I am doing socket programming. The data ($ data) received from the socket contains 4 bytes of length data + json data. I want to trim the length and only parse the json.
I have completed the code and it works fine. But I wonder if there is a more efficient way (algorithm).
Is there an efficient way to move arrays to variables in perl?
@tmpp = split(//,$data); #data = socket data
my $t1 = sprintf("%02x%02x%02x%02x",ord($tmpp[0]),ord($tmpp[1]),ord($tmpp[2]),ord($tmpp[3]));
$t1 = hex($t1); #t1 = length
my $json;
my @tmp = @tmpp[0..-1];
foreach(@tmp){ $json .= $_;}<br>
print $json;
Ok Print ;
This is a standard case for pack/unpack . The N/a
template will unpack a string of length N
(in network byte order):
my( $json ) = unpack 'N/a', $data;
print $json;
If you have what you say you have, you could simply peel off the length prefix.
my $json = substr($data, 4);
But this would mean that the length prefix is useless, which suggests you have a major bug earlier in your program. Did you properly read from the socket?
sub read_bytes {
my ($fh, $bytes_to_read) = @_;
my $buf = '';
while ($bytes_to_read) {
my $bytes_read = read($fh, $buf, $bytes_to_read, length($buf))
die($!) if !defined($bytes_read);
die("Premature EOF") if !$bytes_read;
$bytes_to_read -= $bytes_read;
}
return $buf;
}
sub read_uint32be { unpack('N', read_bytes($_[0], 4)) }
sub read_string {
my ($fh) = @_;
my $len = read_uint32be($fh);
return read_bytes($fh, $len);
}
my $json = read_string($sock);
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