pkg/compression: Set correct brotli settings for edk2

With these settings a recompiled OVMF with linuxboot booted

The scratch buffer size needs to be tuned. We don't know what the
system tool uses. Maybe we can know when the go library compresses

Signed-off-by: Ian Goegebuer <[email protected]>

pkg/compression/systembrotli.go

@@ -38,7 +38,7 @@ func (c *SystemBROTLI) Decode(encodedData []byte) ([]byte, error) {
 
 // Encode encodes a byte slice with BROTLI.
 func (c *SystemBROTLI) Encode(decodedData []byte) ([]byte, error) {
-	cmd := exec.Command(c.brotliPath, "--stdout")
+	cmd := exec.Command(c.brotliPath, "--stdout", "-q", "9")
 	cmd.Stdin = bytes.NewBuffer(decodedData)
 
 	encodedData, err := cmd.Output()
@@ -47,15 +47,16 @@ func (c *SystemBROTLI) Encode(decodedData []byte) ([]byte, error) {
 	}
 
 	// Generate the size of the decoded data for the header
-	buf := &bytes.Buffer{}
-	if err := binary.Write(buf, binary.LittleEndian, uint64(len(decodedData))); err != nil {
+	decodedSize := &bytes.Buffer{}
+	if err := binary.Write(decodedSize, binary.LittleEndian, uint64(len(decodedData))); err != nil {
 		return nil, err
 	}
 
 	// This seems to be the buffer size needed by the UEFI decompressor
-	header := []byte{0x00, 0x00, 0x00, 0x02, 0, 0, 0, 0}
-
-	header = append(buf.Bytes(), header...)
+	// 0x03000000 should suffice. The EDK2 base tools generates this header
+	// using Brotli internals. This needs to be tuned somehow
+	scratchBufferSize := []byte{0x00, 0x00, 0x00, 0x03, 0, 0, 0, 0}
+	header := append(decodedSize.Bytes(), scratchBufferSize...)
 
 	encodedData = append(header, encodedData...)