🚚 Merge Bencode parser

src/ssn/bencodeParser.ts

@@ -0,0 +1,75 @@
+/**
+ * A parser for .torrent files encoded with Bencode <https://en.wikipedia.org/wiki/Bencode>.
+ */
+
+import { TextDecoder } from 'util';
+
+const Decoder = new TextDecoder('utf-8');
+
+/** Takes a Bencoded-encoded file, parses it at the given starting position and returns a JSON object, or rejects on error. */
+export default function bpParse(dv: DataView, posIn: number, reject: (reason?: any) => void): { obj: any, pos: number } {
+  let pos = posIn;
+  let obj;
+  const header = dv.getUint8(pos++);
+  switch (header) {
+      case 0x64: { //'d' - dictionary (key-value object)
+          obj = [];
+          do {
+              //read key
+              const out1 = bpParse(dv, pos, reject);
+              pos = out1.pos;
+              //read value
+              const out2 = bpParse(dv, pos, reject);
+              pos = out2.pos;
+              obj[out1.obj] = out2.obj;
+          } while (dv.getUint8(pos) !== 0x65); //'e' - end
+          pos++;
+          break;
+      }
+      case 0x6C: { //'l' - list (array)
+          obj = [];
+          do {
+              //read entry
+              const out = bpParse(dv, pos, reject);
+              pos = out.pos;
+              obj.push(out.obj);
+          } while (dv.getUint8(pos) !== 0x65); //'e' - end
+          pos++;
+          break;
+      }
+      case 0x69: { //'i' - integer
+          let curChar = dv.getUint8(pos++);
+          let curNumber = 0;
+          while (curChar !== 0x65) { //'e' - end
+              if (curChar < 0x30 || curChar > 0x39) {
+                  reject('Unexpected int char during bencode parsing');
+                  return { obj: null, pos };
+              }
+              curNumber *= 10;
+              curNumber += curChar - 0x30;
+              curChar = dv.getUint8(pos++);
+          }
+          obj = curNumber;
+          break;
+      }
+      case 0x30: case 0x31: case 0x32: case 0x33: case 0x34:
+      case 0x35: case 0x36: case 0x37: case 0x38: case 0x39: { //string prefixed by length
+          //read string length
+          let curChar: number = header;
+          let strLen = 0;
+          while (curChar !== 0x3A) { //':' - integer delimiter, beginning of string
+              strLen *= 10;
+              strLen += curChar - 0x30;
+              curChar = dv.getUint8(pos++);
+          }
+          //read string
+          obj = Decoder.decode(new DataView(dv.buffer, pos, strLen));
+          pos += strLen;
+          break;
+      }
+      default:
+          reject('Unexpected leading char during bencode parsing.');
+          return { obj: null, pos };
+  }
+  return { obj, pos };
+}