PHP file upload and download (Part 1)_PHP tutorial

PHP file upload and download (Part 1)

The uploading and downloading of files in PHP is a very basic function. Generally, websites will have such requirements to some extent. Of course, it does not mean that all files can be uploaded, then the network will be too insecure. Because I haven’t been exposed to PHP for a long time, I will practice writing today. The essay is just a public record.

File upload: that is, upload the client's files to the server, and then move the temporary files on the server to the specified directory. The main idea is to first define and obtain the two-dimensional array variable in $_FILES. You can use the two-dimensional array to obtain it every time, or you can put the first dimension into an array variable, and then obtain the value in the array variable each time. Simplify the amount of code----> Determine whether the error number is 0 or when UPLOAD_ERR_OK is true, it means there is no error and you can upload it----->Move the temporary file on the server to our designated directory, what is it called? name, if the move is successful and returns true, use move_uploaded_file($temporary file name, $destination)-----> Another way is to use the copy($temporary variable name, $destination) function;

$_FILES stores the information about the files uploaded here. This is a two-dimensional array. The first dimension is of course the name of the uploaded file, and the second dimension is the relevant information of the file. After uploading, you can print the Check the parameters in the array---use print_r($_FILES), you can see the contents:

name: the name of the uploaded file;

type: MIME type of uploaded file;

tmp_name: The name of the temporary file uploaded to the server; //very important, because it is this file that will be manipulated on the server in the future

size: the size of the uploaded file;

error: The error number of the uploaded file, success is 0.

Server-side configuration ---php.ini:

file_uploads=on, supports http upload;

upload_tmp_dir=, the directory where temporary files are saved;

upload_max_filesize= 2M ;The size of files allowed to be uploaded;

max_file_uploads=20; The number of files allowed to be uploaded at one time, the default is 20;

max_execution_time=-1; Set the maximum number of execution seconds allowed before the script is parsed and terminated to prevent poor programs (such as infinite loops) from occupying server resources;

max_input_time=60; The maximum number of seconds allowed for the script to parse input data;

max_input_nesting_level=64, sets the nesting depth of input variables;

max_input_vars=60; How many input variables are accepted to reduce the possibility of DOS attacks. If the specified number of variables is exceeded, E_WARNING will be generated, and more input variables will be truncated from the request;

memory_limit=128M. The maximum independent memory usage of a single thread, that is, a web request, gives the definition of the maximum memory usage of a thread.

There are also some error message descriptions, which are basically literal meanings in English. There are 8 error messages in total, such as the temporary directory cannot be found, the size exceeds the limit, and so on. They correspond to the numbers 0-8 respectively but there is no number 5 in the code. For judgment output, according to one-to-one correspondence, you can use switch...case, a total of 7 cases (0 means no need to write if successful) to indicate outputting error information. Make a judgment in the code, and if there is no error output, proceed with the upload operation.

Some configurations on the client---but the configuration on the client often does not really play a restrictive role. The real restrictions must be configured on the server:

Limit the maximum size of uploaded files through form hidden fields

Restrict uploaded file types through the accept attribute

During this practice, I didn’t realize that the maximum upload limit of the form form (determined in the program) and the underlying php judged (php.ini), so if the maximum upload limit of my form is 2M, The judgment in php.ini is 10M, so when the size of the uploaded file exceeds 10M, a code error will be directly prompted. When the uploaded file size is between 2M and 10M, the program can be executed and the corresponding error will be output according to the judgment. information.

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