Send response on quota exceeded

So far, slcl would just close the connection with a client when the
Content-Length of an incoming request exceeded the user quota, without
any meaningful information given back to the user.

Now, slcl responds with a HTML file with meaningful information about
the error.

Limitations:

- While this commits has been successfully tested on ungoogled-chromium,
LibreWolf (and I assume Firefox and any other derivates too) does not
seem to receive the response from the server.
    - However, this issue only occurred during local testing, but not
on remote instances.

7 files changed, 136 insertions, 13 deletions

diff --git a/handler.c b/handler.c
index 05650ca..22699f5 100644
--- a/handler.c
+++ b/handler.c
@@ -112,13 +112,14 @@ static int on_payload(const struct http_payload *const p,
 }
 
 static int on_length(const unsigned long long len,
-    const struct http_cookie *const c, void *const user)
+    const struct http_cookie *const c, struct http_response *const r,
+    void *const user)
 {
     struct client *const cl = user;
     struct handler *const h = cl->h;
 
     if (h->cfg.length)
-        return h->cfg.length(len, c, h->cfg.user);
+        return h->cfg.length(len, c, r, h->cfg.user);
 
     return 0;
 }
diff --git a/handler.h b/handler.h
index d851f65..38de97b 100644
--- a/handler.h
+++ b/handler.h
@@ -11,7 +11,7 @@ struct handler_cfg
 {
     const char *tmpdir;
     int (*length)(unsigned long long len, const struct http_cookie *c,
-        void *user);
+        struct http_response *r, void *user);
     void *user;
 };
 
diff --git a/http.c b/http.c
index dae33d1..726e56a 100644
--- a/http.c
+++ b/http.c
@@ -85,7 +85,7 @@ struct http_ctx
 
     struct write_ctx
     {
-        bool pending;
+        bool pending, close;
         enum state state;
         struct http_response r;
         off_t n;
@@ -372,6 +372,8 @@ static int write_header_cr_line(struct http_ctx *const h, bool *const close)
         return rw_error(res, close);
     else if ((w->n += res) >= d->len)
     {
+        const bool close_pending = w->close;
+
         dynstr_free(d);
 
         if (w->r.n)
@@ -384,6 +386,8 @@ static int write_header_cr_line(struct http_ctx *const h, bool *const close)
             fprintf(stderr, "%s: write_ctx_free failed\n", __func__);
             return -1;
         }
+        else if (close_pending)
+            *close = true;
     }
 
     return 0;
@@ -394,17 +398,24 @@ static int write_body_mem(struct http_ctx *const h, bool *const close)
     struct write_ctx *const w = &h->wctx;
     const struct http_response *const r = &w->r;
     const size_t rem = r->n - w->n;
-    const int res = h->cfg.write((const char *)r->buf.ro + w->n, rem,
+    int res = h->cfg.write((const char *)r->buf.ro + w->n, rem,
         h->cfg.user);
 
     if (res <= 0)
         return rw_error(res, close);
     else if ((w->n += res) >= r->n)
     {
+        const bool close_pending = w->close;
+
         if (h->version == HTTP_1_0)
             *close = true;
 
-        return write_ctx_free(w);
+        if ((res = write_ctx_free(w)))
+            fprintf(stderr, "%s: write_ctx_free failed\n", __func__);
+        else if (close_pending)
+            *close = true;
+
+        return res;
     }
 
     return 0;
@@ -425,16 +436,21 @@ static int write_body_file(struct http_ctx *const h, bool *const close)
         return -1;
     }
 
-    const int res = h->cfg.write(buf, rem, h->cfg.user);
+    int res = h->cfg.write(buf, rem, h->cfg.user);
 
     if (res <= 0)
         return rw_error(res, close);
     else if ((w->n += res) >= r->n)
     {
+        const bool close_pending = w->close;
+
         if (h->version == HTTP_1_0)
             *close = true;
 
-        return write_ctx_free(w);
+        if ((res = write_ctx_free(w)))
+            fprintf(stderr, "%s: write_ctx_free failed\n", __func__);
+        else if (close_pending)
+            *close = true;
     }
 
     return 0;
@@ -810,7 +826,7 @@ static int check_length(struct http_ctx *const h)
         .value = c->value
     };
 
-    return h->cfg.length(c->post.len, &cookie, h->cfg.user);
+    return h->cfg.length(c->post.len, &cookie, &h->wctx.r, h->cfg.user);
 }
 
 static int header_cr_line(struct http_ctx *const h)
@@ -834,7 +850,10 @@ static int header_cr_line(struct http_ctx *const h)
                     const int res = check_length(h);
 
                     if (res)
-                        return res;
+                    {
+                        h->wctx.close = true;
+                        return start_response(h);
+                    }
                 }
 
                 c->state = BODY_LINE;
diff --git a/http.h b/http.h
index 33f42c6..ed0770f 100644
--- a/http.h
+++ b/http.h
@@ -45,6 +45,7 @@ struct http_payload
     X(UNAUTHORIZED, "Unauthorized", 401) \
     X(FORBIDDEN, "Forbidden", 403) \
     X(NOT_FOUND, "Not found", 404) \
+    X(PAYLOAD_TOO_LARGE, "Payload too large", 413) \
     X(INTERNAL_ERROR, "Internal Server Error", 500)
 
 struct http_response
@@ -80,7 +81,7 @@ struct http_cfg
     int (*payload)(const struct http_payload *p, struct http_response *r,
         void *user);
     int (*length)(unsigned long long len, const struct http_cookie *c,
-        void *user);
+        struct http_response *r, void *user);
     const char *tmpdir;
     void *user;
 };
diff --git a/main.c b/main.c
index 6e461b3..89edae3 100644
--- a/main.c
+++ b/main.c
@@ -610,7 +610,8 @@ static int check_quota(const struct auth *const a, const char *const username,
 }
 
 static int check_length(const unsigned long long len,
-    const struct http_cookie *const c, void *const user)
+    const struct http_cookie *const c, struct http_response *const r,
+    void *const user)
 {
     struct auth *const a = user;
     const char *const username = c->field;
@@ -623,7 +624,16 @@ static int check_length(const unsigned long long len,
         return -1;
     }
     else if (has_quota)
-        return check_quota(a, username, len, quota);
+    {
+        int res = check_quota(a, username, len, quota);
+
+        if (res < 0)
+            fprintf(stderr, "%s: check_quota failed\n", __func__);
+        else if (res > 0 && page_quota_exceeded(r, len, quota) < 0)
+            return -1;
+
+        return res;
+    }
 
     return 0;
 }
diff --git a/page.c b/page.c
index 17adb8a..5cbb0a7 100644
--- a/page.c
+++ b/page.c
@@ -1311,3 +1311,93 @@ end:
 
     return ret;
 }
+
+int page_quota_exceeded(struct http_response *const r,
+    const unsigned long long len, const unsigned long long quota)
+{
+    int ret = -1;
+    struct dynstr msg, out;
+    char q[sizeof MAXSIZEFMT], l[sizeof q];
+    struct html_node *const html = html_node_alloc("html"),
+        *head, *body;
+
+    dynstr_init(&msg);
+    dynstr_init(&out);
+
+    if (!html)
+    {
+        fprintf(stderr, "%s: html_node_alloc failed\n", __func__);
+        goto end;
+    }
+    else if (!(head = html_node_add_child(html, "head")))
+    {
+        fprintf(stderr, "%s: html_node_add_child head failed\n", __func__);
+        goto end;
+    }
+    else if (!(body = html_node_add_child(html, "body")))
+    {
+        fprintf(stderr, "%s: html_node_add_child body failed\n", __func__);
+        goto end;
+    }
+    else if (common_head(head, NULL))
+    {
+        fprintf(stderr, "%s: common_head failed\n", __func__);
+        goto end;
+    }
+    else if (size_units(quota, q, sizeof q))
+    {
+        fprintf(stderr, "%s: size_units quota failed\n", __func__);
+        goto end;
+    }
+    else if (size_units(len, l, sizeof l))
+    {
+        fprintf(stderr, "%s: size_units len failed\n", __func__);
+        goto end;
+    }
+    else if (dynstr_append(&msg, "Maximum quota exceeded: %s "
+        "(requested size: %s)", q, l))
+    {
+        fprintf(stderr, "%s: dynstr_append msg failed\n", __func__);
+        goto end;
+    }
+    else if (html_node_set_value(body, msg.str))
+    {
+        fprintf(stderr, "%s: html_node_set_value msg failed\n", __func__);
+        goto end;
+    }
+    else if (dynstr_append(&out, DOCTYPE_TAG))
+    {
+        fprintf(stderr, "%s: dynstr_prepend failed\n", __func__);
+        goto end;
+    }
+    else if (html_serialize(html, &out))
+    {
+        fprintf(stderr, "%s: html_serialize failed\n", __func__);
+        goto end;
+    }
+
+    *r = (const struct http_response)
+    {
+        .status = HTTP_STATUS_PAYLOAD_TOO_LARGE,
+        .buf.rw = out.str,
+        .n = out.len,
+        .free = free
+    };
+
+    if (http_response_add_header(r, "Content-Type", "text/html"))
+    {
+        fprintf(stderr, "%s: http_response_add_header failed\n", __func__);
+        goto end;
+    }
+
+    ret = 0;
+
+end:
+    html_node_free(html);
+    dynstr_free(&msg);
+
+    if (ret)
+        dynstr_free(&out);
+
+    return ret;
+}
diff --git a/page.h b/page.h
index 9df1eea..094a21e 100644
--- a/page.h
+++ b/page.h
@@ -17,5 +17,7 @@ int page_resource(struct http_response *r, const char *dir, const char *root,
     const char *res, const struct page_quota *q);
 int page_public(struct http_response *r, const char *res);
 int page_share(struct http_response *r, const char *path);
+int page_quota_exceeded(struct http_response *r, unsigned long long len,
+    unsigned long long quota);
 
 #endif /* PAGE_H */