dcs: initial handling of DCS in general

Add data structure to term->vt. This structure tracks the free-form
data that is passed-through, and the handler to call at the end.

Intermediates and parameters are collected by the normal VT
parser. Then, when we enter the passthrough state, we call dcs_hook().

This function checks the intermediate(s) and parameters, and selects
the appropriate unhook handler (and optionally does some execution
already).

In passthrough mode, we simply append strings to an internal
buffer. This might have to be changed in the future, if we need to
support a DCS that needs to execute as we go.

In unhook (i.e. when the DCS is terminated), we execute the unhook
handler.

As a proof-of-concept, handlers for BSU/ESU (Begin/End Synchronized
Update) has been added (but are left unimplemented).

dcs.c

@@ -0,0 +1,87 @@
+#include "dcs.h"
+
+#define LOG_MODULE "dcs"
+#define LOG_ENABLE_DBG 0
+#include "log.h"
+#include "vt.h"
+
+static void
+bsu(struct terminal *term)
+{
+    LOG_WARN("unimplemented: BSU - Begin Synchronized Update (params: %.*s)",
+             (int)term->vt.dcs.idx, term->vt.dcs.data);
+}
+
+static void
+esu(struct terminal *term)
+{
+    LOG_WARN("unimplemented: ESU - Begin Synchronized Update (params: %.*s)",
+             (int)term->vt.dcs.idx, term->vt.dcs.data);
+}
+
+void
+dcs_hook(struct terminal *term, uint8_t final)
+{
+    LOG_DBG("hook: %c (intermediate(s): %.2s, param=%d)", final, term->vt.private,
+            vt_param_get(term, 0, 127));
+
+    assert(term->vt.dcs.data == NULL);
+    assert(term->vt.dcs.size == 0);
+    assert(term->vt.dcs.unhook_handler == NULL);
+
+    switch (term->vt.private[0]) {
+    case '=':
+        switch (final) {
+        case 's':
+            switch (vt_param_get(term, 0, 0)) {
+            case 1: term->vt.dcs.unhook_handler = &bsu; return;
+            case 2: term->vt.dcs.unhook_handler = &esu; return;
+            }
+            break;
+        }
+        break;
+    }
+}
+
+static bool
+ensure_size(struct terminal *term, size_t required_size)
+{
+    if (required_size <= term->vt.dcs.size)
+        return true;
+
+    size_t new_size = (required_size + 127) / 128 * 128;
+    assert(new_size > 0);
+
+    uint8_t *new_data = realloc(term->vt.dcs.data, new_size);
+    if (new_data == NULL) {
+        LOG_ERRNO("failed to increase size of DCS buffer");
+        return false;
+    }
+
+    term->vt.dcs.data = new_data;
+    term->vt.dcs.size = new_size;
+    return true;
+}
+
+void
+dcs_put(struct terminal *term, uint8_t c)
+{
+    LOG_DBG("PUT: %c", c);
+    ensure_size(term, term->vt.dcs.idx + 1);
+    term->vt.dcs.data[term->vt.dcs.idx++] = c;
+}
+
+void
+dcs_unhook(struct terminal *term)
+{
+    assert(term->vt.dcs.unhook_handler != NULL);
+    if (term->vt.dcs.unhook_handler != NULL)
+        term->vt.dcs.unhook_handler(term);
+
+    term->vt.dcs.unhook_handler = NULL;
+
+    free(term->vt.dcs.data);
+    term->vt.dcs.data = NULL;
+    term->vt.dcs.size = 0;
+    term->vt.dcs.idx = 0;
+}

dcs.h

@@ -0,0 +1,8 @@
+#pragma once
+
+#include <stdbool.h>
+#include "terminal.h"
+
+void dcs_hook(struct terminal *term, uint8_t final);
+void dcs_put(struct terminal *term, uint8_t c);
+void dcs_unhook(struct terminal *term);

meson.build

@@ -70,6 +70,7 @@ executable(
   'config.c', 'config.h',
   'commands.c', 'commands.h',
   'csi.c', 'csi.h',
+  'dcs.c', 'dcs.h',
   'fdm.c', 'fdm.h',
   'grid.c', 'grid.h',
   'input.c', 'input.h',

terminal.h

@@ -125,6 +125,12 @@ struct vt {
         size_t idx;
         size_t left;
     } utf8;
+    struct {
+        uint8_t *data;
+        size_t size;
+        size_t idx;
+        void (*unhook_handler)(struct terminal *term);
+    } dcs;
     struct attributes attrs;
     struct attributes saved_attrs;
 };

vt.c

@@ -9,6 +9,7 @@
 #define LOG_ENABLE_DBG 0
 #include "log.h"
 #include "csi.h"
+#include "dcs.h"
 #include "grid.h"
 #include "osc.h"
 
@@ -482,16 +483,19 @@ action_osc_put(struct terminal *term, uint8_t c)
 static void
 action_hook(struct terminal *term, uint8_t c)
 {
+    dcs_hook(term, c);
 }
 
 static void
 action_unhook(struct terminal *term, uint8_t c)
 {
+    dcs_unhook(term);
 }
 
 static void
 action_put(struct terminal *term, uint8_t c)
 {
+    dcs_put(term, c);
 }
 
 static void