From 6d148ebb4ad243186834c0509caa68e89949cc68 Mon Sep 17 00:00:00 2001
From: OV2 <OV2@sessionclan.de>
Date: Sat, 3 Dec 2016 17:09:52 +0100
Subject: [PATCH] Add seek capability to unzStream

---
 stream.cpp | 91 +++++++++++++++++++++++++++++++++++-------------------
 stream.h   |  9 ++++--
 2 files changed, 66 insertions(+), 34 deletions(-)

diff --git a/stream.cpp b/stream.cpp
index bb64113d..80af5327 100644
--- a/stream.cpp
+++ b/stream.cpp
@@ -315,8 +315,12 @@ void fStream::closeStream()
 unzStream::unzStream (unzFile &v)
 {
 	file = v;
-	head = NULL;
-	numbytes = 0;
+    pos_in_buf = 0;
+    buf_pos_in_unzipped = unztell(file);
+    bytes_in_buf = 0;
+
+    // remember start pos for seeks
+    unzGetFilePos(file, &unz_file_start_pos);
 }
 
 unzStream::~unzStream (void)
@@ -324,21 +328,31 @@ unzStream::~unzStream (void)
 	return;
 }
 
+size_t unzStream::buffer_remaining()
+{
+    return bytes_in_buf - pos_in_buf;
+}
+
+void unzStream::fill_buffer()
+{
+    buf_pos_in_unzipped = unztell(file);
+    bytes_in_buf = unzReadCurrentFile(file, buffer, unz_BUFFSIZ);
+    pos_in_buf = 0;
+}
+
 int unzStream::get_char (void)
 {
 	unsigned char	c;
 
-	if (numbytes <= 0)
+	if (buffer_remaining() <= 0)
 	{
-		numbytes = unzReadCurrentFile(file, buffer, unz_BUFFSIZ);
-		if (numbytes <= 0)
+        fill_buffer();
+		if (bytes_in_buf <= 0)
 			return (EOF);
-		head = buffer;
 	}
 
-	c = *head;
-	head++;
-	numbytes--;
+	c = *(buffer + pos_in_buf);
+    pos_in_buf++;
 
 	return ((int) c);
 }
@@ -373,28 +387,25 @@ size_t unzStream::read (void *buf, size_t len)
 	if (len == 0)
 		return (len);
 
-	if (len <= numbytes)
-	{
-		memcpy(buf, head, len);
-		numbytes -= len;
-		head += len;
-		return (len);
-	}
+	size_t	to_read = len;
+    uint8 *read_to = (uint8 * )buf;
+    do
+    {
+        size_t in_buffer = buffer_remaining();
+        if (to_read <= in_buffer)
+        {
+            memcpy(read_to, buffer + pos_in_buf, to_read);
+            pos_in_buf += to_read;
+            to_read = 0;
+            break;
+        }
 
-	size_t	numread = 0;
-	if (numbytes > 0)
-	{
-		memcpy(buf, head, numbytes);
-		numread += numbytes;
-		head = NULL;
-		numbytes = 0;
-	}
+        memcpy(read_to, buffer + pos_in_buf, in_buffer);
+        to_read -= in_buffer;
+        fill_buffer();
+    } while (bytes_in_buf);
 
-	int	l = unzReadCurrentFile(file, (uint8 *)buf + numread, len - numread);
-	if (l > 0)
-		numread += l;
-
-	return (numread);
+	return (len - to_read);
 }
 
 // not supported
@@ -405,7 +416,7 @@ size_t unzStream::write (void *buf, size_t len)
 
 size_t unzStream::pos (void)
 {
-    return (unztell(file));
+    return buf_pos_in_unzipped + pos_in_buf;
 }
 
 size_t unzStream::size (void)
@@ -415,10 +426,26 @@ size_t unzStream::size (void)
     return info.uncompressed_size;
 }
 
-// not supported
 int unzStream::revert (size_t from, size_t offset)
 {
-    return -1;
+    size_t target_pos = from + offset;
+
+    // new pos inside buffered data
+    if (target_pos >= buf_pos_in_unzipped && target_pos < buf_pos_in_unzipped + bytes_in_buf)
+    {
+        pos_in_buf = target_pos - buf_pos_in_unzipped;
+    }
+    else // outside of buffer, reset file and read until pos
+    {
+        unzGoToFilePos(file, &unz_file_start_pos);
+        int times_to_read = target_pos / unz_BUFFSIZ + 1;
+        for( int i = 0; i < times_to_read; i++)
+        {
+            fill_buffer();
+        }
+        pos_in_buf = target_pos % unz_BUFFSIZ;
+    }
+    return 0;
 }
 
 void unzStream::closeStream()
diff --git a/stream.h b/stream.h
index ea22df0a..1539dd44 100644
--- a/stream.h
+++ b/stream.h
@@ -252,10 +252,15 @@ class unzStream : public Stream
         virtual void closeStream();
 
 	private:
+        void   fill_buffer();
+        size_t buffer_remaining();
+
 		unzFile	file;
 		char	buffer[unz_BUFFSIZ];
-		char	*head;
-		size_t	numbytes;
+        size_t  pos_in_buf;
+        size_t  buf_pos_in_unzipped;
+		size_t	bytes_in_buf;
+        unz_file_pos unz_file_start_pos;
 };
 
 #endif