2 files changed, 23 insertions, 7 deletions
diff --git a/src/corelib/io/qiodevice.cpp b/src/corelib/io/qiodevice.cpp
index 223df9b..d2e4f75 100644
--- a/src/corelib/io/qiodevice.cpp
+++ b/src/corelib/io/qiodevice.cpp
@@ -1476,10 +1476,13 @@ bool QIODevice::getChar(char *c)
 */
 qint64 QIODevice::peek(char *data, qint64 maxSize)
 {
+    Q_D(QIODevice);
     qint64 readBytes = read(data, maxSize);
-    int i = readBytes;
-    while (i > 0)
-        ungetChar(data[i-- - 1]);
+    if (readBytes <= 0)
+        return readBytes;
+
+    d->buffer.ungetBlock(data, readBytes);
+    d->pos -= readBytes;
     return readBytes;
 }
 
@@ -1502,11 +1505,15 @@ qint64 QIODevice::peek(char *data, qint64 maxSize)
 */
 QByteArray QIODevice::peek(qint64 maxSize)
 {
+    Q_D(QIODevice);
     QByteArray result = read(maxSize);
-    int i = result.size();
-    const char *data = result.constData();
-    while (i > 0)
-        ungetChar(data[i-- - 1]);
+
+    if (result.isEmpty())
+        return result;
+
+    d->buffer.ungetBlock(result.constData(), result.size());
+    d->pos -= result.size();
+
     return result;
 }
 
diff --git a/src/corelib/io/qiodevice_p.h b/src/corelib/io/qiodevice_p.h
index 94dadca..225a0b9 100644
--- a/src/corelib/io/qiodevice_p.h
+++ b/src/corelib/io/qiodevice_p.h
@@ -151,6 +151,15 @@ public:
         len++;
         *first = c;
     }
+    void ungetBlock(const char* block, int size) {
+        if ((first - buf) < size) {
+            // underflow, the existing valid data needs to move to the end of the (potentially bigger) buffer
+            makeSpace(len + size, freeSpaceAtStart);
+            memcpy(first - size, block, size);
+        }
+        first -= size;
+        len += size;
+    }
 
 private:
     enum FreeSpacePos {freeSpaceAtStart, freeSpaceAtEnd};