commit a2f357eb3330a282e36f740beaf3a189fc6fec48
Author: gutmet <me.git@gutmet.org>
Date:   Sun Apr 26 22:57:19 2020 +0200

    Initial commit

diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..1392b88
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,16 @@
+LaymansHex: A layman's hex editor.
+Copyright (C) 2020 Alexander Weinhold
+
+Unless explicitly stated otherwise, the following applies:
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License version 2 as published by
+the Free Software Foundation.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
diff --git a/README b/README
new file mode 100644
index 0000000..d6523f5
--- /dev/null
+++ b/README
@@ -0,0 +1,50 @@
+LaymansHex
+==========
+
+LaymansHex takes a (partial) file description and allows tinkering with
+the values in a binary file. It thus serves as a sort of layman's
+hex editor.
+
+
+File description format
+-----------------------
+
+In EBNF:
+```
+description =
+  { comment }
+  endianness
+  definition
+  { definition }
+.
+
+comment = '#' { LETTER | DIGIT } '\n'.
+
+endianness = ("little endian" | "big endian") '\n'.
+
+definition = name ':' type '\n'.
+
+name = { LETTER | DIGIT }.
+
+type = ( "byte[" INTEGER "]" )
+  | int8    | int16  | int32  | int64
+  | uint8   | uint16 | uint32 | uint64
+  | float32 | float64  
+```
+
+The name of a definition line can be left empty to ignore that particular value.
+Portions of the binary file not covered be the file description are ignored.
+
+
+Usage
+-----
+
+To get values: laymanshex FORMATFILE BINARY
+To set values: laymanshex -set "key123=value123" FORMATFILE BINARY
+
+
+TODO
+----
+
+There is no way to express offset values inside a file yet. Since this is
+relatively common, I will add it at some point.
diff --git a/laymanshex.go b/laymanshex.go
new file mode 100644
index 0000000..d44d5fc
--- /dev/null
+++ b/laymanshex.go
@@ -0,0 +1,380 @@
+package main
+
+import (
+	"bufio"
+	"encoding/binary"
+	"encoding/hex"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func optPanic(msg string, err error) {
+	if err != nil {
+		panic(errors.New(msg + ": " + err.Error()))
+	}
+}
+
+type handling struct {
+	bytes    int64
+	readFrom func(io.Reader, binary.ByteOrder) string
+	writeTo  func(io.Writer, binary.ByteOrder, string)
+}
+
+func binaryRead(r io.Reader, order binary.ByteOrder, pointerTo interface{}) {
+	err := binary.Read(r, order, pointerTo)
+	optPanic(fmt.Sprintf("binary conversion failed (%T)", pointerTo), err)
+}
+
+func binaryWrite(w io.Writer, order binary.ByteOrder, pointerTo interface{}) {
+	err := binary.Write(w, order, pointerTo)
+	optPanic(fmt.Sprintf("binary write failed (%T)", pointerTo), err)
+}
+
+var handlings = map[string]handling{
+	"int8": handling{1,
+		func(r io.Reader, bo binary.ByteOrder) string {
+			var i int8
+			binaryRead(r, bo, &i)
+			return strconv.FormatInt(int64(i), 10)
+		},
+		func(w io.Writer, bo binary.ByteOrder, s string) {
+			i, err := strconv.ParseInt(s, 10, 8)
+			optPanic("conversion of "+s+"to int8 failed", err)
+			binaryWrite(w, bo, int8(i))
+		}},
+	"uint8": handling{1,
+		func(r io.Reader, bo binary.ByteOrder) string {
+			var i uint8
+			binaryRead(r, bo, &i)
+			return strconv.FormatUint(uint64(i), 10)
+		},
+		func(w io.Writer, bo binary.ByteOrder, s string) {
+			i, err := strconv.ParseUint(s, 10, 8)
+			optPanic("conversion of "+s+"to uint8 failed", err)
+			binaryWrite(w, bo, uint8(i))
+		}},
+	"int16": handling{2,
+		func(r io.Reader, bo binary.ByteOrder) string {
+			var i int16
+			binaryRead(r, bo, &i)
+			return strconv.FormatInt(int64(i), 10)
+		},
+		func(w io.Writer, bo binary.ByteOrder, s string) {
+			i, err := strconv.ParseInt(s, 10, 16)
+			optPanic("conversion of "+s+"to int16 failed", err)
+			binaryWrite(w, bo, int16(i))
+		}},
+	"uint16": handling{2,
+		func(r io.Reader, bo binary.ByteOrder) string {
+			var i uint16
+			binaryRead(r, bo, &i)
+			return strconv.FormatUint(uint64(i), 10)
+		},
+		func(w io.Writer, bo binary.ByteOrder, s string) {
+			i, err := strconv.ParseUint(s, 10, 16)
+			optPanic("conversion of "+s+"to uint16 failed", err)
+			binaryWrite(w, bo, uint16(i))
+		}},
+	"int32": handling{4,
+		func(r io.Reader, bo binary.ByteOrder) string {
+			var i int32
+			binaryRead(r, bo, &i)
+			return strconv.FormatInt(int64(i), 10)
+		},
+		func(w io.Writer, bo binary.ByteOrder, s string) {
+			i, err := strconv.ParseInt(s, 10, 32)
+			optPanic("conversion of "+s+"to int32 failed", err)
+			binaryWrite(w, bo, int32(i))
+		}},
+	"uint32": handling{4,
+		func(r io.Reader, bo binary.ByteOrder) string {
+			var i uint32
+			binaryRead(r, bo, &i)
+			return strconv.FormatUint(uint64(i), 10)
+		},
+		func(w io.Writer, bo binary.ByteOrder, s string) {
+			i, err := strconv.ParseUint(s, 10, 32)
+			optPanic("conversion of "+s+"to uint32 failed", err)
+			binaryWrite(w, bo, uint32(i))
+		}},
+	"int64": handling{8,
+		func(r io.Reader, bo binary.ByteOrder) string {
+			var i int64
+			binaryRead(r, bo, &i)
+			return strconv.FormatInt(i, 10)
+		},
+		func(w io.Writer, bo binary.ByteOrder, s string) {
+			i, err := strconv.ParseInt(s, 10, 64)
+			optPanic("conversion of "+s+"to int64 failed", err)
+			binaryWrite(w, bo, i)
+		}},
+	"uint64": handling{8,
+		func(r io.Reader, bo binary.ByteOrder) string {
+			var i uint64
+			binaryRead(r, bo, &i)
+			return strconv.FormatUint(i, 10)
+		},
+		func(w io.Writer, bo binary.ByteOrder, s string) {
+			i, err := strconv.ParseUint(s, 10, 64)
+			optPanic("conversion of "+s+"to uint64 failed", err)
+			binaryWrite(w, bo, i)
+		}},
+	"float32": handling{4,
+		func(r io.Reader, bo binary.ByteOrder) string {
+			var f float32
+			binaryRead(r, bo, &f)
+			return strconv.FormatFloat(float64(f), 'f', -1, 64)
+		},
+		func(w io.Writer, bo binary.ByteOrder, s string) {
+			f, err := strconv.ParseFloat(s, 32)
+			optPanic("conversion of "+s+"to float32 failed", err)
+			binaryWrite(w, bo, float32(f))
+		}},
+	"float64": handling{8,
+		func(r io.Reader, bo binary.ByteOrder) string {
+			var f float64
+			binaryRead(r, bo, &f)
+			return strconv.FormatFloat(f, 'f', -1, 64)
+		},
+		func(w io.Writer, bo binary.ByteOrder, s string) {
+			f, err := strconv.ParseFloat(s, 64)
+			optPanic("conversion of "+s+"to float64 failed", err)
+			binaryWrite(w, bo, float64(f))
+		}},
+}
+
+type filePart struct {
+	name     string
+	parttype string
+	handling handling
+}
+
+func (part *filePart) Line() string {
+	return part.name + " : " + part.parttype
+}
+
+func (part *filePart) setHandling() {
+	if strings.HasPrefix(part.parttype, "byte") {
+		tmp := strings.TrimRight(strings.TrimLeft(part.parttype, "byte["), "]")
+		bytes, err := strconv.ParseInt(tmp, 10, 64)
+		optPanic(part.name, err)
+		readFrom := func(r io.Reader, bo binary.ByteOrder) string {
+			buf := make([]byte, bytes)
+			var i int64
+			for i = 0; i < bytes; i++ {
+				binaryRead(r, bo, &buf[i])
+			}
+			return hex.EncodeToString(buf)
+		}
+		writeTo := func(w io.Writer, bo binary.ByteOrder, s string) {
+			buf, err := hex.DecodeString(s)
+			optPanic("invalid string of hex values: "+s, err)
+			binaryWrite(w, bo, buf)
+		}
+		part.handling = handling{bytes, readFrom, writeTo}
+
+	} else {
+		if handling, ok := handlings[part.parttype]; !ok {
+			panic(part.Line() + ": Don't know type")
+		} else {
+			part.handling = handling
+		}
+	}
+}
+
+type fileDescription struct {
+	byteOrder binary.ByteOrder
+	parts     []filePart
+}
+
+func trim(s string) string {
+	return strings.TrimSpace(s)
+}
+
+var debug bool
+
+func info(i string, s string) {
+	if debug {
+		fmt.Fprintln(os.Stderr, i, "-->", s)
+	}
+}
+
+func readPart(line string) *filePart {
+	part := &filePart{}
+	splitline := strings.Split(line, ":")
+	if len(splitline) != 2 {
+		panic("invalid definition: " + line)
+	}
+	part.name = trim(splitline[0])
+	part.parttype = trim(splitline[1])
+	info("definition", part.Line())
+	part.setHandling()
+	return part
+}
+
+func readFileDescription(path string) fileDescription {
+	errmsg := "read format file"
+	descr := fileDescription{}
+	f, err := os.Open(path)
+	defer f.Close()
+	optPanic("open format file", err)
+	buf := bufio.NewReader(f)
+	/*----------------------------------*/
+	line, err := buf.ReadString('\n')
+	optPanic(errmsg, err)
+	line = trim(line)
+	for strings.HasPrefix(line, "#") {
+		info("comment", line)
+		line, err = buf.ReadString('\n')
+		optPanic(errmsg, err)
+		line = trim(line)
+	}
+	/*----------------------------------*/
+	line = trim(line)
+	if line == "big endian" {
+		descr.byteOrder = binary.BigEndian
+	} else if line == "little endian" {
+		descr.byteOrder = binary.LittleEndian
+	} else {
+		panic(errmsg + ": expected endianness ('little endian' or 'big endian'), got :" + line)
+	}
+	info("endianness", line)
+	/*----------------------------------*/
+	line, err = buf.ReadString('\n')
+	optPanic(errmsg, err)
+	line = trim(line)
+	for err != io.EOF && line != "" {
+		part := readPart(line)
+		descr.parts = append(descr.parts, *part)
+		line, err = buf.ReadString('\n')
+		line = trim(line)
+	}
+	line = trim(line)
+	if err == io.EOF && line != "" {
+		descr.parts = append(descr.parts, *readPart(line))
+	} else if err != io.EOF {
+		optPanic(errmsg, err)
+	}
+	return descr
+}
+
+func readAssignments(descr fileDescription, s string) map[string]string {
+	assignments := strings.Split(s, ",")
+	m := make(map[string]string)
+	for _, assignment := range assignments {
+		kv := strings.Split(assignment, "=")
+		if len(kv) != 2 {
+			panic("weird parameters in set: " + assignment + "\nWant list of comma-separated key=value assignments")
+		}
+		key := trim(kv[0])
+		value := trim(kv[1])
+		found := false
+		for _, part := range descr.parts {
+			if key == part.name {
+				found = true
+			}
+		}
+		if found {
+			m[key] = value
+		} else {
+			panic("unknown key: " + key)
+		}
+	}
+	return m
+}
+
+func backup(binpath string) {
+	bin, err := os.Open(binpath)
+	defer bin.Close()
+	optPanic("failed to open binary", err)
+	timestamp := time.Now().Format("20060102150405")
+	fi, err := bin.Stat()
+	optPanic("failed to get permissions of binary", err)
+	backuppath := binpath + ".bak" + timestamp
+	backup, err := os.OpenFile(backuppath, os.O_RDWR|os.O_CREATE, fi.Mode())
+	defer backup.Close()
+	_, err = io.Copy(backup, bin)
+	optPanic("failed to create backup", err)
+	backup.Chmod(fi.Mode())
+	fmt.Println("Created backup " + backuppath + "\n")
+}
+
+func setValues(descr fileDescription, binpath string, vals map[string]string) {
+	backup(binpath)
+	f, err := os.OpenFile(binpath, os.O_RDWR, 0666)
+	optPanic("failed to write-open binary", err)
+	defer f.Close()
+	for _, part := range descr.parts {
+		needSeek := true
+		if part.name != "" {
+			if val, ok := vals[part.name]; ok {
+				part.handling.writeTo(f, descr.byteOrder, val)
+				needSeek = false
+			}
+		}
+		if needSeek {
+			f.Seek(part.handling.bytes, 1)
+		}
+	}
+}
+
+func getValues(descr fileDescription, binpath string) map[string]string {
+	vals := make(map[string]string)
+	f, err := os.Open(binpath)
+	defer f.Close()
+	optPanic("failed to open binary", err)
+	for _, part := range descr.parts {
+		if part.name == "" {
+			f.Seek(part.handling.bytes, 1)
+		} else {
+			vals[part.name] = part.handling.readFrom(f, descr.byteOrder)
+		}
+	}
+	return vals
+}
+
+func padding(descr fileDescription) string {
+	pad := 0
+	for _, part := range descr.parts {
+		if n := len(part.name); n > pad {
+			pad = n
+		}
+	}
+	return strconv.Itoa(pad)
+}
+
+func printValues(descr fileDescription, vals map[string]string) {
+	for _, part := range descr.parts {
+		if part.name != "" {
+			fmt.Printf("%"+padding(descr)+"s = %s\n", part.name, vals[part.name])
+		}
+	}
+}
+
+func printUsage() {
+	fmt.Fprintf(os.Stderr, "Usage: %s [Options] FORMATFILE BINARY\n", os.Args[0])
+	flag.PrintDefaults()
+}
+
+func main() {
+	var assignments string
+	flag.StringVar(&assignments, "set", "", "key=value pairs (e.g. \"key1=value1,key2=value2\")")
+	flag.BoolVar(&debug, "debug", false, "print recognized parts of the format file")
+	flag.Parse()
+	args := flag.Args()
+	if len(args) != 2 {
+		printUsage()
+		os.Exit(-1)
+	}
+	descr := readFileDescription(args[0])
+	if assignments != "" {
+		setValues(descr, args[1], readAssignments(descr, assignments))
+	}
+	printValues(descr, getValues(descr, args[1]))
+}