done

.idea/.gitignore

@@ -0,0 +1,5 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Editor-based HTTP Client requests
+/httpRequests/

.idea/ctf10k-rpn.iml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="WEB_MODULE" version="4">
+  <component name="NewModuleRootManager">
+    <content url="file://$MODULE_DIR$">
+      <excludeFolder url="file://$MODULE_DIR$/temp" />
+      <excludeFolder url="file://$MODULE_DIR$/.tmp" />
+      <excludeFolder url="file://$MODULE_DIR$/tmp" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>

.idea/jsLibraryMappings.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="JavaScriptLibraryMappings">
+    <includedPredefinedLibrary name="Node.js Core" />
+  </component>
+</project>

.idea/modules.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/.idea/ctf10k-rpn.iml" filepath="$PROJECT_DIR$/.idea/ctf10k-rpn.iml" />
+    </modules>
+  </component>
+</project>

.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>

main.js

@@ -0,0 +1,59 @@
+const Net = require('net');
+
+const port = 8002
+const host = "ctf10k.root-me.org"
+
+const client = new Net.Socket
+
+client.on('data', (data) => {
+    console.log("received data:\n", data.toString())
+
+    regex =/(?<equation>^\d+.*$)/m
+    let message = regex.exec(data.toString()).groups["equation"]
+    console.log("equation:", message)
+
+    let response = interpretRPN(message)
+    console.log("response:", response)
+    let buf = Buffer.from(response+"\n")
+    client.write(buf)
+})
+
+client.on('end', () => {
+    console.log("connection terminated by remote host")
+})
+
+client.connect({port: port, host: host}, () => {
+    console.log("connected")
+})
+
+function interpretRPN(message){
+    const operators = ['-', '+', 'x', '/']
+    let elements = message.split(' ')
+    for (let i = 0; i < elements.length; i++) {
+        if (operators.includes(elements[i])) {
+            let operation = elements.slice(i-2, i+1)
+            let result = computeOperation(operation)
+            elements.splice(i-2, 3, result)
+            i = 0
+        }
+    }
+
+    return elements.toString()
+}
+
+function computeOperation(operation) {
+    switch (operation[2]) {
+        case '-':
+            return BigInt(operation[0]) - BigInt(operation[1])
+        case 'x':
+            return BigInt(operation[0]) * BigInt(operation[1])
+        case '/':
+            return BigInt(operation[0]) / BigInt(operation[1])
+        case '+':
+            return BigInt(operation[0]) + BigInt(operation[1])
+    }
+}
+
+// const example = "994 611 + 357 733 + 82 543 - x x 740 + 136 x 996 +"
+// console.log("response:", interpretRPN(example))
+

package.json

@@ -0,0 +1,6 @@
+{
+  "name": "ctf10k-rpn",
+  "version": "1.0.0",
+  "dependencies": {
+  }
+}