Use a visitor pattern instead of FormattedFields (#12)

This changes a lot of the insides of the crate, but the API is mostly
the same. While the visitor pattern is a bit more verbose, it's also
more flexible and allows for more customization in the future.

Author: cmackenzie1

.github/workflows/rust.yml

@@ -2,21 +2,20 @@ name: Rust
 
 on:
   push:
-    branches: [ "main" ]
+    branches: ["main"]
   pull_request:
-    branches: [ "main" ]
+    branches: ["main"]
 
 env:
   CARGO_TERM_COLOR: always
 
 jobs:
   build:
-
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
-    - name: Build
-      run: cargo build --verbose
-    - name: Run tests
-      run: cargo test --verbose
+      - uses: actions/checkout@v3
+      - name: Build
+        run: cargo build --verbose
+      - name: Run tests
+        run: cargo test --verbose

.rustfmt.toml

@@ -0,0 +1,3 @@
+# rustup install nightly
+group_imports = "StdExternalCrate"
+format_code_in_doc_comments = true

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "tracing-ndjson"
-version = "0.1.3"
+version = "0.2.0"
 edition = "2021"
 license = "MIT"
 authors = ["Cole Mackenzie"]

Makefile

@@ -1,5 +1,5 @@
 fmt:
-	@cargo fmt
+	@cargo +nightly fmt || cargo fmt
 
 build:
 	@cargo build
@@ -8,7 +8,7 @@ clean:
 	@cargo clean
 
 test:
-	@cargo test
+	@cargo test -- --nocapture
 
 lint: fmt
 	@cargo clippy --all-targets -- -D warnings

README.md

@@ -4,14 +4,25 @@
 [![Rust](https://github.com/cmackenzie1/tracing-ndjson/actions/workflows/rust.yml/badge.svg)](https://github.com/cmackenzie1/tracing-ndjson/actions/workflows/rust.yml)
 [![docs.rs](https://img.shields.io/docsrs/tracing-ndjson)](https://docs.rs/tracing-ndjson/latest/tracing_ndjson)
 
-
 A simple library for tracing in new-line delimited JSON format. This library is meant to be used with [tracing](https://github.com/tokio-rs/tracing) as an alternative to the `tracing_subscriber::fmt::json` formatter.
 
+The goal of this crate is to provide a flattend JSON event, comprising of fields from the span attributes and event fields, with customizeable field names and timestamp formats.
+
 ## Features
 
 - Configurable field names for `target`, `message`, `level`, and `timestamp`.
-- Configurable timestamp formats such as RFC3339, UNIX timestamp, or any custom chrono format.
-- Captures all span attributes and event fields in the root of the JSON object.
+- Configurable timestamp formats
+  - RFC3339 (`2023-10-08T03:30:52Z`),
+  - RFC339Nanos (`2023-10-08T03:30:52.123456789Z`)
+  - Unix timestamp (`1672535452`)
+  - UnixMills (`1672535452123`)
+- Captures all span attributes and event fields in the root of the JSON object. Collisions will result in overwriting the existing field.
+
+## Limitations
+
+- When flattening span attributes and event fields, the library will overwrite any existing fields with the same name, including the built-in fields such as `target`, `message`, `level`, `timestamp`, `file`, and `line`.
+- Non-determistic ordering of fields in the JSON object. ([JSON objects are unordered](https://www.json.org/json-en.html))
+- Currently only logs to stdout. (PRs welcome!)
 
 ## Usage
 
@@ -20,24 +31,24 @@ Add this to your `Cargo.toml`:
 ```toml
 [dependencies]
 tracing = "0.1"
-tracing-ndjson = "0.1"
+tracing-ndjson = "0.2"
 ```
 
 ```rust
 use tracing_subscriber::prelude::*;
 
 fn main() {
-    tracing_subscriber::registry()
-        .with(tracing_ndjson::builder().layer())
-        .init();
+    let subscriber = tracing_subscriber::registry().with(tracing_ndjson::layer());
+
+    tracing::subscriber::set_global_default(subscriber).unwrap();
 
     tracing::info!(life = 42, "Hello, world!");
-    // {"level":"info","timestamp":"2023-10-10T20:35:26Z","target":"defaults","message":"Hello, world!","life":42}
+    // {"level":"info","target":"default","life":42,"timestamp":"2023-10-20T21:17:49Z","message":"Hello, world!"}
 
     let span = tracing::info_span!("hello", "request.uri" = "https://example.com");
     span.in_scope(|| {
         tracing::info!("Hello, world!");
-        // {"level":"info","timestamp":"2023-10-10T20:35:26Z","target":"defaults","message":"Hello, world!","request.uri":"https://example.com"}
+        // {"message":"Hello, world!","request.uri":"https://example.com","level":"info","target":"default","timestamp":"2023-10-20T21:17:49Z"}
     });
 }
 ```

examples/README.md

@@ -3,17 +3,11 @@
 ## Defaults
 
 ```bash
-cargo run --example defaults
-
-{"level":"info","timestamp":"2023-10-08T03:35:11Z","target":"defaults","message":"Hello, world!","life":42}
-{"level":"info","timestamp":"2023-10-08T03:35:11Z","target":"defaults","message":"Hello, world!","request.uri":"https://example.com"}
+cargo run --example default
 ```
 
 ## Customized
 
 ```bash
 cargo run --example customize
-
-{"severity":"info","ts":1696736208,"target":"customize","message":"Hello, world!","life":42}
-{"severity":"info","ts":1696736208,"target":"customize","message":"Hello, world!","request.uri":"https://example.com"}
 ```

examples/customize.rs

@@ -1,23 +1,25 @@
 use tracing_subscriber::prelude::*;
-
 fn main() {
-    tracing_subscriber::registry()
-        .with(
-            tracing_ndjson::builder()
-                .with_level_name("severity")
-                .with_message_name("msg")
-                .with_timestamp_name("ts")
-                .with_timestamp_format(tracing_ndjson::TimestampFormat::Unix)
-                .layer(),
-        )
-        .init();
+    let subscriber = tracing_subscriber::registry().with(
+        tracing_ndjson::builder()
+            .with_level_name("severity")
+            .with_level_value_casing(tracing_ndjson::Casing::Uppercase)
+            .with_timestamp_name("ts")
+            .with_timestamp_format(tracing_ndjson::TimestampFormat::UnixMillis)
+            .with_message_name("msg")
+            .with_line_numbers(true)
+            .with_file_names(true)
+            .layer(),
+    );
+
+    tracing::subscriber::set_global_default(subscriber).unwrap();
 
     tracing::info!(life = 42, "Hello, world!");
-    // {"level":"info","timestamp":"2023-10-08T03:30:52Z","target":"default","message":"Hello, world!"}
+    // {"life":42,"msg":"Hello, world!","target":"customize","ts":1697836630814,"file":"examples/customize.rs","line":17,"severity":"INFO"}
 
     let span = tracing::info_span!("hello", "request.uri" = "https://example.com");
     span.in_scope(|| {
         tracing::info!("Hello, world!");
-        // {"level":"info","timestamp":"2023-10-08T03:34:33Z","target":"defaults","message":"Hello, world!","request.uri":"https://example.com"}
+        // {"severity":"INFO","target":"customize","file":"examples/customize.rs","msg":"Hello, world!","ts":1697836630814,"line":22,"request.uri":"https://example.com"}
     });
 }

examples/default.rs

@@ -0,0 +1,15 @@
+use tracing_subscriber::prelude::*;
+fn main() {
+    let subscriber = tracing_subscriber::registry().with(tracing_ndjson::layer());
+
+    tracing::subscriber::set_global_default(subscriber).unwrap();
+
+    tracing::info!(life = 42, "Hello, world!");
+    // {"level":"info","target":"default","life":42,"timestamp":"2023-10-20T21:17:49Z","message":"Hello, world!"}
+
+    let span = tracing::info_span!("hello", "request.uri" = "https://example.com");
+    span.in_scope(|| {
+        tracing::info!("Hello, world!");
+        // {"message":"Hello, world!","request.uri":"https://example.com","level":"info","target":"default","timestamp":"2023-10-20T21:17:49Z"}
+    });
+}