1 files changed, 103 insertions, 0 deletions
diff --git a/getgr/getgr.go b/getgr/getgr.go
new file mode 100644
index 0000000..5470b2c
--- /dev/null
+++ b/getgr/getgr.go
@@ -0,0 +1,103 @@
+package getgr
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+//#define _POSIX_SOURCE // for getgrnam_r(3) in grp.h
+//#include <stdlib.h>   // for free(3)
+//#include <unistd.h>   // for sysconf(3)
+//#include <grp.h>      // for getgrnam_r(3)
+//static char *strary(char **ary, unsigned int n) { return ary[n]; }
+import "C"
+
+type Gid uint
+
+type Group struct {
+	Name   string
+	Passwd string
+	Gid    Gid
+	Mem    []string
+}
+
+func strary(c **C.char) (g []string) {
+	g = make([]string, 0)
+	for i := C.uint(0); true; i++ {
+		cstr := C.strary(c, i)
+		if cstr == nil {
+			return
+		}
+		g = append(g, C.GoString(cstr))
+	}
+	panic("not reached")
+}
+
+// A wrapper around C getgrnam_r
+func ByName(name string) (*Group, error) {
+	nameC := C.CString(name)
+	defer C.free(unsafe.Pointer(nameC))
+
+	buflen := C.sysconf(C._SC_GETGR_R_SIZE_MAX)
+	if buflen < 1 {
+		buflen = 1024
+	}
+	buf := make([]byte, buflen)
+	var grp C.struct_group
+	var ret *C.struct_group
+	for {
+		success, errno := C.getgrnam_r(nameC, &grp, (*C.char)(unsafe.Pointer(&buf[0])), C.size_t(buflen), &ret)
+		if success >= 0 {
+			break
+		}
+		if errno == syscall.ERANGE {
+			buflen += 256
+			buf = make([]byte, buflen)
+		} else {
+			return nil, errno
+		}
+	}
+	if ret == nil {
+		return nil, nil
+	}
+	return &Group{
+		Name:   C.GoString(ret.gr_name),
+		Passwd: C.GoString(ret.gr_passwd),
+		Gid:    Gid(ret.gr_gid),
+		Mem:    strary(ret.gr_mem),
+	}, nil
+}
+
+// A wrapper around C getgrgid_r
+func ByGid(gid int32) (*Group, error) {
+	gidC := C.__gid_t(gid)
+
+	buflen := C.sysconf(C._SC_GETGR_R_SIZE_MAX)
+	if buflen < 1 {
+		buflen = 1024
+	}
+	buf := make([]byte, buflen)
+	var grp C.struct_group
+	var ret *C.struct_group
+	for {
+		success, errno := C.getgrgid_r(gidC, &grp, (*C.char)(unsafe.Pointer(&buf[0])), C.size_t(buflen), &ret)
+		if success >= 0 {
+			break
+		}
+		if errno == syscall.ERANGE {
+			buflen += 256
+			buf = make([]byte, buflen)
+		} else {
+			return nil, errno
+		}
+	}
+	if ret == nil {
+		return nil, nil
+	}
+	return &Group{
+		Name:   C.GoString(ret.gr_name),
+		Passwd: C.GoString(ret.gr_passwd),
+		Gid:    Gid(ret.gr_gid),
+		Mem:    strary(ret.gr_mem),
+	}, nil
+}