add a basic example with HTTP headers

valuable/examples/http_headers.rs

@@ -0,0 +1,83 @@
+use valuable::*;
+
+#[derive(Valuable)]
+struct Headers {
+    user_agent: String,
+    host: String,
+    content_type: ContentType,
+    accept_encoding: Vec<String>,
+}
+
+#[derive(Valuable)]
+struct ContentType {
+    mime: String,
+    charset: String,
+}
+
+// Visit the root of the Headers struct. This visitor will find the
+// `accept_encoding` field on `Headers` and extract the contents. All other fields
+// are ignored.
+struct VisitHeaders {
+    /// The extracted `accept-encoding` header values.
+    accept_encoding: Vec<String>,
+}
+
+// Visit the `accept-encoding` `Vec`. This visitor iterates the items in the
+// list and pushes it into its `accept_encoding` vector.
+struct VisitAcceptEncoding<'a> {
+    accept_encoding: &'a mut Vec<String>,
+}
+
+impl Visit for VisitHeaders {
+    fn visit_value(&mut self, value: Value<'_>) {
+        // We expect a `Structable` representing the `Headers` struct.
+        match value {
+            // Visiting the struct will call `visit_named_fields`.
+            Value::Structable(v) => v.visit(self),
+            // Ignore other patterns
+            _ => {}
+        }
+    }
+
+    fn visit_named_fields(&mut self, named_values: &NamedValues<'_>) {
+        // We only care about `accept_encoding`
+        match named_values.get_by_name("accept_encoding") {
+            Some(Value::Listable(accept_encoding)) => {
+                // Create the `VisitAcceptEncoding` instance to visit the items
+                // in `Listable`.
+                let mut visit = VisitAcceptEncoding {
+                    accept_encoding: &mut self.accept_encoding,
+                };
+                accept_encoding.visit(&mut visit);
+            }
+            _ => {}
+        }
+    }
+}
+
+impl Visit for VisitAcceptEncoding<'_> {
+    /// Method called when visiting a `Listable`.
+    fn visit_value(&mut self, value: Value<'_>) {
+        if let Some(accept_encoding) = value.as_str() {
+            self.accept_encoding.push(accept_encoding.to_string())
+        }
+    }
+}
+
+fn main() {
+    let headers = Headers {
+        user_agent: "Mozilla/4.0 (compatible; MSIE5.01; Windows NT)".to_string(),
+        host: "www.example.com".to_string(),
+        content_type: ContentType {
+            mime: "text/xml".to_string(),
+            charset: "utf-8".to_string(),
+        },
+        accept_encoding: vec!["gzip".to_string(), "deflate".to_string()],
+    };
+
+    // Extract the "accept-encoding" headers
+    let mut visit = VisitHeaders { accept_encoding: vec![] };
+    valuable::visit(&headers, &mut visit);
+
+    assert_eq!(&["gzip", "deflate"], &visit.accept_encoding[..]);
+}