feat(json-pack): 🎸 add BencodeDecoder implementation

Author: streamich

src/json-pack/bencode/BencodeDecoder.ts

@@ -0,0 +1,151 @@
+import {Reader} from '../../util/buffers/Reader';
+import type {BinaryJsonDecoder, PackValue} from '../types';
+
+export class BencodeDecoder implements BinaryJsonDecoder {
+  public reader = new Reader();
+
+  public read(uint8: Uint8Array): unknown {
+    this.reader.reset(uint8);
+    return this.readAny();
+  }
+
+  public decode(uint8: Uint8Array): unknown {
+    this.reader.reset(uint8);
+    return this.readAny();
+  }
+
+  public readAny(): unknown {
+    const reader = this.reader;
+    const x = reader.x;
+    const uint8 = reader.uint8;
+    const char = uint8[x];
+    switch (char) {
+      case 0x69: // i
+        return this.readNum();
+      case 0x64: // d
+        return this.readObj();
+      case 0x6c: // l
+        return this.readArr();
+      case 0x66: // f
+        return this.readFalse();
+      case 0x74: // t
+        return this.readTrue();
+      case 110: // n
+        return this.readNull();
+      case 117: // u 
+        return this.readUndef();
+      default:
+        if (char >= 48 && char <= 57) return this.readBin();
+    }
+    throw new Error('INVALID_BENCODE');
+  }
+
+  public readNull(): null {
+    if (this.reader.u8() !== 0x6e) throw new Error('INVALID_BENCODE');
+    return null;
+  }
+
+  public readUndef(): undefined {
+    if (this.reader.u8() !== 117) throw new Error('INVALID_BENCODE');
+    return undefined;
+  }
+
+  public readTrue(): true {
+    if (this.reader.u8() !== 0x74) throw new Error('INVALID_BENCODE');
+    return true;
+  }
+
+  public readFalse(): false {
+    if (this.reader.u8() !== 0x66) throw new Error('INVALID_BENCODE');
+    return false;
+  }
+
+  public readBool(): unknown {
+    const reader = this.reader;
+    switch (reader.uint8[reader.x]) {
+      case 0x66: // f
+        return this.readFalse();
+      case 0x74: // t
+        return this.readTrue();
+      default:
+        throw new Error('INVALID_BENCODE');
+    }
+  }
+
+  public readNum(): number {
+    const reader = this.reader;
+    const startChar = reader.u8();
+    if (startChar !== 0x69) throw new Error('INVALID_BENCODE');
+    const u8 = reader.uint8;
+    let x = reader.x;
+    let numStr = '';
+    let c = u8[x++];
+    let i = 0;
+    while (c !== 0x65) {
+      numStr += String.fromCharCode(c);
+      c = u8[x++];
+      if (i > 25) throw new Error('INVALID_BENCODE');
+      i++;
+    }
+    if (!numStr) throw new Error('INVALID_BENCODE');
+    reader.x = x;
+    return +numStr;
+  }
+
+  public readStr(): string {
+    const bin = this.readBin();
+    return new TextDecoder().decode(bin);
+  }
+
+  public readBin(): Uint8Array {
+    const reader = this.reader;
+    const u8 = reader.uint8;
+    let lenStr = '';
+    let x = reader.x;
+    let c = u8[x++];
+    let i = 0;
+    while (c !== 0x3a) {
+      if (c < 48 || c > 57) throw new Error('INVALID_BENCODE');
+      lenStr += String.fromCharCode(c);
+      c = u8[x++];
+      if (i > 10) throw new Error('INVALID_BENCODE');
+      i++;
+    }
+    reader.x = x;
+    const len = +lenStr;
+    const bin = reader.buf(len);
+    return bin;
+  }
+
+  public readArr(): unknown[] {
+    const reader = this.reader;
+    if (reader.u8() !== 0x6c) throw new Error('INVALID_BENCODE');
+    const arr: unknown[] = [];
+    const uint8 = reader.uint8;
+    while (true) {
+      const char = uint8[reader.x];
+      if (char === 0x65) {
+        reader.x++;
+        return arr;
+      }
+      arr.push(this.readAny());
+    }
+  }
+
+  public readObj(): PackValue | Record<string, unknown> | unknown {
+    const reader = this.reader;
+    if (reader.u8() !== 0x64) throw new Error('INVALID_BENCODE');
+    const obj: Record<string, unknown> = {};
+    const uint8 = reader.uint8;
+    while (true) {
+      let char = uint8[reader.x];
+      if (char === 0x65) {
+        reader.x++;
+        return obj;
+      }
+      const key = this.readStr();
+      if (key === '__proto__') throw new Error('INVALID_KEY');
+      obj[key] = this.readAny();
+    }
+  }
+}