3 files changed, 228 insertions, 0 deletions
diff --git a/lib/fmtutil/bitfield.go b/lib/fmtutil/bitfield.go
new file mode 100644
index 0000000..b3dbe0a
--- /dev/null
+++ b/lib/fmtutil/bitfield.go
@@ -0,0 +1,54 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package util
+
+import (
+	"fmt"
+	"strings"
+)
+
+type BitfieldFormat uint8
+
+const (
+	HexNone = BitfieldFormat(iota)
+	HexLower
+	HexUpper
+)
+
+func BitfieldString[T ~uint8 | ~uint16 | ~uint32 | ~uint64](bitfield T, bitnames []string, cfg BitfieldFormat) string {
+	var out strings.Builder
+	switch cfg {
+	case HexNone:
+		// do nothing
+	case HexLower:
+		fmt.Fprintf(&out, "0x%0x(", uint64(bitfield))
+	case HexUpper:
+		fmt.Fprintf(&out, "0x%0X(", uint64(bitfield))
+	}
+	if bitfield == 0 {
+		out.WriteString("none")
+	} else {
+		rest := bitfield
+		first := true
+		for i := 0; rest != 0; i++ {
+			if rest&(1<<i) != 0 {
+				if !first {
+					out.WriteRune('|')
+				}
+				if i < len(bitnames) {
+					out.WriteString(bitnames[i])
+				} else {
+					fmt.Fprintf(&out, "(1<<%v)", i)
+				}
+				first = false
+			}
+			rest &^= 1 << i
+		}
+	}
+	if cfg != HexNone {
+		out.WriteRune(')')
+	}
+	return out.String()
+}
diff --git a/lib/fmtutil/fmt.go b/lib/fmtutil/fmt.go
new file mode 100644
index 0000000..c36ba2a
--- /dev/null
+++ b/lib/fmtutil/fmt.go
@@ -0,0 +1,71 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package util
+
+import (
+	"fmt"
+	"strings"
+)
+
+// FmtStateString returns the fmt.Printf string that produced a given
+// fmt.State and verb.
+func FmtStateString(st fmt.State, verb rune) string {
+	var ret strings.Builder
+	ret.WriteByte('%')
+	for _, flag := range []int{'-', '+', '#', ' ', '0'} {
+		if st.Flag(flag) {
+			ret.WriteByte(byte(flag))
+		}
+	}
+	if width, ok := st.Width(); ok {
+		fmt.Fprintf(&ret, "%v", width)
+	}
+	if prec, ok := st.Precision(); ok {
+		if prec == 0 {
+			ret.WriteByte('.')
+		} else {
+			fmt.Fprintf(&ret, ".%v", prec)
+		}
+	}
+	ret.WriteRune(verb)
+	return ret.String()
+}
+
+// FormatByteArrayStringer is function for helping to implement
+// fmt.Formatter for []byte or [n]byte types that have a custom string
+// representation.  Use it like:
+//
+//     type MyType [16]byte
+//
+//     func (val MyType) String() string {
+//         …
+//     }
+//
+//     func (val MyType) Format(f fmt.State, verb rune) {
+//         util.FormatByteArrayStringer(val, val[:], f, verb)
+//     }
+func FormatByteArrayStringer(
+	obj interface {
+		fmt.Stringer
+		fmt.Formatter
+	},
+	objBytes []byte,
+	f fmt.State, verb rune) {
+	switch verb {
+	case 'v':
+		if !f.Flag('#') {
+			FormatByteArrayStringer(obj, objBytes, f, 's') // as a string
+		} else {
+			byteStr := fmt.Sprintf("%#v", objBytes)
+			objType := fmt.Sprintf("%T", obj)
+			objStr := objType + strings.TrimPrefix(byteStr, "[]byte")
+			fmt.Fprintf(f, FmtStateString(f, 's'), objStr)
+		}
+	case 's', 'q': // string
+		fmt.Fprintf(f, FmtStateString(f, verb), obj.String())
+	default:
+		fmt.Fprintf(f, FmtStateString(f, verb), objBytes)
+	}
+}
diff --git a/lib/fmtutil/fmt_test.go b/lib/fmtutil/fmt_test.go
new file mode 100644
index 0000000..0aaebb5
--- /dev/null
+++ b/lib/fmtutil/fmt_test.go
@@ -0,0 +1,103 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package util_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/util"
+)
+
+type FmtState struct {
+	MWidth     int
+	MPrec      int
+	MFlagMinus bool
+	MFlagPlus  bool
+	MFlagSharp bool
+	MFlagSpace bool
+	MFlagZero  bool
+}
+
+func (st FmtState) Width() (int, bool) {
+	if st.MWidth < 1 {
+		return 0, false
+	}
+	return st.MWidth, true
+}
+
+func (st FmtState) Precision() (int, bool) {
+	if st.MPrec < 1 {
+		return 0, false
+	}
+	return st.MPrec, true
+}
+
+func (st FmtState) Flag(b int) bool {
+	switch b {
+	case '-':
+		return st.MFlagMinus
+	case '+':
+		return st.MFlagPlus
+	case '#':
+		return st.MFlagSharp
+	case ' ':
+		return st.MFlagSpace
+	case '0':
+		return st.MFlagZero
+	}
+	return false
+}
+
+func (st FmtState) Write([]byte) (int, error) {
+	panic("not implemented")
+}
+
+func (dst *FmtState) Format(src fmt.State, verb rune) {
+	if width, ok := src.Width(); ok {
+		dst.MWidth = width
+	}
+	if prec, ok := src.Precision(); ok {
+		dst.MPrec = prec
+	}
+	dst.MFlagMinus = src.Flag('-')
+	dst.MFlagPlus = src.Flag('+')
+	dst.MFlagSharp = src.Flag('#')
+	dst.MFlagSpace = src.Flag(' ')
+	dst.MFlagZero = src.Flag('0')
+}
+
+// letters only? No 'p', 'T', or 'w'.
+const verbs = "abcdefghijklmnoqrstuvxyzABCDEFGHIJKLMNOPQRSUVWXYZ"
+
+func FuzzFmtStateString(f *testing.F) {
+	f.Fuzz(func(t *testing.T,
+		width, prec uint8,
+		flagMinus, flagPlus, flagSharp, flagSpace, flagZero bool,
+		verbIdx uint8,
+	) {
+		if flagMinus {
+			flagZero = false
+		}
+		input := FmtState{
+			MWidth:     int(width),
+			MPrec:      int(prec),
+			MFlagMinus: flagMinus,
+			MFlagPlus:  flagPlus,
+			MFlagSharp: flagSharp,
+			MFlagSpace: flagSpace,
+			MFlagZero:  flagZero,
+		}
+		verb := rune(verbs[int(verbIdx)%len(verbs)])
+
+		t.Logf("(%#v, %c) => %q", input, verb, util.FmtStateString(input, verb))
+
+		var output FmtState
+		assert.Equal(t, "", fmt.Sprintf(util.FmtStateString(input, verb), &output))
+		assert.Equal(t, input, output)
+	})
+}