1 files changed, 61 insertions, 0 deletions
diff --git a/server/src/path.rs b/server/src/path.rs
new file mode 100644
index 0000000..17aa263
--- /dev/null
+++ b/server/src/path.rs
@@ -0,0 +1,61 @@
+// Invariants:
+// - 'orig' is a valid path, and in particular, the '/'-split components are non-empty;
+// - 'comps' describes a non-empty prefix of 'orig'.
+#[derive(Debug)]
+pub struct Path<'a> {
+    orig: &'a str,
+    comps: Vec<(usize, &'a str)>,  // (offset, component)
+}
+
+impl<'a> Path<'a> {
+    /// Returns the split path if the path is valid. A valid path has the following requirements:
+    /// * It does not contain unicode control characters;
+    /// * When split on '/', the resulting components are all non-empty and neither start nor end
+    ///   with unicode whitespace characters.
+    pub fn split(s: &str) -> Option<Path> {
+        let mut comps = Vec::new();
+        let mut start = 0;  // of current component
+        for (i, c) in s.char_indices() {
+            match c {
+                '/' if i == start => return None,  // empty component
+                '/' => {
+                    let comp = &s[start..i];
+                    if comp.starts_with(|c2: char| c2.is_whitespace()) ||
+                            comp.ends_with(|c2: char| c2.is_whitespace()) {
+                        return None;
+                    }
+                    comps.push((start, comp));
+                    start = i + 1;
+                },
+                _ if c.is_control() => return None,
+                _ => {},  // include in current component
+            }
+        }
+
+        // check and add the last component
+        if start == s.len() {
+            return None;  // slash at end of input
+        }
+        comps.push((start, &s[start..s.len()]));
+
+        Some(Path { orig: s, comps })
+    }
+
+    pub fn without_last(&self) -> Option<(Path, &str)> {
+        let n = self.comps.len();
+        if n > 1 {
+            Some((Path { orig: self.orig, comps: self.comps[0 .. n - 1].into() }, self.comps[n - 1].1))
+        } else {
+            None
+        }
+    }
+
+    pub fn join(&self) -> &str {
+        if self.comps.len() == 0 {
+            ""
+        } else {
+            let (lastoff, lastcomp) = self.comps[self.comps.len() - 1];
+            &self.orig[0 .. lastoff + lastcomp.len()]
+        }
+    }
+}