From: Paolo Bonzini <pbonzini@redhat.com>
Date: Mon, 24 May 2010 07:39:52 +0000 (+0200)
Subject: implement optional lookahead in json lexer
X-Git-Tag: TizenStudio_2.0_p2.3~4560^2~2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=d6b347c44d293f753cd716c5e936ed6414150f6d;p=sdk%2Femulator%2Fqemu.git

implement optional lookahead in json lexer

Not requiring one extra character when lookahead is not necessary
ensures that clients behave properly even if they, for example,
send QMP requests without a trailing newline.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
---

diff --git a/json-lexer.c b/json-lexer.c
index 1d9b81f..5ea64a7 100644
--- a/json-lexer.c
+++ b/json-lexer.c
@@ -65,6 +65,12 @@ enum json_lexer_state {
 
 #define TERMINAL(state) [0 ... 0x7F] = (state)
 
+/* Return whether TERMINAL is a terminal state and the transition to it
+   from OLD_STATE required lookahead.  This happens whenever the table
+   below uses the TERMINAL macro.  */
+#define TERMINAL_NEEDED_LOOKAHEAD(old_state, terminal) \
+            (json_lexer[(old_state)][0] == (terminal))
+
 static const uint8_t json_lexer[][256] =  {
     [IN_DONE_STRING] = {
         TERMINAL(JSON_STRING),
@@ -284,35 +290,41 @@ void json_lexer_init(JSONLexer *lexer, JSONLexerEmitter func)
 
 static int json_lexer_feed_char(JSONLexer *lexer, char ch)
 {
+    int char_consumed, new_state;
+
     lexer->x++;
     if (ch == '\n') {
         lexer->x = 0;
         lexer->y++;
     }
 
-    lexer->state = json_lexer[lexer->state][(uint8_t)ch];
-
-    switch (lexer->state) {
-    case JSON_OPERATOR:
-    case JSON_ESCAPE:
-    case JSON_INTEGER:
-    case JSON_FLOAT:
-    case JSON_KEYWORD:
-    case JSON_STRING:
-        lexer->emit(lexer, lexer->token, lexer->state, lexer->x, lexer->y);
-    case JSON_SKIP:
-        lexer->state = json_lexer[IN_START][(uint8_t)ch];
-        QDECREF(lexer->token);
-        lexer->token = qstring_new();
-        break;
-    case ERROR:
-        return -EINVAL;
-    default:
-        break;
-    }
-
-    qstring_append_chr(lexer->token, ch);
+    do {
+        new_state = json_lexer[lexer->state][(uint8_t)ch];
+        char_consumed = !TERMINAL_NEEDED_LOOKAHEAD(lexer->state, new_state);
+        if (char_consumed) {
+            qstring_append_chr(lexer->token, ch);
+        }
 
+        switch (new_state) {
+        case JSON_OPERATOR:
+        case JSON_ESCAPE:
+        case JSON_INTEGER:
+        case JSON_FLOAT:
+        case JSON_KEYWORD:
+        case JSON_STRING:
+            lexer->emit(lexer, lexer->token, new_state, lexer->x, lexer->y);
+        case JSON_SKIP:
+            QDECREF(lexer->token);
+            lexer->token = qstring_new();
+            new_state = IN_START;
+            break;
+        case ERROR:
+            return -EINVAL;
+        default:
+            break;
+        }
+        lexer->state = new_state;
+    } while (!char_consumed);
     return 0;
 }
 
@@ -334,7 +346,7 @@ int json_lexer_feed(JSONLexer *lexer, const char *buffer, size_t size)
 
 int json_lexer_flush(JSONLexer *lexer)
 {
-    return json_lexer_feed_char(lexer, 0);
+    return lexer->state == IN_START ? 0 : json_lexer_feed_char(lexer, 0);
 }
 
 void json_lexer_destroy(JSONLexer *lexer)