02-25-2008
Parsing Binary
I have a binary file a particular format.
It contains the Length Bytes and the Type bytes i.e the first four bytes if the file indicate the length of the Type which is to follow.
for eg, if the int value of the first four bytes is 80, then it means that the length of the following "Type" is 80. after i read the 80 bytes, the next four bytes again refer to the length of the next "Type"
I need to open the binary file, read the first four bytes, and then get the obtain the the bytes equaling the length obtained and keep doing this till the end of the file.
The problem i am having is that sometime the length of the file that it detects it wrong and that throws off the entire reading of the file
This is how i am reading the 4 bytes for length and then getting the long value
fread (Len, 1, 4, fp_bin);
long Length =(((((Len[0] << 8) + Len[1]) << 8) + Len[2]) << 8) + Len[3];
where Len is the char array containing the 4 bytes
this is how i am reading in the next 'Length' number of bytes
read(Data, 1, Length, fp_bin);
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LEARN ABOUT PHP
openssl_random_pseudo_bytes
OPENSSL_RANDOM_PSEUDO_BYTES(3) 1 OPENSSL_RANDOM_PSEUDO_BYTES(3)
openssl_random_pseudo_bytes - Generate a pseudo-random string of bytes
SYNOPSIS
string openssl_random_pseudo_bytes (int $length, [bool &$crypto_strong])
DESCRIPTION
Generates a string of pseudo-random bytes, with the number of bytes determined by the $length parameter.
It also indicates if a cryptographically strong algorithm was used to produce the pseudo-random bytes, and does this via the optional
$crypto_strong parameter. It's rare for this to be FALSE, but some systems may be broken or old.
PARAMETERS
o $length
- The length of the desired string of bytes. Must be a positive integer. PHP will try to cast this parameter to a non-null integer
to use it.
o $crypto_strong
- If passed into the function, this will hold a boolean value that determines if the algorithm used was "cryptographically
strong", e.g., safe for usage with GPG, passwords, etc. TRUE if it did, otherwise FALSE
RETURN VALUES
Returns the generated string of bytes on success, or FALSE on failure.
EXAMPLES
Example #1
openssl_random_pseudo_bytes(3) example
<?php
for ($i = -1; $i <= 4; $i++) {
$bytes = openssl_random_pseudo_bytes($i, $cstrong);
$hex = bin2hex($bytes);
echo "Lengths: Bytes: $i and Hex: " . strlen($hex) . PHP_EOL;
var_dump($hex);
var_dump($cstrong);
echo PHP_EOL;
}
?>
The above example will output something similar to:
Lengths: Bytes: -1 and Hex: 0
string(0) ""
NULL
Lengths: Bytes: 0 and Hex: 0
string(0) ""
NULL
Lengths: Bytes: 1 and Hex: 2
string(2) "42"
bool(true)
Lengths: Bytes: 2 and Hex: 4
string(4) "dc6e"
bool(true)
Lengths: Bytes: 3 and Hex: 6
string(6) "288591"
bool(true)
Lengths: Bytes: 4 and Hex: 8
string(8) "ab86d144"
bool(true)
SEE ALSO
random_bytes(3), bin2hex(3), crypt(3), mt_rand(3), uniqid(3).
PHP Documentation Group OPENSSL_RANDOM_PSEUDO_BYTES(3)