C Socket Reading TOO MUCH Data
I am making a server that should be able to accept requests from multiple clients. To ensure I am reading large requests properly, I made the below code segment.
Requests come in the form <START_REQUEST>a long message<END_REQUEST>
read(fd, buffer, BUFFER_SIZE);
// Keep Reading If Entire Message Not Recieved
int buffer_len = strlen(buffer);
char *end_tag = &buffer[buffer_len-strlen("<END_REQUEST>")];
while(strcmp(end_tag, "<END_REQUEST>") != 0) {
char *temp_buffer;
temp_buffer = malloc(BUFFER_SIZE);
valread = read(fd, temp_buffer, BUFFER_SIZE);
strcat(buffer, temp_buffer);
free(temp_buffer);
buffer_len = strlen(buffer);
end_tag = &buffer[buffer_len-strlen("<END_REQUEST>")];
}
However, sometimes (very often) the contents of buffer are something like:
<START_REQUEST>a long message<END_REQUEST>somegarbagedataheremaybefromanotherequest?
and thus the loop never terminates.
Why might this be happening?
c sockets
asked Nov 15 '18 at 21:50
Steven DavisSteven Davis
82
add a comment |
I am making a server that should be able to accept requests from multiple clients. To ensure I am reading large requests properly, I made the below code segment.
Requests come in the form <START_REQUEST>a long message<END_REQUEST>
read(fd, buffer, BUFFER_SIZE);
// Keep Reading If Entire Message Not Recieved
int buffer_len = strlen(buffer);
char *end_tag = &buffer[buffer_len-strlen("<END_REQUEST>")];
while(strcmp(end_tag, "<END_REQUEST>") != 0) {
char *temp_buffer;
temp_buffer = malloc(BUFFER_SIZE);
valread = read(fd, temp_buffer, BUFFER_SIZE);
strcat(buffer, temp_buffer);
free(temp_buffer);
buffer_len = strlen(buffer);
end_tag = &buffer[buffer_len-strlen("<END_REQUEST>")];
}
However, sometimes (very often) the contents of buffer are something like:
<START_REQUEST>a long message<END_REQUEST>somegarbagedataheremaybefromanotherequest?
and thus the loop never terminates.
Why might this be happening?
c sockets
asked Nov 15 '18 at 21:50
Steven DavisSteven Davis
82
read()reads binary data, meaning it doesn't end the buffer withto make it safe to use withstrcat(). Also why are you allocating the buffer only to free it again at every freaking loop? Do it only once.
– Havenard
Nov 15 '18 at 22:00
1
@Havenard Or, better yet, just read the data into wherever you want it in the first place. There's no point in reading it somewhere other than where you want it just to have to copy it to where you wanted it in the first place.
– David Schwartz
Nov 15 '18 at 22:13
@DavidSchwartz Indeed, using an intermediate buffer makes no sense.
– Havenard
Nov 15 '18 at 22:18
add a comment |
I am making a server that should be able to accept requests from multiple clients. To ensure I am reading large requests properly, I made the below code segment.
Requests come in the form <START_REQUEST>a long message<END_REQUEST>
read(fd, buffer, BUFFER_SIZE);
// Keep Reading If Entire Message Not Recieved
int buffer_len = strlen(buffer);
char *end_tag = &buffer[buffer_len-strlen("<END_REQUEST>")];
while(strcmp(end_tag, "<END_REQUEST>") != 0) {
char *temp_buffer;
temp_buffer = malloc(BUFFER_SIZE);
valread = read(fd, temp_buffer, BUFFER_SIZE);
strcat(buffer, temp_buffer);
free(temp_buffer);
buffer_len = strlen(buffer);
end_tag = &buffer[buffer_len-strlen("<END_REQUEST>")];
}
However, sometimes (very often) the contents of buffer are something like:
<START_REQUEST>a long message<END_REQUEST>somegarbagedataheremaybefromanotherequest?
and thus the loop never terminates.
Why might this be happening?
c sockets
asked Nov 15 '18 at 21:50
Steven DavisSteven Davis
82
I am making a server that should be able to accept requests from multiple clients. To ensure I am reading large requests properly, I made the below code segment.
Requests come in the form <START_REQUEST>a long message<END_REQUEST>
read(fd, buffer, BUFFER_SIZE);
// Keep Reading If Entire Message Not Recieved
int buffer_len = strlen(buffer);
char *end_tag = &buffer[buffer_len-strlen("<END_REQUEST>")];
while(strcmp(end_tag, "<END_REQUEST>") != 0) {
char *temp_buffer;
temp_buffer = malloc(BUFFER_SIZE);
valread = read(fd, temp_buffer, BUFFER_SIZE);
strcat(buffer, temp_buffer);
free(temp_buffer);
buffer_len = strlen(buffer);
end_tag = &buffer[buffer_len-strlen("<END_REQUEST>")];
}
However, sometimes (very often) the contents of buffer are something like:
<START_REQUEST>a long message<END_REQUEST>somegarbagedataheremaybefromanotherequest?
and thus the loop never terminates.
Why might this be happening?
c sockets
c sockets
asked Nov 15 '18 at 21:50
Steven DavisSteven Davis
82
asked Nov 15 '18 at 21:50
Steven DavisSteven Davis
82
asked Nov 15 '18 at 21:50
Steven DavisSteven Davis
82
asked Nov 15 '18 at 21:50
Steven DavisSteven Davis
82
asked Nov 15 '18 at 21:50
Steven DavisSteven Davis
82
82
read()reads binary data, meaning it doesn't end the buffer withto make it safe to use withstrcat(). Also why are you allocating the buffer only to free it again at every freaking loop? Do it only once.
– Havenard
Nov 15 '18 at 22:00
1
@Havenard Or, better yet, just read the data into wherever you want it in the first place. There's no point in reading it somewhere other than where you want it just to have to copy it to where you wanted it in the first place.
– David Schwartz
Nov 15 '18 at 22:13
@DavidSchwartz Indeed, using an intermediate buffer makes no sense.
– Havenard
Nov 15 '18 at 22:18
add a comment |
read()reads binary data, meaning it doesn't end the buffer withto make it safe to use withstrcat(). Also why are you allocating the buffer only to free it again at every freaking loop? Do it only once.
– Havenard
Nov 15 '18 at 22:00
1
@Havenard Or, better yet, just read the data into wherever you want it in the first place. There's no point in reading it somewhere other than where you want it just to have to copy it to where you wanted it in the first place.
– David Schwartz
Nov 15 '18 at 22:13
@DavidSchwartz Indeed, using an intermediate buffer makes no sense.
– Havenard
Nov 15 '18 at 22:18
read() reads binary data, meaning it doesn't end the buffer with strcat(). Also why are you allocating the buffer only to free it again at every freaking loop? Do it only once.– Havenard
Nov 15 '18 at 22:00
read() reads binary data, meaning it doesn't end the buffer with strcat(). Also why are you allocating the buffer only to free it again at every freaking loop? Do it only once.– Havenard
Nov 15 '18 at 22:00
1
1
@Havenard Or, better yet, just read the data into wherever you want it in the first place. There's no point in reading it somewhere other than where you want it just to have to copy it to where you wanted it in the first place.
– David Schwartz
Nov 15 '18 at 22:13
@Havenard Or, better yet, just read the data into wherever you want it in the first place. There's no point in reading it somewhere other than where you want it just to have to copy it to where you wanted it in the first place.
– David Schwartz
Nov 15 '18 at 22:13
@DavidSchwartz Indeed, using an intermediate buffer makes no sense.
– Havenard
Nov 15 '18 at 22:18
@DavidSchwartz Indeed, using an intermediate buffer makes no sense.
– Havenard
Nov 15 '18 at 22:18
add a comment |
1 Answer
1
active
oldest
votes
How are you expecting strcat to know how many bytes to append onto the buffer?
valread = read(fd, temp_buffer, BUFFER_SIZE);
strcat(buffer, temp_buffer);
After the call to read, valread holds the number of bytes you read and it's the only thing that holds this information. However, you attempt to append data read onto the existing buffer without using this value -- so there is no possible way strcat could conceivably know how many bytes to append onto the buffer. It's no wonder you append junk that you read before.
Similar problem here:
read(fd, buffer, BUFFER_SIZE);
// Keep Reading If Entire Message Not Recieved
int buffer_len = strlen(buffer);
Here you ignore the return value of read, so you have no way to know how many bytes you read. How are you expecting strlen to figure out how many bytes read put into the buffer?
answered Nov 15 '18 at 21:54
David SchwartzDavid Schwartz
139k14145230
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
How are you expecting strcat to know how many bytes to append onto the buffer?
valread = read(fd, temp_buffer, BUFFER_SIZE);
strcat(buffer, temp_buffer);
After the call to read, valread holds the number of bytes you read and it's the only thing that holds this information. However, you attempt to append data read onto the existing buffer without using this value -- so there is no possible way strcat could conceivably know how many bytes to append onto the buffer. It's no wonder you append junk that you read before.
Similar problem here:
read(fd, buffer, BUFFER_SIZE);
// Keep Reading If Entire Message Not Recieved
int buffer_len = strlen(buffer);
Here you ignore the return value of read, so you have no way to know how many bytes you read. How are you expecting strlen to figure out how many bytes read put into the buffer?
answered Nov 15 '18 at 21:54
David SchwartzDavid Schwartz
139k14145230
add a comment |
How are you expecting strcat to know how many bytes to append onto the buffer?
valread = read(fd, temp_buffer, BUFFER_SIZE);
strcat(buffer, temp_buffer);
After the call to read, valread holds the number of bytes you read and it's the only thing that holds this information. However, you attempt to append data read onto the existing buffer without using this value -- so there is no possible way strcat could conceivably know how many bytes to append onto the buffer. It's no wonder you append junk that you read before.
Similar problem here:
read(fd, buffer, BUFFER_SIZE);
// Keep Reading If Entire Message Not Recieved
int buffer_len = strlen(buffer);
Here you ignore the return value of read, so you have no way to know how many bytes you read. How are you expecting strlen to figure out how many bytes read put into the buffer?
answered Nov 15 '18 at 21:54
David SchwartzDavid Schwartz
139k14145230
add a comment |
How are you expecting strcat to know how many bytes to append onto the buffer?
valread = read(fd, temp_buffer, BUFFER_SIZE);
strcat(buffer, temp_buffer);
After the call to read, valread holds the number of bytes you read and it's the only thing that holds this information. However, you attempt to append data read onto the existing buffer without using this value -- so there is no possible way strcat could conceivably know how many bytes to append onto the buffer. It's no wonder you append junk that you read before.
Similar problem here:
read(fd, buffer, BUFFER_SIZE);
// Keep Reading If Entire Message Not Recieved
int buffer_len = strlen(buffer);
Here you ignore the return value of read, so you have no way to know how many bytes you read. How are you expecting strlen to figure out how many bytes read put into the buffer?
answered Nov 15 '18 at 21:54
David SchwartzDavid Schwartz
139k14145230
How are you expecting strcat to know how many bytes to append onto the buffer?
valread = read(fd, temp_buffer, BUFFER_SIZE);
strcat(buffer, temp_buffer);
After the call to read, valread holds the number of bytes you read and it's the only thing that holds this information. However, you attempt to append data read onto the existing buffer without using this value -- so there is no possible way strcat could conceivably know how many bytes to append onto the buffer. It's no wonder you append junk that you read before.
Similar problem here:
read(fd, buffer, BUFFER_SIZE);
// Keep Reading If Entire Message Not Recieved
int buffer_len = strlen(buffer);
Here you ignore the return value of read, so you have no way to know how many bytes you read. How are you expecting strlen to figure out how many bytes read put into the buffer?
answered Nov 15 '18 at 21:54
David SchwartzDavid Schwartz
139k14145230
edited Nov 15 '18 at 22:11
answered Nov 15 '18 at 21:54
David SchwartzDavid Schwartz
139k14145230
answered Nov 15 '18 at 21:54
David SchwartzDavid Schwartz
139k14145230
answered Nov 15 '18 at 21:54
David SchwartzDavid Schwartz
139k14145230
139k14145230
add a comment |
add a comment |
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read()reads binary data, meaning it doesn't end the buffer withto make it safe to use withstrcat(). Also why are you allocating the buffer only to free it again at every freaking loop? Do it only once.– Havenard
Nov 15 '18 at 22:00
1
@Havenard Or, better yet, just read the data into wherever you want it in the first place. There's no point in reading it somewhere other than where you want it just to have to copy it to where you wanted it in the first place.
– David Schwartz
Nov 15 '18 at 22:13
@DavidSchwartz Indeed, using an intermediate buffer makes no sense.
– Havenard
Nov 15 '18 at 22:18