Comparing two .txt files in PHP (~1MB) - php

I'm writing a program using PHP and cUrl to save the HTML of a particular website to a server once in a while. I only want to actually save the file if something has changed on the website, though, so my question is: how do I compare a long text string (the newest HTML from cUrl) against an existing .txt file? The .txt file is approximately 700kB, to give you an idea of size. I'm mo


strcmp() is likely your best bet.
It returns 0 if the two strings are the same -
so
if(strcmp($savedHTML, $newHTML) !== 0) {
save($newHTML); // this would be your own function for saving
}
Of course, this will not work if there is a minor difference, such as a timestamp that has a different value each time.


I don't know how well behaved the server at the website you are saving is, but if it behaves properly and the website is coded properly it should return a 304 Not Modified status if nothing has changed.
I know they are a couple of big ifs, but you should check that before attempting anything else.
See the section on return values.

Related

How can I code a PHP file upload specificly for json files that is secure and wont allow Php or html to be uploaded

I am working on a site that allows models to be uploaded.
the models are json format like this :
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"}]}
The file is called crocodile.bbmodel
I am looking for a way to allow users to upload .bbmodel files that is safe so that no web shells or malicious code can sneak its way past the upload can you guys help?

From what I know there is no magic button that will let you do this. that said the first thing you will want to do is make sure the uploaded file is valid json. check this Fastest way to check if a string is JSON in PHP?
Next you will need to define which fields in json are valid and what types the value should contain. for this I would create a skeleton versioin of the json string and store it a database field. Examining your json further you might need multiple skeletons for the various repeat or nested elements. eg one for meta like this
"meta":{"format_version":"","model_format":"","box_uv":}
you would want another skeleton for elements probably describing the keys for a single 'element'. and of course validate the textures.source nodes against a base64 encoding.
Next you will want to decide what are acceptable types for each of the field values. compare each field of the submitted json against an acceptable type you define.
once you do all of this validation you can be reasonably sure you have a valid file...I won't say secure or non-malicious but, done properly it will help you ingest the file without errors.
Still not guaranteed to be 'secure' but, it is a reasonable approach and would probably satisfy most due diligence critiques. If anyone can improve and provide more steps or different tricks to secure something like this I'd be glad to hear it.

fopen and write in file

I have some questions about fopen
The first question it’s when i go for add new entry always put to the end of file and no start the file, for example:
$fp=fopen("text.dat","a");
fputs($fp,"Hello 1"."\n");
fclose($fp);
Always the results in this file show to the end:
Hello 1
Hello 2
Hello 3
And no as I want, insert the new comment to the first place for show this as:
Hello 3
Hello 2
Hello 1 ( The most old entry )
By other side my second question, for example if i have 10 users and this 10 users to the same time insert one entry or post inside this text file, it’s possible or can give me some error? Or I need use flock until save each post, which it’s the best method for no give me problems when some users want change something in the file in the same time?

There's no way to prepend the file automatically. So, it is better to store the existing contents in a temp file and then insert it in the file.
$fp=fopen("text.dat","w");
fwrite($fp,"Hello 1"."\n".fread($fp));
fclose($fp);
This will be outputting as:
Hello 3
Hello 2
Hello 1
But as far as lock is considered, I don't think it is possible, or am not the right person to answer for this.

When you write to a file it'll always append at the end. There's no workaround it which I'm aware of, but in order to achieve what you want (which is to display the lines in reverse order) you can read the lines into an array and display the array in reverse order.
As for locking, only one process can hold the lock to a file, so you don't really have to do anything cause if two users try to update the same file at the same time - only one of them will succeed - which actually creates a different problem (one of the users will lose her post). In order to work around it you should send to the backend both the original copy of the post and the new version submitted by the user, before you save the user's edit - check that the original version is updated. If it's not up-to-date it means that another user changed it meanwhile. The "user-friendly" behavior would be to return an error to the user saying that he's version is not up-to-date but also include his edits - so that he won't have to re-write everything from scratch.

For that you need a database, which is more suited for multi-user things and sorting,
Or else use a subdirectory and create every message in its own file, with a file name made up of a sortable timestamp: yyyymmddhhmmss. But then you need to prevent directory caching.
As everyone has the right to be stubborn/cut of an edge: see file_get_contents to load all the contents, and file_put_contents.

Using PHP to replace a line in a flat-file database

There are quite a few different threads about this similar topic, yet I have not been able to fully comprehend a solution to my problem.
What I'd like to do is quite simple, I have a flat-file db, with data stored like this -
$username:$worldLocation:$resources
The issue is I would like to have a submit data html page that would update this line based upon a search of the term using php
search db for - $worldLocation
if $worldLocation found
replace entire line with $username:$worldLocation:$updatedResources
I know there should be a fairly easy way to get this done but I am unable to figure it out at the moment, I will keep trying as this post is up but if you know a way that I could use I would greatly appreciate the help.
Thank you

I always loved c, and functions that came into php from c.
Check out fscanf and fprintf.
These will make your life easier while reading writing in a format. Like say:
$filehandle = fopen("file.txt", "c");
while($values = fscanf($filehandle, "%s\t%s\t%s\n")){
list($a, $b, $c) = $values;
// do something with a,b,c
}
Also, there is no performance workaround for avoiding reading the entire file into memory -> changing one line -> writing the entire file. You have to do it.
This is as efficient as you can get. Because you most probably using native c code since I read some where that php just wraps c's functions in these cases.

You like the hard way so be it....
Make each line the same length. Add space, tab, capital X etc to fill in the blanks
When you want to replace the line, find it and as each line is of a fixed length you can replace it.
For speed and less hassle use a database (even SQLLite)

If you're committed to the flat file, the simplest thing is iterating through each line, writing a new file & changing the one that matches.
Yeah, it sucks.
I'd strongly recommend switching over to a 'proper' database. If you're concerned about resources or the complexity of running a server, you can look into SQLite or Berkeley DB. Both of these use a database that is 'just a file', removing the issue of installing and maintaining a DB server, but still you the ability to quickly & easily search, replace and delete individual records. If you still need the flat file for some other reason, you can easily write some import/export routines.
Another interesting possibility, if you want to be creative, would be to look at your filesystem as a database. Give each user a directory. In each directory, have a file for locations. In each file, update the resources. This means that, to insert a row, you just write to a new file. To update a file, you just rewrite a single file. Deleting a user is just nuking a directory. Sure, there's a bit more overhead in slurping the whole thing into memory.
Other ways of solving the problem might be to make your flat-file write-only, since appending to the end of a file is a trivial operation. You then create a second file that lists "dead" line numbers that should be ignored when reading the flat file. Similarly, you could easily "X" out the existing lines (which, again, is far easier than trying to update lines in a file that might not be the same length) and append your new data to the end.
Those second two ideas aren't really meant to be practical solutions as much as they are to show you that there's always more than one way to solve a problem.

ok.... after a few hours work..this example woorked fine for me...
I intended to code an editing tool...and use it for password update..and it did the
trick!
Not only does this page send and email to user (sorry...address harcoded to avoid
posting aditional code) with new password...but it also edits entry for thew user
and re-writes all file info in new file...
when done, it obviously swaps filenames, storing old file as usuarios_old.txt.
grab the code here (sorry stackoverflow got VERY picky about code posting)
https://www.iot-argentina.xyz/edit_flat_databse.txt

Is that what you are location for :
update `field` from `table` set `field to replace` = '$username:$worldlocation:$updatesResources' where `field` = '$worldLocation';

Compare the size of dynamic output of a function to a destination file, and do a rewrite

I have a function to write a text file based on the form settings, a rather large form.
Shortly, I want to compare the output of a function to a single file, and only do execution (rewriting the file) if the destination file is different from the output. As you guess, it is a performance concern.
Is it doable, BTW?
The process is, I fill up some forms:
A single file is written to contain some "specific" selected options
Some "non-specific" options do not necessarily write anything to the file.
The form is updateable anytime, so the content of the file may grow or shrink based on different options.
It only needs a rewrite to the file if I am at point #1.
When at point #2, nothing should be written.
This is what I tried:
if ($output != file_get_contents($filepath)) {
// save the data
}
But I felt so much delay of execution in this.
I found a almost similar issue here: Can I use file_get_contents() to compare two files?, but my issue is different. Mine is comparing the result of the process to an already existing file which simply the result of the process previously. And only rewrite the file if they are different.
No sensitive data on the form, btw.
Any hint is very much appreciated.
Thanks

To compare a whole file with a string (I suppose it's a string, isn't it?) the only way is to read whole file and do comparison. To improve performance you can read file line by line and stop at first different line, as Explosion Pills said before me.
If your file is really big, and you want to improve performance further, you can do some hashing stuff:
Generate the output, let's say $output.
Calculate md5($output) and store in $output_md5.
Compare $output_md5 with a stored one, let's say in file output.md5.
Are they equal?
If yes, do nothing.
If not, save $output into output.txt and $output_md5 in output.md5.

Rather than load the entire file into memory, it may be faster to read it line-by-line (fgets) and compare it to the input string also line-by-line. You could even go as small as character-by-character, but I think that's overkill.

You could always try a combination of what was in the other post, the sha1_file($file) function, with the sha1($string) function, and check the equality of that.

Delete Range of Data From Text File With PHP

I want to delete a range of data from a text file using PHP. Let's assume the file contains the following:
Hello, World!
I want to delete everything from character 2 to character 7. The actual file I need to do this with is very large, so I don't want to have to read the large file in order to delete just a small, given range of data. The data contained within the given range is not known, so str_replace or preg_replace solutions wouldn't work anyways.
Thanks!

There is no way to remove a chunk in the middle of a file. You will need to read everything following the chunk to move it down to backfill the hole. Copying the relevant data to another file is an easy way to do this.

If you for some reason have to use a file, and it's a big file, you can read in smaller chunks (like one line at the time), and write the data you want to keep out to a temporary file continously. This will cut down on memory requirements.

I took your guys advice, plus I did some brainstorming, and I found a solution to my problem. Basically I took Ignacio's suggestion:
You will need to read everything following the chunk to move it down to backfill the hole. Copying the relevant data to another file is an easy way to do this.
But, instead of moving the data to a temporary file, I simply read each chunk and then immediately moved the file pointer backwards with fseek() and used fwrite() to fill in the hole. Then I truncated the file to the correct length with ftruncate().
Again, thanks everybody for the suggestions!

You don't want but you have to. Read and rewrite the whole file. That's why everyone would use a database for this, not a plain file

Here's a better solution than my original answer, although I'm still not sure it's ideal.
You could open the file for reading, and read in chunks, dropping whatever you read in into a second file which you've opened for writing. Then just skip the portion you're wanting to "delete".
Naturally at the end you'd copy your temp file over the original.
Edit:
Upon further reflection, I feel this is actually probably the most useful answer (unless/until someone has a better idea), but the credit must go to "gnud" for arriving at the same conclusion first.

The simplest way I can think of is to read in the entire file as a string and use array_splice string_splice to remove a segment.
Edit:
Excuse me, I didn't mean array_splice, I meant string_splice, which is a custom function I made for my own use. It's something like this (I don't have it handy at the moment):
function string_splice($string, $start, $length, $replace) {
$string = substr($string, 0, $start).$replace.substr($string,$length);
}
Edit:
This is NOT the ideal solution; please see the comments below. It's a bad idea to read a very large file into a string; in addition to memory consumption, operating on such a large string is very inefficient. A better solution is that proposed by gnud. Thanks.

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