From 9d7a9b6653cdcfd0361aafad63e37ff98a1aec5f Mon Sep 17 00:00:00 2001
From: Pascal Seitz <pascal.seitz@gmail.com>
Date: Tue, 23 Jun 2020 22:07:16 +0200
Subject: [PATCH] parse frame partially

---
 src/frame/mod.rs | 115 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 114 insertions(+), 1 deletion(-)

diff --git a/src/frame/mod.rs b/src/frame/mod.rs
index 64dd1fe0..cf41b47e 100644
--- a/src/frame/mod.rs
+++ b/src/frame/mod.rs
@@ -2,4 +2,117 @@
 pub mod compress;
 pub mod decompress;
 
-pub use compress::compress;
\ No newline at end of file
+pub use compress::compress;
+
+#[allow(dead_code)]
+#[derive(Clone, Copy)]
+pub enum BlockSize {
+    Default = 0, // Default - 64KB
+    Max64KB = 4,
+    Max256KB = 5,
+    Max1MB = 6,
+    Max4MB = 7,
+}
+
+#[allow(dead_code)]
+impl BlockSize {
+    pub fn get_size(&self) -> usize {
+        match self {
+            &BlockSize::Default |
+            &BlockSize::Max64KB => 64 * 1024,
+            &BlockSize::Max256KB => 256 * 1024,
+            &BlockSize::Max1MB => 1 * 1024 * 1024,
+            &BlockSize::Max4MB => 4 * 1024 * 1024,
+        }
+    }
+}
+
+#[allow(dead_code)]
+#[derive(Clone, Copy)]
+#[repr(C)]
+pub enum BlockMode {
+    Linked = 0,
+    Independent,
+}
+
+#[allow(dead_code)]
+#[derive(Clone, Copy)]
+pub enum ContentChecksum {
+    NoChecksum = 0,
+    ChecksumEnabled,
+}
+
+
+/// Frame Descriptor
+/// FLG     BD      (Content Size)  (Dictionary ID)     HC
+/// 1 byte  1 byte  0 - 8 bytes     0 - 4 bytes         1 byte
+#[allow(dead_code)]
+#[repr(C)]
+pub(crate) struct LZ4FFrameInfo {
+    pub content_size: Option<u64>,
+    pub block_size_id: BlockSize,
+    pub block_mode: BlockMode,
+    pub content_checksum_flag: ContentChecksum,
+    // pub reserved: [u32; 5],
+}
+
+#[allow(dead_code)]
+impl LZ4FFrameInfo {
+    fn read(input: &[u8]) -> LZ4FFrameInfo {
+        // read flag bytes
+
+        let flg_byte = input[0];
+        assert!((flg_byte & 0b11000000) == 1); // version is always 01
+
+        let block_mode = if (flg_byte & 1 << 5) == 1 {
+            BlockMode::Independent 
+        }else {
+            BlockMode::Linked 
+        };
+        let content_checksum_flag = if (flg_byte & 1 << 2) == 1 {
+            ContentChecksum::ChecksumEnabled 
+        }else {
+            ContentChecksum::NoChecksum 
+        };
+
+        // let content_size_included = (flg_byte & 1 << 4) == 1;
+
+        LZ4FFrameInfo{
+            block_mode,
+            content_checksum_flag,
+            block_size_id: BlockSize::Default, // TODO
+            content_size: None, // TODO
+        }
+    }
+
+    /// writes flag byte
+    /// 
+    /// FLG byte
+    /// BitNumber   7-6         5                      4               3             2                 1           0
+    /// FieldName   Version     Block Independence     Block-Checksum  Content-Size  Content-Checksum  Reserved    DictID
+    ///
+    /// Content-Size (Optional) - The size of the uncompressed data included within the frame will be present as an 8 bytes unsigned little endian value, after the flags
+    fn write_flg_byte(&self) -> u32 {
+        let version = 1 << 6; // always 01
+        let mut res = version;
+        res |= (self.block_mode as u32) << 5;
+        if self.content_size.is_some() {
+            res |= 1 << 3; // set the content_size flag
+        }
+        res |= (self.content_checksum_flag as u32) << 2;
+        // res |= 0 << 4;
+        res
+
+    }
+
+    /// writes block descriptor byte
+    /// Block Maximum Size
+    /// 
+    /// This information is useful to help the decoder allocate memory. Size here refers to the original (uncompressed) data size.
+    /// Block Maximum Size is one value among the following table :
+    /// 0       1       2       3       4       5       6       7
+    /// N/A     N/A     N/A     N/A     64 KB   256 KB  1 MB    4 MB
+    fn write_bd_byte(&self) -> u32 {
+        1 << (self.block_size_id as u32)
+    }
+}