export

gpx-rs/engine/src/core/io/mod.rs

@@ -1,3 +1,5 @@
 mod parse;
+mod write;
 
 pub use parse::*;
+pub use write::*;

gpx-rs/engine/src/core/io/parse.rs

@@ -4,6 +4,7 @@ use crate::{
 };
 use chrono::DateTime;
 use quick_xml::Error;
+use quick_xml::escape::resolve_predefined_entity;
 use quick_xml::events::Event;
 use quick_xml::events::attributes::Attributes;
 use quick_xml::reader::Reader;
@@ -50,6 +51,208 @@ fn parse_coordinates(attributes: Attributes<'_>) -> LngLat {
     coordinates
 }
 
+/// Whether the element holds a value, which is its text.
+fn holds_text(element: Option<&GPXElement>) -> bool {
+    matches!(
+        element,
+        Some(
+            GPXElement::Name
+                | GPXElement::Comment
+                | GPXElement::Description
+                | GPXElement::Source
+                | GPXElement::Text
+                | GPXElement::Elevation
+                | GPXElement::Time
+                | GPXElement::Temperature
+                | GPXElement::Heartrate
+                | GPXElement::Cadence
+                | GPXElement::Power
+                | GPXElement::Surface
+                | GPXElement::Highway
+                | GPXElement::SacScale
+                | GPXElement::MtbScale
+                | GPXElement::Symbol
+                | GPXElement::Type
+                | GPXElement::Color
+                | GPXElement::Opacity
+                | GPXElement::Width
+        )
+    )
+}
+
+/// Gives the text `e` of the element at the top of the stack, which is removed, to what holds it.
+fn apply_text(
+    stack: &mut Vec<GPXElement>,
+    gpx: &mut File,
+    categories: &mut TrackpointCategories,
+    e: &str,
+) {
+    match stack.last_mut() {
+        Some(GPXElement::Name) => {
+            stack.pop();
+            match stack.last_mut() {
+                Some(GPXElement::Metadata) => {
+                    gpx.info.name = e.to_owned();
+                }
+                Some(GPXElement::Author(author)) => {
+                    author.name = Some(e.to_owned());
+                }
+                Some(GPXElement::Track(trk)) => {
+                    trk.info.name = Some(e.to_owned());
+                }
+                Some(GPXElement::Waypoint(wpt)) => {
+                    wpt.name = Some(e.to_owned());
+                }
+                _ => (),
+            }
+        }
+        Some(GPXElement::Comment) => {
+            stack.pop();
+            match stack.last_mut() {
+                Some(GPXElement::Track(trk)) => {
+                    trk.info.cmt = Some(e.to_owned());
+                }
+                Some(GPXElement::Waypoint(wpt)) => {
+                    wpt.cmt = Some(e.to_owned());
+                }
+                _ => (),
+            }
+        }
+        Some(GPXElement::Description) => {
+            stack.pop();
+            match stack.last_mut() {
+                Some(GPXElement::Metadata) => {
+                    gpx.info.desc = Some(e.to_owned());
+                }
+                Some(GPXElement::Track(trk)) => {
+                    trk.info.desc = Some(e.to_owned());
+                }
+                Some(GPXElement::Waypoint(wpt)) => {
+                    wpt.desc = Some(e.to_owned());
+                }
+                _ => (),
+            }
+        }
+        Some(GPXElement::Source) => {
+            stack.pop();
+            if let Some(GPXElement::Track(trk)) = stack.last_mut() {
+                trk.info.src = Some(e.to_owned());
+            }
+        }
+        Some(GPXElement::Text) => {
+            stack.pop();
+            if let Some(GPXElement::Link(link)) = stack.last_mut() {
+                link.text = Some(e.to_owned());
+            }
+        }
+        Some(GPXElement::Elevation) => {
+            stack.pop();
+            match stack.last_mut() {
+                Some(GPXElement::Trackpoint(trkpt)) => {
+                    trkpt.ele = e.parse().unwrap_or_default();
+                }
+                Some(GPXElement::Waypoint(wpt)) => {
+                    wpt.ele = e.parse().unwrap_or_default();
+                }
+                _ => (),
+            }
+        }
+        Some(GPXElement::Time) => {
+            stack.pop();
+            if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
+                trkpt.time = DateTime::parse_from_rfc3339(e)
+                    .ok()
+                    .map(|time| time.timestamp_millis());
+            }
+        }
+        Some(GPXElement::Temperature) => {
+            stack.pop();
+            if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
+                trkpt.atemp = e.parse().ok();
+            }
+        }
+        Some(GPXElement::Heartrate) => {
+            stack.pop();
+            if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
+                trkpt.hr = e.parse().ok();
+            }
+        }
+        Some(GPXElement::Cadence) => {
+            stack.pop();
+            if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
+                trkpt.cad = e.parse().ok();
+            }
+        }
+        Some(GPXElement::Power) => {
+            stack.pop();
+            if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
+                trkpt.power = e.parse().ok();
+            }
+        }
+        Some(GPXElement::Surface) => {
+            stack.pop();
+            if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
+                trkpt.surface = categories.surface.code(&e);
+            }
+        }
+        Some(GPXElement::Highway) => {
+            stack.pop();
+            if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
+                trkpt.highway = categories.highway.code(&e);
+            }
+        }
+        Some(GPXElement::SacScale) => {
+            stack.pop();
+            if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
+                trkpt.sac_scale = categories.sac_scale.code(&e);
+            }
+        }
+        Some(GPXElement::MtbScale) => {
+            stack.pop();
+            if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
+                trkpt.mtb_scale = categories.mtb_scale.code(&e);
+            }
+        }
+        Some(GPXElement::Symbol) => {
+            stack.pop();
+            if let Some(GPXElement::Waypoint(wpt)) = stack.last_mut() {
+                wpt.sym = Some(e.to_owned());
+            }
+        }
+        Some(GPXElement::Type) => {
+            stack.pop();
+            match stack.last_mut() {
+                Some(GPXElement::Track(trk)) => {
+                    trk.info.type_ = Some(e.to_owned());
+                }
+                Some(GPXElement::Waypoint(wpt)) => {
+                    wpt.type_ = Some(e.to_owned());
+                }
+                _ => (),
+            }
+        }
+        Some(GPXElement::Color) => {
+            stack.pop();
+            if let Some(GPXElement::Track(trk)) = stack.last_mut() {
+                trk.info.color = Some(e.to_owned());
+            }
+        }
+        Some(GPXElement::Opacity) => {
+            stack.pop();
+            if let Some(GPXElement::Track(trk)) = stack.last_mut() {
+                trk.info.opacity = e.parse().ok();
+            }
+        }
+        Some(GPXElement::Width) => {
+            stack.pop();
+            if let Some(GPXElement::Track(trk)) = stack.last_mut() {
+                trk.info.width = e.parse().ok();
+            }
+        }
+        _ => (),
+    }
+}
+
 /// Parses a GPX file. The surface, highway, SAC scale and MTB scale of the trackpoints are stored as codes of
 /// `categories`, which learns the values it does not know yet.
 pub fn parse(data: &[u8], categories: &mut TrackpointCategories) -> Result<File, Error> {
@@ -59,6 +262,8 @@ pub fn parse(data: &[u8], categories: &mut TrackpointCategories) -> Result<File,
     let mut stack: Vec<GPXElement> = vec![];
     let mut trkpt_chunk = TrackpointChunk::default();
     let mut wpt_chunk = WaypointChunk::default();
+    // the text of the element at the top of the stack, up to now
+    let mut text = String::new();
     loop {
         match reader.read_event_into(&mut buf) {
             Ok(Event::Start(e)) => match e.name().as_ref() {
@@ -136,235 +341,101 @@ pub fn parse(data: &[u8], categories: &mut TrackpointCategories) -> Result<File,
                 }
                 _ => (),
             },
-            Ok(Event::End(e)) => match e.name().as_ref() {
-                "gpx" => {
-                    if !wpt_chunk.wpt.is_empty() {
-                        gpx.wpt.push(std::mem::take(&mut wpt_chunk));
+            Ok(Event::End(e)) => {
+                if holds_text(stack.last()) {
+                    let value = std::mem::take(&mut text);
+                    if value.is_empty() {
+                        stack.pop();
+                    } else {
+                        apply_text(&mut stack, &mut gpx, categories, &value);
                     }
                 }
-                "metadata" => {
-                    stack.pop();
-                }
-                "author" => {
-                    if let Some(GPXElement::Author(author)) = stack.pop() {
-                        gpx.info.author = Some(author);
-                    }
-                }
-                "link" => {
-                    if let Some(GPXElement::Link(link)) = stack.pop() {
-                        match stack.last_mut() {
-                            Some(GPXElement::Author(author)) => {
-                                author.link = Some(link);
-                            }
-                            Some(GPXElement::Track(trk)) => {
-                                trk.info.link = Some(link);
-                            }
-                            Some(GPXElement::Waypoint(wpt)) => {
-                                wpt.link = Some(link);
-                            }
-                            _ => (),
-                        }
-                    }
-                }
-                "trk" => {
-                    if let Some(GPXElement::Track(trk)) = stack.pop() {
-                        gpx.trk.push(trk);
-                    }
-                }
-                "trkseg" => {
-                    if let Some(GPXElement::Segment(mut trkseg)) = stack.pop()
-                        && let Some(GPXElement::Track(trk)) = stack.last_mut()
-                    {
-                        // `push` ignores the chunk if it is empty
-                        trkseg.push(std::mem::take(&mut trkpt_chunk));
-                        trkseg.compute_anchors();
-                        trk.trkseg.push(trkseg);
-                    }
-                }
-                "trkpt" => {
-                    if let Some(GPXElement::Trackpoint(trkpt)) = stack.pop()
-                        && let Some(GPXElement::Segment(trkseg)) = stack.last_mut()
-                    {
-                        trkpt_chunk.trkpt.push(trkpt);
-                        if trkpt_chunk.is_full() {
-                            trkseg.push(std::mem::take(&mut trkpt_chunk));
-                        }
-                    }
-                }
-                "wpt" => {
-                    if let Some(GPXElement::Waypoint(wpt)) = stack.pop() {
-                        wpt_chunk.wpt.push(wpt);
-                        if wpt_chunk.is_full() {
+                match e.name().as_ref() {
+                    "gpx" => {
+                        if !wpt_chunk.wpt.is_empty() {
                             gpx.wpt.push(std::mem::take(&mut wpt_chunk));
                         }
                     }
-                }
-                _ => (),
-            },
-            Ok(Event::Text(e)) => match stack.last_mut() {
-                Some(GPXElement::Name) => {
-                    stack.pop();
-                    match stack.last_mut() {
-                        Some(GPXElement::Metadata) => {
-                            gpx.info.name = e.to_string();
+                    "metadata" => {
+                        stack.pop();
+                    }
+                    "author" => {
+                        if let Some(GPXElement::Author(author)) = stack.pop() {
+                            gpx.info.author = Some(author);
                         }
-                        Some(GPXElement::Author(author)) => {
-                            author.name = Some(e.to_string());
+                    }
+                    "link" => {
+                        if let Some(GPXElement::Link(link)) = stack.pop() {
+                            match stack.last_mut() {
+                                Some(GPXElement::Author(author)) => {
+                                    author.link = Some(link);
+                                }
+                                Some(GPXElement::Track(trk)) => {
+                                    trk.info.link = Some(link);
+                                }
+                                Some(GPXElement::Waypoint(wpt)) => {
+                                    wpt.link = Some(link);
+                                }
+                                _ => (),
+                            }
                         }
-                        Some(GPXElement::Track(trk)) => {
-                            trk.info.name = Some(e.to_string());
+                    }
+                    "trk" => {
+                        if let Some(GPXElement::Track(trk)) = stack.pop() {
+                            gpx.trk.push(trk);
                         }
-                        Some(GPXElement::Waypoint(wpt)) => {
-                            wpt.name = Some(e.to_string());
+                    }
+                    "trkseg" => {
+                        if let Some(GPXElement::Segment(mut trkseg)) = stack.pop()
+                            && let Some(GPXElement::Track(trk)) = stack.last_mut()
+                        {
+                            // `push` ignores the chunk if it is empty
+                            trkseg.push(std::mem::take(&mut trkpt_chunk));
+                            trkseg.compute_anchors();
+                            trk.trkseg.push(trkseg);
                         }
-                        _ => (),
                     }
-                }
-                Some(GPXElement::Comment) => {
-                    stack.pop();
-                    match stack.last_mut() {
-                        Some(GPXElement::Track(trk)) => {
-                            trk.info.cmt = Some(e.to_string());
+                    "trkpt" => {
+                        if let Some(GPXElement::Trackpoint(trkpt)) = stack.pop()
+                            && let Some(GPXElement::Segment(trkseg)) = stack.last_mut()
+                        {
+                            trkpt_chunk.trkpt.push(trkpt);
+                            if trkpt_chunk.is_full() {
+                                trkseg.push(std::mem::take(&mut trkpt_chunk));
+                            }
                         }
-                        Some(GPXElement::Waypoint(wpt)) => {
-                            wpt.cmt = Some(e.to_string());
+                    }
+                    "wpt" => {
+                        if let Some(GPXElement::Waypoint(wpt)) = stack.pop() {
+                            wpt_chunk.wpt.push(wpt);
+                            if wpt_chunk.is_full() {
+                                gpx.wpt.push(std::mem::take(&mut wpt_chunk));
+                            }
                         }
-                        _ => (),
+                    }
+                    _ => (),
+                }
+            }
+            // The text of an element comes in pieces: the entities (`&amp;`) are events of their own
+            Ok(Event::Text(e)) => {
+                if holds_text(stack.last()) {
+                    text.push_str(&e);
+                }
+            }
+            Ok(Event::CData(e)) => {
+                if holds_text(stack.last()) {
+                    text.push_str(&e);
+                }
+            }
+            Ok(Event::GeneralRef(e)) => {
+                if holds_text(stack.last()) {
+                    if let Some(c) = e.resolve_char_ref()? {
+                        text.push(c);
+                    } else if let Some(entity) = resolve_predefined_entity(&e) {
+                        text.push_str(entity);
                     }
                 }
-                Some(GPXElement::Description) => {
-                    stack.pop();
-                    match stack.last_mut() {
-                        Some(GPXElement::Metadata) => {
-                            gpx.info.desc = Some(e.to_string());
-                        }
-                        Some(GPXElement::Track(trk)) => {
-                            trk.info.desc = Some(e.to_string());
-                        }
-                        Some(GPXElement::Waypoint(wpt)) => {
-                            wpt.desc = Some(e.to_string());
-                        }
-                        _ => (),
-                    }
-                }
-                Some(GPXElement::Source) => {
-                    stack.pop();
-                    if let Some(GPXElement::Track(trk)) = stack.last_mut() {
-                        trk.info.src = Some(e.to_string());
-                    }
-                }
-                Some(GPXElement::Text) => {
-                    stack.pop();
-                    if let Some(GPXElement::Link(link)) = stack.last_mut() {
-                        link.text = Some(e.to_string());
-                    }
-                }
-                Some(GPXElement::Elevation) => {
-                    stack.pop();
-                    match stack.last_mut() {
-                        Some(GPXElement::Trackpoint(trkpt)) => {
-                            trkpt.ele = e.parse().unwrap_or_default();
-                        }
-                        Some(GPXElement::Waypoint(wpt)) => {
-                            wpt.ele = e.parse().unwrap_or_default();
-                        }
-                        _ => (),
-                    }
-                }
-                Some(GPXElement::Time) => {
-                    stack.pop();
-                    if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
-                        trkpt.time = DateTime::parse_from_rfc3339(e.as_ref())
-                            .ok()
-                            .map(|time| time.timestamp_millis());
-                    }
-                }
-                Some(GPXElement::Temperature) => {
-                    stack.pop();
-                    if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
-                        trkpt.atemp = e.parse().ok();
-                    }
-                }
-                Some(GPXElement::Heartrate) => {
-                    stack.pop();
-                    if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
-                        trkpt.hr = e.parse().ok();
-                    }
-                }
-                Some(GPXElement::Cadence) => {
-                    stack.pop();
-                    if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
-                        trkpt.cad = e.parse().ok();
-                    }
-                }
-                Some(GPXElement::Power) => {
-                    stack.pop();
-                    if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
-                        trkpt.power = e.parse().ok();
-                    }
-                }
-                Some(GPXElement::Surface) => {
-                    stack.pop();
-                    if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
-                        trkpt.surface = categories.surface.code(&e);
-                    }
-                }
-                Some(GPXElement::Highway) => {
-                    stack.pop();
-                    if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
-                        trkpt.highway = categories.highway.code(&e);
-                    }
-                }
-                Some(GPXElement::SacScale) => {
-                    stack.pop();
-                    if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
-                        trkpt.sac_scale = categories.sac_scale.code(&e);
-                    }
-                }
-                Some(GPXElement::MtbScale) => {
-                    stack.pop();
-                    if let Some(GPXElement::Trackpoint(trkpt)) = stack.last_mut() {
-                        trkpt.mtb_scale = categories.mtb_scale.code(&e);
-                    }
-                }
-                Some(GPXElement::Symbol) => {
-                    stack.pop();
-                    if let Some(GPXElement::Waypoint(wpt)) = stack.last_mut() {
-                        wpt.sym = Some(e.to_string());
-                    }
-                }
-                Some(GPXElement::Type) => {
-                    stack.pop();
-                    match stack.last_mut() {
-                        Some(GPXElement::Track(trk)) => {
-                            trk.info.type_ = Some(e.to_string());
-                        }
-                        Some(GPXElement::Waypoint(wpt)) => {
-                            wpt.type_ = Some(e.to_string());
-                        }
-                        _ => (),
-                    }
-                }
-                Some(GPXElement::Color) => {
-                    stack.pop();
-                    if let Some(GPXElement::Track(trk)) = stack.last_mut() {
-                        trk.info.color = Some(e.to_string());
-                    }
-                }
-                Some(GPXElement::Opacity) => {
-                    stack.pop();
-                    if let Some(GPXElement::Track(trk)) = stack.last_mut() {
-                        trk.info.opacity = e.parse().ok();
-                    }
-                }
-                Some(GPXElement::Width) => {
-                    stack.pop();
-                    if let Some(GPXElement::Track(trk)) = stack.last_mut() {
-                        trk.info.width = e.parse().ok();
-                    }
-                }
-                _ => (),
-            },
+            }
             Ok(Event::Eof) => break,
             Err(e) => return Err(e),
             _ => (),
@@ -386,6 +457,26 @@ mod tests {
         .unwrap()
     }
 
+    #[test]
+    fn test_parse_entities_and_cdata_in_text() {
+        let data = r#"<gpx><metadata><name>Tom &amp; Jerry &lt;3 &#233;&#x41; &quot;x&quot; &apos;y&apos;</name>
+            <desc><![CDATA[a <b> & c]]> and &gt; more</desc></metadata>
+            <wpt lat="1" lon="2"><name></name><desc/><ele>3</ele><cmt>&amp;</cmt></wpt>
+            <trk><name>t &amp; u</name><trkseg><trkpt lat="1" lon="2"><ele>4</ele></trkpt></trkseg></trk>
+            </gpx>"#;
+        let gpx = parse(data.as_bytes(), &mut Default::default()).unwrap();
+        assert_eq!(gpx.info.name, "Tom & Jerry <3 éA \"x\" 'y'");
+        assert_eq!(gpx.info.desc.as_deref(), Some("a <b> & c and > more"));
+        let wpt = gpx.wpt.iter().next().unwrap();
+        // empty elements leave the value unknown, and do not get in the way of the next ones
+        assert_eq!(wpt.name, None);
+        assert_eq!(wpt.desc, None);
+        assert_eq!(wpt.ele, 3.0);
+        assert_eq!(wpt.cmt.as_deref(), Some("&"));
+        assert_eq!(gpx.trk[0].info.name.as_deref(), Some("t & u"));
+        assert_eq!(gpx.trk[0].trkseg[0][0].ele, 4.0);
+    }
+
     #[test]
     fn test_parse_self_closing_points() {
         let gpx = parse_data("self_closing_points");

gpx-rs/engine/src/core/io/write.rs

@@ -0,0 +1,490 @@
+use std::io;
+
+use chrono::DateTime;
+use quick_xml::Writer;
+use quick_xml::events::{BytesDecl, BytesText, Event};
+
+use crate::{File, Link, Track, Trackpoint, TrackpointCategories, Waypoint};
+
+/// What the written file contains: the data of the trackpoints that are `false` are left out.
+/// The same type tells which data a file has, see [`File::exportable_data`].
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct ExportOptions {
+    pub time: bool,
+    pub hr: bool,
+    pub cad: bool,
+    pub atemp: bool,
+    pub power: bool,
+    /// The OpenStreetMap data: surface, highway, SAC scale and MTB scale.
+    pub osm: bool,
+}
+
+impl ExportOptions {
+    pub const ALL: Self = Self::of(true);
+    pub const NONE: Self = Self::of(false);
+
+    const fn of(value: bool) -> Self {
+        Self {
+            time: value,
+            hr: value,
+            cad: value,
+            atemp: value,
+            power: value,
+            osm: value,
+        }
+    }
+
+    /// The options that are on in `self` or in `other`.
+    pub fn union(self, other: Self) -> Self {
+        Self {
+            time: self.time || other.time,
+            hr: self.hr || other.hr,
+            cad: self.cad || other.cad,
+            atemp: self.atemp || other.atemp,
+            power: self.power || other.power,
+            osm: self.osm || other.osm,
+        }
+    }
+}
+
+impl File {
+    /// The data that the trackpoints of the file have (and waypoints for the time), which the
+    /// options of [`write`] can leave out.
+    pub fn exportable_data(&self) -> ExportOptions {
+        let mut data = ExportOptions::NONE;
+        for point in self
+            .trk
+            .iter()
+            .flat_map(|trk| &trk.trkseg)
+            .flat_map(|seg| seg.iter())
+        {
+            data.time |= point.time.is_some();
+            data.hr |= point.hr.is_some();
+            data.cad |= point.cad.is_some();
+            data.atemp |= point.atemp.is_some();
+            data.power |= point.power.is_some();
+            data.osm |= point.surface.is_some()
+                || point.highway.is_some()
+                || point.sac_scale.is_some()
+                || point.mtb_scale.is_some();
+            if data == ExportOptions::ALL {
+                break;
+            }
+        }
+        data
+    }
+}
+
+const SCHEMA_LOCATION: &str = "http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd http://www.garmin.com/xmlschemas/GpxExtensions/v3 http://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd http://www.garmin.com/xmlschemas/TrackPointExtension/v1 http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd http://www.garmin.com/xmlschemas/PowerExtension/v1 http://www.garmin.com/xmlschemas/PowerExtensionv1.xsd http://www.topografix.com/GPX/gpx_style/0/2 http://www.topografix.com/GPX/gpx_style/0/2/gpx_style.xsd";
+
+type XmlWriter = Writer<Vec<u8>>;
+
+/// Writes a file as GPX 1.1, in UTF-8. The surface, highway, SAC scale and MTB scale of the trackpoints are
+/// the names of their codes in `categories`.
+pub fn write(file: &File, categories: &TrackpointCategories, options: ExportOptions) -> Vec<u8> {
+    let mut writer = Writer::new_with_indent(Vec::new(), b' ', 4);
+    // writing to memory does not fail
+    write_file(&mut writer, file, categories, options).expect("writing to memory");
+    writer.into_inner()
+}
+
+fn write_file(
+    w: &mut XmlWriter,
+    file: &File,
+    categories: &TrackpointCategories,
+    options: ExportOptions,
+) -> io::Result<()> {
+    w.write_event(Event::Decl(BytesDecl::new("1.0", Some("UTF-8"), None)))?;
+    w.create_element("gpx")
+        .with_attributes([
+            ("creator", "https://gpx.studio"),
+            ("version", "1.1"),
+            ("xmlns", "http://www.topografix.com/GPX/1/1"),
+            ("xmlns:xsi", "http://www.w3.org/2001/XMLSchema-instance"),
+            ("xsi:schemaLocation", SCHEMA_LOCATION),
+            (
+                "xmlns:gpxtpx",
+                "http://www.garmin.com/xmlschemas/TrackPointExtension/v1",
+            ),
+            (
+                "xmlns:gpxx",
+                "http://www.garmin.com/xmlschemas/GpxExtensions/v3",
+            ),
+            (
+                "xmlns:gpxpx",
+                "http://www.garmin.com/xmlschemas/PowerExtension/v1",
+            ),
+            (
+                "xmlns:gpx_style",
+                "http://www.topografix.com/GPX/gpx_style/0/2",
+            ),
+        ])
+        .write_inner_content(|w| {
+            write_metadata(w, file, options)?;
+            for wpt in file.wpt.iter() {
+                write_waypoint(w, wpt, options)?;
+            }
+            for trk in &file.trk {
+                // a single unnamed track is named like the file
+                let name = match (&trk.info.name, file.trk.len()) {
+                    (Some(name), _) if !name.is_empty() => Some(name.as_str()),
+                    (_, 1) => Some(file.info.name.as_str()),
+                    _ => None,
+                };
+                write_track(w, trk, name, categories, options)?;
+            }
+            Ok(())
+        })?;
+    Ok(())
+}
+
+fn text(w: &mut XmlWriter, name: &str, value: &str) -> io::Result<()> {
+    if !value.is_empty() {
+        w.create_element(name)
+            .write_text_content(BytesText::new(value))?;
+    }
+    Ok(())
+}
+
+fn optional_text(w: &mut XmlWriter, name: &str, value: &Option<String>) -> io::Result<()> {
+    text(w, name, value.as_deref().unwrap_or_default())
+}
+
+fn number(w: &mut XmlWriter, name: &str, value: impl std::fmt::Display) -> io::Result<()> {
+    text(w, name, &value.to_string())
+}
+
+fn time(w: &mut XmlWriter, millis: Option<i64>) -> io::Result<()> {
+    if let Some(time) = millis.and_then(DateTime::from_timestamp_millis) {
+        text(
+            w,
+            "time",
+            &time.format("%Y-%m-%dT%H:%M:%S%.3fZ").to_string(),
+        )?;
+    }
+    Ok(())
+}
+
+fn link(w: &mut XmlWriter, link: &Option<Link>) -> io::Result<()> {
+    if let Some(link) = link.as_ref().filter(|link| !link.href.is_empty()) {
+        w.create_element("link")
+            .with_attribute(("href", link.href.as_str()))
+            .write_inner_content(|w| optional_text(w, "text", &link.text))?;
+    }
+    Ok(())
+}
+
+fn write_metadata(w: &mut XmlWriter, file: &File, options: ExportOptions) -> io::Result<()> {
+    let info = &file.info;
+    let time = options.time.then_some(info.time).flatten();
+    if info.name.is_empty()
+        && info.desc.is_none()
+        && info.author.is_none()
+        && info.link.is_none()
+        && time.is_none()
+    {
+        return Ok(());
+    }
+    w.create_element("metadata").write_inner_content(|w| {
+        text(w, "name", &info.name)?;
+        optional_text(w, "desc", &info.desc)?;
+        if let Some(author) = &info.author {
+            w.create_element("author").write_inner_content(|w| {
+                optional_text(w, "name", &author.name)?;
+                if let Some((id, domain)) = author.email.as_deref().and_then(|e| e.split_once('@'))
+                {
+                    w.create_element("email")
+                        .with_attributes([("id", id), ("domain", domain)])
+                        .write_empty()?;
+                }
+                link(w, &author.link)
+            })?;
+        }
+        link(w, &info.link)?;
+        self::time(w, time)
+    })?;
+    Ok(())
+}
+
+fn write_coordinates<'a>(
+    w: &'a mut XmlWriter,
+    name: &'a str,
+    coordinates: crate::LngLat,
+) -> quick_xml::writer::ElementWriter<'a, Vec<u8>> {
+    w.create_element(name).with_attributes([
+        ("lat", coordinates.lat.to_string().as_str()),
+        ("lon", coordinates.lng.to_string().as_str()),
+    ])
+}
+
+fn write_waypoint(w: &mut XmlWriter, wpt: &Waypoint, options: ExportOptions) -> io::Result<()> {
+    write_coordinates(w, "wpt", wpt.coordinates).write_inner_content(|w| {
+        number(w, "ele", wpt.ele)?;
+        if options.time {
+            time(w, wpt.time)?;
+        }
+        optional_text(w, "name", &wpt.name)?;
+        optional_text(w, "cmt", &wpt.cmt)?;
+        optional_text(w, "desc", &wpt.desc)?;
+        link(w, &wpt.link)?;
+        optional_text(w, "sym", &wpt.sym)?;
+        optional_text(w, "type", &wpt.type_)
+    })?;
+    Ok(())
+}
+
+fn write_track(
+    w: &mut XmlWriter,
+    trk: &Track,
+    name: Option<&str>,
+    categories: &TrackpointCategories,
+    options: ExportOptions,
+) -> io::Result<()> {
+    let info = &trk.info;
+    w.create_element("trk").write_inner_content(|w| {
+        text(w, "name", name.unwrap_or_default())?;
+        optional_text(w, "cmt", &info.cmt)?;
+        optional_text(w, "desc", &info.desc)?;
+        optional_text(w, "src", &info.src)?;
+        link(w, &info.link)?;
+        optional_text(w, "type", &info.type_)?;
+        if info.color.is_some() || info.opacity.is_some() || info.width.is_some() {
+            w.create_element("extensions").write_inner_content(|w| {
+                w.create_element("gpx_style:line")
+                    .write_inner_content(|w| {
+                        optional_text(w, "gpx_style:color", &info.color)?;
+                        if let Some(opacity) = info.opacity {
+                            number(w, "gpx_style:opacity", opacity)?;
+                        }
+                        if let Some(width) = info.width {
+                            number(w, "gpx_style:width", width)?;
+                        }
+                        Ok(())
+                    })?;
+                Ok(())
+            })?;
+        }
+        for segment in &trk.trkseg {
+            w.create_element("trkseg").write_inner_content(|w| {
+                for point in segment.iter() {
+                    write_trackpoint(w, point, categories, options)?;
+                }
+                Ok(())
+            })?;
+        }
+        Ok(())
+    })?;
+    Ok(())
+}
+
+fn write_trackpoint(
+    w: &mut XmlWriter,
+    point: &Trackpoint,
+    categories: &TrackpointCategories,
+    options: ExportOptions,
+) -> io::Result<()> {
+    let atemp = point.atemp.filter(|_| options.atemp);
+    let hr = point.hr.filter(|_| options.hr);
+    let cad = point.cad.filter(|_| options.cad);
+    let power = point.power.filter(|_| options.power);
+    let osm = [
+        ("surface", point.surface, &categories.surface),
+        ("highway", point.highway, &categories.highway),
+        ("sac_scale", point.sac_scale, &categories.sac_scale),
+        ("mtb_scale", point.mtb_scale, &categories.mtb_scale),
+    ]
+    .map(|(name, code, categories)| {
+        let value = code
+            .filter(|_| options.osm)
+            .and_then(|code| categories.name(code));
+        (name, value)
+    });
+    let has_osm = osm.iter().any(|(_, value)| value.is_some());
+    let has_track_point_extension = atemp.is_some() || hr.is_some() || cad.is_some() || has_osm;
+
+    write_coordinates(w, "trkpt", point.coordinates).write_inner_content(|w| {
+        number(w, "ele", point.ele)?;
+        if options.time {
+            time(w, point.time)?;
+        }
+        if !has_track_point_extension && power.is_none() {
+            return Ok(());
+        }
+        w.create_element("extensions").write_inner_content(|w| {
+            if has_track_point_extension {
+                w.create_element("gpxtpx:TrackPointExtension")
+                    .write_inner_content(|w| {
+                        if let Some(atemp) = atemp {
+                            number(w, "gpxtpx:atemp", atemp)?;
+                        }
+                        if let Some(hr) = hr {
+                            number(w, "gpxtpx:hr", hr)?;
+                        }
+                        if let Some(cad) = cad {
+                            number(w, "gpxtpx:cad", cad)?;
+                        }
+                        if has_osm {
+                            w.create_element("gpxtpx:Extensions")
+                                .write_inner_content(|w| {
+                                    for (name, value) in osm {
+                                        text(w, name, value.unwrap_or_default())?;
+                                    }
+                                    Ok(())
+                                })?;
+                        }
+                        Ok(())
+                    })?;
+            }
+            if let Some(power) = power {
+                w.create_element("gpxpx:PowerExtension")
+                    .write_inner_content(|w| number(w, "gpxpx:PowerInWatts", power))?;
+            }
+            Ok(())
+        })?;
+        Ok(())
+    })?;
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::parse;
+
+    use super::*;
+
+    fn read(name: &str) -> (File, TrackpointCategories) {
+        let mut categories = TrackpointCategories::default();
+        let data = std::fs::read(format!("data/{name}.gpx")).unwrap();
+        (parse(&data, &mut categories).unwrap(), categories)
+    }
+
+    fn written_text(
+        file: &File,
+        categories: &TrackpointCategories,
+        options: ExportOptions,
+    ) -> String {
+        String::from_utf8(write(file, categories, options)).unwrap()
+    }
+
+    /// Writes a file and reads it again.
+    fn round_trip(name: &str, options: ExportOptions) -> (File, File, TrackpointCategories) {
+        let (file, mut categories) = read(name);
+        let written = write(&file, &categories, options);
+        let again = parse(&written, &mut categories).unwrap();
+        (file, again, categories)
+    }
+
+    fn points(file: &File) -> Vec<Trackpoint> {
+        file.trk
+            .iter()
+            .flat_map(|trk| &trk.trkseg)
+            .flat_map(|seg| seg.iter().cloned())
+            .collect()
+    }
+
+    fn same_points(a: &[Trackpoint], b: &[Trackpoint]) {
+        assert_eq!(a.len(), b.len());
+        for (a, b) in a.iter().zip(b) {
+            assert_eq!(a.coordinates.lat, b.coordinates.lat);
+            assert_eq!(a.coordinates.lng, b.coordinates.lng);
+            assert_eq!(a.ele, b.ele);
+            assert_eq!(a.time, b.time);
+            assert_eq!(a.atemp, b.atemp);
+            assert_eq!(a.hr, b.hr);
+            assert_eq!(a.cad, b.cad);
+            assert_eq!(a.power, b.power);
+            assert_eq!(a.surface, b.surface);
+            assert_eq!(a.highway, b.highway);
+            assert_eq!(a.sac_scale, b.sac_scale);
+            assert_eq!(a.mtb_scale, b.mtb_scale);
+        }
+    }
+
+    #[test]
+    fn test_files_survive_a_round_trip() {
+        for name in [
+            "simple",
+            "with_time",
+            "with_hr",
+            "with_cad",
+            "with_temp",
+            "with_power_1",
+            "with_power_2",
+            "with_surface",
+            "with_highway",
+            "with_style",
+            "with_waypoint",
+            "with_tracks_and_segments",
+            "self_closing_points",
+        ] {
+            let (file, again, _) = round_trip(name, ExportOptions::ALL);
+            assert_eq!(file.info.name, again.info.name, "{name}");
+            assert_eq!(file.info.desc, again.info.desc, "{name}");
+            assert_eq!(file.info.author, again.info.author, "{name}");
+            assert_eq!(file.trk.len(), again.trk.len(), "{name}");
+            for (a, b) in file.trk.iter().zip(&again.trk) {
+                assert_eq!(a.info, b.info, "{name}");
+                assert_eq!(a.trkseg.len(), b.trkseg.len(), "{name}");
+            }
+            same_points(&points(&file), &points(&again));
+            let waypoints: Vec<_> = file.wpt.iter().collect();
+            let again_waypoints: Vec<_> = again.wpt.iter().collect();
+            assert_eq!(waypoints.len(), again_waypoints.len(), "{name}");
+            for (a, b) in waypoints.iter().zip(&again_waypoints) {
+                assert!(a.same_content(b), "{name}");
+            }
+        }
+    }
+
+    #[test]
+    fn test_options_leave_data_out() {
+        let (file, categories) = read("with_hr");
+        assert!(points(&file).iter().any(|p| p.hr.is_some()));
+        let options = ExportOptions {
+            hr: false,
+            ..ExportOptions::ALL
+        };
+        let written = written_text(&file, &categories, options);
+        assert!(!written.contains("hr>"));
+
+        let (file, categories) = read("with_time");
+        let options = ExportOptions {
+            time: false,
+            ..ExportOptions::ALL
+        };
+        assert!(!written_text(&file, &categories, options).contains("<time>"));
+        assert!(
+            written_text(&file, &categories, ExportOptions::ALL)
+                .contains("<time>2023-12-31T23:00:00.000Z</time>")
+        );
+    }
+
+    #[test]
+    fn test_text_is_escaped_and_the_single_track_gets_the_name_of_the_file() {
+        let (mut file, categories) = read("simple");
+        file.info.name = "a <b> & c".into();
+        file.trk.truncate(1);
+        file.trk[0].info.name = None;
+        let written = write(&file, &categories, ExportOptions::ALL);
+        let text = String::from_utf8(written.clone()).unwrap();
+        assert!(text.contains("a &lt;b&gt; &amp; c"));
+        // the track has the name of the file
+        assert_eq!(text.matches("a &lt;b&gt; &amp; c").count(), 2);
+        // and it is read back as it was
+        let mut categories = categories;
+        let again = parse(&written, &mut categories).unwrap();
+        assert_eq!(again.info.name, "a <b> & c");
+        assert_eq!(again.trk[0].info.name.as_deref(), Some("a <b> & c"));
+    }
+
+    #[test]
+    fn test_exportable_data() {
+        let (file, _) = read("with_time");
+        let data = file.exportable_data();
+        assert!(data.time && !data.hr && !data.osm);
+        let (file, _) = read("with_surface");
+        assert!(file.exportable_data().osm);
+        let (file, _) = read("with_power_2");
+        assert!(file.exportable_data().power);
+    }
+}