Golang implements file monitoring

As software systems become more and more complex, file operations are becoming more and more important in software systems. Monitoring file operations is one of the keys to ensuring system stability. This article will introduce how to use Go language to implement file monitoring.

Go language is an open source, concurrent, statically typed programming language. Due to its excellent concurrency performance, Go language is becoming more and more popular in the field of server-side programming. At the same time, the Go language also provides a powerful standard library, including file operations, network operations, etc. In the scenario of file monitoring, the file operation interface in the os package provided by the standard library of the Go language is very practical.

In Go language, you can open, close, read, write, rename, delete files, etc. through the interface provided by the os package. The following introduces several commonly used file operation functions:

1. Open file

First you need to use the os.Open function to open a file:

func Open(name string) (*File, error)

Parameter name is the name of the file to be opened, and the return value is a pointer to the File type and an error object.

2. Close the file

After the file operation is completed, the file needs to be closed and related resources released. Use the Close method of the os.File type to close the file.

func (f *File) Close() error

3. Read the file

Use the Read method of the os.File type to read the file content:

func (f *File) Read(b []byte) (n int, err error)

The parameter b is the byte type of the received content Slice, the return value is the number of bytes read and an error object.

4. Write the file

Use the Write method of the os.File type to write the content into the file:

func (f *File) Write(b []byte) (n int, err error)

Parameter b is the value to be written Content, the return value is the number of bytes written and an error object.

5. Delete files

Use the os.Remove function to delete files:

func Remove(name string) error

The parameter name is the name of the file to be deleted, and the return value is an error object .

The above are several commonly used functions in file operations. Next, we will use these functions to implement file monitoring.

The implementation of file monitoring requires the implementation of two functions. The first is to monitor file changes, and the second is to respond to changes.

1. Monitor file changes

Use the Stat method of the File class of the os package to obtain file information (such as size, modification time, etc.), and obtain the same file again after a period of time Information, if the information is different, it means that the file has changed. The specific implementation is as follows:

package main

import (
    "fmt"
    "os"
    "time"
)

func main() {
    file := "./example.txt"

    fileInfo, _ := os.Stat(file)

    fileCreateTime := fileInfo.ModTime()

    for {
        time.Sleep(1 * time.Second)
        fileInfo, err := os.Stat(file)
        if err != nil {
            fmt.Println(err)
            continue
        }

        if fileInfo.ModTime() != fileCreateTime {
            fmt.Println("file changed: ", file)
            break
        }
    }
}

In the above code, the FileInfo object of the file to be monitored is first obtained. Then, use the object's ModTime method to get the file modification time. Then, execute a loop every 1 second to obtain the new FileInfo object of the file and compare whether the ModTime values ​​of the two FileInfo objects are the same. If different then the file has changed.

2. Response to file changes

When the file changes, the file changes need to be responded to. In actual operation, what usually needs to be done is to re-read the contents of the file and perform corresponding business operations. The following is a simple example:

package main

import (
    "fmt"
    "os"
    "time"
)

func main() {
    file := "./example.txt"
    fileList := []string{file}
    readFile(fileList)

    for {
        before := getFileModTime(fileList)

        time.Sleep(1 * time.Second)
        after := getFileModTime(fileList)

        for k, v := range before {
            if v != after[k] {
                fmt.Printf("file changed: %v
", k)
                readFile(fileList)
            }
        }
    }
}

func getFileModTime(fileList []string) map[string]time.Time {
    ret := map[string]time.Time{}
    for _, v := range fileList {
        fileInfo, _ := os.Stat(v)
        modTime := fileInfo.ModTime()
        ret[v] = modTime
    }
    return ret
}

func readFile(fileList []string) {
    for _, v := range fileList {
        f, err := os.Open(v)
        if err != nil {
            fmt.Println("read file failed: ", err)
            continue
        }
        defer f.Close()

        b := make([]byte, 1024)
        n, err := f.Read(b)
        if err != nil {
            fmt.Println("read file failed: ", err)
            continue
        }

        fmt.Printf("file content of %s: %s
", v, string(b[:n]))
    }
}

In the above code, we save the files that need to be monitored in a string slice fileList, and read the file once at startup. The monitoring part is similar to the above, except that after comparing the Stat information of the two files, it responds to the changed files. The response part uses a readFile function, which opens the file, uses the Read method of the os.File type to read the file content, and performs business processing on the read content.

At this point, a simple file monitoring implementation is completed. Readers can implement the monitoring and response functions in more detail according to actual needs.

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