docs(examples): add annotations to the get example

examples/get.rs

@@ -1,46 +1,98 @@
-// example to show fetching a URL and saving to a file
-
-use std::path::Path;
+/// This is an example to show fetching a file from a webiste and saving to a file
+///
+/// The example consts of:
+///
+/// - The main program, in `main()` - demonstrates how to setup `kxio` for use in prod
+/// - A test module - demonstrates how to use `kxio` in tests
+/// - sample functions - showing how to use `kxio` the body of your program, and be testable
+///
+/// NOTE: running this program with `cargo run --example get` will create and delete the file
+/// `example-readme.md` in the current directory.
+use std::path::{Path, PathBuf};
 
 #[tokio::main]
 async fn main() -> kxio::Result<()> {
-    let net = kxio::net::new();
-    let fs = kxio::fs::temp()?;
+    // Create a `Net` object for making real network requests.
+    let net: kxio::net::Net = kxio::net::new();
 
+    // Create a `FileSystem` object for accessing files within the current directory.
+    // The object created will return a `PathTraveral` error result if there is an attempt to\
+    // access a file outside of this directory.
+    let fs: kxio::fs::FileSystem = kxio::fs::new(PathBuf::from("./"));
+
+    // The URL we will fetch - the readme for this library.
     let url = "https://git.kemitix.net/kemitix/kxio/raw/branch/main/README.md";
-    let file_path = fs.base().join("README.md");
 
-    download_and_save(url, &file_path, &fs, &net).await?;
+    // Create a PathBuf to a file within the directory that the `fs` object has access to.
+    let file_path = fs.base().join("example-readme.md");
 
-    print_file(&file_path, &fs)?;
+    // Create a generic handle for the file. This doesn't open the file, and always succeeds.
+    let path: kxio::fs::PathReal<kxio::fs::PathMarker> = fs.path(&file_path);
+
+    // Other options are;
+    // `fs.file(&file_path)` - for a file
+    // `fs.dir(&dir_path)` - for a directory
+
+    // Checks if the path exists (whether a file, directory, etc)
+    if path.exists()? {
+        // extracts the path from the handle
+        let pathbuf = path.as_pathbuf();
+        eprintln!("The file {} already exists. Aborting!", pathbuf.display());
+        return Ok(());
+    }
+
+    // Passes a reference to the `fs` and `net` objects for use by your program.
+    // Your programs should not know whether they are handling a mock or the real thing.
+    // Any file or network access should be made using these handlers to be properly testable.
+    download_and_save_to_file(url, &file_path, &fs, &net).await?;
+    delete_file(&file_path, &fs)?;
 
     Ok(())
 }
 
-async fn download_and_save(
+/// An function that uses a `FileSystem` and a `Net` object to interact with the outside world.
+async fn download_and_save_to_file(
     url: &str,
     file_path: &Path,
+    // The file system abstraction
     fs: &kxio::fs::FileSystem,
+    // The network abstraction
     net: &kxio::net::Net,
 ) -> kxio::Result<()> {
     println!("fetching: {url}");
-    let request = net.client().get(url);
-    let response = net.send(request).await?;
+
+    // Uses the network abstraction to create a perfectly normal `reqwest::ResponseBuilder`.
+    let request: reqwest::RequestBuilder = net.client().get(url);
+
+    // Rather than calling `.build().send()?` on the request, pass it to the `net`
+    // This allows the `net` to either make the network request as normal, or, if we are
+    // under test, to handle the request as the test dictates.
+    // NOTE: if the `.build().send()` is called on the `request` then that WILL result in
+    // a real network request being made, even under test conditions. Only ever use the
+    // `net.send(...)` function to keep your code testable.
+    let response: reqwest::Response = net.send(request).await?;
+
     let body = response.text().await?;
     println!("fetched {} bytes", body.bytes().len());
 
     println!("writing file: {}", file_path.display());
-    let file = fs.file(file_path);
+    // Uses the file system abstraction to create a handle for a file.
+    let file: kxio::fs::PathReal<kxio::fs::FileMarker> = fs.file(file_path);
+    // Writes the body to the file.
     file.write(body)?;
 
     Ok(())
 }
 
-fn print_file(file_path: &Path, fs: &kxio::fs::FileSystem) -> kxio::Result<()> {
+/// An function that uses a `FileSystem` object to interact with the outside world.
+fn delete_file(file_path: &Path, fs: &kxio::fs::FileSystem) -> kxio::Result<()> {
     println!("reading file: {}", file_path.display());
-    let file = fs.file(file_path);
-    let reader = file.reader()?;
-    let contents = reader.as_str();
+
+    // Uses the file system abstraction to create a handle for a file.
+    let file: kxio::fs::PathReal<kxio::fs::FileMarker> = fs.file(file_path);
+    // Creates a `Reader` which loaded the file into memory.
+    let reader: kxio::fs::Reader = file.reader()?;
+    let contents: &str = reader.as_str();
     println!("{contents}");
 
     Ok(())
@@ -48,31 +100,44 @@ fn print_file(file_path: &Path, fs: &kxio::fs::FileSystem) -> kxio::Result<()> {
 
 #[cfg(test)]
 mod tests {
+    use kxio::net::MatchOn;
+
     use super::*;
 
+    // This test demonstrates how to use the `kxio` to test your program.
     #[tokio::test]
     async fn should_save_remote_body() {
         //given
-        let net = kxio::net::mock();
+        // Create a fake/mock network abstraction
+        // When `net` goes out of scope it will check that all the expected network requests (see
+        // `net.on(...)` below) were all made. If there are any that were not made, the test will
+        // be failed. If you want to avoid this, then call `net.reset()` before your test ends. 
+        let net: kxio::net::MockNet = kxio::net::mock();
         let url = "http://localhost:8080";
-        net.on(net.client().get(url).build().expect("request"))
-            .respond(
-                net.response()
+
+        // declare what response should be made for a given request
+        let response: http::Response<&str> = net.response()
                     .body("contents")
-                    .expect("response body")
-                    .into(),
-            )
+                    .expect("response body");
+        let request = net.client().get(url).build().expect("request");
+        net.on(request)
+            // By default, the METHOD and URL must match, equivalent to:
+            //.match_on(vec![MatchOn::Method, MatchOn::Url])
+            .respond(response.into())
             .expect("mock");
 
+        // Create a temporary directory that will be deleted with `fs` goes out of scope 
         let fs = kxio::fs::temp().expect("temp fs");
         let file_path = fs.base().join("foo");
 
         //when
-        download_and_save(url, &file_path, &fs, &net.into())
+        // Pass the file sytsem and network abstractions to the code to be tested
+        download_and_save_to_file(url, &file_path, &fs, &net.into())
             .await
             .expect("system under test");
 
         //then
+        // Open a file and read it
         let file = fs.file(&file_path);
         let reader = file.reader().expect("reader");
         let contents = reader.as_str();