Allow for no-std build (extracts std feature, on by default)

CHANGELOG.md

@@ -1,6 +1,7 @@
 # ChangeLog
 
 ## Unreleased
+- Extracted RtpPacketBuilder::build and Errors to 'std' feature, which is on by default. 
 
 ### Changed
  - Switched to Rust 2021 edition.

Cargo.toml

@@ -20,3 +20,7 @@ criterion = "0.5"
 [[bench]]
 name = "bench"
 harness = false
+
+[features]
+default = ["std"]
+std = []

src/builder.rs

@@ -314,6 +314,7 @@ impl<'a> RtpPacketBuilder<'a> {
 
     /// Build the RTP packet.
     /// On success, it returns a buffer containing the target packet.
+    #[cfg(feature = "std")]
     pub fn build(&self) -> Result<Vec<u8>, RtpPacketBuildError> {
         self.validate_content()?;
 
@@ -324,7 +325,7 @@ impl<'a> RtpPacketBuilder<'a> {
 
         Ok(buffer)
     }
-
+    
     fn validate_content(&self) -> Result<(), RtpPacketBuildError> {
         if (self.payload_type & (!0x7F)) != 0 {
             return Err(RtpPacketBuildError::PayloadTypeInvalid);
@@ -344,10 +345,12 @@ impl<'a> RtpPacketBuilder<'a> {
     }
 }
 
+// When Rust 1.81 drops with Error in core, this feature gate can be removed.
+#[cfg(feature = "std")]
 impl std::error::Error for RtpPacketBuildError {}
 
-impl std::fmt::Display for RtpPacketBuildError {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Display for RtpPacketBuildError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         write!(
             f,
             "{}",
@@ -367,54 +370,57 @@ mod test {
 
     #[test]
     fn test_padded() {
-        let payload = vec![1u8];
-        let packet = RtpPacketBuilder::new()
+        let payload = [1u8];
+        let mut buffer = [0u8; 16];
+        RtpPacketBuilder::new()
             .payload_type(1)
             .payload(&payload)
             .padded(Pad::round_to(4))
-            .build()
+            .build_into(&mut buffer)
             .unwrap();
 
-        assert_eq!(packet.len() & 0x03, 0);
-        assert!(crate::reader::RtpReader::new(&packet)
+        assert_eq!(buffer[0] & 0x03, 0);
+        assert!(crate::reader::RtpReader::new(&buffer)
             .unwrap()
             .padding()
             .is_some());
     }
 
     #[test]
     fn test_padding_not_needed() {
-        let payload = vec![1u8; 4];
-        let packet = RtpPacketBuilder::new()
+        let mut buffer = [0u8; 16];
+        let payload = [1u8; 4];
+        let packet_len = RtpPacketBuilder::new()
             .payload_type(1)
             .payload(&payload)
             .padded(Pad::round_to(4))
-            .build()
+            .build_into(&mut buffer)
             .unwrap();
 
         // assert the length is not increased beyond the 12 bytes of header + the payload
-        assert_eq!(packet.len(), 12 + payload.len());
-        assert!(crate::reader::RtpReader::new(&packet)
+        assert_eq!(packet_len, 12 + payload.len());
+        assert!(crate::reader::RtpReader::new(&buffer[..packet_len])
             .unwrap()
             .padding()
             .is_none());
     }
 
     #[test]
     fn test_not_padded() {
-        let payload = vec![1u8];
-        let packet = RtpPacketBuilder::new()
+        let mut buffer = [0u8; 16];
+        let payload = [1u8];
+        let packet_len = RtpPacketBuilder::new()
             .payload_type(1)
             .payload(&payload)
-            .build()
+            .build_into(&mut buffer)
             .unwrap();
 
-        assert_eq!(packet.len() & 0x03, 1);
+        assert_eq!(packet_len & 0x03, 1);
     }
 
     #[test]
     fn test_would_run() {
-        let extension = vec![1u8, 2, 3, 4];
+        let extension = [1u8, 2, 3, 4];
         let builder = RtpPacketBuilder::new()
             .payload_type(12)
             .extension(1, &extension);

src/lib.rs

@@ -19,7 +19,8 @@
 //! ```
 //! use rtp_rs::*;
 //!
-//! let payload = vec![0u8, 2, 5, 4, 6];
+//! let mut buffer = [0u8; 1024];
+//! let payload = [0u8, 2, 5, 4, 6];
 //! let result = RtpPacketBuilder::new()
 //!     .payload_type(111)
 //!     .ssrc(1337)
@@ -28,15 +29,39 @@
 //!     .padded(Pad::round_to(4))
 //!     .marked(true)
 //!     .payload(&payload)
-//!     .build();
-//! if let Ok(packet) = result {
-//!     println!("Packet: {:?}", packet);
+//!     .build_into(&mut buffer);
+//!
+//! if let Ok(len) = result {
+//!     println!("Packet: {:?}", &buffer[..len]);
 //! }
 //! ```
+#![cfg_attr(feature = "std", doc = r#"
+
+Building a packet with std enabled lets you skip the buffer;
+
+```
+use rtp_rs::*;
+
+let payload = vec![0u8, 2, 5, 4, 6];
+let result = RtpPacketBuilder::new()
+    .payload_type(111)
+    .ssrc(1337)
+    .sequence(Seq::from(1234))
+    .timestamp(666657)
+    .padded(Pad::round_to(4))
+    .marked(true)
+    .payload(&payload)
+    .build();
+if let Ok(packet) = result {
+    println!("Packet: {:?}", packet);
+}
+```"#)]
 
 #![forbid(unsafe_code)]
 #![deny(rust_2018_idioms, future_incompatible, missing_docs)]
 
+#![cfg_attr(not(feature = "std"), no_std)]
+
 /// 16 bit RTP sequence number value, as obtained from the `sequence_number()` method of RtpReader.
 ///
 /// ```
@@ -104,32 +129,32 @@ impl From<u16> for Seq {
 /// `1` (rather than `-65535`).
 ///
 /// This is for symmetry with addition, where for example `Seq(0xffff) + 1` gives `Seq(0x0000)`
-impl std::ops::Sub for Seq {
+impl core::ops::Sub for Seq {
     type Output = i32;
 
     fn sub(self, rhs: Seq) -> Self::Output {
         let delta = i32::from(self.0) - i32::from(rhs.0);
-        if delta < std::i16::MIN as i32 {
-            std::u16::MAX as i32 + 1 + delta
-        } else if delta > std::i16::MAX as i32 {
-            delta - std::u16::MAX as i32 - 1
+        if delta < core::i16::MIN as i32 {
+            core::u16::MAX as i32 + 1 + delta
+        } else if delta > core::i16::MAX as i32 {
+            delta - core::u16::MAX as i32 - 1
         } else {
             delta
         }
     }
 }
 impl PartialOrd for Seq {
-    fn partial_cmp(&self, other: &Seq) -> Option<std::cmp::Ordering> {
+    fn partial_cmp(&self, other: &Seq) -> Option<core::cmp::Ordering> {
         Some(self.cmp(other))
     }
 }
 impl Ord for Seq {
-    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+    fn cmp(&self, other: &Self) -> core::cmp::Ordering {
         (*self - *other).cmp(&0)
     }
 }
 
-impl std::ops::Add<u16> for Seq {
+impl core::ops::Add<u16> for Seq {
     type Output = Seq;
 
     fn add(self, rhs: u16) -> Self::Output {
@@ -142,7 +167,7 @@ pub trait IntoSeqIterator {
     /// Produce an `Iterator` over sequence number values
     fn seq_iter(self) -> SeqIter;
 }
-impl IntoSeqIterator for std::ops::Range<Seq> {
+impl IntoSeqIterator for core::ops::Range<Seq> {
     fn seq_iter(self) -> SeqIter {
         SeqIter(self.start, self.end)
     }

src/reader.rs

@@ -1,5 +1,5 @@
 use crate::{RtpPacketBuilder, Seq};
-use std::fmt;
+use core::fmt;
 
 /// Wrapper around a byte-slice of RTP data, providing accessor methods for the RTP header fields.
 pub struct RtpReader<'a> {
@@ -281,10 +281,13 @@ impl<'a> fmt::Debug for RtpReader<'a> {
     }
 }
 
+// When Rust 1.81 drops with Error in core, this feature gate can be removed.
+#[cfg(feature = "std")]
 impl std::error::Error for RtpReaderError {}
 
-impl std::fmt::Display for RtpReaderError {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Display for RtpReaderError {
+    #[cfg(feature = "std")]
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         write!(
             f,
             "{}",
@@ -301,6 +304,20 @@ impl std::fmt::Display for RtpReaderError {
             }
         )
     }
+
+    #[cfg(not(feature = "std"))]
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(
+            f,
+            "{}",
+            match self {
+                RtpReaderError::BufferTooShort(_) => "buffer too short",
+                RtpReaderError::UnsupportedVersion(_) => "unsupported version",
+                RtpReaderError::HeadersTruncated  { header_len: _, buffer_len: _ } => "headers truncated",
+                RtpReaderError::PaddingLengthInvalid(_) => "padding length invalid",
+            }
+        )
+    }
 }
 
 #[cfg(test)]
@@ -368,7 +385,7 @@ mod tests {
         assert_eq!(1_692_665_255, reader.timestamp());
         assert_eq!(0xa242_af01, reader.ssrc());
         assert_eq!(379, reader.payload().len());
-        format!("{:?}", reader);
+        format_args!("{:?}", reader);
     }
 
     #[test]
@@ -395,30 +412,33 @@ mod tests {
     #[test]
     fn builder_juggle() {
         let reader = RtpReader::new(&TEST_RTP_PACKET).unwrap();
-        let buffer = reader.create_builder().build().unwrap();
+        let mut buffer = [0u8; 1024];
+        let buf_len = reader.create_builder().build_into(&mut buffer).unwrap();
 
-        assert_eq!(buffer.as_slice(), &TEST_RTP_PACKET[..]);
+        assert_eq!(&buffer[..buf_len], &TEST_RTP_PACKET[..]);
     }
 
     #[test]
     fn builder_juggle_extension() {
         let reader = RtpReader::new(&TEST_RTP_PACKET_WITH_EXTENSION).unwrap();
-        let buffer = reader.create_builder().build().unwrap();
-        assert_eq!(buffer.as_slice(), &TEST_RTP_PACKET_WITH_EXTENSION[..]);
+        let mut buffer = [0u8; 1024];
+        let buf_len = reader.create_builder().build_into(&mut buffer).unwrap();
+        assert_eq!(&buffer[..buf_len], &TEST_RTP_PACKET_WITH_EXTENSION[..]);
     }
 
     #[test]
     fn builder_juggle_clear_payload() {
-        let new_payload = vec![];
+        let new_payload = [0u8; 0];
         let reader = RtpReader::new(&TEST_RTP_PACKET_WITH_EXTENSION).unwrap();
-        let buffer = reader
+        let mut buffer = [0u8; 1024];
+        let buf_len = reader
             .create_builder()
             .payload(&new_payload)
-            .build()
+            .build_into(&mut buffer)
             .unwrap();
 
         let expected = &TEST_RTP_PACKET_WITH_EXTENSION[0..(3 + 4) * 4];
-        assert_eq!(buffer.as_slice(), expected);
+        assert_eq!(&buffer[..buf_len], expected);
     }
 
     #[test]