diff --git a/lib/zip_source_crc.c b/lib/zip_source_crc.c
new file mode 100644
index 0000000..e13141c
--- /dev/null
+++ b/lib/zip_source_crc.c
@@ -0,0 +1,142 @@
+/*
+  zip_source_crc.c -- pass-through source that calculates CRC32
+  Copyright (C) 2009 Dieter Baron and Thomas Klausner
+
+  This file is part of libzip, a library to manipulate ZIP archives.
+  The authors can be contacted at <libzip@nih.at>
+
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions
+  are met:
+  1. Redistributions of source code must retain the above copyright
+     notice, this list of conditions and the following disclaimer.
+  2. Redistributions in binary form must reproduce the above copyright
+     notice, this list of conditions and the following disclaimer in
+     the documentation and/or other materials provided with the
+     distribution.
+  3. The names of the authors may not be used to endorse or promote
+     products derived from this software without specific prior
+     written permission.
+ 
+  THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS
+  OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+  ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
+  DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
+  GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
+  IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+  OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
+  IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "zipint.h"
+
+struct crc {
+    struct zip_source *src;
+    int eof;
+    zip_uint64_t size;
+    zip_uint32_t crc;
+};
+
+static zip_int64_t crc_read(void *, void *, zip_uint64_t, enum zip_source_cmd);
+
+
+
+ZIP_EXTERN struct zip_source *
+zip_source_crc(struct zip *za, struct zip_source *src)
+{
+    struct crc *ctx;
+
+    if (za == NULL || src == NULL) {
+	_zip_error_set(&za->error, ZIP_ER_INVAL, 0);
+	return NULL;
+    }
+
+    if ((ctx=(struct crc *)malloc(sizeof(*ctx))) == NULL) {
+	_zip_error_set(&za->error, ZIP_ER_MEMORY, 0);
+	return NULL;
+    }
+
+    ctx->eof = 0;
+    ctx->crc = crc32(0, NULL, 0);
+    ctx->size = 0;
+    ctx->src = src;
+
+
+    return zip_source_function(za, crc_read, ctx);
+}
+
+
+
+static zip_int64_t
+crc_read(void *_ctx, void *data, zip_uint64_t len, enum zip_source_cmd cmd)
+{
+    struct crc *ctx;
+    zip_int64_t n;
+
+    ctx = (struct crc *)_ctx;
+
+    switch (cmd) {
+    case ZIP_SOURCE_OPEN:
+	if (zip_source_call(ctx->src, data, len, cmd) < 0)
+	    return -1;
+
+	return 0;
+
+    case ZIP_SOURCE_READ:
+	if (ctx->eof || len == 0)
+	    return 0;
+
+	if ((n=zip_source_call(ctx->src, data, len, cmd)) < 0)
+	    return -1;
+
+	if (n == 0)
+	    ctx->eof = 1;
+	else {
+	    ctx->size += n;
+	    ctx->crc = crc32(ctx->crc, data, n);
+	}
+	return n;
+
+    case ZIP_SOURCE_CLOSE:
+	if (zip_source_call(ctx->src, data, len, cmd) < 0)
+	    return -1;
+	return 0;
+
+    case ZIP_SOURCE_STAT:
+	if (zip_source_call(ctx->src, data, len, cmd) < 0)
+	    return -1;
+	else {
+	    struct zip_stat *st;
+
+	    st = (struct zip_stat *)data;
+
+	    if (ctx->eof) {
+		/* XXX: error if mismatch with what src provided? */
+		st->size = ctx->size;
+		st->crc = ctx->crc;
+		st->valid |= ZIP_STAT_SIZE|ZIP_STAT_CRC;
+	    }
+	}
+	return 0;
+	
+    case ZIP_SOURCE_ERROR:
+	return zip_source_call(ctx->src, data, len, cmd);
+
+    case ZIP_SOURCE_FREE:
+	zip_source_call(ctx->src, data, len, cmd);
+	free(ctx);
+	return 0;
+
+    default:
+	return zip_source_call(ctx->src, data, len, cmd);
+    }
+    
+}