hardening

parser.ts

@@ -1,5 +1,6 @@
 import { readdirSync, statSync, readFileSync } from "node:fs"
 import { join } from "node:path"
+import { TextDecoder } from "node:util"
 
 export type TemplateVariable = {
   path: string
@@ -8,10 +9,12 @@ export type TemplateVariable = {
 
 const IF_RE = /<@(?:if|elseif)\((.+?)\)>/g
 const VAR_RE = /<@var\(context\.(.+?)(?::(\w+))?\)>/g
+const DIRECTIVE_RE = /<@(if|elseif|else|endif)(?:\((.+?)\))?>/g
 const EQ_RE = /^eq\(context\.(.+?),\s*"(.*)"\)$/
 const PATH_RE = /^context\.(.+)$/
 
-function extractCondition(expr: string, vars: TemplateVariable[]) {
+function extractCondition(expr: string | undefined, vars: TemplateVariable[]) {
+  if (!expr) throw new Error("Missing condition expression")
   const eqMatch = expr.match(EQ_RE)
   if (eqMatch) {
     vars.push({ path: eqMatch[1]!, type: "string" })
@@ -20,7 +23,9 @@ function extractCondition(expr: string, vars: TemplateVariable[]) {
   const pathMatch = expr.match(PATH_RE)
   if (pathMatch) {
     vars.push({ path: pathMatch[1]!, type: "boolean" })
+    return
   }
+  throw new Error(`Invalid condition expression: ${expr}`)
 }
 
 function extractFromString(text: string, vars: TemplateVariable[]) {
@@ -32,6 +37,47 @@ function extractFromString(text: string, vars: TemplateVariable[]) {
   }
 }
 
+function validateIfBlocks(content: string, vars: TemplateVariable[]) {
+  const stack: { sawElse: boolean }[] = []
+
+  for (const match of content.matchAll(DIRECTIVE_RE)) {
+    const directive = match[1]!
+    const condition = match[2]
+
+    if (directive === "if") {
+      extractCondition(condition!, vars)
+      stack.push({ sawElse: false })
+    } else if (directive === "elseif") {
+      const frame = stack[stack.length - 1]
+      if (!frame) throw new Error("Unexpected <@elseif> without <@if>")
+      if (frame.sawElse) throw new Error("Unexpected <@elseif> after <@else>")
+      extractCondition(condition!, vars)
+    } else if (directive === "else") {
+      const frame = stack[stack.length - 1]
+      if (!frame) throw new Error("Unexpected <@else> without <@if>")
+      if (frame.sawElse) throw new Error("Unexpected duplicate <@else>")
+      frame.sawElse = true
+    } else if (directive === "endif") {
+      if (stack.length === 0) throw new Error("Unexpected <@endif> without <@if>")
+      stack.pop()
+    }
+  }
+
+  if (stack.length > 0) {
+    throw new Error("Unmatched <@if> without <@endif>")
+  }
+}
+
+function isUtf8Text(buffer: Buffer): boolean {
+  if (buffer.indexOf(0) !== -1) return false
+  try {
+    new TextDecoder("utf-8", { fatal: true }).decode(buffer)
+    return true
+  } catch {
+    return false
+  }
+}
+
 function walkDir(dirPath: string, vars: TemplateVariable[]) {
   const entries = readdirSync(dirPath).sort()
   for (const entry of entries) {
@@ -42,8 +88,12 @@ function walkDir(dirPath: string, vars: TemplateVariable[]) {
     if (stat.isDirectory()) {
       walkDir(fullPath, vars)
     } else if (stat.isFile()) {
-      const content = readFileSync(fullPath, "utf-8")
-      extractFromString(content, vars)
+      const content = readFileSync(fullPath)
+      if (isUtf8Text(content)) {
+        const text = content.toString("utf-8")
+        extractFromString(text, vars)
+        validateIfBlocks(text, vars)
+      }
     }
   }
 }