refactor(content-type): rewrite parser to use lexmatch and handle quoted parameters

The previous implementation used manual string splitting and trimming, which was error-prone for quoted parameter values containing special characters like semicolons. The new implementation uses lexmatch for more robust tokenization and properly handles quoted values, allowing semicolons within quoted strings.

Add test cases to verify quoted parameter parsing and invalid media type handling.

Author: oboard

content_type.mbt

@@ -7,31 +7,53 @@ priv struct ContentType {
 
 ///|
 fn parse_content_type(s : StringView) -> ContentType? {
-  let parts = s.split(";").to_array()
-  if parts.is_empty() {
-    None
-  } else {
-    let main_part_str = parts[0].trim()
-    let media_type_parts = main_part_str.split("/").to_array()
-    if media_type_parts.length() != 2 {
-      None
+  fn dequote(value : StringView) -> StringView {
+    if value is ['"', .. rest, '"'] {
+      rest
     } else {
-      let media_type = media_type_parts[0].trim()
-      let subtype = media_type_parts[1].trim()
-      let params = {}
-      for i in 1..<parts.length() {
-        let param_part = parts[i].trim()
-        let eq_index = param_part.find("=")
-
-        if eq_index is Some(idx) {
-          let key = param_part[0:idx].trim()
-          let value = param_part[idx + 1:].trim()
-          params[key] = value
-        }
+      value
+    }
+  }
+
+  let params = Map::new()
+  let (media_type, subtype, rest) = lexmatch s with longest {
+    (
+      "[ \t]*"
+      ("[^ \t/;=]+" as media_type)
+      "[ \t]*"
+      "/"
+      "[ \t]*"
+      ("[^ \t/;=]+" as subtype)
+      "[ \t]*",
+      rest
+    ) => (media_type, subtype, rest)
+    _ => return None
+  }
+
+  for curr = rest {
+    lexmatch curr with longest {
+      ("[ \t]+", rest) => continue rest
+      (
+        ";"
+        "[ \t]*"
+        ("[^ \t=;]+" as key)
+        "[ \t]*"
+        "="
+        "[ \t]*"
+        ("(\"[^\"]*\"|[^ \t;]*)" as value)
+        "[ \t]*",
+        rest
+      ) => {
+        params.set(key, dequote(value))
+        continue rest
       }
-      Some({ media_type, subtype, params })
+      (";" "[ \t]*", rest) => continue rest
+      "" => break
+      _ => break
     }
   }
+
+  Some({ media_type, subtype, params })
 }
 
 ///|
@@ -44,6 +66,28 @@ test "parse_content_type" {
   )
 }
 
+///|
+test "parse_content_type_with_quoted_params" {
+  inspect(
+    parse_content_type(
+      "multipart/form-data; boundary=\"foo;bar\"; charset = utf-8",
+    ),
+    content=(
+      #|Some({media_type: "multipart", subtype: "form-data", params: {"boundary": "foo;bar", "charset": "utf-8"}})
+    ),
+  )
+}
+
+///|
+test "parse_content_type_invalid" {
+  inspect(
+    parse_content_type("application"),
+    content=(
+      #|None
+    ),
+  )
+}
+
 ///|
 test "parse_form_data" {
   inspect(