feat: Support table view for C client.

[shibd]

Motivation

Support table view for C client.

Modifications

• Add table_view for C client.
• Add table_view_configuration for C client.

Verifying this change

• Add CTableViewTest cover it.

Documentation

• doc-required
  (Your PR needs to update docs and you will update later)

• doc-not-needed
  (Please explain why)

• doc
  (Your PR contains doc changes)

• doc-complete
  (Docs have been already added)

[BewareMyPower]

In addition, I don't think use a null-terminated string as the tableview value is good for C API. The value is actually a byte array rather than a null-terminated string. Unlike the TableView class, it's okay to return a std::string, which is actually a byte array in C++. For example, if the producer sends 4 bytes: [0x01, 0x00, 0x02, 0x00], you can never know the length.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static void get_value(char **value) {
  char *data = (char *)malloc(4);
  data[0] = 0x01;
  data[1] = 0x00;
  data[2] = 0x02;
  data[3] = 0x00;
  *value = data;
}

int main(int argc, char *argv[]) {
  char *value;
  get_value(&value);
  printf("length: %zu\n", strlen(value));
  return 0;
}

The code example is a demo to show the difference between a byte array and a null-terminated string.

So it's better to add a length parameter like:

#include <stdio.h>
#include <stdlib.h>

static void get_value(char **value_ptr, size_t *value_len) {
  char *data = (char *)malloc(4);
  data[0] = 0x01;
  data[1] = 0x00;
  data[2] = 0x02;
  data[3] = 0x00;
  *value_ptr = data;
  *value_len = 4;
}

int main(int argc, char *argv[]) {
  char *value;
  size_t len;
  get_value(&value, &len);
  printf("length: %zu\n", len);
  for (size_t i = 0; i < len; i++) {
    printf("0x%02x%c", value[i], (i < len - 1) ? ' ' : '\n');
  }
  return 0;
}

Output:

length: 4
0x01 0x00 0x02 0x00

[shibd]

In addition, I don't think use a null-terminated string as the tableview value is good for C API. The value is actually a byte array rather than a null-terminated string. Unlike the TableView class, it's okay to return a std::string, which is actually a byte array in C++. For example, if the producer sends 4 bytes: [0x01, 0x00, 0x02, 0x00], you can never know the length.

Thanks explain, that makes sense to me.

New commit modifications:

1. Add *value_size param on pulsar_table_view_get_value, pulsar_table_view_retrieve_value method and pulsar_table_view_action.
2. Change *value type from char **value to void **value.
3. Remove pulsar_string_map_t *pulsar_table_view_snapshot(pulsar_table_view_t *table_view) method. Because on this case.

• pulsar_string_map_get also does not return value_size,
• this string_map may not be suitable for table_view for C.
• I think the table_view currently provided interface can meet the user use case.
• If needed, I'll add it in another PR.

PTAL.

[BewareMyPower]

LGTM except the example is still wrong.