Move documentation for MessageReader

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

@@ -6,23 +6,18 @@ 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;
-//  Value indicating that next byte sequence from ue-server reports amount of bytes received by
-//  that server so far. Value itself is arbitrary.
-
+//  Arbitrary value indicating that next byte sequence from ue-server reports amount of bytes
+//  received by that server so far.
 const HEAD_UE_RECEIVED: u8 = 85;
-//  Value indicating that next byte sequence from ue-server contains JSON message.
-//  Value itself is arbitrary.
+//  Arbitrary value indicating that next byte sequence from ue-server contains JSON message.
 const HEAD_UE_MESSAGE: u8 = 42;
 //  Maximum allowed size of JSON message sent from ue-server.
 const MAX_UE_MESSAGE_LENGTH: usize = 25 * 1024 * 1024;
 
-//  We do not expect to receive more that this much messages at once from ue-server
-const EXPECTED_LIMIT_TO_UE_MESSAGES: usize = 100;
-
 custom_error! { pub ReadingStreamError
     InvalidHead{input: u8}          = "Invalid byte used as a HEAD: {input}",
     MessageTooLong{length: usize}   = "Message to receive is too long: {length}",
@@ -37,21 +32,10 @@ enum ReadingState {
     Payload,
 }
 
-pub struct MessageReader {
-    is_broken: bool,
-    reading_state: ReadingState,
-    read_bytes: usize,
-    buffer: [u8; 4],
-    current_message_length: usize,
-    current_message: Vec<u8>,
-    read_messages: VecDeque<String>,
-    ue_received_bytes: u64,
-}
-
 ///     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]
@@ -59,17 +43,29 @@ pub struct MessageReader {
 /// never recovers from it.
 ///     Use either `push_byte()` or `push()` to input byte stream from ue-server and `pop()` to
 /// retrieve resulting messages.
+pub struct MessageReader {
+    is_broken: bool,
+    reading_state: ReadingState,
+    read_bytes: usize,
+    length_buffer: [u8; 4],
+    current_message_length: usize,
+    current_message: Vec<u8>,
+    read_messages: VecDeque<String>,
+    ue_received_bytes: u64,
+}
+
 impl MessageReader {
     pub fn new() -> MessageReader {
         MessageReader {
             is_broken: false,
             reading_state: ReadingState::Head,
             read_bytes: 0,
-            buffer: [0; 4],
+            length_buffer: [0; 4],
             current_message_length: 0,
             //  Will be recreated with `with_capacity` in `push_byte()`
             current_message: Vec::new(),
-            read_messages: VecDeque::with_capacity(EXPECTED_LIMIT_TO_UE_MESSAGES),
+            //  This value should be more than enough for typical use
+            read_messages: VecDeque::with_capacity(100),
             ue_received_bytes: 0,
         }
     }
@@ -90,19 +86,18 @@ impl MessageReader {
                 }
             }
             ReadingState::ReceivedBytes => {
-                self.buffer[self.read_bytes] = input;
+                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.buffer) as u64;
+                    self.ue_received_bytes += array_of_u8_to_u16(self.length_buffer) as u64;
                     self.change_state(ReadingState::Head);
                 }
             }
             ReadingState::Length => {
-                self.buffer[self.read_bytes] = input;
+                self.length_buffer[self.read_bytes] = input;
                 self.read_bytes += 1;
                 if self.read_bytes >= UE_LENGTH_FIELD_SIZE {
-                    self.current_message_length = array_of_u8_to_u32(self.buffer) as usize;
-                    self.change_state(ReadingState::Payload);
+                    self.current_message_length = array_of_u8_to_u32(self.length_buffer) as usize;
                     if self.current_message_length > MAX_UE_MESSAGE_LENGTH {
                         self.is_broken = true;
                         return Err(ReadingStreamError::MessageTooLong {
@@ -110,6 +105,7 @@ impl MessageReader {
                         });
                     }
                     self.current_message = Vec::with_capacity(self.current_message_length);
+                    self.change_state(ReadingState::Payload);
                 }
             }
             ReadingState::Payload => {
@@ -157,11 +153,15 @@ 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]
@@ -203,21 +203,15 @@ 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(243).unwrap();
-    assert_eq!(reader.ue_received_bytes(), 243);
+    reader.push_byte(0xf3).unwrap();
+    assert_eq!(reader.ue_received_bytes(), 0xf3);
     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
     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(), 1092203255);
+    assert_eq!(reader.ue_received_bytes(), 0xb2_f7);
 }
 
 #[test]
@@ -225,9 +219,7 @@ 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();
@@ -237,11 +229,9 @@ 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);
 }
@@ -253,9 +243,7 @@ fn pushing_many_bytes_at_once() {
         .push(&[
             HEAD_UE_RECEIVED,
             0,
-            0,
-            0,
-            243,
+            0xf3,
             HEAD_UE_MESSAGE,
             0,
             0,
@@ -265,13 +253,11 @@ 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);
 }
@@ -281,9 +267,7 @@ 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)

src/main.rs

@@ -7,8 +7,7 @@ fn main() {
     let args: Vec<String> = env::args().collect();
     let filename = &args[1];
     let config = unreal_config::load_file(Path::new(filename));
-    match config {
-        Ok(config) => print!("{}", config),
-        _ => (),
+    if let Ok(config) = config {
+        print!("{}", config);
     }
 }