reduce amount of code generated for each logpoint (also prepare for tid)

include/picotls.h

diff --git a/include/picotls.h b/include/picotls.h
index 2b4105a..f6cdfc7 100644
--- a/include/picotls.h
+++ b/include/picotls.h
@@ -1403,17 +1403,13 @@
         do {                                                                                                                       \
             char smallbuf[128];                                                                                                    \
             ptls_buffer_t ptlslogbuf;                                                                                              \
-            ptls_buffer_init(&ptlslogbuf, smallbuf, sizeof(smallbuf));                                                             \
-            PTLS_LOG__DO_PUSH_SAFESTR("{\"module\":\"" PTLS_TO_STR(module) "\",\"type\":\"" PTLS_TO_STR(name) "\"");               \
+            ptls_log__do_write_start(&logpoint, &ptlslogbuf, smallbuf, sizeof(smallbuf));                                          \
             do {                                                                                                                   \
                 block                                                                                                              \
             } while (0);                                                                                                           \
-            PTLS_LOG__DO_PUSH_SAFESTR("}\n");                                                                                      \
-            if (!ptlslog_skip)                                                                                                     \
-                ptlslog_include_appdata =                                                                                          \
-                    ptls_log__do_write(&logpoint, (conn_state), (get_sni), (get_sni_arg), &ptlslogbuf, ptlslog_include_appdata);   \
-            ptls_buffer_dispose(&ptlslogbuf);                                                                                      \
-        } while (!ptlslog_skip && ptlslog_include_appdata);                                                                        \
+            ptlslog_include_appdata = ptls_log__do_write_end(ptlslog_skip ? NULL : &logpoint, (conn_state), (get_sni),             \
+                                                             (get_sni_arg), &ptlslogbuf, ptlslog_include_appdata);                 \
+        } while (ptlslog_include_appdata);                                                                                         \
     } while (0)
 
 #define PTLS_LOG_DEFINE_POINT(_module, _name, _var)                                                                                \
@@ -1640,8 +1636,9 @@
 int ptls_log__do_push_signed64(ptls_buffer_t *buf, int64_t v);
 int ptls_log__do_push_unsigned32(ptls_buffer_t *buf, uint32_t v);
 int ptls_log__do_push_unsigned64(ptls_buffer_t *buf, uint64_t v);
-int ptls_log__do_write(struct st_ptls_log_point_t *point, struct st_ptls_log_conn_state_t *conn, const char *(*get_sni)(void *),
-                       void *get_sni_arg, const ptls_buffer_t *buf, int includes_appdata);
+void ptls_log__do_write_start(struct st_ptls_log_point_t *point, ptls_buffer_t *buf, void *smallbuf, size_t smallbufsize);
+int ptls_log__do_write_end(struct st_ptls_log_point_t *point, struct st_ptls_log_conn_state_t *conn, const char *(*get_sni)(void *),
+                           void *get_sni_arg, ptls_buffer_t *buf, int includes_appdata);
 
 /**
  * create a client object to handle new TLS connection

lib/picotls.c

diff --git a/lib/picotls.c b/lib/picotls.c
index 37151e6..81661db 100644
--- a/lib/picotls.c
+++ b/lib/picotls.c
@@ -7102,12 +7102,31 @@
 #endif
 }
 
-int ptls_log__do_write(struct st_ptls_log_point_t *point, struct st_ptls_log_conn_state_t *conn, const char *(*get_sni)(void *),
-                       void *get_sni_arg, const ptls_buffer_t *buf, int includes_appdata)
+void ptls_log__do_write_start(struct st_ptls_log_point_t *point, ptls_buffer_t *buf, void *smallbuf, size_t smallbufsize)
 {
+    const char *colon_at = strchr(point->name, ':');
+
+    ptls_buffer_init(buf, smallbuf, smallbufsize);
+
+    int written = snprintf((char *)buf->base, buf->capacity, "{\"module\":\"%.*s\",\"type\":\"%s\"", (int)(colon_at - point->name),
+                           point->name, colon_at + 1);
+    assert(written > 0 && written < buf->capacity && "caller MUST provide smallbuf suffient to emit the prefix");
+    buf->off = (size_t)written;
+}
+
+int ptls_log__do_write_end(struct st_ptls_log_point_t *point, struct st_ptls_log_conn_state_t *conn, const char *(*get_sni)(void *),
+                           void *get_sni_arg, ptls_buffer_t *buf, int includes_appdata)
+{
+    int needs_appdata = 0;
+
 #if PTLS_HAVE_LOG
     uint32_t active;
-    int needs_appdata = 0;
+
+    /* point == NULL indicates skip */
+    if (point == NULL || ptls_buffer_reserve(buf, 2) != 0)
+        goto Exit;
+    buf->base[buf->off++] = '}';
+    buf->base[buf->off++] = '\n';
 
     pthread_mutex_lock(&logctx.mutex);
 
@@ -7152,9 +7171,9 @@
 
     if (includes_appdata)
         assert(!needs_appdata);
-
-    return needs_appdata;
-#else
-    return 0;
 #endif
+
+Exit:
+    ptls_buffer_dispose(buf);
+    return needs_appdata;
 }