[FFmpeg-devel] [PATCH] ffprobe: redesign json_escape_str(), to make use of a global buffer
Stefano Sabatini
stefasab at gmail.com
Fri Oct 14 17:50:59 CEST 2011
The new code avoids to call av_malloc/av_free when escaping is needed
(possibly faster), and avoids an integer overflow in case of a huge
string and provides feedback when a string cannot be escaped.
When a string cannot be escaped, a special string is printed instead.
---
ffprobe.c | 113 +++++++++++++++++++++++++++++++++++++++++-------------------
1 files changed, 77 insertions(+), 36 deletions(-)
diff --git a/ffprobe.c b/ffprobe.c
index 593d369..a7fa18f 100644
--- a/ffprobe.c
+++ b/ffprobe.c
@@ -335,6 +335,8 @@ fail:
return NULL;
}
+#define INIT_BUF_SIZE 256
+
/* WRITERS */
/* Default output */
@@ -410,39 +412,83 @@ static Writer default_writer = {
typedef struct {
int multiple_entries; ///< tells if the given chapter requires multiple entries
+ char *buf;
+ size_t buf_size;
} JSONContext;
-static char *json_escape_str(const char *s)
+static av_cold int json_init(WriterContext *wctx, const char *args, void *opaque)
+{
+ JSONContext *json = wctx->priv;
+
+ json->buf_size = INIT_BUF_SIZE;
+ if (!(json->buf = av_malloc(json->buf_size)))
+ return AVERROR(ENOMEM);
+
+ return 0;
+}
+
+static av_cold void json_uninit(WriterContext *wctx)
+{
+ JSONContext *json = wctx->priv;
+ av_freep(&json->buf);
+}
+
+#define ESCAPE_CHECK_SIZE(src, size, max_size) \
+ if (size > max_size) { \
+ char buf[64]; \
+ snprintf(buf, sizeof(buf), "%s", src); \
+ av_log(log_ctx, AV_LOG_WARNING, \
+ "String '%s...' with is too big\n", buf); \
+ return "FFPROBE_TOO_BIG_STRING"; \
+ }
+
+#define ESCAPE_REALLOC_BUF(dst_size_p, dst_p, src, size) \
+ if (*dst_size_p < size) { \
+ char *q = av_realloc(*dst_p, size); \
+ if (!q) { \
+ char buf[64]; \
+ snprintf(buf, sizeof(buf), "%s", src); \
+ av_log(log_ctx, AV_LOG_WARNING, \
+ "String '%s...' could not be escaped\n", buf); \
+ return "FFPROBE_THIS_STRING_COULD_NOT_BE_ESCAPED"; \
+ } \
+ *dst_size_p = size; \
+ *dst = q; \
+ }
+
+static const char *json_escape_str(char **dst, size_t *dst_size, const char *src,
+ void *log_ctx)
{
static const char json_escape[] = {'"', '\\', '\b', '\f', '\n', '\r', '\t', 0};
static const char json_subst[] = {'"', '\\', 'b', 'f', 'n', 'r', 't', 0};
- char *ret, *p;
- int i, len = 0;
+ const char *p;
+ char *q;
+ size_t size = 1;
// compute the length of the escaped string
- for (i = 0; s[i]; i++) {
- if (strchr(json_escape, s[i])) len += 2; // simple escape
- else if ((unsigned char)s[i] < 32) len += 6; // handle non-printable chars
- else len += 1; // char copy
+ for (p = src; *p; p++) {
+ ESCAPE_CHECK_SIZE(src, size, SIZE_MAX-6);
+ if (strchr(json_escape, *p)) size += 2; // simple escape
+ else if ((unsigned char)*p < 32) size += 6; // handle non-printable chars
+ else size += 1; // char copy
}
-
- p = ret = av_malloc(len + 1);
- if (!p)
- return NULL;
- for (i = 0; s[i]; i++) {
- char *q = strchr(json_escape, s[i]);
- if (q) {
- *p++ = '\\';
- *p++ = json_subst[q - json_escape];
- } else if ((unsigned char)s[i] < 32) {
- snprintf(p, 7, "\\u00%02x", s[i] & 0xff);
- p += 6;
+ ESCAPE_REALLOC_BUF(dst_size, dst, src, size);
+
+ q = *dst;
+ for (p = src; *p; p++) {
+ char *s = strchr(json_escape, *p);
+ if (s) {
+ *q++ = '\\';
+ *q++ = json_subst[s - json_escape];
+ } else if ((unsigned char)*p < 32) {
+ snprintf(q, 7, "\\u00%02x", *p & 0xff);
+ q += 6;
} else {
- *p++ = s[i];
+ *q++ = *p;
}
}
- *p = 0;
- return ret;
+ *q = 0;
+ return *dst;
}
static void json_print_header(WriterContext *wctx)
@@ -458,15 +504,12 @@ static void json_print_footer(WriterContext *wctx)
static void json_print_chapter_header(WriterContext *wctx, const char *chapter)
{
JSONContext *json = wctx->priv;
- char *chapter_esc;
if (wctx->nb_chapter)
printf(",");
json->multiple_entries = !strcmp(chapter, "packets") || !strcmp(chapter, "streams");
- chapter_esc = json_escape_str(chapter);
- printf("\n \"%s\":%s", chapter_esc ? chapter_esc : "",
+ printf("\n \"%s\":%s", json_escape_str(&json->buf, &json->buf_size, chapter, wctx),
json->multiple_entries ? " [" : " ");
- av_free(chapter_esc);
}
static void json_print_chapter_footer(WriterContext *wctx, const char *chapter)
@@ -492,14 +535,10 @@ static inline void json_print_item_str(WriterContext *wctx,
const char *key, const char *value,
const char *indent)
{
- char *key_esc = json_escape_str(key);
- char *value_esc = json_escape_str(value);
+ JSONContext *json = wctx->priv;
- printf("%s\"%s\": \"%s\"", indent,
- key_esc ? key_esc : "",
- value_esc ? value_esc : "");
- av_free(key_esc);
- av_free(value_esc);
+ printf("%s\"%s\":", indent, json_escape_str(&json->buf, &json->buf_size, key, wctx));
+ printf(" \"%s\"", json_escape_str(&json->buf, &json->buf_size, value, wctx));
}
#define INDENT " "
@@ -512,11 +551,11 @@ static void json_print_str(WriterContext *wctx, const char *key, const char *val
static void json_print_int(WriterContext *wctx, const char *key, int value)
{
- char *key_esc = json_escape_str(key);
+ JSONContext *json = wctx->priv;
if (wctx->nb_item) printf(",\n");
- printf(INDENT "\"%s\": %d", key_esc ? key_esc : "", value);
- av_free(key_esc);
+ printf(INDENT "\"%s\": %d",
+ json_escape_str(&json->buf, &json->buf_size, key, wctx), value);
}
static void json_show_tags(WriterContext *wctx, AVDictionary *dict)
@@ -538,6 +577,8 @@ static Writer json_writer = {
.name = "json",
.priv_size = sizeof(JSONContext),
+ .init = json_init,
+ .uninit = json_uninit,
.print_header = json_print_header,
.print_footer = json_print_footer,
.print_chapter_header = json_print_chapter_header,
--
1.7.4.1
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