feat: support for wildcard byte patterns

README.MD

@@ -107,9 +107,26 @@ _**getBitsString**_|Get string representation for the next "length" bits from th
 _**getBitsReversedValue**_|Get number value representation of the next "length" bits from the stream, preliminary reversed
 _**toString**_|Represent remaining bits in "BitStream" as a string
 
+## Wildcard byte patterns
+
+The _ByteStream_ class provides an option to use wildcard byte patterns. These are useful in searching for magic bytes [in a file format](https://en.wikipedia.org/wiki/List_of_file_signatures).
+
+Example of using wildcard byte patterns:
+```javascript
+let wildcard = "?".charCodeAt(0);
+let searchPattern = new ByteStream({
+	// set wildcard byte value
+	wildcard: wildcard,
+	// set search pattern with wildcard bytes ("s??e ")
+	view: new Uint8Array([0x73, wildcard, wildcard, 0x65, 0x20])
+});
+let dataPattern = new ByteStream({ data: 'some random data 0x00 0x00 0x01 0x45' });
+dataPattern.findPattern(searchPattern); // find search pattern in data pattern
+```
+
 ## parseByteMap functionality
 
-The `parseByteMap` function is intended to parse and check byte streams with determinated structure.
+The `parseByteMap` function is intended to parse and check byte streams with determined structure.
 
 Example of _map_ used as a kind of _template_. Exactly this _map_ is using for parsing PDF _xref_ table:
 ```javascript

src/byte_stream.ts

@@ -1,22 +1,24 @@
-export interface ByteStreamEmptyParameters { }
-export interface ByteStreamLengthParameters {
-  length: number;
-  stub?: number;
+export interface ByteStreamEmptyParameters {
+  readonly wildcard?: number;
+}
+export interface ByteStreamLengthParameters extends ByteStreamEmptyParameters {
+  readonly length: number;
+  readonly stub?: number;
 }
-export interface ByteStreamViewParameters {
-  view: Uint8Array;
+export interface ByteStreamViewParameters extends ByteStreamEmptyParameters {
+  readonly view: Uint8Array;
 }
 
-export interface ByteStreamBufferParameters {
-  buffer: ArrayBuffer;
+export interface ByteStreamBufferParameters extends ByteStreamEmptyParameters {
+  readonly buffer: ArrayBuffer;
 }
 
-export interface ByteStreamStringParameters {
-  string: string;
+export interface ByteStreamStringParameters extends ByteStreamEmptyParameters {
+  readonly string: string;
 }
 
-export interface ByteStreamHexParameters {
-  hexstring: string;
+export interface ByteStreamHexParameters extends ByteStreamEmptyParameters {
+  readonly hexstring: string;
 }
 
 export type ByteStreamParameters =
@@ -81,7 +83,7 @@ export class ByteStream {
    * Constructor for ByteStream class
    * @param parameters
    */
-  constructor(parameters: ByteStreamParameters = {}) {
+  constructor(readonly parameters: ByteStreamParameters = {}) {
     if ("view" in parameters) {
       this.fromUint8Array(parameters.view);
     } else if ("buffer" in parameters) {
@@ -502,6 +504,9 @@ export class ByteStream {
       const equalStart = (backward) ? (start - patternLength - i) : (start + i);
 
       for (let j = 0; j < patternLength; j++) {
+        if (pattern.parameters.wildcard === patternArray[j]) {
+          continue;
+        }
         if (this.view[j + equalStart] != patternArray[j]) {
           equal = false;
           break;

test/funcTest.spec.ts

@@ -126,6 +126,16 @@ context("Functional testing", () => {
 			])
 		});
 
+		const wildcardStream = new ByteStream({
+			wildcard: 0x3F, // "?"
+			view: new Uint8Array([
+				0x20,
+				0x3F,
+				0x3F,
+				0x23,
+			])
+		});
+
 		let result;
 
 		result = dataStream.findFirstNotIn([separatorStream, separatorStream2]);
@@ -138,6 +148,8 @@ context("Functional testing", () => {
 		assert.strictEqual(result, 1, "Incorrect result for findPattern #1");
 		result = dataStream.findPattern(separatorStream4);
 		assert.strictEqual(result, 5, "Incorrect result for findPattern #2");
+		result = dataStream.findPattern(wildcardStream);
+		assert.strictEqual(result, 5, "Incorrect result for wildcardStream #1");
 		result = dataStream.findFirstIn([separatorStream, separatorStream2]);
 		assert.strictEqual(result.position, 1, "Incorrect result for findFirstIn #2");
 		result = dataStream.findFirstNotIn([separatorStream, separatorStream2, separatorStream3]);