style: Move length delimiter encoding to separate module

Leave a alias in `lib.rs` to prevent a breaking change.

prost/src/encoding.rs

@@ -19,6 +19,11 @@ use crate::Message;
 pub mod varint;
 pub use varint::{decode_varint, encode_varint, encoded_len_varint};
 
+pub mod length_delimiter;
+pub use length_delimiter::{
+    decode_length_delimiter, encode_length_delimiter, length_delimiter_len,
+};
+
 /// Additional information passed to every decode/merge function.
 ///
 /// The context should be passed by value and can be freely cloned. When passing

prost/src/encoding/length_delimiter.rs

@@ -0,0 +1,53 @@
+pub use crate::error::{DecodeError, EncodeError, UnknownEnumValue};
+pub use crate::message::Message;
+pub use crate::name::Name;
+
+use bytes::{Buf, BufMut};
+
+use crate::encoding::varint::{decode_varint, encode_varint, encoded_len_varint};
+
+/// Encodes a length delimiter to the buffer.
+///
+/// See [Message.encode_length_delimited] for more info.
+///
+/// An error will be returned if the buffer does not have sufficient capacity to encode the
+/// delimiter.
+pub fn encode_length_delimiter(length: usize, buf: &mut impl BufMut) -> Result<(), EncodeError> {
+    let length = length as u64;
+    let required = encoded_len_varint(length);
+    let remaining = buf.remaining_mut();
+    if required > remaining {
+        return Err(EncodeError::new(required, remaining));
+    }
+    encode_varint(length, buf);
+    Ok(())
+}
+
+/// Returns the encoded length of a length delimiter.
+///
+/// Applications may use this method to ensure sufficient buffer capacity before calling
+/// `encode_length_delimiter`. The returned size will be between 1 and 10, inclusive.
+pub fn length_delimiter_len(length: usize) -> usize {
+    encoded_len_varint(length as u64)
+}
+
+/// Decodes a length delimiter from the buffer.
+///
+/// This method allows the length delimiter to be decoded independently of the message, when the
+/// message is encoded with [Message.encode_length_delimited].
+///
+/// An error may be returned in two cases:
+///
+///  * If the supplied buffer contains fewer than 10 bytes, then an error indicates that more
+///    input is required to decode the full delimiter.
+///  * If the supplied buffer contains more than 10 bytes, then the buffer contains an invalid
+///    delimiter, and typically the buffer should be considered corrupt.
+pub fn decode_length_delimiter(mut buf: impl Buf) -> Result<usize, DecodeError> {
+    let length = decode_varint(&mut buf)?;
+    if length > usize::MAX as u64 {
+        return Err(DecodeError::new(
+            "length delimiter exceeds maximum usize value",
+        ));
+    }
+    Ok(length as usize)
+}

prost/src/lib.rs

@@ -17,65 +17,18 @@ mod types;
 #[doc(hidden)]
 pub mod encoding;
 
+pub use crate::encoding::length_delimiter::{
+    decode_length_delimiter, encode_length_delimiter, length_delimiter_len,
+};
 pub use crate::error::{DecodeError, EncodeError, UnknownEnumValue};
 pub use crate::message::Message;
 pub use crate::name::Name;
 
-use bytes::{Buf, BufMut};
-
-use crate::encoding::varint::{decode_varint, encode_varint, encoded_len_varint};
-
 // See `encoding::DecodeContext` for more info.
 // 100 is the default recursion limit in the C++ implementation.
 #[cfg(not(feature = "no-recursion-limit"))]
 const RECURSION_LIMIT: u32 = 100;
 
-/// Encodes a length delimiter to the buffer.
-///
-/// See [Message.encode_length_delimited] for more info.
-///
-/// An error will be returned if the buffer does not have sufficient capacity to encode the
-/// delimiter.
-pub fn encode_length_delimiter(length: usize, buf: &mut impl BufMut) -> Result<(), EncodeError> {
-    let length = length as u64;
-    let required = encoded_len_varint(length);
-    let remaining = buf.remaining_mut();
-    if required > remaining {
-        return Err(EncodeError::new(required, remaining));
-    }
-    encode_varint(length, buf);
-    Ok(())
-}
-
-/// Returns the encoded length of a length delimiter.
-///
-/// Applications may use this method to ensure sufficient buffer capacity before calling
-/// `encode_length_delimiter`. The returned size will be between 1 and 10, inclusive.
-pub fn length_delimiter_len(length: usize) -> usize {
-    encoded_len_varint(length as u64)
-}
-
-/// Decodes a length delimiter from the buffer.
-///
-/// This method allows the length delimiter to be decoded independently of the message, when the
-/// message is encoded with [Message.encode_length_delimited].
-///
-/// An error may be returned in two cases:
-///
-///  * If the supplied buffer contains fewer than 10 bytes, then an error indicates that more
-///    input is required to decode the full delimiter.
-///  * If the supplied buffer contains more than 10 bytes, then the buffer contains an invalid
-///    delimiter, and typically the buffer should be considered corrupt.
-pub fn decode_length_delimiter(mut buf: impl Buf) -> Result<usize, DecodeError> {
-    let length = decode_varint(&mut buf)?;
-    if length > usize::MAX as u64 {
-        return Err(DecodeError::new(
-            "length delimiter exceeds maximum usize value",
-        ));
-    }
-    Ok(length as usize)
-}
-
 // Re-export #[derive(Message, Enumeration, Oneof)].
 // Based on serde's equivalent re-export [1], but enabled by default.
 //