[GSoC][RFC][PATCH 2/2] STRBUF_INIT_CONST: Adapting strbuf_* functions

[Robear Selwans <rwagih.rw@gmail.com>]

In a previous commit, a new function `STRBUF_INIT_CONST(const_str)`,
which would allow for the quick initialization of constant `strbuf`s,
was introduced.

In this commit, I check through the strbuf_* functions to edit the ones
that would try to edit the passed `strbuf` so that they are guaranteed to
behave in a predictable way when met with a constant.

Added Functions:
    `strbuf_make_var`

Updated Functions:
    `strbuf_grow`
    `strbuf_setlen`
    `strbuf_trim`
    `strbuf_trim_trailing_dir_sep`
    `strbuf_trim_trailing_newline`
    `strbuf_tolower`
    `strbuf_splice`

Functions where comments were added to clarify the expected behavior:
    `strbuf_getcwd`

Signed-off-by: Robear Selwans <robear.selwans@outlook.com>
---
 strbuf.c | 25 +++++++++++++++++++++++++
 strbuf.h | 14 ++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/strbuf.c b/strbuf.c
index f19da55b07..48af039b6e 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -89,6 +89,8 @@ void strbuf_attach(struct strbuf *sb, void *buf, size_t len, size_t alloc)
 
 void strbuf_grow(struct strbuf *sb, size_t extra)
 {
+	if (sb->len > sb->alloc)
+		strbuf_make_var(sb);
 	int new_buf = !sb->alloc;
 	if (unsigned_add_overflows(extra, 1) ||
 	    unsigned_add_overflows(sb->len, extra + 1))
@@ -100,8 +102,18 @@ void strbuf_grow(struct strbuf *sb, size_t extra)
 		sb->buf[0] = '\0';
 }
 
+void strbuf_make_var(struct strbuf *sb)
+{
+	char* str_cpy;
+	ALLOC_ARRAY(str_cpy, sb->len + 1);
+	memcpy(str_cpy, sb->buf, sb->len);
+	strbuf_attach(sb, str_cpy, sb->len, sb->len + 1);
+}
+
 void strbuf_trim(struct strbuf *sb)
 {
+	if (sb->len > sb->alloc)
+		strbuf_make_var(sb);
 	strbuf_rtrim(sb);
 	strbuf_ltrim(sb);
 }
@@ -115,6 +127,8 @@ void strbuf_rtrim(struct strbuf *sb)
 
 void strbuf_trim_trailing_dir_sep(struct strbuf *sb)
 {
+	if (sb->len > sb->alloc)
+		strbuf_make_var(sb);
 	while (sb->len > 0 && is_dir_sep((unsigned char)sb->buf[sb->len - 1]))
 		sb->len--;
 	sb->buf[sb->len] = '\0';
@@ -122,6 +136,9 @@ void strbuf_trim_trailing_dir_sep(struct strbuf *sb)
 
 void strbuf_trim_trailing_newline(struct strbuf *sb)
 {
+	if (sb->buf[sb->len - 1] == '\n')
+		if (sb->len > sb->alloc)
+			strbuf_make_var(sb);
 	if (sb->len > 0 && sb->buf[sb->len - 1] == '\n') {
 		if (--sb->len > 0 && sb->buf[sb->len - 1] == '\r')
 			--sb->len;
@@ -158,6 +175,8 @@ int strbuf_reencode(struct strbuf *sb, const char *from, const char *to)
 
 void strbuf_tolower(struct strbuf *sb)
 {
+	if (sb->len > sb->alloc)
+		strbuf_make_var(sb);
 	char *p = sb->buf, *end = sb->buf + sb->len;
 	for (; p < end; p++)
 		*p = tolower(*p);
@@ -234,6 +253,8 @@ void strbuf_splice(struct strbuf *sb, size_t pos, size_t len,
 		die("`pos' is too far after the end of the buffer");
 	if (pos + len > sb->len)
 		die("`pos + len' is too far after the end of the buffer");
+	if (sb->len > sb->alloc)
+		strbuf_make_var(sb);
 
 	if (dlen >= len)
 		strbuf_grow(sb, dlen - len);
@@ -572,6 +593,10 @@ int strbuf_readlink(struct strbuf *sb, const char *path, size_t hint)
 
 int strbuf_getcwd(struct strbuf *sb)
 {
+	/*
+	 * If sb was a constant, then an error would lead to 
+	 * strbuf_release() being called on the sb.
+	 */
 	size_t oldalloc = sb->alloc;
 	size_t guessed_len = 128;
 
diff --git a/strbuf.h b/strbuf.h
index 1a1753424c..a33bc4d90e 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -128,6 +128,10 @@ static inline void strbuf_swap(struct strbuf *a, struct strbuf *b)
 	SWAP(*a, *b);
 }
 
+/**
+ * Constant string buffer is turned into a variable one.
+ */
+void strbuf_make_var(struct strbuf *sb);
 
 /**
  * Functions related to the size of the buffer
@@ -160,6 +164,16 @@ void strbuf_grow(struct strbuf *sb, size_t amount);
  */
 static inline void strbuf_setlen(struct strbuf *sb, size_t len)
 {
+	if (sb->len > sb->alloc)
+	{
+		if (!len)
+		{
+			sb->buf = strbuf_slopbuf;
+			return;
+		}
+		else
+			strbuf_make_var(sb);
+	}
 	if (len > (sb->alloc ? sb->alloc - 1 : 0))
 		die("BUG: strbuf_setlen() beyond buffer");
 	sb->len = len;
-- 
2.17.1