Change `UE_RECEIVED_FIELD_SIZE` to 2

ue-server is only supposed to receive up to 4095 bytes at once and is
expected to report after reading them, therefore 4 bytes for the amount
of received bytes is excessive and 2 will suffice.

src/link/mod.rs

@@ -6,7 +6,7 @@ use custom_error::custom_error;
 
 //  Defines how many bytes is used to encode "AMOUNT" field in the response from ue-server about
 //  amount of bytes it received since the last update
-const UE_RECEIVED_FIELD_SIZE: usize = 4;
+const UE_RECEIVED_FIELD_SIZE: usize = 2;
 //  Defines how many bytes is used to encode "LENGTH" field, describing length of
 //  next JSON message from ue-server
 const UE_LENGTH_FIELD_SIZE: usize = 4;
@@ -49,7 +49,7 @@ pub struct MessageReader {
 ///     For converting byte stream that is expected from the ue-server into actual messages.
 /// Expected format is a sequence of either:
 ///     1.  [HEAD_UE_RECEIVED: marker byte | 1 byte]
-///         [AMOUNT: amount of bytes received by ue-server since last update | 4 bytes: u32 BE]
+///         [AMOUNT: amount of bytes received by ue-server since last update | 2 bytes: u16 BE]
 ///     2.  [HEAD_UE_MESSAGE: marker byte | 1 byte]
 ///         [LENGTH: length of the JSON message in utf8 encoding | 4 bytes: u32 BE]
 ///         [PAYLOAD: utf8-encoded string | `LENGTH` bytes]
@@ -91,7 +91,7 @@ impl MessageReader {
                 self.length_buffer[self.read_bytes] = input;
                 self.read_bytes += 1;
                 if self.read_bytes >= UE_RECEIVED_FIELD_SIZE {
-                    self.ue_received_bytes += array_of_u8_to_u32(self.length_buffer) as u64;
+                    self.ue_received_bytes += array_of_u8_to_u16(self.length_buffer) as u64;
                     self.change_state(ReadingState::Head);
                 }
             }
@@ -155,11 +155,15 @@ impl MessageReader {
     }
 }
 
-fn array_of_u8_to_u32(bytes: [u8; 4]) -> u64 {
-    (u64::from(bytes[0]) << 24)
-        + (u64::from(bytes[1]) << 16)
-        + (u64::from(bytes[2]) << 8)
-        + (u64::from(bytes[3]))
+fn array_of_u8_to_u16(bytes: [u8; 4]) -> u16 {
+    (u16::from(bytes[0]) << 8) + u16::from(bytes[1])
+}
+
+fn array_of_u8_to_u32(bytes: [u8; 4]) -> u32 {
+    (u32::from(bytes[0]) << 24)
+        + (u32::from(bytes[1]) << 16)
+        + (u32::from(bytes[2]) << 8)
+        + (u32::from(bytes[3]))
 }
 
 #[test]
@@ -201,21 +205,15 @@ fn received_push_byte() {
     let mut reader = MessageReader::new();
     reader.push_byte(HEAD_UE_RECEIVED).unwrap();
     reader.push_byte(0).unwrap();
-    reader.push_byte(0).unwrap();
-    reader.push_byte(0).unwrap();
     reader.push_byte(0xf3).unwrap();
     assert_eq!(reader.ue_received_bytes(), 0xf3);
     reader.push_byte(HEAD_UE_RECEIVED).unwrap();
-    reader.push_byte(0x41).unwrap();
-    reader.push_byte(0x19).unwrap();
     reader.push_byte(0xb2).unwrap();
     reader.push_byte(0x04).unwrap();
-    assert_eq!(reader.ue_received_bytes(), 0x41_19_b2_f7); // 0xf7 = 0x04 + 0xf3
+    assert_eq!(reader.ue_received_bytes(), 0xb2_f7); // 0xf7 = 0x04 + 0xf3
     reader.push_byte(HEAD_UE_RECEIVED).unwrap();
     reader.push_byte(231).unwrap();
-    reader.push_byte(34).unwrap();
-    reader.push_byte(154).unwrap();
-    assert_eq!(reader.ue_received_bytes(), 0x41_19_b2_f7);
+    assert_eq!(reader.ue_received_bytes(), 0xb2_f7);
 }
 
 #[test]
@@ -223,9 +221,7 @@ fn mixed_push_byte() {
     let mut reader = MessageReader::new();
     reader.push_byte(HEAD_UE_RECEIVED).unwrap();
     reader.push_byte(0).unwrap();
-    reader.push_byte(0).unwrap();
-    reader.push_byte(0).unwrap();
-    reader.push_byte(243).unwrap();
+    reader.push_byte(0xf3).unwrap();
     reader.push_byte(HEAD_UE_MESSAGE).unwrap();
     reader.push_byte(0).unwrap();
     reader.push_byte(0).unwrap();
@@ -235,11 +231,9 @@ fn mixed_push_byte() {
     reader.push_byte(b'o').unwrap();
     reader.push_byte(b'!').unwrap();
     reader.push_byte(HEAD_UE_RECEIVED).unwrap();
-    reader.push_byte(65).unwrap();
-    reader.push_byte(25).unwrap();
-    reader.push_byte(178).unwrap();
-    reader.push_byte(4).unwrap();
-    assert_eq!(reader.ue_received_bytes(), 1092203255);
+    reader.push_byte(0xb2).unwrap();
+    reader.push_byte(0x04).unwrap();
+    assert_eq!(reader.ue_received_bytes(), 0xb2_f7); // 0xf7 = 0x04 + 0xf3
     assert_eq!(reader.pop().unwrap(), "Yo!");
     assert_eq!(reader.pop(), None);
 }
@@ -251,9 +245,7 @@ fn pushing_many_bytes_at_once() {
         .push(&[
             HEAD_UE_RECEIVED,
             0,
-            0,
-            0,
-            243,
+            0xf3,
             HEAD_UE_MESSAGE,
             0,
             0,
@@ -263,13 +255,11 @@ fn pushing_many_bytes_at_once() {
             b'o',
             b'!',
             HEAD_UE_RECEIVED,
-            65,
-            25,
-            178,
-            4,
+            0xb2,
+            0x04,
         ])
         .unwrap();
-    assert_eq!(reader.ue_received_bytes(), 1092203255);
+    assert_eq!(reader.ue_received_bytes(), 0xb2_f7);
     assert_eq!(reader.pop().unwrap(), "Yo!");
     assert_eq!(reader.pop(), None);
 }
@@ -279,9 +269,7 @@ fn generates_error_invalid_head() {
     let mut reader = MessageReader::new();
     reader.push_byte(HEAD_UE_RECEIVED).unwrap();
     reader.push_byte(0).unwrap();
-    reader.push_byte(0).unwrap();
-    reader.push_byte(0).unwrap();
-    reader.push_byte(243).unwrap();
+    reader.push_byte(0xf3).unwrap();
     assert!(!reader.is_broken());
     reader
         .push_byte(25)