Tolerate garbage preceding logfmt

Accommodates Rails's default tagged logger.

Nom doesn't support just dropping the garbage[^1], it's accumulated in a
newly allocated vector.

[^1]: rust-bakery/nom#1594

src/parser.rs

@@ -3,9 +3,9 @@ use std::collections::HashMap;
 use nom::{
     branch::alt,
     bytes::complete::{escaped_transform, tag, take_while1},
-    character::complete::{none_of, one_of, space0},
-    combinator::{eof, opt},
-    multi::fold_many1,
+    character::complete::{anychar, none_of, one_of, space0},
+    combinator::{eof, opt, peek},
+    multi::{fold_many1, many_till},
     sequence::{delimited, terminated, tuple},
     IResult,
 };
@@ -49,7 +49,9 @@ fn pairs(input: &str) -> IResult<&str, HashMap<String, Option<String>>> {
 }
 
 pub fn parse(message: &str) -> Option<HashMap<String, Option<String>>> {
-    pairs(message).map(|(_, result)| result).ok()
+    tuple((many_till(anychar, peek(pair)), pairs))(message)
+        .map(|(_rest, (_garbage, result))| result)
+        .ok()
 }
 
 #[cfg(test)]
@@ -98,6 +100,27 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_lograge_lines_with_rails_tagged_prefix() {
+        assert_eq!(
+            Some(HashMap::from([
+                pair("at", Some("info")),
+                pair("method", Some("POST")),
+                pair("path", Some("/foo/bar")),
+                pair("host", Some("example.com")),
+                pair("request_id", Some("f116113c-b8ed-41ea-bbf3-a031313dd936")),
+                pair("fwd", Some("0.0.0.0")),
+                pair("dyno", Some("web.1")),
+                pair("connect", Some("0ms")),
+                pair("service", Some("25ms")),
+                pair("status", Some("204")),
+                pair("bytes", Some("490")),
+                pair("protocol", Some("http")),
+            ])),
+            parse("I, [2022-08-05T15:55:06.335844 #56]  INFO -- : [242dc622-3727-4e5e-ac6e-fcf121a1a532] at=info method=POST path=\"/foo/bar\" host=example.com request_id=f116113c-b8ed-41ea-bbf3-a031313dd936 fwd=\"0.0.0.0\" dyno=web.1 connect=0ms service=25ms status=204 bytes=490 protocol=http")
+        );
+    }
+
     #[test]
     fn test_edge_cases() {
         // leading whitespace is discarded