Issue #67: support boot/vendor_boot headerVersion downgrade from 4 to 3

boot: correct header size, trim bootSignature
vendor_boot: correct header size, trim vrt

bbootimg/src/main/kotlin/bootimg/v3/BootHeaderV3.kt

@@ -72,6 +72,22 @@ class BootHeaderV3(
         )
     }
 
+    fun feature67(): BootHeaderV3 {
+        val newHeaderSize = when (headerVersion) {
+            3 -> BOOT_IMAGE_HEADER_V3_SIZE
+            else -> BOOT_IMAGE_HEADER_V4_SIZE
+        }
+        if (newHeaderSize != headerSize) {
+            log.warn("wrong headerSize, fixed.($headerSize -> $newHeaderSize)")
+            headerSize = newHeaderSize
+        }
+        if (signatureSize != 0 && headerVersion == 3) {
+            log.warn("trim bootSignature for headerVersion=3")
+            signatureSize = 0
+        }
+        return this
+    }
+
     override fun toString(): String {
         return "BootImgHeaderV3(kernelSize=$kernelSize, ramdiskSize=$ramdiskSize, osVersion=$osVersion, osPatchLevel=$osPatchLevel, headerSize=$headerSize, headerVersion=$headerVersion, cmdline='$cmdline')"
     }

bbootimg/src/main/kotlin/bootimg/v3/BootV3.kt

@@ -187,7 +187,7 @@ data class BootV3(
             headerSize = info.headerSize,
             cmdline = info.cmdline,
             signatureSize = info.signatureSize
-        )
+        ).feature67()
     }
 
     fun extractImages(): BootV3 {

bbootimg/src/main/kotlin/bootimg/v3/VendorBoot.kt

@@ -307,7 +307,7 @@ data class VendorBoot(
             vrtEntryNum = ramdisk_table.ramdidks.size,
             vrtEntrySize = ramdisk_table.eachEntrySize,
             bootconfigSize = File(bootconfig.file).length().toInt()
-        )
+        ).feature67()
     }
 
     fun extractImages(): VendorBoot {

bbootimg/src/main/kotlin/bootimg/v3/VendorBootHeader.kt

@@ -70,6 +70,26 @@ class VendorBootHeader(
         }
     }
 
+    // https://github.com/cfig/Android_boot_image_editor/issues/67
+    // support vendor_boot headerVersion downgrade from 4 to 3 during re-pack
+    fun feature67(): VendorBootHeader {
+        val newHeaderSize = when (this.headerVersion) {
+            3 -> VendorBootHeader.VENDOR_BOOT_IMAGE_HEADER_V3_SIZE
+            else -> VendorBootHeader.VENDOR_BOOT_IMAGE_HEADER_V4_SIZE
+        }
+        if (newHeaderSize != headerSize) {
+            log.warn("wrong headerSize, fixed.($headerSize -> $newHeaderSize)")
+            headerSize = newHeaderSize
+        }
+        if (vrtSize != 0 && headerVersion == 3) {
+            log.warn("trim vrt for headerVersion=3")
+            vrtSize = 0
+            vrtEntryNum = 0
+            vrtEntrySize = 0
+        }
+        return this
+    }
+
     fun encode(): ByteArray {
         return Struct3(FORMAT_STRING).pack(
             magic,