Add string buffer util

This will help to build strings incrementally.

app/meson.build

@@ -27,6 +27,7 @@ src = [
     'src/util/log.c',
     'src/util/net.c',
     'src/util/process.c',
+    'src/util/strbuf.c',
     'src/util/str_util.c',
     'src/util/thread.c',
     'src/util/tick.c',
@@ -204,6 +205,10 @@ if get_option('buildtype') == 'debug'
         ['test_queue', [
             'tests/test_queue.c',
         ]],
+        ['test_strbuf', [
+            'tests/test_strbuf.c',
+            'src/util/strbuf.c',
+        ]],
         ['test_strutil', [
             'tests/test_strutil.c',
             'src/util/str_util.c',

app/src/util/strbuf.c

@@ -0,0 +1,87 @@
+#include "strbuf.h"
+
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <stdio.h>
+
+bool
+sc_strbuf_init(struct sc_strbuf *buf, size_t init_cap) {
+    buf->s = malloc(init_cap + 1); // +1 for '\0'
+    if (!buf->s) {
+        return false;
+    }
+
+    buf->len = 0;
+    buf->cap = init_cap;
+    return true;
+}
+
+static bool
+sc_strbuf_reserve(struct sc_strbuf *buf, size_t len) {
+    if (buf->len + len > buf->cap) {
+        size_t new_cap = buf->cap * 3 / 2 + len;
+        char *s = realloc(buf->s, new_cap + 1); // +1 for '\0'
+        if (!s) {
+            // Leave the old buf->s
+            return false;
+        }
+        buf->s = s;
+        buf->cap = new_cap;
+    }
+    return true;
+}
+
+bool
+sc_strbuf_append(struct sc_strbuf *buf, const char *s, size_t len) {
+    assert(s);
+    assert(*s);
+    assert(strlen(s) >= len);
+    if (!sc_strbuf_reserve(buf, len)) {
+        return false;
+    }
+
+    memcpy(&buf->s[buf->len], s, len);
+    buf->len += len;
+    buf->s[buf->len] = '\0';
+
+    return true;
+}
+
+bool
+sc_strbuf_append_char(struct sc_strbuf *buf, const char c) {
+    if (!sc_strbuf_reserve(buf, 1)) {
+        return false;
+    }
+
+    buf->s[buf->len] = c;
+    buf->len ++;
+    buf->s[buf->len] = '\0';
+
+    return true;
+}
+
+bool
+sc_strbuf_append_n(struct sc_strbuf *buf, const char c, size_t n) {
+    if (!sc_strbuf_reserve(buf, n)) {
+        return false;
+    }
+
+    memset(&buf->s[buf->len], c, n);
+    buf->len += n;
+    buf->s[buf->len] = '\0';
+
+    return true;
+}
+
+void
+sc_strbuf_shrink(struct sc_strbuf *buf) {
+    assert(buf->len <= buf->cap);
+    if (buf->len != buf->cap) {
+        char *s = realloc(buf->s, buf->len + 1); // +1 for '\0'
+        assert(s); // decreasing the size may not fail
+        buf->s = s;
+        buf->cap = buf->len;
+    }
+}

app/src/util/strbuf.h

@@ -0,0 +1,73 @@
+#ifndef SC_STRBUF_H
+#define SC_STRBUF_H
+
+#include "common.h"
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <string.h>
+
+struct sc_strbuf {
+    char *s;
+    size_t len;
+    size_t cap;
+};
+
+/**
+ * Initialize the string buffer
+ *
+ * `buf->s` must be manually freed by the caller.
+ */
+bool
+sc_strbuf_init(struct sc_strbuf *buf, size_t init_cap);
+
+/**
+ * Append a string
+ *
+ * Append `len` characters from `s` to the buffer.
+ */
+bool
+sc_strbuf_append(struct sc_strbuf *buf, const char *s, size_t len);
+
+/**
+ * Append a char
+ *
+ * Append a single character to the buffer.
+ */
+bool
+sc_strbuf_append_char(struct sc_strbuf *buf, const char c);
+
+/**
+ * Append a char `n` times
+ *
+ * Append the same characters `n` times to the buffer.
+ */
+bool
+sc_strbuf_append_n(struct sc_strbuf *buf, const char c, size_t n);
+
+/**
+ * Append a NUL-terminated string
+ */
+static inline bool
+sc_strbuf_append_str(struct sc_strbuf *buf, const char *s) {
+    return sc_strbuf_append(buf, s, strlen(s));
+}
+
+/**
+ * Append a static string
+ *
+ * Append a string whose size is known at compile time (for
+ * example a string literal).
+ */
+#define sc_strbuf_append_staticstr(BUF, S) \
+    sc_strbuf_append(BUF, S, sizeof(S) - 1)
+
+/**
+ * Shrink the buffer capacity to its current length
+ *
+ * This resizes `buf->s` to fit the content.
+ */
+void
+sc_strbuf_shrink(struct sc_strbuf *buf);
+
+#endif

app/tests/test_strbuf.c

@@ -0,0 +1,47 @@
+#include "common.h"
+
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "util/strbuf.h"
+
+static void test_strbuf_simple(void) {
+    struct sc_strbuf buf;
+    bool ok = sc_strbuf_init(&buf, 10);
+    assert(ok);
+
+    ok = sc_strbuf_append_staticstr(&buf, "Hello");
+    assert(ok);
+
+    ok = sc_strbuf_append_char(&buf, ' ');
+    assert(ok);
+
+    ok = sc_strbuf_append_staticstr(&buf, "world");
+    assert(ok);
+
+    ok = sc_strbuf_append_staticstr(&buf, "!\n");
+    assert(ok);
+
+    ok = sc_strbuf_append_staticstr(&buf, "This is a test");
+    assert(ok);
+
+    ok = sc_strbuf_append_n(&buf, '.', 3);
+    assert(ok);
+
+    assert(!strcmp(buf.s, "Hello world!\nThis is a test..."));
+
+    sc_strbuf_shrink(&buf);
+    assert(buf.len == buf.cap);
+    assert(!strcmp(buf.s, "Hello world!\nThis is a test..."));
+
+    free(buf.s);
+}
+
+int main(int argc, char *argv[]) {
+    (void) argc;
+    (void) argv;
+
+    test_strbuf_simple();
+    return 0;
+}