Use a C++ string for StringBuf internally

Eventually we'll want to just replace the whole thing with native
strings, but it's used in several places so changing is fairly invasive.

The "proper" way to do stripTrailingBlanksStringBuf() in modern C++
would be using lambdas and whatnot, for now settling for something
that is easy to understand from a C background.

build/misc.c

@@ -3,6 +3,9 @@
  */
 #include "system.h"
 
+#include <string>
+#include <algorithm>
+
 #include <ctype.h>
 #include <stdlib.h>
 #include <rpm/rpmstring.h>
@@ -12,72 +15,36 @@
 #define BUF_CHUNK 1024
 
 struct StringBufRec {
- char *buf;
- char *tail; /* Points to first "free" char */
- int allocated;
- int free;
+ std::string buf;
 };
 
 StringBuf newStringBuf(void)
 {
- StringBuf sb = (StringBuf)xmalloc(sizeof(*sb));
-
- sb->free = sb->allocated = BUF_CHUNK;
- sb->buf = (char *)xcalloc(sb->allocated, sizeof(*sb->buf));
- sb->buf[0] = '\0';
- sb->tail = sb->buf;
-
- return sb;
+ return new StringBufRec {};
 }
 
 StringBuf freeStringBuf(StringBuf sb)
 {
- if (sb) {
- sb->buf = _free(sb->buf);
- sb = _free(sb);
- }
- return sb;
+ delete sb;
+ return NULL;
 }
 
 void stripTrailingBlanksStringBuf(StringBuf sb)
 {
- while (sb->free != sb->allocated) {
- if (! risspace(*(sb->tail - 1)))
- break;
- sb->free++;
- sb->tail--;
- }
- sb->tail[0] = '\0';
+ while (!sb->buf.empty() && risspace(sb->buf.back()))
+ sb->buf.erase(sb->buf.size() - 1);
 }
 
 const char * getStringBuf(StringBuf sb)
 {
- return (sb != NULL) ? sb->buf : NULL;
+ return (sb != NULL) ? sb->buf.c_str() : NULL;
 }
 
 void appendStringBufAux(StringBuf sb, const char *s, int nl)
 {
- int l;
-
- l = strlen(s);
- /* If free == l there is no room for NULL terminator! */
- while ((l + nl + 1) > sb->free) {
- sb->allocated += BUF_CHUNK;
- sb->free += BUF_CHUNK;
- sb->buf = xrealloc(sb->buf, sb->allocated);
- sb->tail = sb->buf + (sb->allocated - sb->free);
- }
-
- /* FIX: shrug */
- strcpy(sb->tail, s);
- sb->tail += l;
- sb->free -= l;
- if (nl) {
- sb->tail[0] = '\n';
- sb->tail[1] = '\0';
- sb->tail++;
- sb->free--;
- }
+ sb->buf += s;
+ if (nl)
+ sb->buf += '\n';
 }
 
 int parseUnsignedNum(const char * line, uint32_t * res)