handle unaligned fields > than 1 byte in setters

codegen/rust/src/header.rs

@@ -71,10 +71,12 @@ impl<'a> HeaderGenerator<'a> {
                     // the p4 confused-endian data model.
                     let mut v = b.into_vec();
                     v.reverse();
-                    let mut b = BitVec::<u8, Msb0>::from_vec(v);
-                    if (#end-#offset) < 8 {
-                        b.shift_left(#offset % 8);
+                    if ((#end-#offset) % 8) != 0 {
+                        if let Some(x) = v.iter_mut().last() {
+                            *x <<= (#offset % 8);
+                        }
                     }
+                    let mut b = BitVec::<u8, Msb0>::from_vec(v);
                     b.resize(#end-#offset, false);
                     b
                 }

test/src/lib.rs

@@ -20,6 +20,8 @@ mod mac_rewrite;
 mod range;
 #[cfg(test)]
 mod table_in_egress_and_ingress;
+#[cfg(test)]
+mod vlan;
 
 pub mod data;
 pub mod packet;

test/src/p4/vlan_header.p4

@@ -0,0 +1,43 @@
+header ethernet_h {
+    bit<48> dst;
+    bit<48> src;
+    bit<16> ether_type;
+}
+
+header vlan_h {
+    bit<3> pcp;
+    bit<1> dei;
+    bit<12> vid;
+    bit<16> ether_type;
+}
+
+header sidecar_h {
+    bit<8> sc_code;
+    bit<8> sc_pad;
+    bit<16> sc_ingress;
+    bit<16> sc_egress;
+    bit<16> sc_ether_type;
+    bit<128> sc_payload;
+}
+
+header ipv4_h {
+    bit<4>      version;
+    bit<4>      ihl;
+    bit<8>      diffserv;
+    bit<16>     total_len;
+    bit<16>     identification;
+    bit<3>      flags;
+    bit<13>     frag_offset;
+    bit<8>      ttl;
+    bit<8>      protocol;
+    bit<16>     hdr_checksum;
+    bit<32>     src;
+    bit<32>     dst;
+}
+
+struct headers_t {
+    ethernet_h ethernet;
+    vlan_h vlan;
+    sidecar_h sidecar;
+    ipv4_h ipv4;
+}

test/src/vlan.rs

@@ -0,0 +1,22 @@
+p4_macro::use_p4!("test/src/p4/vlan_header.p4");
+
+#[test]
+fn test_vlan_parse() -> anyhow::Result<()> {
+    let mut data = [0u8; 256];
+    data[0] = 0x0;
+    data[1] = 0x47;
+    let mut pkt = vlan_h::new();
+    pkt.set(&data).unwrap();
+    let vid: u16 = pkt.vid.to_owned().load_le();
+    assert_eq!(vid, 0x47);
+
+    let mut data = [0u8; 256];
+    data[0] = 0x77;
+    data[1] = 0x47;
+    let mut pkt = vlan_h::new();
+    pkt.set(&data).unwrap();
+    let vid: u16 = pkt.vid.to_owned().load_le();
+    assert_eq!(vid, 0x747);
+
+    Ok(())
+}