I am implementing the recvall() function to be sure that the data is completely sent. Also I modified the send() function to sendall() like this:
int sendall (int consocket, char* buf, int* len)
{
int total = 0;
int bytesleft = *len; // how many we have left to send
int n;
while(total < *len) {
n = send(consocket, buf+total, bytesleft, 0);
if (n == -1) { break; }
total += n;
bytesleft -= n;
*len = total; // return number actually sent here
return n==-1?-1:0; // return -1 on failure, 0 on success
}
}
How can I implement recvall()? Say I sent from the server a struct of 14 bytes and I check in the client and get 12 bytes.. now in an unreliable situation how should I manage to get the other two bytes... I have spent time trying... any help welcomed.
You may loop over a select with an appropriate timeout . Select will wait until new data is received or until time is elapsed or an error occurs. This gives you a greater control than just blocing on a recv.
Related
// Copy from kernel to user.
// Copy len bytes from src to virtual address dstva in a given page table.
// Return 0 on success, -1 on error.
int
copyout(pagetable_t pagetable, uint64 dstva, char *src, uint64 len)
{
uint64 n, va0, pa0;
while(len > 0){
va0 = PGROUNDDOWN(dstva);
pa0 = walkaddr(pagetable, va0);
if(pa0 == 0)
return -1;
n = PGSIZE - (dstva - va0);
if(n > len)
n = len;
memmove((void *)(pa0 + (dstva - va0)), src, n);
len -= n;
src += n;
dstva = va0 + PGSIZE;
}
return 0;
}
The function used in xv6 kernel for copying out data from the kernel to user-space process accepts a pagetable as argument and uses that pagetable to access the physical address behind that user-space address. However, neither copyout() nor walkaddr() performs any locking operation on the page table. How are race conditions avoided in this case? Is it possible for the page table to change after getting the physical address and before the actual reading and cause issues? And how is it avoided in xv6?
If I am not wrong, the copyout() is invoked by the kernel in the
piperead() and pipewrite() located in pipewrite.c function. Prior to calling this
function the calling process's spinlock is already held.
I am facing an error whenever I call a recvfrom() function for UDP in server side:
buffer overflow detected ***: terminated Aborted
What is the meaning of this error? I am not able to understand.
unsigned int len;
int rv,i;
int tmp;
//char msg[200],command=0;
unsigned short *Fptr;
float Float_Temp;
//make socket blocking
FD_ZERO(&readnbs);
FD_SET(g_iUDP_datalogger_soc, &readnbs);
g_UDP_Blocktimervalue.tv_sec = 0;
g_UDP_Blocktimervalue.tv_usec = UDP_REC_BLOCKTIME;
rv = select(g_iUDP_datalogger_soc + 1, &readnbs, NULL, NULL, &g_UDP_Blocktimervalue);
len = sizeof(g_UDP_ClientAddr);
if (rv == 1) {
printf(" \n\n\n\n\n rv=%d\n\n\n\n",rv);
tmp = recvfrom(g_iUDP_datalogger_soc, &tmp, SIZE_UDP_MSG, 0,(struct sockaddr *) &g_UDP_ClientAddr, &len);
tmp = recvfrom(g_iUDP_datalogger_soc, [YOUR BUFFER ?] , SIZE_UDP_MSG, 0,(struct sockaddr *)...
You're trying to buffer the received data into a single int (tmp) object, which you are also using as the return value from the recvfrom(), and even not checking in any way - either for error, nor for received data.
You are asking recvfrom() to read SIZE_UDP_MSG number of bytes into tmp, which is an int. You did not show what SIZE_UDP_MSG is defined as, but if SIZE_UDP_MSG > sizeof(int), you are going to be writing bytes past the bounds of tmp into surrounding memory, corrupting the memory. That is a buffer overflow.
Perhaps you meant to receive the bytes into your (commented out) msg buffer instead?
char msg[SIZE_UDP_MSG];
tmp = recvfrom(..., msg, SIZE_UDP_MSG, ...);
While going through the implementation of the DPDK MPSC (multi-produce & single-consumer) Ring Buffer API, i found the code to move the head of the producer for inserting new elements in the Ring buffer. The function is as follows :
static __rte_always_inline unsigned int
__rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp,
unsigned int n, enum rte_ring_queue_behavior behavior,
uint32_t *old_head, uint32_t *new_head,
uint32_t *free_entries)
{
const uint32_t capacity = r->capacity;
uint32_t cons_tail;
unsigned int max = n;
int success;
*old_head = __atomic_load_n(&r->prod.head, __ATOMIC_RELAXED);
do {
/* Reset n to the initial burst count */
n = max;
/* Ensure the head is read before tail */
__atomic_thread_fence(__ATOMIC_ACQUIRE);
/* load-acquire synchronize with store-release of ht->tail
* in update_tail.
*/
cons_tail = __atomic_load_n(&r->cons.tail,
__ATOMIC_ACQUIRE);
/* The subtraction is done between two unsigned 32bits value
* (the result is always modulo 32 bits even if we have
* *old_head > cons_tail). So 'free_entries' is always between 0
* and capacity (which is < size).
*/
*free_entries = (capacity + cons_tail - *old_head);
/* check that we have enough room in ring */
if (unlikely(n > *free_entries))
n = (behavior == RTE_RING_QUEUE_FIXED) ?
0 : *free_entries;
if (n == 0)
return 0;
*new_head = *old_head + n;
if (is_sp)
r->prod.head = *new_head, success = 1;
else
/* on failure, *old_head is updated */
success = __atomic_compare_exchange_n(&r->prod.head,
old_head, *new_head,
0, __ATOMIC_RELAXED,
__ATOMIC_RELAXED);
} while (unlikely(success == 0));
return n;
}
The load and compare exchange of the producer's head is done using __ATOMIC_RELAXED memory ordering. Isn't this a problem when multiple producers from different threads produce to the queue. Or am I missing something?
https://doc.dpdk.org/guides/prog_guide/ring_lib.html describes the basic mechanism that DPDK uses for implementing the Ring buffer.
I need to implement my own packets to send over UDP. I decided that I would do this by sending a char buffer which has the sequence number, checksum, size, and the data of the packet which is bytes from a file. The string i'm sending separates each field by a semicolon. Then, when I receive the string (which is my packet) I want to extract each felid, use them accordingly (the sequence number, size, and checksum) and write the bytes to a file. So far I have wrote a method to create 100 packets, and I'm trying to extract and write the bytes to a file (I'm not doing it in the receiver yet, first I'm testing the parsing in the sender). For some reason, the bytes written to my file are incorrect and I'm getting "JPEG DATATSTREAM CONTAINS NO IMAGE" error when I try to open it.
struct packetNode{
char packet[1052]; // this is the entire packet data including the header
struct packetNode *next;
};
This is how I'm creating my packets:
//populate initial window of size 100
for(i = 0; i < 100; i++){
memset(&data[0], 0, sizeof(data));
struct packetNode *p; // create packet node
p = (struct packetNode *)malloc(sizeof(struct packetNode));
bytes = fread(data, 1, sizeof(data), fp); // read 1024 bytes from file into data buffer
int b = fwrite(data, 1, bytes, fpNew);
printf("read: %d\n", bytes);
memset(&p->packet[0], 0, sizeof(p->packet));
sprintf(p->packet, "%d;%d;%d;%s", s, 0, numPackets, data); // create packet
//calculate checksum
int check = checksum8(p->packet, sizeof(p->packet));
sprintf(p->packet, "%d;%d;%d;%s", s, check, numPackets, data); //put checksum in packet
s++; //incremenet sequence number
if(i == 0){
head = p;
tail = p;
tail->next = NULL;
}
else{
tail->next = p;
tail = p;
tail->next = NULL;
}
}
fclose(fp);
and this is where I parse and write the bytes to a file:
void test(){
FILE *fpNew = fopen("test.jpg", "w");
struct packetNode *ptr = head;
char *tokens;
int s, c, size;
int i = 0;
char data[1024];
while(ptr != NULL){
memset(&data[0], 0, sizeof(data));
tokens = strtok(ptr->packet,";");
s = atoi(tokens);
tokens = strtok(NULL, ";");
c = atoi(tokens);
tokens = strtok(NULL, ";");
size = atoi(tokens);
tokens = strtok(NULL, ";");
if(tokens != NULL)
strcpy(data, tokens);
printf("sequence: %d, checksum: %d, size: %d\n", s,c,size);
int b = fwrite(data, 1, sizeof(data), fpNew);
ptr = ptr->next;
i++;
}
fclose(fpNew);
}
Since there is transfer of binary data, a JPEG stream, this data cannot be treated as a string. It's better to go all binary. For instance, instead of
sprintf(p->packet, "%d;%d;%d;%s", s, 0, numPackets, data); // create packet
you would do
sprintf(p->packet, "%d;%d;%d;", s, 0, numPackets);
memcpy(&p->packet[strlen(p->packet)], data, bytes);
but this leads to parsing problems: we would need to change this:
tokens = strtok(NULL, ";");
if(tokens != NULL)
strcpy(data, tokens);
to something like this:
tokens += 1 + ( size < 10 ? 1 : size < 100 ? 2 : size < 1000 ? 3 : size < 10000 ? 4 : 5 );
memcpy(data, tokens, sizeof(data));
#Binary Protocol
It's easier to use a binary packet:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#pragma push(pack,1)
typedef struct Packet {
int seq, maxseq, size;
unsigned short cksum;
unsigned char payload[];
} Packet;
#pragma pop(pack)
typedef struct PacketNode{
struct PacketNode * next;
Packet packet;
} PacketNode;
PacketNode * allocPacketNode(int maxPayloadSize) {
void * ptr = malloc(sizeof(PacketNode) + maxPayloadSize); // FIXME: error checking
memset(ptr, 0, sizeof(PacketNode) + maxPayloadSize); // mallocz wouldn't cooperate
return (PacketNode*) ptr;
}
PacketNode * prepare(FILE * fp, int fsize, int chunksize)
{
PacketNode * head = allocPacketNode(chunksize);
PacketNode * pn = head;
int rd, seq = 0;
int maxseq = fsize / chunksize + ( fsize % chunksize ? 1 : 0 );
while ( ( rd = fread(pn->packet.payload, 1, chunksize, fp ) ) > 0 )
{
printf("read %d bytes\n", rd);
pn->packet.seq = seq++;
pn->packet.maxseq = maxseq;
pn->packet.size = rd + sizeof(Packet);
pn->packet.cksum = 0;
pn->packet.cksum = ~checksum(&pn->packet, pn->packet.size);
if ( rd == chunksize )
pn = pn->next = allocPacketNode(chunksize);
}
return head;
}
int checksum(unsigned char * data, int len)
{
int sum = 0, i;
for ( i = 0; i < len; i ++ )
sum += data[i];
if ( sum > 0xffff )
sum = (sum & 0xffff) + (sum>>16);
return sum;
}
void test( PacketNode * ptr ) {
FILE *fpNew = fopen("test.jpg", "w");
while (ptr != NULL)
{
printf("sequence: %d/%d, checksum: %04x, size: %d\n",
ptr->packet.seq,
ptr->packet.maxseq,
ptr->packet.cksum,
ptr->packet.size - sizeof(Packet)
);
int b = fwrite(ptr->packet.payload, ptr->packet.size - sizeof(Packet), 1, fpNew);
ptr = ptr->next;
}
fclose(fpNew);
}
void fatal( const char * msg ) { printf("FATAL: %s\n", msg); exit(1); }
int main(int argc, char** argv)
{
if ( ! argv[1] ) fatal( "missing filename argument" );
FILE * fp = fopen( argv[1], "r" );
if ( ! fp ) fatal( "cannot open file" );
fseek( fp, 0, SEEK_END );
long fsize = ftell(fp);
fseek( fp, 0, SEEK_SET );
printf("Filesize: %d\n", fsize );
test( prepare(fp, fsize, 1024) );
}
The #pragma push(pack,1) changes how the compiler aligns fields of the struct. We want them to be compact, for network transport. Using 1 is byte-aligned. The #pragma pop(pack) restores the previous setting of the pack pragma.
A note on the checksum method
First we calculate the sum of all the bytes in the packet:
int sum = 0, i;
for ( i = 0; i < len; i ++ )
sum += data[i];
Since the packet uses an unsigned short (16 bits, max value 65535 or 0xffff) to store the checksum, we make sure that the result will fit:
if ( sum > 0xffff ) // takes up more than 16 bits.
Getting the low 16 bits of this int is done using sum & 0xffff, masking out everything but the low 16 bits. We could simply return this value, but we would loose the information from higher checksum bits. So, we will add the upper 16 bits to the lower 16 bits. Accessing the higher 16 bits is done by shifting the int to the right 16 bits, like so: sum >> 16. This is the same as sum / 65536, since 65536 = 216 = 1 << 16.
sum = (sum & 0xffff) + (sum>>16); // add low 16 bits and high 16 bits
I should note that network packet checksums are usually computed 2 bytes (or 'octets' as they like to call them there) at a time. For that, the data should be cast to an unsigned short *, and len should be divided by 2. However! len may be odd, so in that case we'll need to take special care of the last byte. For instance, assuming that the maximum packet size is even, and that the len argument is always <= max_packet_size:
unsigned short * in = (unsigned short *) data;
if ( len & 1 ) data[len] = 0; // make sure last byte is 0
len = (len + 1) / 2;
The rest of the checksum method can remain the same, except that it should operate on in instead of data.
My application is receiving information from smart heart device. Now i can see pulse value. Could you please help me to parse R-R Interval value? How can i check device support R-R Interval value or Not ?
Any advise from you
Thanks
Have you checked the Bluetooth spec? The sample code below is in C#, but I think it shows the way to parse the data in each heart rate packet.
//first byte of heart rate record denotes flags
byte flags = heartRateRecord[0];
ushort offset = 1;
bool HRC2 = (flags & 1) == 1;
if (HRC2) //this means the BPM is un uint16
{
short hr = BitConverter.ToInt16(heartRateRecord, offset);
offset += 2;
}
else //BPM is uint8
{
byte hr = heartRateRecord[offset];
offset += 1;
}
//see if EE is available
//if so, pull 2 bytes
bool ee = (flags & (1 << 3)) != 0;
if (ee)
offset += 2;
//see if RR is present
//if so, the number of RR values is total bytes left / 2 (size of uint16)
bool rr = (flags & (1 << 4)) != 0;
if (rr)
{
int count = (heartRateRecord.Length - offset)/2;
for (int i = 0; i < count; i++)
{
//each existence of these values means an R-Wave was already detected
//the ushort means the time (1/1024 seconds) since last r-wave
ushort value = BitConverter.ToUInt16(heartRateRecord, offset);
double intervalLengthInSeconds = value/1024.0;
offset += 2;
}
}
This post is a little old but a full answer has not been given.
As I run into this post and it did help me at the end, I would like to share my final code. Hopefully it will help others.
The code provided by Daniel Judge is actually right, but as he already wrote, it is C#. HIs code is a bit better compared to what Simon M came up with at the end as the code of Daniel Judge takes into account there can be more than two RR-values within one message.
Here is the actual spec of the Heart_rate_measurement characteristic
I have translated Daniel Judge his code to Objective-C:
// Instance method to get the heart rate BPM information
- (void) getHeartBPMData:(CBCharacteristic *)characteristic error:(NSError *)error
{
// Get the BPM //
// https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicViewer.aspx?u=org.bluetooth.characteristic.heart_rate_measurement.xml //
// Convert the contents of the characteristic value to a data-object //
NSData *data = [characteristic value];
// Get the byte sequence of the data-object //
const uint8_t *reportData = [data bytes];
// Initialise the offset variable //
NSUInteger offset = 1;
// Initialise the bpm variable //
uint16_t bpm = 0;
// Next, obtain the first byte at index 0 in the array as defined by reportData[0] and mask out all but the 1st bit //
// The result returned will either be 0, which means that the 2nd bit is not set, or 1 if it is set //
// If the 2nd bit is not set, retrieve the BPM value at the second byte location at index 1 in the array //
if ((reportData[0] & 0x01) == 0) {
// Retrieve the BPM value for the Heart Rate Monitor
bpm = reportData[1];
offset = offset + 1; // Plus 1 byte //
}
else {
// If the second bit is set, retrieve the BPM value at second byte location at index 1 in the array and //
// convert this to a 16-bit value based on the host’s native byte order //
bpm = CFSwapInt16LittleToHost(*(uint16_t *)(&reportData[1]));
offset = offset + 2; // Plus 2 bytes //
}
NSLog(#"bpm: %i", bpm);
// Determine if EE data is present //
// If the 3rd bit of the first byte is 1 this means there is EE data //
// If so, increase offset with 2 bytes //
if ((reportData[0] & 0x03) == 1) {
offset = offset + 2; // Plus 2 bytes //
}
// Determine if RR-interval data is present //
// If the 4th bit of the first byte is 1 this means there is RR data //
if ((reportData[0] & 0x04) == 0)
{
NSLog(#"%#", #"Data are not present");
}
else
{
// The number of RR-interval values is total bytes left / 2 (size of uint16) //
NSUInteger length = [data length];
NSUInteger count = (length - offset)/2;
NSLog(#"RR count: %lu", (unsigned long)count);
for (int i = 0; i < count; i++) {
// The unit for RR interval is 1/1024 seconds //
uint16_t value = CFSwapInt16LittleToHost(*(uint16_t *)(&reportData[offset]));
value = ((double)value / 1024.0 ) * 1000.0;
offset = offset + 2; // Plus 2 bytes //
NSLog(#"RR value %lu: %u", (unsigned long)i, value);
}
}
}
EDIT:
this work for me, i get the correct rr values:
In some cases you can find two values at the same time for rr.
- (void) updateWithHRMData:(NSData *)datas {
const uint8_t *reportData = [datas bytes];
uint16_t bpm = 0;
uint16_t bpm2 = 0;
if ((reportData[0] & 0x04) == 0)
{
NSLog(#"%#", #"Data are not present");
}
else
{
bpm = CFSwapInt16LittleToHost(*(uint16_t *)(&reportData[2]));
bpm2 = CFSwapInt16LittleToHost(*(uint16_t *)(&reportData[4]));
if (bpm != 0 || bpm2 != 0) {
NSLog(#"%u", bpm);
if (bpm2 != 0) {
NSLog(#"%u", bpm2);
}
}
}
}
in #Brabbeldas solution i had to use a different flag to get rri values. but might depend on device used.
if ((reportData[0] & 0x10) == 0)
instead of
if ((reportData[0] & 0x04) == 0)
Parse heart rate parameters in "C"
I uploaded the sample application to GitHub Heart-Rate-Bluegiga
void ble_evt_attclient_attribute_value(const struct ble_msg_attclient_attribute_value_evt_t *msg)
{
if (msg->value.len < 2) {
printf("Not enough fields in Heart Rate Measurement value");
change_state(state_finish);
}
// Heart Rate Profile defined flags
const unsigned char HEART_RATE_VALUE_FORMAT = 0x01;
const unsigned char ENERGY_EXPENDED_STATUS = 0x08;
const unsigned char RR_INTERVAL = 0x10;
unsigned char current_offset = 0;
unsigned char flags = msg->value.data[current_offset];
int is_heart_rate_value_size_long = ((flags & HEART_RATE_VALUE_FORMAT) != 0);
int has_expended_energy = ((flags & ENERGY_EXPENDED_STATUS) != 0);
int has_rr_intervals = ((flags & RR_INTERVAL) != 0);
current_offset++;
uint16 heart_rate_measurement_value = 0;
if (is_heart_rate_value_size_long)
{
heart_rate_measurement_value = (uint16)((msg->value.data[current_offset + 1] << 8) +
msg->value.data[current_offset]);
current_offset += 2;
}
else
{
heart_rate_measurement_value = msg->value.data[current_offset];
current_offset++;
}
printf("Heart rate measurment value: %d ", heart_rate_measurement_value);
uint16 expended_energy_value = 0;
if (has_expended_energy)
{
expended_energy_value = (uint16)((msg->value.data[current_offset + 1] << 8) +
msg->value.data[current_offset]);
current_offset += 2;
printf(" Expended energy value: %d ", expended_energy_value);
}
uint16 rr_intervals[10] = {0};
if (has_rr_intervals)
{
printf(" Rr intervals: ");
int rr_intervals_count = (msg->value.len - current_offset) / 2;
for (int i = 0; i < rr_intervals_count; i++)
{
int raw_rr_interval = (uint16)((msg->value.data[current_offset + 1] << 8) +
msg->value.data[current_offset]);
rr_intervals[i] = ((double)raw_rr_interval / 1024) * 1000;
current_offset += 2;
printf("%d ", rr_intervals[i]);
}
printf("\n");
}
}