git/strbuf.h

#ifndef STRBUF_H
#define STRBUF_H

/*
 * Strbuf's can be use in many ways: as a byte array, or to store arbitrary
 * long, overflow safe strings.
 *
 * Strbufs has some invariants that are very important to keep in mind:
 *
 * 1. the ->buf member is always malloc-ed, hence strbuf's can be used to
 *    build complex strings/buffers whose final size isn't easily known.
 *
 *    It is legal to copy the ->buf pointer away. Though if you want to reuse
 *    the strbuf after that, setting ->buf to NULL isn't legal.
 *    `strbuf_detach' is the operation that detachs a buffer from its shell
 *    while keeping the shell valid wrt its invariants.
 *
 * 2. the ->buf member is a byte array that has at least ->len + 1 bytes
 *    allocated. The extra byte is used to store a '\0', allowing the ->buf
 *    member to be a valid C-string. Every strbuf function ensure this
 *    invariant is preserved.
 *
 *    Note that it is OK to "play" with the buffer directly if you work it
 *    that way:
 *
 *    strbuf_grow(sb, SOME_SIZE);
 *    // ... here the memory areay starting at sb->buf, and of length
 *    // sb_avail(sb) is all yours, and you are sure that sb_avail(sb) is at
 *    // least SOME_SIZE
 *    strbuf_setlen(sb, sb->len + SOME_OTHER_SIZE);
 *
 *    Of course, SOME_OTHER_SIZE must be smaller or equal to sb_avail(sb).
 *
 *    Doing so is safe, though if it has to be done in many places, adding the
 *    missing API to the strbuf module is the way to go.
 *
 *    XXX: do _not_ assume that the area that is yours is of size ->alloc - 1
 *         even if it's true in the current implementation. Alloc is somehow a
 *         "private" member that should not be messed with.
 */

#include <assert.h>

struct strbuf {
	size_t alloc;
	size_t len;
	int eof;
	char *buf;
};

#define STRBUF_INIT  { 0, 0, 0, NULL }

/*----- strbuf life cycle -----*/
extern void strbuf_init(struct strbuf *, size_t);
extern void strbuf_release(struct strbuf *);
extern void strbuf_reset(struct strbuf *);
extern char *strbuf_detach(struct strbuf *);
extern void strbuf_attach(struct strbuf *, void *, size_t, size_t);

/*----- strbuf size related -----*/
static inline size_t strbuf_avail(struct strbuf *sb) {
    return sb->alloc ? sb->alloc - sb->len - 1 : 0;
}
static inline void strbuf_setlen(struct strbuf *sb, size_t len) {
    assert (len < sb->alloc);
    sb->len = len;
    sb->buf[len] = '\0';
}

extern void strbuf_grow(struct strbuf *, size_t);

/*----- content related -----*/
extern void strbuf_rtrim(struct strbuf *);

/*----- add data in your buffer -----*/
static inline void strbuf_addch(struct strbuf *sb, int c) {
	strbuf_grow(sb, 1);
	sb->buf[sb->len++] = c;
	sb->buf[sb->len] = '\0';
}

/* inserts after pos, or appends if pos >= sb->len */
extern void strbuf_insert(struct strbuf *, size_t pos, const void *, size_t);

/* splice pos..pos+len with given data */
extern void strbuf_splice(struct strbuf *, size_t pos, size_t len,
						  const void *, size_t);

extern void strbuf_add(struct strbuf *, const void *, size_t);
static inline void strbuf_addstr(struct strbuf *sb, const char *s) {
	strbuf_add(sb, s, strlen(s));
}
static inline void strbuf_addbuf(struct strbuf *sb, struct strbuf *sb2) {
	strbuf_add(sb, sb2->buf, sb2->len);
}

__attribute__((format(printf,2,3)))
extern void strbuf_addf(struct strbuf *sb, const char *fmt, ...);

extern size_t strbuf_fread(struct strbuf *, size_t, FILE *);
/* XXX: if read fails, any partial read is undone */
extern ssize_t strbuf_read(struct strbuf *, int fd, size_t hint);

extern void read_line(struct strbuf *, FILE *, int);

#endif /* STRBUF_H */