feat: Added parseFITSHeaderBlock() to header module.

src/header/index.ts

@@ -1,3 +1,5 @@
 export { getFITSHeaders } from './getFITSHeaders'
 
+export { parseFITSHeaderBlock } from './parseFITSHeaderBlock'
+
 export { parseFITSHeaderRow } from './parseFITSHeaderRow'

src/header/parseFITSHeaderBlock.ts

@@ -0,0 +1,61 @@
+import { FITS_BLOCK_LENGTH, FITS_ROW_LENGTH } from '../fits/constants'
+
+/**
+ *
+ * parseFITSHeaderBlock()
+ *
+ * parses a FITS block specifically as a header (looking for the "END" of the
+ * FITS header)
+ *
+ * @param block
+ * @returns the raw parsed string value for the ArrayBuffer, and two booleans
+ * specifying that the block has both been parsed and the END has been located.
+ */
+export const parseFITSHeaderBlock = (
+  block: ArrayBuffer
+): { s: string; end: boolean; parsed: boolean } => {
+  const arr = new Uint8Array(block)
+
+  let rows = FITS_BLOCK_LENGTH / FITS_ROW_LENGTH
+
+  let s = ''
+
+  // We need to mark when we are at the END of a FITS header:
+  let end = false
+
+  // Just a flag to distinguish between a block that has been parsed and a block
+  // that hasn't:
+  let parsed = false
+
+  // Check the current block one row at a time starting from the end:
+  while (rows--) {
+    const rowIndex = rows * FITS_ROW_LENGTH
+
+    const cchar = arr[rowIndex]
+
+    if (cchar === 32) {
+      continue
+    }
+
+    // Check for END keyword with trailing space (69 "E", 78 "N", 68 "D", 32 " ")
+    if (
+      cchar === 69 &&
+      arr[rowIndex + 1] === 78 &&
+      arr[rowIndex + 2] === 68 &&
+      arr[rowIndex + 3] === 32
+    ) {
+      for (let value of Array.from(arr)) {
+        s += String.fromCharCode(value)
+      }
+      end = true
+      parsed = true
+      break
+    }
+  }
+
+  return {
+    s,
+    end,
+    parsed
+  }
+}

src/index.ts

@@ -2,7 +2,7 @@
 export { B, I, J, hasDataUnit, swopEndian } from './dataunit'
 
 // Flexible Image Transport System (FITS) Header
-export { getFITSHeaders, parseFITSHeaderRow } from './header'
+export { getFITSHeaders, parseFITSHeaderBlock, parseFITSHeaderRow } from './header'
 
 // Flexible Image Transport System (FITS)
 export { getFITSBlocks } from './fits'

src/tests/header.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it, suite } from 'vitest'
 
-import { getFITSHeaders, parseFITSHeaderRow } from '../header'
+import { getFITSHeaders, parseFITSHeaderBlock, parseFITSHeaderRow } from '../header'
 
 suite('@observerly/fits Header', () => {
   describe('FITS File Header Extraction', () => {
@@ -27,7 +27,13 @@ suite('@observerly/fits Header', () => {
     })
   })
 
-  describe('FITS File Header Parsing', () => {
+  describe('FITS File Header Block Parsing', () => {
+    it('parseFITSHeaderBlock should be defined', () => {
+      expect(parseFITSHeaderBlock).toBeDefined()
+    })
+  })
+
+  describe('FITS File Header Row Parsing', () => {
     it('parseFITSHeaderRow should be defined', () => {
       expect(parseFITSHeaderRow).toBeDefined()
     })