From 808a5a44ec58b5f0d0ae7164a71ccce01b7d4a3a Mon Sep 17 00:00:00 2001
From: Matteo Collina <hello@matteocollina.com>
Date: Fri, 9 Oct 2026 17:05:34 +0200
Subject: [PATCH] fix: reject partial start lines at EOF

---
 parser/src/lib.rs              |  4 ++--
 parser/tests/basic.rs          | 18 +++++++++++++++++-
 parser/wasm/test/basic.test.js | 14 ++++++++++++++
 3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/parser/src/lib.rs b/parser/src/lib.rs
index f5f0b50..95b28db 100644
--- a/parser/src/lib.rs
+++ b/parser/src/lib.rs
@@ -265,8 +265,8 @@ impl Parser {
   /// put the parser in the error state.
   pub fn finish(&mut self) {
     match self.state {
-      // If the parser is one of the initial states, simply jump to finish
-      STATE_START | STATE_REQUEST_LINE | STATE_STATUS_LINE | STATE_FINISH => {
+      // An untouched or already finished parser can finish cleanly.
+      STATE_START | STATE_FINISH => {
         self.state = STATE_FINISH;
       }
       STATE_BODY_WITH_NO_LENGTH => {
diff --git a/parser/tests/basic.rs b/parser/tests/basic.rs
index 278d194..65c335a 100644
--- a/parser/tests/basic.rs
+++ b/parser/tests/basic.rs
@@ -4,7 +4,7 @@ mod helpers;
 use std::ffi::c_uchar;
 
 use milo_parser::{
-  CALLBACK_ACTIVE_ON_HEADERS, ERROR_NONE, ERROR_UNEXPECTED_CHARACTER, ERROR_UNEXPECTED_STATE,
+  CALLBACK_ACTIVE_ON_HEADERS, ERROR_NONE, ERROR_UNEXPECTED_CHARACTER, ERROR_UNEXPECTED_EOF, ERROR_UNEXPECTED_STATE,
   EVENT_ACTIVE_ON_HEADER_NAME, EVENT_ACTIVE_ON_HEADER_VALUE, STATE_BODY_DECISION, STATE_ERROR, STATE_FINISH,
   STATE_HEADER, STATE_START,
 };
@@ -678,6 +678,22 @@ fn basic_finish_logic() {
   assert_eq!(parser.state, STATE_HEADER);
   parser.finish();
   assert_eq!(parser.state, STATE_ERROR);
+
+  parser.reset(false);
+  let partial_request = b"G";
+  assert_eq!(parser.parse(partial_request.as_ptr(), partial_request.len()), 0);
+  parser.finish();
+  assert_eq!(parser.state, STATE_ERROR);
+  assert_eq!(parser.error_code, ERROR_UNEXPECTED_EOF);
+
+  parser.reset(false);
+  parser.autodetect = false;
+  parser.is_request = false;
+  let partial_response = b"HTTP";
+  assert_eq!(parser.parse(partial_response.as_ptr(), partial_response.len()), 0);
+  parser.finish();
+  assert_eq!(parser.state, STATE_ERROR);
+  assert_eq!(parser.error_code, ERROR_UNEXPECTED_EOF);
 }
 
 #[test]
diff --git a/parser/wasm/test/basic.test.js b/parser/wasm/test/basic.test.js
index 716ccd2..ea8b4ce 100644
--- a/parser/wasm/test/basic.test.js
+++ b/parser/wasm/test/basic.test.js
@@ -491,6 +491,20 @@ it('basic_finish_logic', t => {
   assert.equal(milo.getState(parser), milo.STATE_HEADER)
   milo.finish(parser)
   assert.equal(milo.getState(parser), milo.STATE_ERROR)
+
+  milo.reset(parser, false)
+  assert.equal(parse('G'), 0)
+  milo.finish(parser)
+  assert.equal(milo.getState(parser), milo.STATE_ERROR)
+  assert.equal(milo.getErrorCode(parser), milo.ERROR_UNEXPECTED_EOF)
+
+  milo.reset(parser, false)
+  milo.setShouldAutodetect(parser, false)
+  milo.setIsRequest(parser, false)
+  assert.equal(parse('HTTP'), 0)
+  milo.finish(parser)
+  assert.equal(milo.getState(parser), milo.STATE_ERROR)
+  assert.equal(milo.getErrorCode(parser), milo.ERROR_UNEXPECTED_EOF)
 })
 
 it('basic_empty_fields', t => {