strbuf: added strbuf_setlen

docs/technical/strbuf.txt

@@ -24,6 +24,12 @@ NOTE: ->alloc_size and ->len should *not* be messed with, only `strbuf_*` functi
 Functions
 ~~~~~~~~~
 
+`strbuf_setlen()`::
+
+    Sets the length of the buffer. +
+    This function will not allocate memory, it only sets ->len and
+    assure that the string is null-terminated at the new position.
+
 `strbuf_append()`::
 
     This function will append the buffer with the contents of 'ptr'

src/strbuf.c

@@ -46,6 +46,17 @@ void strbuf_reduce(strbuf_t *s, size_t len) {
     s->buf[s->len] = '\0';
 }
 
+void strbuf_setlen(strbuf_t *s, size_t len) {
+
+    if (!s->alloc_size)
+        return;
+
+    if (len >= s->alloc_size)
+        len = s->alloc_size - 1;
+    s->len = len;
+    s->buf[s->len] = '\0';
+}
+
 char* strbuf_release(strbuf_t *s) {
 
 	char *ret;

src/strbuf.h

@@ -29,6 +29,8 @@ void strbuf_expand(strbuf_t *s, size_t len);
 
 void strbuf_reduce(strbuf_t *s, size_t len);
 
+void strbuf_setlen(strbuf_t *s, size_t len);
+
 char* strbuf_release(strbuf_t *s);
 
 void strbuf_free(strbuf_t *s);

test/t_strbuf.c

@@ -14,6 +14,31 @@ void print_strbuf(strbuf_t *s) {
     printf("block: %u, len: %u |%s|\n", (uint)s->alloc_size, (uint)s->len, s->buf);
 }
 
+void test_setlen() {
+
+    strbuf_t b = STRBUF_INIT;
+
+    strbuf_setlen(&b, 25);
+    assert(b.len == 0);
+    
+    strbuf_expand(&b, 25);
+    strbuf_setlen(&b, b.alloc_size);
+    assert(b.len == b.alloc_size-1);
+
+    strbuf_setlen(&b, 0);
+    assert(b.len == 0);
+
+    strbuf_append_str(&b, "testing...");
+    print_strbuf(&b);
+
+    strbuf_setlen(&b, 7);
+    assert(b.len == 7);
+
+    print_strbuf(&b);
+
+    strbuf_free(&b);
+}
+
 void test_release() {
 
     strbuf_t b = STRBUF_INIT;
@@ -193,6 +218,7 @@ int main() {
 
     test_release_empty();
     test_release();
+    test_setlen();
     test_reduce();
     test_rev();
     test_squeeze();