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package bencode
// https://wiki.theory.org/BitTorrentSpecification#Bencoding
import (
"embed"
"strconv"
"github.com/wader/fq/format"
"github.com/wader/fq/pkg/decode"
"github.com/wader/fq/pkg/interp"
"github.com/wader/fq/pkg/scalar"
)
//go:embed bencode.jq
//go:embed bencode.md
var bencodeFS embed.FS
func init() {
interp.RegisterFormat(
format.Bencode,
&decode.Format{
Description: "BitTorrent bencoding",
DecodeFn: decodeBencode,
Functions: []string{"torepr"},
})
interp.RegisterFS(bencodeFS)
}
var typeToNames = scalar.StrMapSymStr{
"d": "dictionary",
"i": "integer",
"l": "list",
"0": "string",
"1": "string",
"2": "string",
"3": "string",
"4": "string",
"5": "string",
"6": "string",
"7": "string",
"8": "string",
"9": "string",
}
func decodeStrIntUntil(b byte) func(d *decode.D) int64 {
return func(d *decode.D) int64 {
// 21 is sign + longest 64 bit in base 10
i := d.PeekFindByte(b, 21)
if i == -1 {
d.Fatalf("decodeStrIntUntil: failed to find %v", b)
}
s := d.UTF8(int(i))
n, err := strconv.ParseInt(s, 10, 64)
if err != nil {
d.Fatalf("decodeStrIntUntil: %q: %s", s, err)
}
return n
}
}
func decodeBencodeValue(d *decode.D) {
typ := d.FieldUTF8("type", 1, typeToNames)
switch typ {
case "0", "1", "2", "3", "4", "5", "6", "7", "8", "9":
d.SeekRel(-8)
length := d.FieldSintFn("length", decodeStrIntUntil(':'))
d.FieldUTF8("separator", 1, d.StrAssert(":"))
d.FieldUTF8("value", int(length))
case "i":
d.FieldSintFn("value", decodeStrIntUntil('e'))
d.FieldUTF8("end", 1, d.StrAssert("e"))
case "l":
d.FieldArray("values", func(d *decode.D) {
for d.PeekUintBits(8) != 'e' {
d.FieldStruct("value", decodeBencodeValue)
}
})
d.FieldUTF8("end", 1, d.StrAssert("e"))
case "d":
d.FieldArray("pairs", func(d *decode.D) {
for d.PeekUintBits(8) != 'e' {
d.FieldStruct("pair", func(d *decode.D) {
d.FieldStruct("key", decodeBencodeValue)
d.FieldStruct("value", decodeBencodeValue)
})
}
})
d.FieldUTF8("end", 1, d.StrAssert("e"))
default:
d.Fatalf("unknown type %v", typ)
}
}
func decodeBencode(d *decode.D) any {
decodeBencodeValue(d)
return nil
}
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