feat(lex): add snapshot recording and appling features

docs/Melon Developer Guide.txt

@@ -787,6 +787,12 @@ Their definitions can be found in melon/include/mln_types.h.
             MLN_LEX_EMANYMACRODEF
             MLN_LEX_EINVMACRO
 
+     p) mln_lex_off_t mln_lex_snapshot_record(mln_lex_t *lex);
+        Snapshotted the current input stream position.
+
+     q) void mln_lex_snapshot_apply(mln_lex_t *lex, mln_lex_off_t off);
+        Apply the snapshot to the current input stream, restoring the read offset to the snapshot position.
+
   10) Configuration
      As shown below, this is the architecture of configuration.
      -------       -------        -------       -------

docs/book/cn/lex.md

@@ -424,6 +424,30 @@ mln_lex_init_with_hooks(PREFIX_NAME,lex_ptr,attr_ptr)
 
 
 
+#### mln_lex_snapshot_record
+
+```c
+mln_lex_off_t mln_lex_snapshot_record(mln_lex_t *lex);
+```
+
+描述：记录当前输入流的位置信息。
+
+返回值：文件内偏移或内存地址
+
+
+
+#### mln_lex_snapshot_apply
+
+```c
+void mln_lex_snapshot_apply(mln_lex_t *lex, mln_lex_off_t off);
+```
+
+描述：恢复当前输入流的读取偏移到快照的位置。注意，这个函数应用时应确保当前输入流是`mln_lex_snapshot_record`调用时的输入流，函数中会进行一定的检查，但并不能确保万无一失。
+
+返回值：无
+
+
+
 ### 示例
 
 ```c

docs/book/en/lex.md

@@ -418,6 +418,30 @@ Return value: There is no return value, but it should be checked whether `lex_pt
 
 
 
+#### mln_lex_snapshot_record
+
+```c
+mln_lex_off_t mln_lex_snapshot_record(mln_lex_t *lex);
+```
+
+Description: Records the position information of the current input stream.
+
+Return value: File offset or memory address
+
+
+
+#### mln_lex_snapshot_apply
+
+```c
+void mln_lex_snapshot_apply(mln_lex_t *lex, mln_lex_off_t off);
+```
+
+Description: Restores the read offset of the current input stream to the position of the snapshot. Note that this function should ensure that the current input stream is the one when `mln_lex_snapshot_record` was called. The function performs some checks, but does not guarantee complete safety.
+
+Return value: None.
+
+
+
 ### Example
 
 ```c

include/mln_lex.h

@@ -136,6 +136,11 @@ struct mln_lex_attr {
     mln_string_t       *data;
 };
 
+typedef union {
+    mln_u8ptr_t         soff;
+    off_t               foff;
+} mln_lex_off_t;
+
 typedef struct {
     mln_u32_t           type;
     int                 fd;
@@ -207,6 +212,8 @@ extern int mln_lex_condition_test(mln_lex_t *lex) __NONNULL1(1);
 extern mln_lex_input_t *
 mln_lex_input_new(mln_lex_t *lex, mln_u32_t type, mln_string_t *data, int *err, mln_u64_t line) __NONNULL3(1,3,4);
 extern void mln_lex_input_free(void *in);
+extern mln_lex_off_t mln_lex_snapshot_record(mln_lex_t *lex);
+extern void mln_lex_snapshot_apply(mln_lex_t *lex, mln_lex_off_t off);
 #define mln_lex_get_pool(lex) ((lex)->pool)
 #define mln_lex_result_clean(lex) ((lex)->result_pos = (lex)->result_buf)
 #define mln_lex_get_cur_filename(lex) \

src/mln_lex.c

@@ -742,3 +742,39 @@ MLN_FUNC(, int, mln_lex_condition_test, (mln_lex_t *lex), (lex), {
     return reverse? 0: 1;
 })
 
+MLN_FUNC(, mln_lex_off_t, mln_lex_snapshot_record, (mln_lex_t *lex), (lex), {
+    mln_lex_off_t ret;
+    mln_lex_input_t *input = lex->cur;
+
+    if (input == NULL && (input = mln_stack_top(lex->stack)) == NULL) {
+        ret.soff = NULL;
+        return ret;
+    }
+
+    if (input->type == M_INPUT_T_BUF) {
+        ret.soff = input->pos;
+    } else {
+        ret.foff = lseek(input->fd, 0, SEEK_CUR) - (input->buf_len - (input->pos - input->buf));
+    }
+
+    return ret;
+})
+
+MLN_FUNC_VOID(, void, mln_lex_snapshot_apply, (mln_lex_t *lex, mln_lex_off_t off), (lex, off), {
+    mln_lex_input_t *input = lex->cur;
+
+    if (input == NULL && (input = mln_stack_top(lex->stack)) == NULL) {
+        return;
+    }
+    if (input->type == M_INPUT_T_BUF) {
+        if (off.soff < input->buf || off.soff >= input->buf + input->buf_len) return;
+
+        input->pos = off.soff;
+    } else {
+        off_t foff = lseek(input->fd, 0, SEEK_CUR);
+        if (off.foff >= foff || off.foff < foff - input->buf_len) return;
+        lseek(input->fd, off.foff, SEEK_SET);
+        input->pos = input->buf + input->buf_len;
+    }
+})
+