replace readRange with readRanges that opens file only once

lib/fs.mjs

@@ -4,8 +4,11 @@ const rangeToFSOpts = (range, size = Infinity) => {
   size = Number(size);
 
   let [start, end] = range.split('-').map($ => $ === '' ? null : Number($));
+  start ?? (end === null
+    ? start = 0
+    : (start = size - end, end = size - 1)
+  );
   end ??= size - 1;
-  start ?? (start = size - end || 0, end = size - 1);
 
   if (end > size - 1)
     throw new RangeError(`end (${end}) exceeds size (${size}) - 1`);
@@ -17,22 +20,24 @@ const rangeToFSOpts = (range, size = Infinity) => {
   return { length: end - start + 1, position: start };
 };
 
-const readRange = async (range, size, url) => {
-  const { length, position } = rangeToFSOpts(range, size);
-
-  let fd;
+const readRanges = async (url, ranges, size, fd) => {
   try {
-    fd = await open(url);
-    return fd.read(new Uint8Array(length), {
-      length,
-      position,
-    }).then(({ buffer }) => buffer);
+    fd ??= await open(url);
+
+    return Promise.all(ranges.map(range => {
+      const { length, position } = rangeToFSOpts(range, size);
+
+      return fd.read(new Uint8Array(length), {
+        length,
+        position,
+      }).then(({ buffer }) => buffer);
+    }));
   } finally {
     await fd?.close();
   }
 };
 
-const writeRange = async (range, url, body, flag) => {
+const writeRange = async (url, range, body, flag) => {
   let { length, position } = rangeToFSOpts(range);
 
   let fd;
@@ -54,6 +59,6 @@ const writeRange = async (range, url, body, flag) => {
 };
 
 export {
-  readRange,
+  readRanges,
   writeRange,
 };

lib/methods.mjs

@@ -18,7 +18,7 @@ import {
   validatedBody,
 } from './sri.mjs';
 import {
-  readRange,
+  readRanges,
   writeRange,
 } from './fs.mjs';
 
@@ -33,7 +33,7 @@ const GET = async (url, { headers, integrity, signal }) => {
 
   // TODO: rewrite this so only one filehandle is needed
   return ranges.length
-    ? Promise.all(ranges.map(range => readRange(range, size, url)))
+    ? readRanges(url, ranges, size)
       .then($ => validatedBody(integrity, $))
       .then(
         async body => [
@@ -64,7 +64,7 @@ const POSTorPUT = async (url, { body, headers, method }) => {
 
   const flag = method === 'PUT' ? 'w+' : 'r+';
   const [range] = getRanges(headers);
-  return writeRange(range ?? '-', url, body, flag).then(() => genericResponse(201));
+  return writeRange(url, range ?? '-', body, flag).then(() => genericResponse(201));
 };
 
 const methods = new Map([