Fix memory leak on failed realloc(3)

According to C99 §7.20.3.4:

If memory for the new object cannot be allocated, the old object is not
deallocated and its value is unchanged.

Therefore, a temporary pointer must be used to ensure the original
object can still be deallocated should realloc(3) return a null pointer.

4 files changed, 79 insertions, 33 deletions

diff --git a/handler.c b/handler.c
index b152cf1..1d378a9 100644
--- a/handler.c
+++ b/handler.c
@@ -310,27 +310,33 @@ struct handler *handler_alloc(const char *const tmpdir)
 int handler_add(struct handler *const h, const char *url,
     const enum http_op op, const handler_fn f, void *const user)
 {
-    if (!h || !(h->cfg = realloc(h->cfg, (h->n_cfg + 1) * sizeof *h->cfg)))
+    const size_t n = h->n_cfg + 1;
+    struct handler_cfg *const cfgs = realloc(h->cfg, n * sizeof *h->cfg),
+        *c = NULL;
+
+    if (!cfgs)
     {
         fprintf(stderr, "%s: realloc(3): %s\n", __func__, strerror(errno));
         return -1;
     }
 
-    char *const new = strdup(url);
-
-    if (!new)
-    {
-        fprintf(stderr, "%s: malloc(3): %s\n", __func__, strerror(errno));
-        return -1;
-    }
+    c = &cfgs[h->n_cfg];
 
-    h->cfg[h->n_cfg++] = (const struct handler_cfg)
+    *c = (const struct handler_cfg)
     {
-        .url = new,
+        .url = strdup(url),
         .op = op,
         .f = f,
         .user = user
     };
 
+    if (!c->url)
+    {
+        fprintf(stderr, "%s: strdup(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    h->cfg = cfgs;
+    h->n_cfg = n;
     return 0;
 }
diff --git a/html.c b/html.c
index f5ea336..95d26b9 100644
--- a/html.c
+++ b/html.c
@@ -101,25 +101,30 @@ int html_node_set_value_unescaped(struct html_node *const n,
 int html_node_add_attr(struct html_node *const n, const char *const attr,
     const char *const val)
 {
-    if (!(n->attrs = realloc(n->attrs, (n->n + 1) * sizeof *n->attrs)))
+    const size_t el = n->n + 1;
+    struct html_attribute *const attrs = realloc(n->attrs,
+        el * sizeof *n->attrs), *a = NULL;
+
+    if (!attrs)
     {
         fprintf(stderr, "%s: realloc(3): %s\n", __func__, strerror(errno));
         return -1;
     }
 
-    struct html_attribute *const a = &n->attrs[n->n++];
-
+    a = &attrs[n->n];
     *a = (const struct html_attribute){0};
 
     if (!(a->attr = strdup(attr))
         || (val && !(a->value = strdup(val))))
     {
-        fprintf(stderr, "%s: malloc(3): %s\n", __func__, strerror(errno));
+        fprintf(stderr, "%s: strdup(3): %s\n", __func__, strerror(errno));
         free(a->attr);
         free(a->value);
         return -1;
     }
 
+    n->attrs = attrs;
+    n->n = el;
     return 0;
 }
 
diff --git a/http.c b/http.c
index 629f356..448de24 100644
--- a/http.c
+++ b/http.c
@@ -470,14 +470,17 @@ static int http_write(struct http_ctx *const h, bool *const close)
 int http_response_add_header(struct http_response *const r,
     const char *const header, const char *const value)
 {
-    if (!(r->headers = realloc(r->headers,
-        sizeof (r->n_headers + 1) *sizeof *r->headers)))
+    const size_t n = r->n_headers + 1;
+    struct http_header *const headers = realloc(r->headers,
+        n * sizeof *r->headers), *h = NULL;
+
+    if (!headers)
     {
         fprintf(stderr, "%s: realloc(3): %s\n", __func__, strerror(errno));
         return -1;
     }
 
-    struct http_header *const h = &r->headers[r->n_headers++];
+    h = &headers[r->n_headers];
 
     *h = (const struct http_header)
     {
@@ -487,13 +490,14 @@ int http_response_add_header(struct http_response *const r,
 
     if (!h->header || !h->value)
     {
-        fprintf(stderr, "%s: malloc(3): %s\n", __func__, strerror(errno));
+        fprintf(stderr, "%s: strdup(3): %s\n", __func__, strerror(errno));
         free(h->header);
         free(h->value);
-        free(h);
         return -1;
     }
 
+    r->headers = headers;
+    r->n_headers = n;
     return 0;
 }
 
@@ -984,16 +988,21 @@ static int set_content_disposition(struct http_ctx *const h,
             __func__, (int)(sep - c), c);
         return 1;
     }
-    else if (!(m->forms = realloc(m->forms,
-        (m->nforms + 1) * sizeof *m->forms)))
+
+    const size_t n = m->nforms + 1;
+    struct form *const forms = realloc(m->forms, n * sizeof *m->forms);
+
+    if (!forms)
     {
         fprintf(stderr, "%s: realloc(3): %s\n", __func__, strerror(errno));
         return -1;
     }
 
-    struct form *const f = &m->forms[m->nforms++];
+    struct form *const f = &forms[m->nforms];
 
     *f = (const struct form){0};
+    m->nforms = n;
+    m->forms = forms;
     return cd_fields(h, f, sep);
 }
 
@@ -1193,13 +1202,17 @@ static int apply_from_file(struct http_ctx *const h, struct form *const f)
 
     m->fd = -1;
 
-    if (!(m->files = realloc(m->files, (m->nfiles + 1) * sizeof *m->files)))
+    const size_t n = m->nfiles + 1;
+    struct http_post_file *const files = realloc(m->files,
+        n * sizeof *m->files);
+
+    if (!files)
     {
         fprintf(stderr, "%s: realloc(3): %s\n", __func__, strerror(errno));
         return -1;
     }
 
-    struct http_post_file *const pf = &m->files[m->nfiles++];
+    struct http_post_file *const pf = &files[m->nfiles];
 
     *pf = (const struct http_post_file)
     {
@@ -1207,6 +1220,8 @@ static int apply_from_file(struct http_ctx *const h, struct form *const f)
         .filename = f->filename
     };
 
+    m->files = files;
+    m->nfiles = n;
     return 0;
 }
 
@@ -1575,13 +1590,18 @@ char *http_decode_url(const char *url)
 
     while (*url)
     {
-        if (!(ret = realloc(ret, n + 1)))
+        char *const r = realloc(ret, n + 1);
+
+        if (!r)
         {
             fprintf(stderr, "%s: realloc(3) loop: %s\n",
                 __func__, strerror(errno));
             goto failure;
         }
-        else if (*url != '%')
+
+        ret = r;
+
+        if (*url != '%')
             ret[n++] = *url++;
         else if (*(url + 1) && *(url + 2))
         {
@@ -1597,12 +1617,15 @@ char *http_decode_url(const char *url)
         }
     }
 
-    if (!(ret = realloc(ret, n + 1)))
+    char *const r = realloc(ret, n + 1);
+
+    if (!r)
     {
         fprintf(stderr, "%s: realloc(3) end: %s\n", __func__, strerror(errno));
         goto failure;
     }
 
+    ret = r;
     ret[n] = '\0';
     return ret;
 
diff --git a/server.c b/server.c
index d867b59..f00a37c 100644
--- a/server.c
+++ b/server.c
@@ -58,12 +58,17 @@ int server_client_close(struct server *const s, struct server_client *const c)
             {
                 memcpy(ref, ref + 1, s->n - i);
 
-                if (!(s->c = realloc(s->c, (s->n - 1) * sizeof *s->c)))
+                const size_t n = s->n - 1;
+                struct server_client *const c = realloc(s->c, n * sizeof *s->c);
+
+                if (!c)
                 {
                     fprintf(stderr, "%s: realloc(3): %s\n",
                         __func__, strerror(errno));
                     return -1;
                 }
+
+                s->c = c;
             }
             else
             {
@@ -127,19 +132,26 @@ static struct server_client *alloc_client(struct server *const s)
             __func__, strerror(errno));
         return NULL;
     }
-    else if (!(s->c = realloc(s->c, (s->n + 1) * sizeof *s->c)))
+
+    const size_t n = s->n + 1;
+    struct server_client *const clients = realloc(s->c, n * sizeof *s->c);
+
+    if (!clients)
     {
-        fprintf(stderr, "%s: realloc(3): %s\n",
-            __func__, strerror(errno));
+        fprintf(stderr, "%s: realloc(3): %s\n", __func__, strerror(errno));
         return NULL;
     }
 
-    s->c[s->n] = (const struct server_client)
+    struct server_client *const c = &clients[s->n];
+
+    *c = (const struct server_client)
     {
         .fd = fd
     };
 
-    return &s->c[s->n++];
+    s->c = clients;
+    s->n = n;
+    return c;
 }
 
 void server_client_write_pending(struct server_client *const c,