feat: Added readBlockAsArrayBuffer() in utilities module.

src/index.ts

@@ -8,4 +8,4 @@ export { getFITSHeaders, parseFITSHeaderRow } from './header'
 export { getFITSBlocks } from './fits'
 
 // Utilities
-export { getExcessByteSize } from './utilities'
+export { getExcessByteSize, readBlockAsArrayBuffer } from './utilities'

src/types/block.ts

@@ -5,6 +5,12 @@ export interface FITSBlock {
    *
    */
   buffer: string | ArrayBuffer
+  /**
+   *
+   * The ArrayBuffer as a raw parsed string
+   *
+   */
+  s?: string
   /**
    *
    *

src/utilities/index.ts

@@ -1 +1,3 @@
 export { getExcessByteSize } from './getExcessByteSize'
+
+export { readBlockAsArrayBuffer } from './readBlockAsArrayBuffer'

src/utilities/readBlockAsArrayBuffer.ts

@@ -0,0 +1,35 @@
+/**
+ *
+ * readBlockAsArrayBuffer()
+ *
+ * @description asynchronously reads a file slice as an ArrayBuffer
+ * and onloadend will pass the ArrayBuffer result to a callback function.
+ *
+ * @param block represents a File or File.slice
+ * @param callback function callback to be called onloadend passing
+ * @returns a Promise which resolves the callback of the callback function provided
+ */
+export const readBlockAsArrayBuffer = async (
+  block: Blob,
+  callback: (result: ArrayBuffer) => { s: string; end: boolean; parsed: boolean }
+): Promise<{ s: string; end: boolean; parsed: boolean }> => {
+  return new Promise((resolve, reject) => {
+    const reader = new FileReader()
+
+    reader.onloadend = (e: ProgressEvent<FileReader>) => {
+      if (e.target?.result && e.target.result instanceof ArrayBuffer) {
+        resolve(callback(e.target.result))
+      }
+
+      resolve({
+        s: '',
+        end: false,
+        parsed: false
+      })
+    }
+
+    reader.onerror = reject
+
+    reader.readAsArrayBuffer(block)
+  })
+}