feat(read): add sync support for low-level content read

Author: zkat

lib/content/read.js

@@ -33,6 +33,21 @@ function read (cache, integrity, opts) {
   })
 }
 
+module.exports.sync = readSync
+function readSync (cache, integrity, opts) {
+  opts = ReadOpts(opts)
+  return withContentSriSync(cache, integrity, (cpath, sri) => {
+    const data = fs.readFileSync(cpath)
+    if (typeof opts.size === 'number' && opts.size !== data.length) {
+      throw sizeError(opts.size, data.length)
+    } else if (ssri.checkData(data, sri)) {
+      return data
+    } else {
+      throw integrityError(sri, cpath)
+    }
+  })
+}
+
 module.exports.stream = readStream
 module.exports.readStream = readStream
 function readStream (cache, integrity, opts) {
@@ -112,6 +127,28 @@ function withContentSri (cache, integrity, fn) {
   })
 }
 
+function withContentSriSync (cache, integrity, fn) {
+  const sri = ssri.parse(integrity)
+  // If `integrity` has multiple entries, pick the first digest
+  // with available local data.
+  const algo = sri.pickAlgorithm()
+  const digests = sri[algo]
+  if (digests.length <= 1) {
+    const cpath = contentPath(cache, digests[0])
+    return fn(cpath, digests[0])
+  } else {
+    let lastErr = null
+    for (const meta of sri[sri.pickAlgorithm()]) {
+      try {
+        return withContentSriSync(cache, meta, fn)
+      } catch (err) {
+        lastErr = err
+      }
+    }
+    if (lastErr) { throw lastErr }
+  }
+}
+
 function sizeError (expected, found) {
   var err = new Error(Y`Bad data size: expected inserted data to be ${expected} bytes, but got ${found} instead`)
   err.expected = expected

test/content.read.js

@@ -29,6 +29,18 @@ test('read: returns a BB with cache content data', function (t) {
   })
 })
 
+test('read.sync: reads synchronously', t => {
+  const CONTENT = Buffer.from('foobarbaz')
+  const INTEGRITY = ssri.fromData(CONTENT)
+  const fixture = new Tacks(CacheContent({
+    [INTEGRITY]: CONTENT
+  }))
+  fixture.create(CACHE)
+  const data = read.sync(CACHE, INTEGRITY)
+  t.deepEqual(data, CONTENT, 'cache contents read correctly')
+  t.done()
+})
+
 test('read.stream: returns a stream with cache content data', function (t) {
   const CONTENT = Buffer.from('foobarbaz')
   const INTEGRITY = ssri.fromData(CONTENT)