[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH 2/6] json: Clean up how lexer consumes "end of i

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH 2/6] json: Clean up how lexer consumes "end of input"
Date: Mon, 27 Aug 2018 11:58:28 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 08/27/2018 02:00 AM, Markus Armbruster wrote:
When the lexer isn't in its start state at the end of input, it's
working on a token.  To flush it out, it needs to transit to its start
state on "end of input" lookahead.

There are two ways to the start state, depending on the current state:

* If the lexer is in a TERMINAL(JSON_FOO) state, it can emit a
   JSON_FOO token.

* Else, it can go to IN_ERROR state, and emit a JSON_ERROR token.

There are complications, however:

* The transition to IN_ERROR state consumes the input character and
   adds it to the JSON_ERROR token.  The latter is inappropriate for
   the "end of input" character, so we suppress that.  See also recent
   commit "json: Fix lexer to include the bad character in JSON_ERROR

Now commit a2ec6be7

* The transition to a TERMINAL(JSON_FOO) state doesn't consume the
   input character.  In that case, the lexer normally loops until it is
   consumed.  We have to suppress that for the "end of input" input
   character.  If we didn't, the lexer would consume it by entering
   IN_ERROR state, emitting a bogus JSON_ERROR token.  We fixed that in
   commit bd3924a33a6.

However, simply breaking the loop this way assumes that the lexer
needs exactly one state transition to reach its start state.  That
assumption is correct now, but it's unclean, and I'll soon break it.
Clean up: instead of breaking the loop after one iteration, break it
after it reached the start state.

Signed-off-by: Markus Armbruster <address@hidden>
  qobject/json-lexer.c | 17 +++++++++--------
  1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/qobject/json-lexer.c b/qobject/json-lexer.c
index 4867839f66..ec3aec726f 100644
--- a/qobject/json-lexer.c
+++ b/qobject/json-lexer.c
@@ -261,7 +261,8 @@ void json_lexer_init(JSONLexer *lexer, bool 
static void json_lexer_feed_char(JSONLexer *lexer, char ch, bool flush)
-    int char_consumed, new_state;
+    int new_state;
+    bool char_consumed = false;

Yay for the switch to bool.

Reviewed-by: Eric Blake <address@hidden>

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

reply via email to

[Prev in Thread] Current Thread [Next in Thread]