sdp_types/

writer.rs

// Copyright (C) 2019 Sebastian Dröge <sebastian@centricular.com>
//
// Licensed under the MIT license, see the LICENSE file or <http://opensource.org/licenses/MIT>

use super::*;

fn format_time<W: std::io::Write + ?Sized>(w: &mut W, t: u64) -> Result<(), std::io::Error> {
    if t == 0 {
        write!(w, "{t}")?;
    } else if t % 86_400 == 0 {
        write!(w, "{}d", t / 86_400)?;
    } else if t % 3_600 == 0 {
        write!(w, "{}h", t / 3_600)?;
    } else if t % 60 == 0 {
        write!(w, "{}m", t / 60)?;
    } else {
        write!(w, "{t}")?;
    }

    Ok(())
}

// NUL, CR and LF characters are not allowed inside SDP lines (RFC 8866,
// section 5). The string fields of the data model are arbitrary strings, so
// strip those characters when writing to prevent injecting additional lines
// into the generated session description.
struct FreeText<'a>(&'a str);

impl std::fmt::Display for FreeText<'_> {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        for c in self.0.chars().filter(|c| !matches!(c, '\0' | '\r' | '\n')) {
            std::fmt::Write::write_char(f, c)?;
        }
        Ok(())
    }
}

impl Origin {
    fn write<W: std::io::Write + ?Sized>(&self, w: &mut W) -> Result<(), std::io::Error> {
        writeln!(
            w,
            "o={username} {sess_id} {sess_version} {nettype} {addrtype} {unicast_address}\r",
            username = match self.username {
                Some(ref username) if !username.is_empty() => FreeText(username),
                _ => FreeText("-"),
            },
            sess_id = FreeText(&self.sess_id),
            sess_version = self.sess_version,
            nettype = FreeText(self.nettype.as_str()),
            addrtype = FreeText(self.addrtype.as_str()),
            unicast_address = FreeText(&self.unicast_address),
        )
    }
}

impl Connection {
    fn write<W: std::io::Write + ?Sized>(&self, w: &mut W) -> Result<(), std::io::Error> {
        writeln!(
            w,
            "c={nettype} {addrtype} {connection_address}\r",
            nettype = FreeText(self.nettype.as_str()),
            addrtype = FreeText(self.addrtype.as_str()),
            connection_address = FreeText(&self.connection_address)
        )
    }
}

impl Bandwidth {
    fn write<W: std::io::Write + ?Sized>(&self, w: &mut W) -> Result<(), std::io::Error> {
        writeln!(
            w,
            "b={bwtype}:{bw}\r",
            bwtype = FreeText(&self.bwtype),
            bw = self.bandwidth
        )
    }
}

impl Time {
    fn write<W: std::io::Write + ?Sized>(&self, w: &mut W) -> Result<(), std::io::Error> {
        writeln!(
            w,
            "t={start_time} {stop_time}\r",
            start_time = self.start_time,
            stop_time = self.stop_time,
        )
    }
}

impl Repeat {
    fn write<W: std::io::Write + ?Sized>(&self, w: &mut W) -> Result<(), std::io::Error> {
        write!(w, "r=")?;
        format_time(w, self.repeat_interval)?;
        write!(w, " ")?;
        format_time(w, self.active_duration)?;

        for offset in &self.offsets {
            write!(w, " ")?;
            format_time(w, *offset)?;
        }

        writeln!(w, "\r")
    }
}

impl TimeZone {
    fn write<W: std::io::Write + ?Sized>(
        w: &mut W,
        zones: &[TimeZone],
    ) -> Result<(), std::io::Error> {
        write!(w, "z=")?;

        let mut first = true;
        for zone in zones {
            if !first {
                write!(w, " ")?;
            }

            write!(w, "{} ", zone.adjustment_time)?;
            if zone.offset < 0 {
                write!(w, "-")?;
                // unsigned_abs to avoid overflow for i64::MIN
                format_time(w, zone.offset.unsigned_abs())?;
            } else {
                format_time(w, zone.offset as u64)?;
            }
            first = false;
        }
        writeln!(w, "\r")
    }
}

impl Key {
    fn write<W: std::io::Write + ?Sized>(&self, w: &mut W) -> Result<(), std::io::Error> {
        if let Some(ref encryption_key) = self.encryption_key {
            writeln!(
                w,
                "k={method}:{encryption_key}\r",
                method = FreeText(&self.method),
                encryption_key = FreeText(encryption_key)
            )
        } else {
            writeln!(w, "k={method}\r", method = FreeText(&self.method))
        }
    }
}

impl Attribute {
    fn write<W: std::io::Write + ?Sized>(&self, w: &mut W) -> Result<(), std::io::Error> {
        if let Some(ref value) = self.value {
            writeln!(
                w,
                "a={name}:{value}\r",
                name = FreeText(&self.attribute),
                value = FreeText(value)
            )
        } else {
            writeln!(w, "a={name}\r", name = FreeText(&self.attribute))
        }
    }
}

impl Media {
    fn write<W: std::io::Write + ?Sized>(&self, w: &mut W) -> Result<(), std::io::Error> {
        write!(
            w,
            "m={media} {port}",
            media = FreeText(&self.media),
            port = self.port
        )?;

        if let Some(ref num_ports) = self.num_ports {
            write!(w, "/{num_ports}")?;
        }
        writeln!(w, " {} {}\r", FreeText(&self.proto), FreeText(&self.fmt))?;

        if let Some(ref media_title) = self.media_title {
            writeln!(w, "i={}\r", FreeText(media_title))?;
        }

        for connection in &self.connections {
            connection.write(w)?;
        }

        for bandwidth in &self.bandwidths {
            bandwidth.write(w)?;
        }

        if let Some(ref key) = self.key {
            key.write(w)?;
        }

        for attribute in &self.attributes {
            attribute.write(w)?;
        }

        Ok(())
    }
}

impl Session {
    /// Write the SDP session description to a `std::io::Write`.
    ///
    /// The values are written as-is without further validation, see the
    /// crate-level documentation for details. If the session description has
    /// no time description, a `t=0 0` line is written instead.
    pub fn write<W: std::io::Write + ?Sized>(&self, w: &mut W) -> Result<(), std::io::Error> {
        writeln!(w, "v=0\r")?;
        self.origin.write(w)?;
        writeln!(w, "s={}\r", FreeText(&self.session_name))?;

        if let Some(ref session_description) = self.session_description {
            writeln!(w, "i={}\r", FreeText(session_description))?;
        }

        if let Some(ref uri) = self.uri {
            writeln!(w, "u={}\r", FreeText(uri))?;
        }

        for email in &self.emails {
            writeln!(w, "e={}\r", FreeText(email))?;
        }

        for phone in &self.phones {
            writeln!(w, "p={}\r", FreeText(phone))?;
        }

        if let Some(ref connection) = self.connection {
            connection.write(w)?;
        }

        for bandwidth in &self.bandwidths {
            bandwidth.write(w)?;
        }

        if !self.times.is_empty() {
            for time in &self.times {
                time.write(w)?;

                for repeat in &time.repeats {
                    repeat.write(w)?;
                }
            }
        } else {
            writeln!(w, "t=0 0\r")?;
        }

        if !self.time_zones.is_empty() {
            TimeZone::write(w, &self.time_zones)?;
        }

        if let Some(ref key) = self.key {
            key.write(w)?;
        }

        for attribute in &self.attributes {
            attribute.write(w)?;
        }

        for media in &self.medias {
            media.write(w)?;
        }

        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn write_sdp() {
        let sdp = Session {
            origin: Origin {
                username: Some("jdoe".into()),
                sess_id: "2890844526".into(),
                sess_version: 2890842807,
                nettype: "IN".into(),
                addrtype: "IP4".into(),
                unicast_address: "10.47.16.5".into(),
            },
            session_name: "SDP Seminar".into(),
            session_description: Some("A Seminar on the session description protocol".into()),
            uri: Some("http://www.example.com/seminars/sdp.pdf".into()),
            emails: vec!["j.doe@example.com (Jane Doe)".into()],
            phones: vec!["+1 617 555-6011".into()],
            connection: Some(Connection {
                nettype: "IN".into(),
                addrtype: "IP4".into(),
                connection_address: "224.2.17.12/127".into(),
            }),
            bandwidths: vec![Bandwidth {
                bwtype: "AS".into(),
                bandwidth: 128,
            }],
            times: vec![Time {
                start_time: 2873397496,
                stop_time: 2873404696,
                repeats: vec![Repeat {
                    repeat_interval: 604800,
                    active_duration: 3600,
                    offsets: vec![0, 90000],
                }],
            }],
            time_zones: vec![
                TimeZone {
                    adjustment_time: 2882844526,
                    offset: -3600,
                },
                TimeZone {
                    adjustment_time: 2898848070,
                    offset: 0,
                },
            ],
            key: Some(Key {
                method: "clear".into(),
                encryption_key: Some("1234".into()),
            }),
            attributes: vec![Attribute {
                attribute: "recvonly".into(),
                value: None,
            }],
            medias: vec![
                Media {
                    media: "audio".into(),
                    port: 49170,
                    num_ports: None,
                    proto: "RTP/AVP".into(),
                    fmt: "0".into(),
                    media_title: None,
                    connections: vec![],
                    bandwidths: vec![],
                    key: None,
                    attributes: vec![],
                },
                Media {
                    media: "video".into(),
                    port: 51372,
                    num_ports: Some(2),
                    proto: "RTP/AVP".into(),
                    fmt: "99".into(),
                    media_title: None,
                    connections: vec![],
                    bandwidths: vec![],
                    key: None,
                    attributes: vec![Attribute {
                        attribute: "rtpmap".into(),
                        value: Some("99 h263-1998/90000".into()),
                    }],
                },
            ],
        };

        let mut written = vec![];
        sdp.write(&mut written).unwrap();

        let expected = "v=0\r
o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5\r
s=SDP Seminar\r
i=A Seminar on the session description protocol\r
u=http://www.example.com/seminars/sdp.pdf\r
e=j.doe@example.com (Jane Doe)\r
p=+1 617 555-6011\r
c=IN IP4 224.2.17.12/127\r
b=AS:128\r
t=2873397496 2873404696\r
r=7d 1h 0 25h\r
z=2882844526 -1h 2898848070 0\r
k=clear:1234\r
a=recvonly\r
m=audio 49170 RTP/AVP 0\r
m=video 51372/2 RTP/AVP 99\r
a=rtpmap:99 h263-1998/90000\r
";

        assert_eq!(String::from_utf8_lossy(&written), expected);
    }

    #[test]
    fn write_sdp_strips_line_breaks() {
        let sdp = Session {
            origin: Origin {
                username: Some("user\r\ns=evil".into()),
                sess_id: "123\n456".into(),
                sess_version: 1,
                nettype: "I\r\nN".into(),
                addrtype: "IP\r4".into(),
                unicast_address: "10.0.0.1".into(),
            },
            session_name: "test\r\nm=audio 0 RTP/AVP 0".into(),
            session_description: Some("desc\0x".into()),
            uri: None,
            emails: vec![],
            phones: vec![],
            connection: Some(Connection {
                nettype: "I\r\nN".into(),
                addrtype: "IP\r4".into(),
                connection_address: "224.0.0.1\r\na=evil".into(),
            }),
            bandwidths: vec![Bandwidth {
                bwtype: "AS".into(),
                bandwidth: 128,
            }],
            times: vec![Time {
                start_time: 0,
                stop_time: 0,
                repeats: vec![],
            }],
            time_zones: vec![],
            key: Some(Key {
                method: "clear".into(),
                encryption_key: Some("12\r\n34".into()),
            }),
            attributes: vec![Attribute {
                attribute: "recvonly".into(),
                value: Some("a\r\nb".into()),
            }],
            medias: vec![Media {
                media: "audio".into(),
                port: 49170,
                num_ports: None,
                proto: "RTP/AVP".into(),
                fmt: "0".into(),
                media_title: Some("ti\r\ntle".into()),
                connections: vec![],
                bandwidths: vec![],
                key: None,
                attributes: vec![],
            }],
        };

        let mut written = vec![];
        sdp.write(&mut written).unwrap();

        let expected = "v=0\r
o=users=evil 123456 1 IN IP4 10.0.0.1\r
s=testm=audio 0 RTP/AVP 0\r
i=descx\r
c=IN IP4 224.0.0.1a=evil\r
b=AS:128\r
t=0 0\r
k=clear:1234\r
a=recvonly:ab\r
m=audio 49170 RTP/AVP 0\r
i=title\r
";

        assert_eq!(String::from_utf8_lossy(&written), expected);

        // The output must still parse back into exactly one session with one
        // media, i.e. no lines were injected.
        let parsed = Session::parse(&written).unwrap();
        assert_eq!(parsed.medias.len(), 1);
        assert_eq!(parsed.session_name, "testm=audio 0 RTP/AVP 0");
    }

    #[test]
    fn write_time_zone_min_offset() {
        // Negating i64::MIN overflows, so it must not be written via `-offset`.
        let sdp = Session {
            origin: Origin {
                username: None,
                sess_id: "0".into(),
                sess_version: 0,
                nettype: "IN".into(),
                addrtype: "IP4".into(),
                unicast_address: "0.0.0.0".into(),
            },
            session_name: "-".into(),
            session_description: None,
            uri: None,
            emails: vec![],
            phones: vec![],
            connection: None,
            bandwidths: vec![],
            times: vec![],
            time_zones: vec![TimeZone {
                adjustment_time: 2882844526,
                offset: i64::MIN,
            }],
            key: None,
            attributes: vec![],
            medias: vec![],
        };

        let mut written = vec![];
        sdp.write(&mut written).unwrap();

        let expected = "v=0\r
o=- 0 0 IN IP4 0.0.0.0\r
s=-\r
t=0 0\r
z=2882844526 -9223372036854775808\r
";
        assert_eq!(String::from_utf8_lossy(&written), expected);

        // The written offset must parse back again.
        let parsed = Session::parse(&written[..]).unwrap();
        assert_eq!(parsed.time_zones, sdp.time_zones);
    }
}