39 lines
1.3 KiB
Go
39 lines
1.3 KiB
Go
package godaemon
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import (
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"bytes"
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"os"
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"syscall"
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)
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// Readlink returns the file pointed to by the given soft link, or an error of
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// type PathError otherwise. This mimics the os.Readlink() function, but works
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// around a bug we've seen in CentOS 5.10 (kernel 2.6.27.10 on x86_64) where the
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// underlying OS function readlink() returns a wrong number of bytes for the
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// result (see man readlink). Here we don't rely blindly on that value; if
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// there's a zero byte among that number of bytes, then we keep only up to that
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// point.
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//
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// NOTE: We chose not to use os.Readlink() and then search on its result to
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// avoid an extra overhead of converting back to []byte. The function to search
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// for a byte over the string itself (strings.IndexByte()) is only available
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// starting with Go 1.2. Also, we're not searching at every iteration to save
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// some CPU time, even though that could mean extra iterations for systems
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// affected with this bug. But it's wiser to optimize for the general case
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// (i.e., those not affected).
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func Readlink(name string) (string, error) {
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for len := 128; ; len *= 2 {
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b := make([]byte, len)
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n, e := syscall.Readlink(name, b)
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if e != nil {
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return "", &os.PathError{"readlink", name, e}
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}
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if n < len {
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if z := bytes.IndexByte(b[:n], 0); z >= 0 {
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n = z
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}
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return string(b[:n]), nil
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}
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}
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}
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