Why Am I Getting a 'Bad File Descriptor' Error When Appending to a Go Logging File?

File Descriptor Issues in Golang: "Bad File Descriptor" Resolved

When attempting to append to a logging file within a Go routine, developers may encounter a "bad file descriptor" error. This issue can be particularly puzzling when the file exists and has appropriate permissions.

Initially, it may seem that multiple routines attempting to open the file concurrently could cause the problem. However, even after implementing a mutex to prevent this, the same error persists.

The solution lies in adding the O_WRONLY flag to the file opening statement. By default, the open operation opens the file in read-only mode. Without explicitly specifying a write-only flag, any attempt to write to the file will fail with the "bad file descriptor" error.

Here is a modified version of the code snippet that includes the O_WRONLY flag:

if f, err := os.OpenFile("./log.log", os.O_APPEND|os.O_WRONLY, os.ModeAppend); err != nil {
    panic(err)
}

With this modification, the file will be opened with both append and write-only permissions, resolving the "bad file descriptor" error and allowing for successful writing to the logging file.

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