From 5c8b8eb94bd764e074b7a3ca72ca550fbfcd1990 Mon Sep 17 00:00:00 2001
From: Kleissner <peter@kleissner.investments>
Date: Thu, 6 Jan 2022 04:11:28 +0100
Subject: [PATCH] Implement backend.Stdout that can be subscribed/unsubscribed.

---
 Commands.go |  3 ++-
 Filter.go   | 45 +++++++++++++++++++++++++++++++++++++++++++++
 Peernet.go  |  4 ++++
 3 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/Commands.go b/Commands.go
index 1613fb5..9a7b413 100644
--- a/Commands.go
+++ b/Commands.go
@@ -8,6 +8,7 @@ package core
 
 import (
 	"bytes"
+	"encoding/hex"
 	"fmt"
 
 	"github.com/PeernetOfficial/core/dht"
@@ -214,7 +215,7 @@ func (peer *PeerInfo) cmdPong(msg *protocol.MessageRaw, connection *Connection)
 
 // cmdChat handles a chat message [debug]
 func (peer *PeerInfo) cmdChat(msg *protocol.MessageRaw, connection *Connection) {
-	fmt.Printf("Chat from '%s': %s\n", connection.Address.String(), string(msg.PacketRaw.Payload))
+	fmt.Fprintf(peer.Backend.Stdout, "Chat from %s '%s': %s\n", hex.EncodeToString(peer.PublicKey.SerializeCompressed()), connection.Address.String(), string(msg.PacketRaw.Payload))
 }
 
 // cmdLocalDiscovery handles an incoming announcement via local discovery
diff --git a/Filter.go b/Filter.go
index c782746..cd69e85 100644
--- a/Filter.go
+++ b/Filter.go
@@ -9,12 +9,15 @@ Filters allow the caller to intercept events. The filter functions must not modi
 package core
 
 import (
+	"io"
 	"log"
+	"sync"
 
 	"github.com/PeernetOfficial/core/blockchain"
 	"github.com/PeernetOfficial/core/btcec"
 	"github.com/PeernetOfficial/core/dht"
 	"github.com/PeernetOfficial/core/protocol"
+	"github.com/google/uuid"
 )
 
 // Filters contains all functions to install the hook. Use nil for unused.
@@ -123,3 +126,45 @@ func (backend *Backend) initFilters() {
 func DefaultLogError(function, format string, v ...interface{}) {
 	log.Printf("["+function+"] "+format, v...)
 }
+
+// MultiWriter code that allows to subscribe/unsubscribe.
+type multiWriter struct {
+	writers map[uuid.UUID]io.Writer
+	sync.Mutex
+}
+
+// Creates a new writer that duplicates its writes to all the subscribed writers.
+// Each write is written to each subscribed writer, one at a time. If any writer returns an error, the entire write operation continues.
+func newMultiWriter() *multiWriter {
+	return &multiWriter{writers: make(map[uuid.UUID]io.Writer)}
+}
+
+// Subscribe a new writer to the list of writers
+func (m *multiWriter) Subscribe(writer io.Writer) (id uuid.UUID) {
+	m.Lock()
+	defer m.Unlock()
+
+	id = uuid.New()
+	m.writers[id] = writer
+
+	return id
+}
+
+// Unsubscribe a writer from the list of writers
+func (m *multiWriter) Unsubscribe(id uuid.UUID) {
+	m.Lock()
+	defer m.Unlock()
+
+	delete(m.writers, id)
+}
+
+// Write a slice of byte to each of the subscribed writers. It will not return any errors.
+func (m *multiWriter) Write(p []byte) (n int, err error) {
+	m.Lock()
+	defer m.Unlock()
+
+	for _, w := range m.writers {
+		w.Write(p)
+	}
+	return len(p), nil
+}
diff --git a/Peernet.go b/Peernet.go
index db28a03..8f9c8d6 100644
--- a/Peernet.go
+++ b/Peernet.go
@@ -29,6 +29,7 @@ func Init(UserAgent string, ConfigFilename string, Filters *Filters) (backend *B
 	backend = &Backend{
 		ConfigFilename: ConfigFilename,
 		userAgent:      UserAgent,
+		Stdout:         newMultiWriter(),
 	}
 
 	if Filters != nil {
@@ -108,4 +109,7 @@ type Backend struct {
 
 	// peerMonitor is a list of channels receiving information about new peers
 	peerMonitor []chan<- *PeerInfo
+
+	// Stdout bundles any output for the end-user. Writers may subscribe/unsubscribe.
+	Stdout *multiWriter
 }