helper functions to fetch amf values

src/demux/flv.rs

@@ -71,7 +71,7 @@ impl FLVReader {
 
 impl input::FileReader for FLVReader {
     fn init(&mut self) -> Result<util::Metadata, Box<dyn Error>> {
-        self.skip_init_header();
+        self.skip_init_header()?;
         return self.read_metadata()
     }
     fn read_nalu(&mut self) -> Result<util::NALUPacket, Box<dyn Error>> {
@@ -85,6 +85,64 @@ pub fn new_reader(stdin: io::Stdin) -> Result<FLVReader, Box<dyn Error>> {
     return Ok(reader);
 }
 
-fn process_metadata(data: Vec<u8>) -> Result<util::Metadata, Box<dyn Error>> {
+fn process_metadata(mut data: Vec<u8>) -> Result<util::Metadata, Box<dyn Error>> {
+    data.drain(..13);
+    let ecma_sync_byte = data.drain(..1).next().unwrap();
+    if ecma_sync_byte != 8 {
+        return Err(Box::new(util::DemuxerError::FLVMetadataSyncFail));
+    }
+    let arr_len = u32::fetch_amf_val(&mut data);
     todo!();
 }
+
+trait FetchAMFVal {
+    type Primitive;
+    fn fetch_amf_val(data: &mut Vec<u8>) -> Self::Primitive;
+}
+
+impl FetchAMFVal for u32 {
+    type Primitive = u32;
+    fn fetch_amf_val(data: &mut Vec<u8>) -> Self::Primitive {
+        let mut buff = [0u8; 4];
+        buff.copy_from_slice(data.drain(..4).as_slice());
+        return u32::from_be_bytes(buff);
+    }
+}
+
+impl FetchAMFVal for u16 {
+    type Primitive = u16;
+    fn fetch_amf_val(data: &mut Vec<u8>) -> Self::Primitive {
+        let mut buff = [0u8; 2];
+        buff.copy_from_slice(data.drain(..2).as_slice());
+        return u16::from_be_bytes(buff);
+    }
+}
+
+impl FetchAMFVal for f64 {
+    type Primitive = f64;
+    fn fetch_amf_val(data: &mut Vec<u8>) -> Self::Primitive {
+        let mut buff = [0u8; 8];
+        buff.copy_from_slice(data.drain(..8).as_slice());
+        return f64::from_be_bytes(buff);
+    }
+}
+
+impl FetchAMFVal for bool {
+    type Primitive = bool;
+    fn fetch_amf_val(data: &mut Vec<u8>) -> Self::Primitive {
+        let mut buff = [0u8; 1];
+        buff.copy_from_slice(data.drain(..1).as_slice());
+        return !(buff[0] == 0)
+    }
+}
+
+impl FetchAMFVal for String {
+    type Primitive = String;
+    fn fetch_amf_val(data: &mut Vec<u8>) -> Self::Primitive {
+        let mut len_buff = [0u8; 2];
+        len_buff.copy_from_slice(data.drain(..2).as_slice());
+        let str_len = u16::from_be_bytes(len_buff) as usize;
+        let str_buff = data.drain(..str_len).collect::<Vec<u8>>();
+        return String::from_utf8(str_buff).unwrap();
+    }
+}