支持了按 chunk 返回的 HTTP 客户端 #1718

#include "workflow/WFHttpChunkedClient.h"
#include "workflow/WFFacilities.h"
#include <stdio.h>

void extract(WFHttpChunkedTask *task)
{
    protocol::HttpResponse *resp = task->get_resp();   // 可以获得resp的header等信息。
    protocol::HttpMessageChunk *chunk = task->get_chunk();
    const void *chunk_data;
    size_t chunk_size;

    chunk->get_chunk_data(&chunk_data, &chunk_size);    // extract函数里，get_chunk_data必然成功
    printf("Chunk size = %zu. Chunk data:\n", chunk_size);
    fwrite(chunk_data, chunk_size, 1, stdout);
    printf("\n");
}

WFFacilities::WaitGroup wg(1);

void callback(WFHttpChunkedTask *task)
{
    protocol::HttpResponse *resp = task->get_resp();
    printf("state = %d, error = %d\n", task->get_state(), task->get_error());
    if (task->get_state() == WFT_STATE_SUCCESS)
        printf("%s %s %s", resp->get_http_version(), resp->get_status_code(), resp->get_reason_phrase());

    wg.done();
}

int main()
{
    WFHttpChunkedTask *task = WFHttpChunkedClient::create_chunked_task("http://github.com/", 3, extract, callback);
    task->start();
    wg.wait();
}

void extract(WFHttpChunkedTask *task)
{
    protocol::HttpMessageChunk *chunk = task->get_chunk();
    auto *c = new protocol::HttpMessageChunk(std::move(*chunk));
    ...
}