fix(utf32): reassemble split codepoint from overflow buffer, not source index

encodings/utf32.js

@@ -113,9 +113,9 @@ Utf32Decoder.prototype.write = function (src) {
       // NOTE: codepoint is a signed int32 and can be negative.
       // NOTE: We copied this block from below to help V8 optimize it (it works with array, not buffer).
       if (isLE) {
-        codepoint = overflow[i] | (overflow[i + 1] << 8) | (overflow[i + 2] << 16) | (overflow[i + 3] << 24)
+        codepoint = overflow[0] | (overflow[1] << 8) | (overflow[2] << 16) | (overflow[3] << 24)
       } else {
-        codepoint = overflow[i + 3] | (overflow[i + 2] << 8) | (overflow[i + 1] << 16) | (overflow[i] << 24)
+        codepoint = overflow[3] | (overflow[2] << 8) | (overflow[1] << 16) | (overflow[0] << 24)
       }
       overflow.length = 0
 

test/utf32-test.js

@@ -63,6 +63,14 @@ describe("UTF-32LE codec", function () {
     assert.equal(iconv.decode(Buffer.from([0x61, 0, 0, 0, 0]), "UTF32-LE"), "a")
   })
 
+  it("decodes correctly when codepoints are split across stream chunks", function () {
+    for (var at = 1; at < utf32leBuf.length; at++) {
+      var decoder = iconv.getDecoder("utf-32le")
+      var res = decoder.write(utf32leBuf.slice(0, at)) + decoder.write(utf32leBuf.slice(at)) + (decoder.end() || "")
+      assert.equal(res, testStr, "split at byte " + at)
+    }
+  })
+
   it("handles invalid surrogates gracefully", function () {
     var encoded = iconv.encode(testStr2, "UTF32-LE")
     assert.equal(escape(iconv.decode(encoded, "UTF32-LE")), escape(testStr2))
@@ -114,6 +122,14 @@ describe("UTF-32BE codec", function () {
     assert.equal(iconv.decode(Buffer.from([0, 0, 0, 0x61, 0]), "UTF32-BE"), "a")
   })
 
+  it("decodes correctly when codepoints are split across stream chunks", function () {
+    for (var at = 1; at < utf32beBuf.length; at++) {
+      var decoder = iconv.getDecoder("utf-32be")
+      var res = decoder.write(utf32beBuf.slice(0, at)) + decoder.write(utf32beBuf.slice(at)) + (decoder.end() || "")
+      assert.equal(res, testStr, "split at byte " + at)
+    }
+  })
+
   it("handles invalid surrogates gracefully", function () {
     var encoded = iconv.encode(testStr2, "UTF32-BE")
     assert.equal(escape(iconv.decode(encoded, "UTF32-BE")), escape(testStr2))