Implement thread-unique poster ID

frontend/sass/global/_img.scss

@@ -261,4 +261,10 @@ div.inlinepostprev {
 	padding: 4px;
 	display: inline-block;
 	background: colors.$hashtagbg;
+}
+
+.poster-id {
+	font-size: 0.8em;
+	padding: 0 5px;
+	border-radius: 1em;
 }

html/css/global.css

@@ -280,6 +280,12 @@ div.inlinepostprev {
   background: rgba(0, 0, 0, 0.1019607843);
 }
 
+.poster-id {
+  font-size: 0.8em;
+  padding: 0 5px;
+  border-radius: 1em;
+}
+
 div.section-block {
   margin-bottom: 8px;
 }

pkg/building/posts.go

@@ -3,6 +3,7 @@ package building
 import (
 	"bytes"
 	"context"
+	"crypto/sha256"
 	"fmt"
 	"net"
 	"path"
@@ -79,6 +80,7 @@ type Post struct {
 	Country      geoip.Country `json:"-"`
 	thread       gcsql.Thread
 	uploadPath   string
+	uniqueID     string
 }
 
 // TitleText returns the text to be used for the title of the page
@@ -102,6 +104,29 @@ func (p *Post) ThreadPath() string {
 	return config.WebPath(p.BoardDir, "res", strconv.Itoa(threadID)+".html")
 }
 
+// ThreadUniqueID returns a 6-character hexidecimal ID for the user in a thread, allowing anonymity while discouraging sockpuppetting
+func (p *Post) ThreadUniqueID() string {
+	if p.uniqueID != "" {
+		return p.uniqueID
+	}
+	hash := sha256.New()
+	hash.Write(p.IP)
+	hash.Write([]byte(p.BoardDir))
+	hash.Write([]byte(strconv.Itoa(p.ParentID)))
+	p.uniqueID = fmt.Sprintf("%02x", hash.Sum(nil)[:3])
+	return p.uniqueID
+}
+
+// ThreadUniqueIDColorIsDark returns true if the color represented by the thread unique ID has a dark luminance
+func (p *Post) ThreadUniqueIDColorIsDark() bool {
+	id := p.ThreadUniqueID()
+	red, _ := strconv.ParseInt(id[0:2], 16, 0)
+	green, _ := strconv.ParseInt(id[2:4], 16, 0)
+	blue, _ := strconv.ParseInt(id[4:6], 16, 0)
+	luminance := 0.299*float32(red) + 0.587*float32(green) + 0.114*float32(blue)
+	return luminance < 128
+}
+
 // Timestamp returns the time the post was created.
 // Deprecated: Use CreatedOn instead.
 func (p *Post) Timestamp() time.Time {

templates/post.html

@@ -18,6 +18,10 @@
 	{{- end -}}
 	{{- if ne .post.Email ""}}</a>{{end}}</span>
 	{{- if ne .post.Tripcode ""}}<span class="tripcode">!{{.post.Tripcode}}</span>{{end -}}
+	{{- if .global.boardConfig.ShowPosterID -}}
+		{{$uniqueID := .post.ThreadUniqueID}}
+		<span class="poster-id-container">(ID: <span class="poster-id" style="background: #{{$uniqueID}}; color: {{if .post.ThreadUniqueIDColorIsDark}}white{{else}}black{{end}}">{{$uniqueID}}</span>)</span>
+	{{- end -}}
 	{{- if ne .post.Country.Flag ""}}{{template "post_flag" .post.Country}}{{end}}
 	<time datetime="{{formatTimestampAttribute .post.Timestamp}}">{{formatTimestamp .post.Timestamp}}</time>
 </label> <a href="{{.post.WebPath}}">No.</a> <a href="javascript:quote({{.post.ID}})" class="backlink-click">{{.post.ID}}</a>