can)
extern void __assert_fail(const char *__assertion, const char *__file, unsigned int __line, const char *__function)
{
    char msg[256];

    sprintf(msg, "Assertion failed: %s, %s:%d", __assertion, __file, __line);

    set_pyerror(msg);
    longjmp(python_entry, 1);
}


static unsigned get_field_size(int field_type) {
    unsigned fieldSize;

    switch(field_type) 
    {
    case MAVLINK_TYPE_CHAR: 
        fieldSize = 1;
        break;
    case MAVLINK_TYPE_UINT8_T:
        fieldSize = 1;
        break;
    case MAVLINK_TYPE_INT8_T:
        fieldSize = 1;
        break;
    case MAVLINK_TYPE_UINT16_T:
        fieldSize = 2;
        break;
    case MAVLINK_TYPE_INT16_T:
        fieldSize = 2;
        break;
    case MAVLINK_TYPE_UINT32_T:
        fieldSize = 4;
        break;
    case MAVLINK_TYPE_INT32_T:
        fieldSize = 4;
        break;
    case MAVLINK_TYPE_UINT64_T:
        fieldSize = 8;
        break;
    case MAVLINK_TYPE_INT64_T:                 
        fieldSize = 8;
        break;
    case MAVLINK_TYPE_FLOAT:              
        fieldSize = 4;
        break;
    case MAVLINK_TYPE_DOUBLE:      
        fieldSize = 8;
        break;            
    default:
        mavdebug("BAD MAV TYPE %d\n", field_type);
        set_pyerror("Unexpected mavlink type");
        fieldSize = 1;
    }

    return fieldSize;
}


static int get_py_typeinfo(char type_char, int array_size, unsigned *wire_offset)
{
    int type_code;

    switch(type_char) 
    {
    case 'f': type_code = MAVLINK_TYPE_FLOAT; break;
    case 'd': type_code = MAVLINK_TYPE_DOUBLE; break;
    case 'c': type_code = MAVLINK_TYPE_CHAR; break;
    case 'v': type_code = MAVLINK_TYPE_UINT8_T; break;
    case 'b': type_code = MAVLINK_TYPE_INT8_T; break;
    case 'B': type_code = MAVLINK_TYPE_UINT8_T; break;
    case 'h': type_code = MAVLINK_TYPE_INT16_T; break;
    case 'H': type_code = MAVLINK_TYPE_UINT16_T; break;
    case 'i': type_code = MAVLINK_TYPE_INT32_T; break;
    case 'I': type_code = MAVLINK_TYPE_UINT32_T; break;
    case 'q': type_code = MAVLINK_TYPE_INT64_T; break;
    case 'Q': type_code = MAVLINK_TYPE_UINT64_T; break;
    default:
        assert(0);
    }

    int total_len = get_field_size(type_code) * (array_size == 0 ? 1 : array_size);

    *wire_offset += total_len;

    return type_code;
}

static void init_message_info(PyObject *mavlink_map) {
    // static const mavlink_message_info_t src[256] = MAVLINK_MESSAGE_INFO;
    
    PyObject *items_list = PyDict_Values(mavlink_map);
    assert(items_list); // A list of the tuples in mavlink_map

    Py_ssize_t numMsgs = PyList_Size(items_list);

    int i;
    for(i = 0; i < numMsgs; i++) {
        PyObject *type_class = PyList_GetItem(items_list, i); // returns a _borrowed_ reference
        assert(type_class);

        PyObject *id_obj = PyObject_GetAttrString(type_class, "id"); // A _new_ reference
        assert(id_obj);
        PyObject *name_obj = PyObject_GetAttrString(type_class, "name"); // A new reference
        assert(name_obj);
        PyObject *crc_extra_obj = PyObject_GetAttrString(type_class, "crc_extra"); // A new reference
        assert(crc_extra_obj);
        PyObject *fieldname_list = PyObject_GetAttrString(type_class, "ordered_fieldnames"); // A new reference
        assert(fieldname_list);
        //PyObject *order_list = PyObject_GetAttrString(type_class, "orders"); // A new reference
        //assert(order_list);
        PyObject *arrlen_list = PyObject_GetAttrString(type_class, "array_lengths"); // A new reference
        assert(arrlen_list);
        PyObject *type_format = PyObject_GetAttrString(type_class, "native_format"); // A new reference
        assert(type_format);
        char *type_str = PyByteArray_AsString(type_format);
        assert(type_str);
               
        Py_ssize_t num_fields = PyList_Size(fieldname_list);

        uint8_t id = (uint8_t) PyInt_AsLong(id_obj);
        py_message_info_t *d = &py_message_info[id];

        d->id = id_obj;
        d->name = name_obj;
        d->num_fields = num_fields;
        d->crc_extra = PyInt_AsLong(crc_extra_obj);
        d->fieldnames = PyObject_GetAttrString(type_class, "fieldnames"); // A new reference
        assert(d->fieldnames);

        int fnum;
        unsigned wire_offset = 0;
        for(fnum = 0; fnum < num_fields; fnum++) {
            PyObject *field_name_obj = PyList_GetItem(fieldname_list, fnum); // returns a _borrowed_ reference
            assert(field_name_obj);
            Py_INCREF(field_name_obj);

            PyObject *len_obj = PyList_GetItem(arrlen_list, fnum); // returns a _borrowed_ reference
            assert(len_obj);                        

            d->fields[fnum].name = field_name_obj;
            d->fields[fnum].array_length = PyInt_AsLong(len_obj);
            char type_char = type_str[1 + fnum];
            d->fields[fnum].wire_offset = wire_offset; // Store the current offset before advancing
            d->fields[fnum].type = get_py_typeinfo(type_char, d->fields[fnum].array_length, &wire_offset);            
        }
        d->len = wire_offset;

        Py_DECREF(crc_extra_obj);
        Py_DECREF(arrlen_list);
        Py_DECREF(type_format);
        //Py_DECREF(order_list);
    }

    Py_DECREF(items_list);
}

static PyObject *createPyNone(void)
{
    Py_INCREF(Py_None);
    return Py_None;
}



static void set_attribute(PyObject *obj, const char *attrName, PyObject *val) {
    assert(val);
    PyObject_SetAttrString(obj, attrName, val);
    Py_DECREF(val);
}



static PyObject *pyextract_mavlink(const mavlink_message_t *msg, const py_field_info_t *field) {
    unsigned offset = field->wire_offset;
    int index;

    // For arrays of chars we build the result in a string instead of an array
    PyObject *arrayResult =  (field->array_length != 0 && field->type != MAVLINK_TYPE_CHAR) ? PyList_New(field->array_length) : NULL;
    PyObject *stringResult = (field->array_length != 0 && field->type == MAVLINK_TYPE_CHAR) ? PyByteString_FromString("") : NULL;
    PyObject *result = NULL;

    int numValues = (field->array_length == 0) ? 1 : field->array_length;
    unsigned fieldSize = get_field_size(field->type);

    uint8_t string_ended = FALSE;

    if(arrayResult != NULL)
        result = arrayResult;

    // Either build a full array of results, or return a single value 
    for(index = 0; index < numValues; index++) {
        PyObject *val = NULL;

        switch(field->type) {
            case MAVLINK_TYPE_CHAR: {
                // If we are building a string, stop writing when we see a null char
                char c = _MAV_RETURN_char(msg, offset);

                if(stringResult && c == 0) 
                    string_ended = TRUE;

                val = PyByteString_FromStringAndSize(&c, 1);
                break;
                }
            case MAVLINK_TYPE_UINT8_T:
                val = PyInt_FromLong(_MAV_RETURN_uint8_t(msg, offset));
                break;
            case MAVLINK_TYPE_INT8_T:
                val = PyInt_FromLong(_MAV_RETURN_int8_t(msg, offset));
                break;
            case MAVLINK_TYPE_UINT16_T:
                val = PyInt_FromLong(_MAV_RETURN_uint16_t(msg, offset));
                break;
            case MAVLINK_TYPE_INT16_T:
                val = PyInt_FromLong(_MAV_RETURN_int16_t(msg, offset));
                break;
            case MAVLINK_TYPE_UINT32_T:
                val = PyLong_FromLong(_MAV_RETURN_uint32_t(msg, offset));
                break;
            case MAVLINK_TYPE_INT32_T:
                val = PyInt_FromLong(_MAV_RETURN_int32_t(msg, offset));   
                break;
            case MAVLINK_TYPE_UINT64_T:
                val = PyLong_FromLongLong(_MAV_RETURN_uint64_t(msg, offset));
                break;
            case MAVLINK_TYPE_INT64_T:
                val = PyLong_FromLongLong(_MAV_RETURN_int64_t(msg, offset));
                break;
            case MAVLINK_TYPE_FLOAT:
                val = PyFloat_FromDouble(_MAV_RETURN_float(msg, offset));
                break;
            case MAVLINK_TYPE_DOUBLE:
                val = PyFloat_FromDouble(_MAV_RETURN_double(msg, offset));
                break;            
            default:
                mavdebug("BAD MAV TYPE %d\n", field->type);
                set_pyerror("Unexpected mavlink type");
                return NULL;
        }
        offset += fieldSize;

        assert(val);
        if(arrayResult != NULL)  
            PyList_SetItem(arrayResult, index, val);
        else if(stringResult != NULL) {
            if(!string_ended)
                PyByteString_ConcatAndDel(&stringResult, val);
            else
                Py_DECREF(val); // We didn't use this char

            result = stringResult;
        }
        else // Not building an array
            result = val;
    }

    assert(result);
    return result;
}


static PyObject *msg_to_py(PyObject* msgclass, const py_message_t *pymsg) {
    const mavlink_message_t *msg = &pymsg->msg;
    const py_message_info_t *info = &py_message_info[msg->msgid];

    mavdebug("Found a msg: %s\n", PyString_AS_STRING(info->name));

    /* Call the class object to create our instance */
    // PyObject *obj = PyObject_CallObject((PyObject *) &NativeConnectionType, null);
    PyObject *argList = PyTuple_Pack(2, info->id, info->name);
    PyObject *obj = PyObject_CallObject(msgclass, argList);
    uint8_t objValid = TRUE;
    assert(obj);
    Py_DECREF(argList);

    // Find the header subobject
    PyObject *header = PyObject_GetAttrString(obj, "_header");
    assert(header);

    // msgid already set in the constructor call
    set_attribute(header, "mlen", PyInt_FromLong(msg->len));
    set_attribute(header, "seq", PyInt_FromLong(msg->seq));
    set_attribute(header, "srcSystem", PyInt_FromLong(msg->sysid));
    set_attribute(header, "srcComponent", PyInt_FromLong(msg->compid));
    Py_DECREF(header);
    header = NULL;

    // FIXME - we should generate this expensive field only as needed (via a getattr override)
    set_attribute(obj, "_msgbuf", PyByteArray_FromStringAndSize((const char *) pymsg->bytes, pymsg->numBytes));

    // Now add all the fields - FIXME - do this lazily using getattr overrides
    PyObject_SetAttrString(obj, "_fieldnames", info->fieldnames); // Will increment the reference count

    // FIXME - reuse the fieldnames list from python - so it is in the right order

    int fnum;
    for(fnum = 0; fnum < info->num_fields && objValid; fnum++) {
        const py_field_info_t *f = &info->fields[fnum];
        PyObject *val = pyextract_mavlink(msg, f);

        if(val != NULL) {
            PyObject_SetAttr(obj, f->name, val);
            Py_DECREF(val); // We no longer need val, the attribute will keep a ref
        }
        else 
            objValid = FALSE;
    }

    if(objValid)
        return obj;
    else {
        Py_DECREF(obj);
        return NULL;
    }
}


static int get_expectedlength(NativeConnection *self)
{
    int desired;

    mavlink_message_t *msg = &self->msg.msg;

    switch(self->mav_status.parse_state) {
        case MAVLINK_PARSE_STATE_UNINIT: 
        case MAVLINK_PARSE_STATE_IDLE: 
            desired = 8;
            break;
        case MAVLINK_PARSE_STATE_GOT_STX: 
            desired = 7;
            break;
        case MAVLINK_PARSE_STATE_GOT_LENGTH:
            desired = msg->len + 6;
            break;
        case MAVLINK_PARSE_STATE_GOT_SEQ: 
            desired = msg->len + 5;
            break;
        case MAVLINK_PARSE_STATE_GOT_SYSID: 
            desired = msg->len + 4;
            break;        
        case MAVLINK_PARSE_STATE_GOT_COMPID:
            desired = msg->len + 3;
            break;         
        case MAVLINK_PARSE_STATE_GOT_MSGID: 
            desired = msg->len - self->mav_status.packet_idx + 2;
            break;          
        case MAVLINK_PARSE_STATE_GOT_PAYLOAD:
            desired = 2;
            break;          
        case MAVLINK_PARSE_STATE_GOT_CRC1: 
            desired = 1;
            break;  
        default:
            // Huh?  Just claim 1
            desired = 1;
            break;
    } 
    
    mavdebug("in state %d, expected_length=%d\n", (int) self->mav_status.parse_state, desired);
    return desired;
}


static PyObject *NativeConnection_getexpectedlength(NativeConnection *self, void *closure)
{
    return PyInt_FromLong(get_expectedlength(self));
}

static PyObject *
py_parse_chars(NativeConnection *self, PyObject *args)
{
    PYTHON_ENTRY

    PyObject* byteObj;
    if (!PyArg_ParseTuple(args, "O", &byteObj)) {
        set_pyerror("Invalid arguments");
        return NULL;
    }
    
    assert(PyByteArray_Check(byteObj));
    Py_ssize_t numBytes = PyByteArray_Size(byteObj);    
    mavdebug("numbytes %u\n", (unsigned) numBytes);

    char *start = PyByteArray_AsString(byteObj);
    assert(start);
    char *bytes = start;
    PyObject *result = NULL;

    // Generate a list of messages found 
    while(numBytes) {
        char c = *bytes++;
        numBytes--;
        get_expectedlength(self); mavdebug("parse 0x%x\n", (unsigned char) c);

        if (py_mavlink_parse_char(c, &self->msg, &self->mav_status)) {
            mavdebug("got packet\n");
            result = msg_to_py(self->MAVLinkMessage, &self->msg);
            if(result != NULL)
                break;
        }
    }

    // We didn't process all bytes provided by the caller, so fixup their array
    memmove(start, bytes, numBytes);
    PyByteArray_Resize(byteObj, numBytes);

    if(result != NULL) 
        return result;
    else
        return createPyNone();

    PYTHON_EXIT
}

static PyObject *
py_parse_buffer(NativeConnection *self, PyObject *args)
{
    PYTHON_ENTRY

    mavdebug("Enter py_parse_buffer\n");

    const char *bytes;
    Py_ssize_t numBytes = 0;

    if (!PyArg_ParseTuple(args, "s#", &bytes, &numBytes)) {
        set_pyerror("Invalid arguments");
        return NULL;
    }
    
    // mavdebug("numbytes %u\n", (unsigned) numBytes);

    PyObject* list = PyList_New(0);

    // Generate a list of messages found 
    while(numBytes--) {
        char c = *bytes++;
        // mavdebug("parse %c\n", c);

        if (py_mavlink_parse_char(c, &self->msg, &self->mav_status)) {
            PyObject *obj = msg_to_py(self->MAVLinkMessage, &self->msg);
            if(obj != NULL) {
                PyList_Append(list, obj);
            
                // Append will have bummped up the ref count on obj, so we need to release our count
                Py_DECREF(obj);
            }
        }
    }

    return list;

    PYTHON_EXIT
}

static PyObject *
NativeConnection_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    NativeConnection *self = (NativeConnection *)type->tp_alloc(type, 0);

    mavdebug("new connection\n");
    return (PyObject *)self;
}


static int
NativeConnection_init(NativeConnection *self, PyObject *args, PyObject *kwds)
{
    PYTHON_ENTRY

    mavdebug("Enter init\n");

    memset(&self->mav_status, 0, sizeof(self->mav_status));

    PyObject* msgclass, *mavlink_map;
    if (!PyArg_ParseTuple(args, "OO", &msgclass, &mavlink_map)) {
        set_pyerror("Invalid arguments");
        return -1;
    }

    // keep a ref to our mavlink instance constructor
    assert(msgclass);
    self->MAVLinkMessage = msgclass;
    Py_INCREF(msgclass);

    assert(mavlink_map);
    if(!info_inited) {
        init_message_info(mavlink_map);
        info_inited = TRUE;
    }

    mavdebug("inited connection\n");
    return 0;

    PYTHON_EXIT_INT
}

static void NativeConnection_dealloc(NativeConnection* self)
{
    Py_XDECREF(self->MAVLinkMessage);
    Py_TYPE(self)->tp_free((PyObject*)self);
}

static PyMemberDef NativeConnection_members[] = {
    {NULL}  /* Sentinel */
};

static PyGetSetDef NativeConnection_getseters[] = {
    {"expected_length", 
     (getter)NativeConnection_getexpectedlength, NULL,
     "How many characters would the state-machine like to read now",
     NULL},
    {NULL}  /* Sentinel */
};

static PyMethodDef NativeConnection_methods[] = {
    {"parse_chars",  (PyCFunction) py_parse_chars, METH_VARARGS,
     "Given a msg class and an array of bytes, Parse chars, returning a message or None"},    
    {"parse_buffer",  (PyCFunction) py_parse_buffer, METH_VARARGS,
     "Given a msg class and a string like object, Parse chars, returning a (possibly empty) list of messages"},
    {NULL,  NULL},
};

// FIXME - delete this?
static PyTypeObject NativeConnectionType = {
#if PY_MAJOR_VERSION >= 3
    PyVarObject_HEAD_INIT(NULL, 0)
#else
    PyObject_HEAD_INIT(NULL)
    0,                       /* ob_size */
#endif
    "mavnative.NativeConnection",      /* tp_name */
    sizeof(NativeConnection),          /* tp_basicsize */
    0,                       /* tp_itemsize */
    (destructor)NativeConnection_dealloc,  /* tp_dealloc */
    0,                       /* tp_print */
    0,                       /* tp_getattr */
    0,                       /* tp_setattr */
    0,                       /* tp_compare */
    0,                       /* tp_repr */
    0,                       /* tp_as_number */
    0,                       /* tp_as_sequence */
    0,                       /* tp_as_mapping */
    0,                       /* tp_hash */
    0,                       /* tp_call */
    0,                       /* tp_str */
    0,                       /* tp_getattro */
    0,                       /* tp_setattro */
    0,                       /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT |
      Py_TPFLAGS_BASETYPE,   /* tp_flags */
    "NativeConnection objects",  /* tp_doc */
    0,                       /* tp_traverse */
    0,                       /* tp_clear */
    0,                       /* tp_richcompare */
    0,                       /* tp_weaklistoffset */
    0,                       /* tp_iter */
    0,                       /* tp_iternext */
    NativeConnection_methods,  /* tp_methods */
    NativeConnection_members,  /* tp_members */
    NativeConnection_getseters,  /* tp_getset */
    0,                       /* tp_base */
    0,                       /* tp_dict */
    0,                       /* tp_descr_get */
    0,                       /* tp_descr_set */
    0,                       /* tp_dictoffset */
    (initproc)NativeConnection_init,   /* tp_init */
    0,                       /* tp_alloc */
    NativeConnection_new,    /* tp_new */
};

#if PY_MAJOR_VERSION >= 3
#define MOD_RETURN(m) return m
#else
#define MOD_RETURN(m) return
#endif

PyMODINIT_FUNC
#if PY_MAJOR_VERSION >= 3
    PyInit_mavnative(void)
#else
    initmavnative(void)
#endif
{
    if (PyType_Ready(&NativeConnectionType) < 0)
        MOD_RETURN(NULL);

#if PY_MAJOR_VERSION < 3
    static PyMethodDef ModuleMethods[] = {
        {NULL, NULL, 0, NULL}        /* Sentinel */
    };

    PyObject *m = Py_InitModule3("mavnative", ModuleMethods, "Mavnative module");
    if (m == NULL)
        MOD_RETURN(m);
#else
    static PyModuleDef mod_def = {
        PyModuleDef_HEAD_INIT,
        "mavnative",
        "EMavnative module",
        -1,
        NULL, NULL, NULL, NULL, NULL
    };

    PyObject *m = PyModule_Create(&mod_def);
#endif

    MAVNativeError = PyErr_NewException("mavnative.error", NULL, NULL);
    Py_INCREF(MAVNativeError);
    PyModule_AddObject(m, "error", MAVNativeError);

    Py_INCREF(&NativeConnectionType);
    PyModule_AddObject(m, "NativeConnection", (PyObject *) &NativeConnectionType);
    MOD_RETURN(m);
}