bitcoin_blkdat,bitcoin_block: Make sure there is a header if blkdat

Makes bitcoin_blkdat fails fast as it is part of probe group.
Speeds up reading a big JSON file etc.

format/all/help.fqtest

@@ -188,11 +188,17 @@ out   # Decode value as bitcoin_blkdat
 out   ... | bitcoin_blkdat
 "help(bitcoin_block)"
 out bitcoin_block: Bitcoin block decoder
+out Options:
+out   has_header=false  Has blkdat header
 out Examples:
 out   # Decode file as bitcoin_block
 out   $ fq -d bitcoin_block . file
 out   # Decode value as bitcoin_block
 out   ... | bitcoin_block
+out   # Decode file using bitcoin_block options
+out   $ fq -d bitcoin_block -o has_header=false . file
+out   # Decode value as bitcoin_block
+out   ... | bitcoin_block({has_header:false})
 "help(bitcoin_script)"
 out bitcoin_script: Bitcoin script decoder
 out Examples:

format/bitcoin/bitcoin_blkdat.go

@@ -25,7 +25,7 @@ func init() {
 func decodeBlkDat(d *decode.D, in interface{}) interface{} {
 	validBlocks := 0
 	for !d.End() {
-		d.FieldFormat("block", bitcoinBlockFormat, nil)
+		d.FieldFormat("block", bitcoinBlockFormat, format.BitCoinBlockIn{HasHeader: true})
 		validBlocks++
 	}
 

format/bitcoin/bitcoin_block.go

@@ -21,6 +21,9 @@ func init() {
 			{Names: []string{format.BITCOIN_TRANSACTION}, Group: &bitcoinTranscationFormat},
 		},
 		DecodeFn: decodeBitcoinBlock,
+		DecodeInArg: format.BitCoinBlockIn{
+			HasHeader: false,
+		},
 	})
 }
 
@@ -32,19 +35,24 @@ var rawHexReverse = scalar.Fn(func(s scalar.S) (scalar.S, error) {
 })
 
 func decodeBitcoinBlock(d *decode.D, in interface{}) interface{} {
+	bbi, _ := in.(format.BitCoinBlockIn)
 	size := d.BitsLeft()
 
-	// TODO: move to blkdat but how to model it?
-	switch d.PeekBits(32) {
-	case 0xf9beb4d9,
-		0x0b110907,
-		0xfabfb5da:
-		d.FieldU32("magic", scalar.UToSymStr{
-			0xf9beb4d9: "mainnet",
-			0x0b110907: "testnet3",
-			0xfabfb5da: "regtest",
-		}, scalar.ActualHex)
-		size = int64(d.FieldU32LE("size")) * 8
+	if bbi.HasHeader {
+		magic := d.PeekBits(32)
+		switch magic {
+		case 0xf9beb4d9,
+			0x0b110907,
+			0xfabfb5da:
+			d.FieldU32("magic", scalar.UToSymStr{
+				0xf9beb4d9: "mainnet",
+				0x0b110907: "testnet3",
+				0xfabfb5da: "regtest",
+			}, scalar.ActualHex)
+			size = int64(d.FieldU32LE("size")) * 8
+		default:
+			d.Fatalf("unknown magic %x", magic)
+		}
 	}
 
 	d.Endian = decode.LittleEndian

format/format.go

@@ -310,3 +310,7 @@ type CSVLIn struct {
 	Comma   string `doc:"Separator character"`
 	Comment string `doc:"Comment line character"`
 }
+
+type BitCoinBlockIn struct {
+	HasHeader bool `doc:"Has blkdat header"`
+}