Add writeAttachmentData module

app/types/attachment/write_attachment_data.js

@@ -0,0 +1,45 @@
+const crypto = require('crypto');
+const FSE = require('fs-extra');
+const isArrayBuffer = require('lodash/isArrayBuffer');
+const isBuffer = require('lodash/isBuffer');
+const isString = require('lodash/isString');
+const Path = require('path');
+
+
+exports.writeAttachmentData = (root) => {
+  if (!isString(root)) {
+    throw new TypeError('`root` must be a path');
+  }
+
+  return async (arrayBuffer) => {
+    if (!isArrayBuffer(arrayBuffer)) {
+      throw new TypeError('`arrayBuffer` must be an array buffer');
+    }
+
+    const buffer = new Buffer(arrayBuffer);
+    const path = Path.join(root, exports._getAttachmentPath(buffer));
+    await FSE.ensureFile(path);
+    await FSE.writeFile(path, buffer);
+    return path;
+  };
+};
+
+exports._getAttachmentName = (buffer) => {
+  if (!isBuffer(buffer)) {
+    throw new TypeError('`buffer` must be a buffer');
+  }
+
+  const hash = crypto.createHash('sha256');
+  hash.update(buffer);
+  return hash.digest('hex');
+};
+
+exports._getAttachmentPath = (buffer) => {
+  if (!isBuffer(buffer)) {
+    throw new TypeError('`buffer` must be a buffer');
+  }
+
+  const name = exports._getAttachmentName(buffer);
+  const prefix = name.slice(0, 3);
+  return Path.join(prefix, name);
+};