return false by default

.gitignore

@@ -1,3 +1,5 @@
+cmd/hashcash/hashcash
+
 # ---> Go
 # Binaries for programs and plugins
 *.exe

README.md

@@ -4,4 +4,39 @@ HTTP Hashcash implemented in Go.
 
 Explanation at https://therootcompany.com/blog/http-hashcash/
 
-Go docs at https://godoc.org/git.rootprojects.org/root/hashcash
+Go API docs at https://pkg.go.dev/git.rootprojects.org/root/hashcash?tab=doc
+
+# CLI Usage
+
+Install:
+
+```bash
+go get git.rootprojects.org/root/hashcash/cmd/hashcash
+```
+
+Usage:
+
+```txt
+Usage:
+	hashcash new [subject *] [expires in 5m] [difficulty 10]
+	hashcash parse <hashcash>
+	hashcash solve <hashcash>
+	hashcash hash <hashcash>
+	hashcash verify <hashcash> [subject *]
+```
+
+Example:
+
+```bash
+my_hc=$(hashcash new)
+echo New: $my_hc
+hashcash parse "$my_hc"
+echo ""
+
+my_hc=$(hashcash solve "$my_hc")
+echo Solved: $my_hc
+hashcash parse "$my_hc"
+echo ""
+
+hashcash verify "$my_hc"
+```

cmd/hashcash/hashcash.go

@@ -0,0 +1,162 @@
+package main
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"os"
+	"strconv"
+	"time"
+
+	"git.rootprojects.org/root/hashcash"
+)
+
+func help() {
+	fmt.Println("Usage:")
+	fmt.Println("\thashcash new [subject *] [difficulty 10] [expires in 5m]")
+	fmt.Println("\thashcash parse <hashcash>")
+	fmt.Println("\thashcash solve <hashcash>")
+	fmt.Println("\thashcash hash <hashcash>")
+	fmt.Println("\thashcash verify <hashcash> [subject *]")
+}
+
+func main() {
+	args := os.Args[:]
+	nargs := len(args)
+
+	if nargs < 2 {
+		help()
+		os.Exit(1)
+		return
+	}
+
+	switch args[1] {
+	case "new":
+		var subject string
+		if nargs >= 3 {
+			subject = args[2]
+		}
+
+		var difficulty int
+		if nargs >= 4 {
+			var err error
+			difficulty, err = strconv.Atoi(args[3])
+			if nil != err {
+				help()
+				os.Exit(1)
+				return
+			}
+		}
+
+		var expIn time.Duration
+		if nargs >= 5 {
+			var err error
+			expIn, err = time.ParseDuration(args[4])
+			if nil != err {
+				fmt.Println(err)
+				help()
+				os.Exit(1)
+				return
+			}
+		} else {
+			expIn = 5 * time.Minute
+		}
+
+		h := hashcash.New(hashcash.Hashcash{
+			Subject:    subject,
+			Difficulty: difficulty,
+			ExpiresAt:  time.Now().Add(expIn),
+		})
+
+		fmt.Println(h.String())
+		return
+	case "parse":
+		var token string
+		if 3 != nargs {
+			help()
+			os.Exit(1)
+			return
+		}
+		token = args[2]
+		h, err := hashcash.Parse(token)
+		if nil != err {
+			fmt.Fprintf(os.Stderr, "%s\n", err)
+			return
+		}
+		b, _ := json.MarshalIndent(h, "", "  ")
+		fmt.Println(string(b))
+		return
+	case "solve":
+		var token string
+		if 3 != nargs {
+			help()
+			os.Exit(1)
+			return
+		}
+		token = args[2]
+		h, err := hashcash.Parse(token)
+		if nil != err {
+			fmt.Fprintf(os.Stderr, "%s\n", err)
+			os.Exit(1)
+			return
+		}
+		err = h.Solve(22)
+		if nil != err {
+			fmt.Fprintf(os.Stderr, "%s\n", err)
+			os.Exit(1)
+			return
+		}
+
+		fmt.Println(h.String())
+		return
+	case "hash":
+		var token string
+		if 3 != nargs {
+			help()
+			os.Exit(1)
+			return
+		}
+		token = args[2]
+		hash := sha256.Sum256([]byte(token))
+		fmt.Println(hex.EncodeToString(hash[:]))
+		return
+	case "verify":
+		var token string
+		if nargs < 3 {
+			help()
+			os.Exit(1)
+			return
+		}
+		token = args[2]
+		h, err := hashcash.Parse(token)
+		if nil != err {
+			fmt.Fprintf(os.Stderr, "%s\n", err)
+			return
+		}
+
+		subject := "*"
+		if nargs >= 4 {
+			subject = args[3]
+		}
+
+		err = h.Verify(subject)
+		if nil != err {
+			fmt.Fprintf(os.Stderr, "%s\n", err)
+			return
+		}
+
+		var duration string
+		dur := h.ExpiresAt.Sub(time.Now())
+		if dur > 365*24*time.Hour {
+			duration = "...a long, long time"
+		} else {
+			duration = dur.Truncate(time.Second).String()
+		}
+		fmt.Println("valid for", duration)
+		return
+	default:
+		help()
+		os.Exit(1)
+	}
+}

hashcash.go

@@ -216,6 +216,10 @@ func (h *Hashcash) Verify(subject string) error {
 }
 
 func verifyBits(hash []byte, bits, n int) bool {
+	if 0 == bits {
+		return true
+	}
+
 	for i := 0; i < n; i++ {
 		if bits > 8 {
 			bits -= 8
@@ -227,15 +231,12 @@ func verifyBits(hash []byte, bits, n int) bool {
 
 		// (bits % 8) == bits
 		pad := 8 - bits
-		if 0 != hash[i]>>pad {
+		if 0 == hash[i]>>pad {
+			return true
+		}
+	}
+
 	return false
-		}
-
-		return true
-	}
-
-	// 0 == bits
-	return true
 }
 
 // Solve will search for a solution, returning an error if the difficulty is