ossfuzz: add zip_write_alt_compress_fuzzer for bzip2/zstd/xz codec paths

ossfuzz/CMakeLists.txt

@@ -17,3 +17,9 @@ endforeach()
 add_custom_target(list-fuzzers
         COMMAND echo FUZZERS: ${FUZZ_PROGRAMS}
 )
+
+add_fuzzer(zip_write_alt_compress_fuzzer zip_write_alt_compress_fuzzer.c)
+target_link_libraries(zip_write_alt_compress_fuzzer
+  libzip
+  ${FUZZING_ENGINE}
+)

ossfuzz/zip_write_alt_compress_fuzzer.c

@@ -0,0 +1,78 @@
+/*
+ * zip_write_alt_compress_fuzzer.c
+ *
+ * Fuzz harness for libzip alternative compression codec write paths:
+ * BZIP2 (method 12), ZSTD (method 93), and XZ/LZMA (method 95/14).
+ *
+ * The existing zip_write_roundtrip_fuzzer covers only STORE and DEFLATE.
+ * This harness exercises the remaining codec paths in a full write->read
+ * roundtrip, covering lib/zip_algorithm_bzip2.c, zip_algorithm_zstd.c,
+ * and zip_algorithm_xz.c.
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "zip.h"
+#include "zipint.h"
+
+static uint8_t consume_u8(const uint8_t **data, size_t *size) {
+    if (*size == 0) return 0;
+    uint8_t v = **data; (*data)++; (*size)--; return v;
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+    if (size < 4) return 0;
+
+    static const zip_int32_t methods[] = {
+        ZIP_CM_BZIP2, ZIP_CM_ZSTD, ZIP_CM_XZ, ZIP_CM_LZMA, ZIP_CM_STORE,
+    };
+    static const size_t num_methods = sizeof(methods) / sizeof(methods[0]);
+
+    zip_int32_t  method     = methods[consume_u8(&data, &size) % num_methods];
+    zip_uint32_t comp_level = consume_u8(&data, &size) % 10;
+
+    size_t content_len = size / 2;
+    size_t comment_len = size - content_len;
+    const uint8_t *content = data;
+    const uint8_t *comment = data + content_len;
+
+    /* Write phase */
+    zip_source_t *src = zip_source_buffer_create(NULL, 0, 1, NULL);
+    if (!src) return 0;
+
+    zip_t *za = zip_open_from_source(src, ZIP_TRUNCATE, NULL);
+    if (!za) { zip_source_free(src); return 0; }
+
+    zip_source_t *file_src = zip_source_buffer(za, content, content_len, 0);
+    if (!file_src) { zip_discard(za); return 0; }
+
+    zip_int64_t idx = zip_file_add(za, "fuzz.bin", file_src, ZIP_FL_ENC_UTF_8);
+    if (idx < 0) { zip_discard(za); return 0; }
+
+    zip_set_file_compression(za, (zip_uint64_t)idx, method, comp_level);
+
+    if (comment_len > 0 && comment_len <= 65535)
+        zip_set_archive_comment(za, (const char *)comment, (zip_uint16_t)comment_len);
+
+    if (zip_close(za) != 0) return 0;
+
+    /* Read-back phase */
+    zip_source_keep(src);
+    zip_source_seek(src, 0, SEEK_SET);
+
+    zip_t *za_r = zip_open_from_source(src, ZIP_RDONLY, NULL);
+    if (za_r) {
+        zip_file_t *zf = zip_fopen_index(za_r, 0, 0);
+        if (zf) {
+            uint8_t buf[4096];
+            while (zip_fread(zf, buf, sizeof(buf)) > 0) {}
+            zip_fclose(zf);
+        }
+        zip_discard(za_r);
+    }
+    zip_source_free(src);
+    return 0;
+}