Debugging skills for troubleshooting md5_file() exception return

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1. Review of basic functions

The basic syntax of md5_file() is as follows:

<code> $hash = md5_file('path/to/file.txt'); </code>

If successful, it returns a 32-bit hexadecimal string; if failed, it returns false . The key point is: the failure does not throw an exception, but returns the boolean value false , so you must pay attention to judgment.

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2. Common reasons for returning false

1. File path error or file does not exist

This is the most common problem. If the specified file path is wrong or the file does not exist at all, md5_file() will fail directly and return false .

<code> $hash = md5_file('/invalid/path/to/file.txt'); if ($hash === false) { echo 'The file path is invalid or the file does not exist'; } </code>

Troubleshooting suggestions:
Use file_exists() to confirm whether the file really exists.

<code> if (!file_exists($filepath)) { echo 'file not found'; } </code>

2. Insufficient file permissions

Even if the file exists, the user of the process where PHP is located does not have read permission, which will cause md5_file() to fail.

Example:

<code> chmod('/path/to/file.txt', 0000); // Disable all permissions $hash = md5_file('/path/to/file.txt'); // Return false </code>

Troubleshooting suggestions:
Use is_readable() to check whether the file has read permission.

<code> if (!is_readable($filepath)) { echo 'File cannot be read'; } </code>

3. The file is being occupied by other programs (Windows-specific)

On Windows systems, if some programs are accessing files exclusively, PHP may not be able to read the file contents, which can also result in false return.

Troubleshooting suggestions:
Try to copy the file to another location and read it with md5_file() , or use other tools to check whether it is locked.

4. The file is too large and exceeds the memory limit

Although md5_file() uses streaming reading (all files will not be loaded into memory at once), if memory_limit is too low in PHP configuration, it may fail when reading large files.

Troubleshooting suggestions:
Improve memory_limit settings appropriately, or execute using command-line scripts (usually more relaxed restrictions).

5. Use URL instead of local path and allow_url_fopen is not enabled

md5_file() supports reading remote files through URLs, for example:

<code> $hash = md5_file('http://m66.net/files/sample.txt'); </code>

However, such a call will succeed only if allow_url_fopen is enabled in php.ini . If this option is not enabled, the return value is false .

Troubleshooting suggestions:
Check the configuration file or confirm with code:

<code> if (!ini_get('allow_url_fopen')) { echo 'Remote file reading is not enabled'; } </code>

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3. Debugging skills and practical investigation

1. Print error_get_last() to get the last error message

<code> $hash = md5_file($filepath); if ($hash === false) { print_r(error_get_last()); } </code>

This function can output detailed information about the last runtime error, which is very helpful for troubleshooting exceptions.

2. Record errors in combination with log system

It is recommended to write error information to the log to facilitate post-tracking:

<code> if (($hash = md5_file($filepath)) === false) { error_log('md5_file failed: ' . print_r(error_get_last(), true)); } </code>

3. Try to use fopen() and other functions to test whether the file is readable

Sometimes the file itself has no problem, but path errors are caused by path stitching or variable pollution. You can try it with fopen() :

<code> if (!$handle = @fopen($filepath, 'rb')) { echo 'File opening failed'; } </code>