add hw2

node_modules/text-decoder/lib/utf8-decoder.js

@@ -0,0 +1,104 @@
+const b4a = require('b4a')
+
+/**
+ * https://encoding.spec.whatwg.org/#utf-8-decoder
+ */
+module.exports = class UTF8Decoder {
+  constructor () {
+    this.codePoint = 0
+    this.bytesSeen = 0
+    this.bytesNeeded = 0
+    this.lowerBoundary = 0x80
+    this.upperBoundary = 0xbf
+  }
+
+  get remaining () {
+    return this.bytesSeen
+  }
+
+  decode (data) {
+    // If we have a fast path, just sniff if the last part is a boundary
+    if (this.bytesNeeded === 0) {
+      let isBoundary = true
+
+      for (let i = Math.max(0, data.byteLength - 4), n = data.byteLength; i < n && isBoundary; i++) {
+        isBoundary = data[i] <= 0x7f
+      }
+
+      if (isBoundary) return b4a.toString(data, 'utf8')
+    }
+
+    let result = ''
+
+    for (let i = 0, n = data.byteLength; i < n; i++) {
+      const byte = data[i]
+
+      if (this.bytesNeeded === 0) {
+        if (byte <= 0x7f) {
+          result += String.fromCharCode(byte)
+        } else {
+          this.bytesSeen = 1
+
+          if (byte >= 0xc2 && byte <= 0xdf) {
+            this.bytesNeeded = 2
+            this.codePoint = byte & 0x1f
+          } else if (byte >= 0xe0 && byte <= 0xef) {
+            if (byte === 0xe0) this.lowerBoundary = 0xa0
+            else if (byte === 0xed) this.upperBoundary = 0x9f
+            this.bytesNeeded = 3
+            this.codePoint = byte & 0xf
+          } else if (byte >= 0xf0 && byte <= 0xf4) {
+            if (byte === 0xf0) this.lowerBoundary = 0x90
+            if (byte === 0xf4) this.upperBoundary = 0x8f
+            this.bytesNeeded = 4
+            this.codePoint = byte & 0x7
+          } else {
+            result += '\ufffd'
+          }
+        }
+
+        continue
+      }
+
+      if (byte < this.lowerBoundary || byte > this.upperBoundary) {
+        this.codePoint = 0
+        this.bytesNeeded = 0
+        this.bytesSeen = 0
+        this.lowerBoundary = 0x80
+        this.upperBoundary = 0xbf
+
+        result += '\ufffd'
+
+        continue
+      }
+
+      this.lowerBoundary = 0x80
+      this.upperBoundary = 0xbf
+
+      this.codePoint = (this.codePoint << 6) | (byte & 0x3f)
+      this.bytesSeen++
+
+      if (this.bytesSeen !== this.bytesNeeded) continue
+
+      result += String.fromCodePoint(this.codePoint)
+
+      this.codePoint = 0
+      this.bytesNeeded = 0
+      this.bytesSeen = 0
+    }
+
+    return result
+  }
+
+  flush () {
+    const result = this.bytesNeeded > 0 ? '\ufffd' : ''
+
+    this.codePoint = 0
+    this.bytesNeeded = 0
+    this.bytesSeen = 0
+    this.lowerBoundary = 0x80
+    this.upperBoundary = 0xbf
+
+    return result
+  }
+}