In PHP What Does It Mean by a Function Being Binary-Safe

In PHP what does it mean by a function being binary-safe?

It means the function will work correctly when you pass it arbitrary binary data (i.e. strings containing non-ASCII bytes and/or null bytes).

For example, a non-binary-safe function might be based on a C function which expects null-terminated strings, so if the string contains a null character, the function would ignore anything after it.

This is relevant because PHP does not cleanly separate string and binary data.

In PHP what does it mean by a binary safe string comparison?

1. If the two strings have identical BEGINNING parts, they are truncated from both strings.
2. The resulting strings are compared with two possible outcomes:

• if one of the resulting strings is an empty string, then the length of the non-empty string is returned (the sign depending on the order in which you pass the arguments to the function)
• in any other case just the numerical values of the FIRST characters are compared. The result is +1 or -1 no matter how big is the difference between the numerical values.

source

What are the functions PHP which are said not to be binary safe? To which libraries these non-binary safe functions hand off the strings? And why?

Like arkascha explained, the issue of "binary-safe" and "non-binary-safe" has nothing to do with the language.

Using a null byte (0x00) to indicate the end of the string is simpler (which is probably why C went with it),
but the downside is you can't have a null byte anywhere in the string
which is a big limitation if you have to be able to handle all kinds of data.
Storing the length as a metadata part of a string is more complex, as shown by Pete, but it allows you to handle any kind of data.

Regarding which functions that are "binary-safe" or "non-binary-safe",
just read the PHP Manual before using the functions.
That's what I do.
There is no need to construct a list because the PHP Manual already explains what you need to know about the functions, including if they are binary-safe or not.

Most of your post, I believe, is due to a misunderstanding of PHP Manual's explanation that you quoted, particularly this part:

however, a few functions, said in this manual not to be “binary safe”, may hand off the strings to libraries that ignore data after a NUL byte.

Let me try making it clearer by adding some of my own words:

however, a few functions, said in this manual not to be “binary safe”, are the functions that may hand off the strings to libraries that ignore data after a NUL byte.

So it really doesn't say "non-binary safe functions hand off the strings to libraries", this is a misinterpretation.
What it means is "functions that may hand off the strings to libraries that ignore data after a NUL byte, are said in this manual as not binary-safe".

"Handing off to libraries" is just another way of saying "calling functions from other libraries".
"Ignoring data after a NUL byte" is a behavior that is called not binary-safe.

Another way of putting it is:

A few functions in this manual are said not to be "binary safe" because they may call other functions that are also not "binary safe" (functions that ignore data after a NUL byte).

I hope this clears it up for you.

php functions binary safe?

It means two things. First the function works on strings that contain \0 the NUL byte. This is not a given, because functions are often implemented in C which would treat that as string terminator. PHP however uses length-denominated strings.

Second, in some contexts it means that a particular string function ignores the character set and does not try to interpret UTF-8 sequences. For raw binary data the UTF-8 sequencing would be wrong, thus making functions fail if they try to treat it as text.

Why are there binary safe AND binary unsafe functions in php?

The short answer to "why" is simply history.

PHP was originally written as a way to script C functions so they could be called easily while generating HTML. Therefore PHP strings were just C strings, which are a set of any bytes. So in modern PHP terms we would say nothing was binary-safe, simply because it wasn't planned to be anything else.

Early PHP was not intended to be a new programming language, and grew organically, with Lerdorf noting in retrospect: "I don’t know how to stop it, there was never any intent to write a programming language […] I have absolutely no idea how to write a programming language, I just kept adding the next logical step on the way."

Over time the language grew to support more elaborate string-processing functions, many taking the string's specific bytes into account and becoming "binary-safe". According to the recently written formal PHP specification:

As to how the bytes in a string translate into characters is unspecified. Although a user of a string might choose to ascribe special semantics to bytes having the value \0, from PHP's perspective, such null bytes have no special meaning. PHP does not assume strings contain any specific data or assign special values to any bytes or sequences.

As a language that has grown organically, there hasn't been a move to universally treat strings in a manner different from C. Therefore functions and libraries are binary-safe on a case-by-case basis.

Is === in PHP binary-safe in string comparison?

All Comparison operators are binary safe and == and ===(compares with type ) are comparison operators so they are .......

Binary-safe function for sending chunks of files in PHP

For small files you should use readfile, that makes all for you to send a file to the client. For really big files these function probably don't work due to memory problems.

Also there is a function file_get_contents to get all file content into a variable if you require to process it before send. Like readfile is recommended only for "small" files. "small" depends on the memory allowed to run a PHP process (memory_limit parameter in php.ini). Usually servers set it from 8M to 128M and by default is 16MB.

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