Zopfli is not always smaller

native/jni/magiskboot/bootimg.cpp

@@ -541,6 +541,14 @@ void repack(const char *src_img, const char *out_img, bool skip_comp) {
         } else {
             hdr->kernel_size() = xwrite(fd, raw_buf, raw_size);
         }
+
+        if (boot.flags[ZIMAGE_KERNEL] &&
+            boot.k_fmt == GZIP && hdr->kernel_size() > boot.hdr->kernel_size()) {
+            // Revert and try zipfoli
+            ftruncate(fd, lseek(fd, -hdr->kernel_size(), SEEK_CUR));
+            hdr->kernel_size() = compress(ZOPFLI, fd, raw_buf, raw_size);
+        }
+
         munmap(raw_buf, raw_size);
     }
     if (boot.flags[ZIMAGE_KERNEL]) {

native/jni/magiskboot/compress.cpp

@@ -624,8 +624,9 @@ stream_ptr get_encoder(format_t type, stream_ptr &&base) {
             return make_unique<LZ4_encoder>(std::move(base), false);
         case LZ4_LG:
             return make_unique<LZ4_encoder>(std::move(base), true);
-        case GZIP:
+        case ZOPFLI:
             return make_unique<zopfli_encoder>(std::move(base));
+        case GZIP:
         default:
             return make_unique<gz_encoder>(std::move(base));
     }
@@ -643,6 +644,7 @@ stream_ptr get_decoder(format_t type, stream_ptr &&base) {
         case LZ4_LEGACY:
         case LZ4_LG:
             return make_unique<LZ4_decoder>(std::move(base));
+        case ZOPFLI:
         case GZIP:
         default:
             return make_unique<gz_decoder>(std::move(base));

native/jni/magiskboot/format.cpp

@@ -47,6 +47,8 @@ const char *Fmt2Name::operator[](format_t fmt) {
     switch (fmt) {
         case GZIP:
             return "gzip";
+        case ZOPFLI:
+            return "zopfli";
         case LZOP:
             return "lzop";
         case XZ:
@@ -73,6 +75,7 @@ const char *Fmt2Name::operator[](format_t fmt) {
 const char *Fmt2Ext::operator[](format_t fmt) {
     switch (fmt) {
         case GZIP:
+        case ZOPFLI:
             return ".gz";
         case LZOP:
             return ".lzo";
@@ -96,6 +99,7 @@ const char *Fmt2Ext::operator[](format_t fmt) {
 format_t Name2Fmt::operator[](std::string_view name) {
     if (0) {}
     CHECK("gzip", GZIP)
+    CHECK("zopfli", ZOPFLI)
     CHECK("xz", XZ)
     CHECK("lzma", LZMA)
     CHECK("bzip2", BZIP2)

native/jni/magiskboot/format.hpp

@@ -12,6 +12,7 @@ typedef enum {
     BLOB,
 /* Compression formats */
     GZIP,
+    ZOPFLI,
     XZ,
     LZMA,
     BZIP2,