c语言解析 form-data数据

要解析form-data数据，需要先了解一下form-data的格式。form-data是一种常见的HTTP POST请求体格式，用于向服务器发送表单数据。其格式如下：

Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryxyzabc

------WebKitFormBoundaryxyzabc
Content-Disposition: form-data; name="field1"

value1
------WebKitFormBoundaryxyzabc
Content-Disposition: form-data; name="field2"; filename="example.txt"
Content-Type: text/plain

file contents
------WebKitFormBoundaryxyzabc--

其中，boundary指定了分隔符。在解析form-data数据时，需要按照分隔符将数据分割成多个部分，然后对每个部分进行解析。

以下是一个简单的C语言代码示例，用于解析form-data数据：

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

int main() {
    char *data = "------WebKitFormBoundaryxyzabc\r\nContent-Disposition: form-data; name=\"field1\"\r\n\r\nvalue1\r\n------WebKitFormBoundaryxyzabc\r\nContent-Disposition: form-data; name=\"field2\"; filename=\"example.txt\"\r\nContent-Type: text/plain\r\n\r\nfile contents\r\n------WebKitFormBoundaryxyzabc--\r\n";
    char *boundary = "------WebKitFormBoundaryxyzabc";
    
    // find the first part boundary
    char *part_start = strstr(data, boundary);
    if (part_start == NULL) {
        printf("Error: cannot find the first part boundary.\n");
        return 1;
    }
    
    // parse each part
    while (1) {
        // find the next part boundary
        char *part_end = strstr(part_start + strlen(boundary), boundary);
        if (part_end == NULL) {
            printf("Error: cannot find the next part boundary.\n");
            return 1;
        }
        
        // get the part data
        char *part_data_start = part_start + strlen(boundary) + 2;  // skip CRLF
        char *part_data_end = part_end - 2;  // skip CRLF
        int part_data_len = part_data_end - part_data_start;
        char part_data[part_data_len + 1];
        memcpy(part_data, part_data_start, part_data_len);
        part_data[part_data_len] = '\0';
        
        // parse the part data
        char *name_start = strstr(part_start, "name=\"");
        if (name_start == NULL) {
            printf("Error: cannot find the name attribute.\n");
            return 1;
        }
        name_start += 6;  // skip "name=\""
        char *name_end = strstr(name_start, "\"");
        if (name_end == NULL) {
            printf("Error: cannot find the end of the name attribute.\n");
            return 1;
        }
        int name_len = name_end - name_start;
        char name[name_len + 1];
        memcpy(name, name_start, name_len);
        name[name_len] = '\0';
        
        char *filename_start = strstr(part_start, "filename=\"");
        if (filename_start != NULL) {
            // this is a file part
            filename_start += 10;  // skip "filename=\""
            char *filename_end = strstr(filename_start, "\"");
            if (filename_end == NULL) {
                printf("Error: cannot find the end of the filename attribute.\n");
                return 1;
            }
            int filename_len = filename_end - filename_start;
            char filename[filename_len + 1];
            memcpy(filename, filename_start, filename_len);
            filename[filename_len] = '\0';
            
            printf("Part name: %s, filename: %s, data: %s\n", name, filename, part_data);
        } else {
            // this is a regular part
            printf("Part name: %s, data: %s\n", name, part_data);
        }
        
        part_start = part_end;
        if (part_start[2] == '-') {
            break;  // end of data
        }
    }
    
    return 0;
}

该代码将form-data数据解析为多个部分，并对每个部分进行解析。如果是文件部分，会输出文件名和文件内容；否则，只输出表单字段名和值。