Add EncodeConcatenatedHashes with test. (#432)

dcrjson/parse.go

@@ -13,6 +13,18 @@ import (
 	"github.com/decred/dcrd/chaincfg/chainhash"
 )
 
+// EncodeConcatenatedHashes serializes a slice of chainhash.Hash values into a
+// string of hex-encoded bytes.
+func EncodeConcatenatedHashes(hashSlice []chainhash.Hash) string {
+	length := len(hashSlice) * chainhash.HashSize
+	hashBytes := make([]byte, 0, length)
+	for i := range hashSlice {
+		hashBytes = append(hashBytes, hashSlice[i][:]...)
+	}
+
+	return hex.EncodeToString(hashBytes)
+}
+
 // DecodeConcatenatedHashes return a slice of contiguous chainhash.Hash objects
 // created by decoding a single string of concatenated hex-encoded hashes.
 //

dcrjson/parse_test.go

@@ -13,6 +13,7 @@ import (
 	"github.com/decred/dcrd/blockchain/stake"
 	"github.com/decred/dcrd/chaincfg/chainhash"
 	"github.com/decred/dcrd/dcrjson"
+	"strings"
 )
 
 func decodeHash(reversedHash string) chainhash.Hash {
@@ -23,6 +24,39 @@ func decodeHash(reversedHash string) chainhash.Hash {
 	return *h
 }
 
+func TestEncodeConcatenatedHashes(t *testing.T) {
+	// Input Hash slice. Data taken from Decred's first three mainnet blocks.
+	hashSlice := []chainhash.Hash{
+		decodeHash("298e5cc3d985bfe7f81dc135f360abe089edd4396b86d2de66b0cef42b21d980"),
+		decodeHash("000000000000437482b6d47f82f374cde539440ddb108b0a76886f0d87d126b9"),
+		decodeHash("000000000000c41019872ff7db8fd2e9bfa05f42d3f8fee8e895e8c1e5b8dcba"),
+	}
+	hashLen := hex.EncodedLen(len(hashSlice[0]))
+
+	// Expected output. The string representations of the underlying byte arrays
+	// in the input []chainhash.Hash
+	blockHashes := []string{
+		"80d9212bf4ceb066ded2866b39d4ed89e0ab60f335c11df8e7bf85d9c35c8e29",
+		"b926d1870d6f88760a8b10db0d4439e5cd74f3827fd4b6827443000000000000",
+		"badcb8e5c1e895e8e8fef8d3425fa0bfe9d28fdbf72f871910c4000000000000",
+	}
+	concatenatedHashes := strings.Join(blockHashes, "")
+
+	// Test from 0 to N of the hashes
+	for j := 0; j < len(hashSlice)+1; j++ {
+		// Expected output string
+		concatRef := concatenatedHashes[:j*hashLen]
+
+		// Encode to string
+		concatenated := dcrjson.EncodeConcatenatedHashes(hashSlice[:j])
+		// Verify output
+		if concatenated != concatRef {
+			t.Fatalf("EncodeConcatenatedHashes failed (%v!=%v)",
+				concatenated, concatRef)
+		}
+	}
+}
+
 func TestDecodeConcatenatedHashes(t *testing.T) {
 	// Test data taken from Decred's first three mainnet blocks
 	testHashes := []chainhash.Hash{