Subject: Re: [PATCH] strbuf: allocate enough space when strbuf_setlen() is called first time

From: René Scharfe <[email-masked]>
Date: Tue, 26 Apr 2011 23:26:57 +0200

Am 26.04.2011 19:18, schrieb Junio C Hamano:
> Nguyễn Thái Ngọc Duy<[email-masked]>  writes:
> 
>> strbuf_grow(sb, 0) may allocate less than requested len and violate the
>> next assertion.
>>
>> Signed-off-by: Nguyễn Thái Ngọc Duy<[email-masked]>
>> ---
>>   strbuf.h |    2 +-
>>   1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/strbuf.h b/strbuf.h
>> index 07060ce..ab213da 100644
>> --- a/strbuf.h
>> +++ b/strbuf.h
>> @@ -34,7 +34,7 @@ extern void strbuf_grow(struct strbuf *, size_t);
>>
>>   static inline void strbuf_setlen(struct strbuf *sb, size_t len) {
>>   	if (!sb->alloc)
>> -		strbuf_grow(sb, 0);
>> +		strbuf_grow(sb, len);
>>   	assert(len<  sb->alloc);
> 
> Wait.  Isn't _setlen() meant to be used only to truncate at the length,
> and isn't that clearly documented?
> 
> I don't think we need this patch at all.

How about something like this instead?  The call to strbuf_grow() was
introduced in a8f3e2219 when there was no strbuf_slopbuf buffer that
nowadays makes sure we always have a place to write an initial NUL.
We can take it out again now, simplifying the code and hopefully
avoiding future confusion.

 strbuf.h |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/strbuf.h b/strbuf.h
index 07060ce..b157ede 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -33,9 +33,7 @@ static inline size_t strbuf_avail(const struct strbuf *sb) {
 extern void strbuf_grow(struct strbuf *, size_t);
 
 static inline void strbuf_setlen(struct strbuf *sb, size_t len) {
-	if (!sb->alloc)
-		strbuf_grow(sb, 0);
-	assert(len < sb->alloc);
+	assert(len < (sb->alloc ? sb->alloc : 1));
 	sb->len = len;
 	sb->buf[len] = '\0';
 }