fix: do not parse mpeg-ts files as typescript files

MPEG-TS files consist of frames each 188 bytes long.
These files should not be parsed as typescript files
and therefore we look into the first 50 frames and
check if we find a 'valid' header.

Closes microsoft#21136

Author: KnisterPeter

src/compiler/sys.ts

@@ -582,6 +582,7 @@ namespace ts {
             const Buffer: {
                 new (input: string, encoding?: string): any;
                 from?(input: string, encoding?: string): any;
+                alloc(length: number): any;
             } = require("buffer").Buffer;
 
             const nodeVersion = getNodeMajorVersion();
@@ -984,6 +985,30 @@ namespace ts {
                 if (!fileExists(fileName)) {
                     return undefined;
                 }
+
+                {
+                    // GH#21136: check if this is an MPEG-TS file
+                    const buffer = Buffer.alloc(50 * 188);
+                    const fd = _fs.openSync(fileName);
+                    try {
+                        const bytesRead = _fs.readSync(fd, buffer, 0, 50 * 188);
+                        // check if we have a multiple of 188 bytes (frames)
+                        if (bytesRead % 188 === 0) {
+                            let allHex47 = true;
+                            for (let i = 0, n = i * 188; i < n; i = i + 188) {
+                                if (i < bytesRead && buffer[i] !== 0x47) {
+                                    allHex47 = false;
+                                }
+                            }
+                            if (allHex47) {
+                                return undefined;
+                            }
+                        }
+                    } finally {
+                        _fs.closeSync(fd);
+                    }
+                }
+
                 const buffer = _fs.readFileSync(fileName);
                 let len = buffer.length;
                 if (len >= 2 && buffer[0] === 0xFE && buffer[1] === 0xFF) {