From b2f3b566c0c0edd41b0314fcbf516a3d7876e14b Mon Sep 17 00:00:00 2001
From: Roland Reichwein <mail@reichwein.it>
Date: Sun, 29 Jan 2023 17:54:14 +0100
Subject: Fix concurrent edit, tests

---
 diff.cpp            | 12 +++++++++---
 diff.h              |  2 ++
 html/whiteboard.js  | 19 ++++++++++++++++++-
 tests/test-diff.cpp | 32 ++++++++++++++++++++++++++++++++
 whiteboard.cpp      | 12 +++++++-----
 5 files changed, 68 insertions(+), 9 deletions(-)

diff --git a/diff.cpp b/diff.cpp
index ea9b04e..85d3167 100644
--- a/diff.cpp
+++ b/diff.cpp
@@ -21,9 +21,10 @@ std::string Diff::apply(const std::string& old_version) const
 {
  std::string result{old_version};
 
- result.erase(m_pos0, m_pos1 - m_pos0);
-
- result.insert(m_pos0, m_data);
+ if (m_pos0 <= m_pos1 && m_pos1 <= old_version.size()) {
+  result.erase(m_pos0, m_pos1 - m_pos0);
+  result.insert(m_pos0, m_data);
+ }
  
  return result;
 }
@@ -143,6 +144,11 @@ void Diff::create(const std::string& xml)
  create(ptree);
 }
 
+bool Diff::empty() const
+{
+ return m_pos0 == m_pos1 && m_data.empty();
+}
+
 boost::property_tree::ptree Diff::get_structure() const
 {
  pt::ptree ptree;
diff --git a/diff.h b/diff.h
index 09d0936..5c2c335 100644
--- a/diff.h
+++ b/diff.h
@@ -19,6 +19,8 @@ public:
 
  std::string apply(const std::string& old_version) const;
 
+ bool empty() const;
+
  boost::property_tree::ptree get_structure() const;
  std::string get_xml() const;
 
diff --git a/html/whiteboard.js b/html/whiteboard.js
index a6dc089..b11dc96 100644
--- a/html/whiteboard.js
+++ b/html/whiteboard.js
@@ -4,6 +4,7 @@ function init() {
 }
 
 var revision;
+var modify_in_progress = 0;
 var baseline = ""; // data contents relating to revision, acknowledged by server
 var baseline_candidate = ""; // will become baseline, after ack by server
 
@@ -51,7 +52,7 @@ function on_getfile(data, rev, pos)
 function on_getdiff(diff, rev, pos)
 {
         if (rev != revision + 1)
-         alert("Revision skipped: " + rev + " after " + revision);
+         console.log("Revision skipped on diff receive: " + rev + " after " + revision);
 
 	var board = document.getElementById("board");
 
@@ -95,8 +96,12 @@ function on_version(version)
 
 function on_modify_ack(rev)
 {
+        if (rev != revision + 1)
+         console.log("Revision skipped on published local change: " + rev + " after " + revision);
+
 	revision = rev;
         baseline = baseline_candidate;
+        modify_in_progress = 0;
 }
 
 function on_message(e) {
@@ -228,6 +233,13 @@ function redirect_to_new_page()
 // local change done
 function on_input()
 {
+        if (modify_in_progress == 1) {
+                console.log("Deferring on_input handler by 100ms");
+                setTimeout(function(){on_input();}, 100); // re-try after 100ms
+                return;
+        }
+        modify_in_progress = 1;
+
 	var parser = new DOMParser();
 	var xmlDocument = parser.parseFromString("<request></request>", "text/xml");
 	
@@ -243,6 +255,11 @@ function on_input()
 
         baseline_candidate = document.getElementById("board").value;
 
+        if (baseline == baseline_candidate) {
+         modify_in_progress = 0;
+         return;
+        }
+
 	var revisionElement = xmlDocument.createElement("baserev");
 	revisionElement.appendChild(document.createTextNode(revision));
 	requestElement.appendChild(revisionElement);
diff --git a/tests/test-diff.cpp b/tests/test-diff.cpp
index 1625716..d09c58e 100644
--- a/tests/test-diff.cpp
+++ b/tests/test-diff.cpp
@@ -147,6 +147,38 @@ TEST_F(DiffTest, constructor)
   Diff d{"baaaab", "baab"};
   EXPECT_EQ(d.get_xml(), "<diff><start>1</start><end>3</end><data/></diff>");
  }
+ {
+  Diff d{"baaaab", "baaaaaaab"};
+  EXPECT_EQ(d.get_xml(), "<diff><start>1</start><end>1</end><data>aaa</data></diff>");
+ }
+}
+
+TEST_F(DiffTest, empty)
+{
+ {
+  Diff d;
+  EXPECT_TRUE(d.empty());
+ }
+
+ {
+  Diff d{"<diff><start>1</start><end>3</end><data/></diff>"};
+  EXPECT_FALSE(d.empty());
+ }
+ 
+ {
+  Diff d{"<diff><start>1</start><end>1</end><data/></diff>"};
+  EXPECT_TRUE(d.empty());
+ }
+ 
+ {
+  Diff d{"<diff><start>1</start><end>1</end><data>abc</data></diff>"};
+  EXPECT_FALSE(d.empty());
+ }
+
+ {
+  Diff d{"<diff><start>0</start><end>0</end><data/></diff>"};
+  EXPECT_TRUE(d.empty());
+ }
 }
 
 TEST_F(DiffTest, diff_create)
diff --git a/whiteboard.cpp b/whiteboard.cpp
index fcfdca8..8736726 100644
--- a/whiteboard.cpp
+++ b/whiteboard.cpp
@@ -167,12 +167,14 @@ std::string Whiteboard::handle_request(Whiteboard::connection& c, const std::str
    pt::ptree ptree;
    ptree.put_child("diff", xml.get_child("request.diff"));
    Diff d{ptree};
-   std::string data {m_storage->getDocument(id)};
-   data = d.apply(data);
+   if (!d.empty()) {
+    std::string data {m_storage->getDocument(id)};
+    data = d.apply(data);
 
-   m_storage->setDocument(id, data);
-   m_registry.setId(c, id);
-   notify_other_connections_diff(c, id, d);
+    m_storage->setDocument(id, data);
+    m_registry.setId(c, id);
+    notify_other_connections_diff(c, id, d);
+   }
    
    int pos {xml.get<int>("request.pos")};
    if (m_storage->getCursorPos(id) != pos) {
-- 
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