parseExtraFields()

README.md

@@ -182,6 +182,18 @@ if (errorMessage != null) throw new Error(errorMessage);
 This function is automatically run for each entry, as long as `decodeStrings` is `true`.
 See `open()`, `strictFileNames`, and `Event: "entry"` for more information.
 
+### parseExtraFields(extraFieldBuffer)
+
+This function is used internally by yauzl to compute [`entry.extraFields`](#extrafields).
+It is exported in case you want to call it on [`localFileHeader.extraField`](#class-localfileheader).
+
+`extraFieldBuffer` is a `Buffer`, such as `localFileHeader.extraField`.
+Returns an `Array` with each item in the form `{id: id, data: data}`,
+where `id` is a `Number` and `data` is a `Buffer`.
+Throws an `Error` if the data encodes an item with a size that exceeds the bounds of the buffer.
+
+You may want to surround calls to this function with `try { ... } catch (err) { ... }` to handle the error.
+
 ### Class: ZipFile
 
 The constructor for the class is not part of the public API.
@@ -437,7 +449,7 @@ Furthermore, no automatic file name validation is performed for this file name.
 
 #### extraFields
 
-`Array` with each entry in the form `{id: id, data: data}`,
+`Array` with each item in the form `{id: id, data: data}`,
 where `id` is a `Number` and `data` is a `Buffer`.
 
 This library looks for and reads the ZIP64 Extended Information Extra Field (0x0001)
@@ -520,6 +532,7 @@ See the zipfile spec for what these fields mean.
 
 Note that unlike `Class: Entry`, the `fileName` and `extraField` are completely unprocessed.
 This notably lacks Unicode and ZIP64 handling as well as any kind of safety validation on the file name.
+See also [`parseExtraFields()`](#parseextrafields-extrafieldbuffer).
 
 Also note that if your object is missing some of these fields,
 make sure to read the docs on the `minimal` option in `readLocalFileHeader()`.

index.js

@@ -14,6 +14,7 @@ exports.fromBuffer = fromBuffer;
 exports.fromRandomAccessReader = fromRandomAccessReader;
 exports.dosDateTimeToDate = dosDateTimeToDate;
 exports.validateFileName = validateFileName;
+exports.parseExtraFields = parseExtraFields;
 exports.ZipFile = ZipFile;
 exports.Entry = Entry;
 exports.LocalFileHeader = LocalFileHeader;
@@ -305,21 +306,10 @@ ZipFile.prototype._readEntry = function() {
       // 46+n - Extra field
       var fileCommentStart = entry.fileNameLength + entry.extraFieldLength;
       var extraFieldBuffer = buffer.slice(entry.fileNameLength, fileCommentStart);
-      entry.extraFields = [];
-      var i = 0;
-      while (i < extraFieldBuffer.length - 3) {
-        var headerId = extraFieldBuffer.readUInt16LE(i + 0);
-        var dataSize = extraFieldBuffer.readUInt16LE(i + 2);
-        var dataStart = i + 4;
-        var dataEnd = dataStart + dataSize;
-        if (dataEnd > extraFieldBuffer.length) return emitErrorAndAutoClose(self, new Error("extra field length exceeds extra field buffer size"));
-        var dataBuffer = newBuffer(dataSize);
-        extraFieldBuffer.copy(dataBuffer, 0, dataStart, dataEnd);
-        entry.extraFields.push({
-          id: headerId,
-          data: dataBuffer,
-        });
-        i = dataEnd;
+      try {
+        entry.extraFields = parseExtraFields(extraFieldBuffer);
+      } catch (err) {
+        return emitErrorAndAutoClose(self, err);
       }
 
       // 46+n+m - File comment
@@ -670,6 +660,26 @@ function validateFileName(fileName) {
   return null;
 }
 
+function parseExtraFields(extraFieldBuffer) {
+  var extraFields = [];
+  var i = 0;
+  while (i < extraFieldBuffer.length - 3) {
+    var headerId = extraFieldBuffer.readUInt16LE(i + 0);
+    var dataSize = extraFieldBuffer.readUInt16LE(i + 2);
+    var dataStart = i + 4;
+    var dataEnd = dataStart + dataSize;
+    if (dataEnd > extraFieldBuffer.length) throw new Error("extra field length exceeds extra field buffer size");
+    var dataBuffer = newBuffer(dataSize);
+    extraFieldBuffer.copy(dataBuffer, 0, dataStart, dataEnd);
+    extraFields.push({
+      id: headerId,
+      data: dataBuffer,
+    });
+    i = dataEnd;
+  }
+  return extraFields;
+}
+
 function readAndAssertNoEof(reader, buffer, offset, length, position, callback) {
   if (length === 0) {
     // fs.read will throw an out-of-bounds error if you try to read 0 bytes from a 0 byte file

test/test.js

@@ -96,7 +96,7 @@ listZipFiles([path.join(__dirname, "success"), path.join(__dirname, "wrong-entry
             // Do this asynchronously because it's not critical,
             // and this way it might find race condition bugs with autoclose.
             zipfile.readLocalFileHeader(entry, function(err, localFileHeader) {
-              // This is the one field unique to the local file header.
+              // Just check one of non-minumal fields fields.
               if (localFileHeader.versionNeededToExtract == null) throw new Error(messagePrefix + "local file header missing versionNeededToExtract field");
               // This field is the most mechnically important field.
               if (localFileHeader.fileDataStart == null) throw new Error(messagePrefix + "local file header missing fileDataStart field");