this post was submitted on 27 Oct 2023
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Programming

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I am trying to create a program that downloads a JSON file and I'm trying to convert it to sqlite.

Why?:

  • I believe the training data on Deepdanbooru is weak compaired to Rule34 or Gelbooru. I have tried compiling the C# for linux, but I decided it was too hard.

I am a mainly a Web developer who uses basic JS/HTML/CSS. These don't help as I need it to be in C. (Not ++/#). I have tried using AI to assist, but no matter what language I use (Python, Ruby, Java, C), It will fail.

Here is the closest I gotten ( 〔〕 --> ><:

#include 〔stdio.h〕
#include 〔stdlib.h〕
#include 〔string.h〕
#include 〔curl/curl.h〕
#include "cJSON.h"
#include "sqlite3.h"

#define URL "https://danbooru.donmai.us/posts.json?page=1&amp;limit=1000&amp;tags=duck&amp;json=1"

#define DB_NAME "data.db"

static int callback(void *NotUsed, int argc, char **argv, char **azColName) {
    int i;
    for (i = 0; i &lt; argc; i++) {
        printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
    }
    printf("\n");
    return 0;
}

int main() {
    CURL *curl;
    CURLcode res;
    FILE *fp;
    char *url = URL;
    char outfilename[FILENAME_MAX] = "data.json";
    curl = curl_easy_init();
    if (curl) {
        fp = fopen(outfilename, "wb");
        curl_easy_setopt(curl, CURLOPT_URL, url);
        curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
        curl_easy_setopt(curl, CURLOPT_USERAGENT, "Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)");
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, NULL);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
        res = curl_easy_perform(curl);
        curl_easy_cleanup(curl);
        fclose(fp);
    }
    sqlite3 *db;
    char *err_msg = 0;
    int rc = sqlite3_open(DB_NAME, &amp;db);
    if (rc != SQLITE_OK) {
        fprintf(stderr, "Cannot open database: %s\n", sqlite3_errmsg(db));
        sqlite3_close(db);
        return 1;
    }
    char *sql = "CREATE TABLE data (id INT PRIMARY KEY NOT NULL, md5 TEXT NOT NULL, tag_string TEXT NOT NULL, tag_count_general INT NOT NULL);";
    if (rc != SQLITE_OK) {
        fprintf(stderr, "SQL error: %s\n", err_msg);
        sqlite3_free(err_msg);
        sqlite3_close(db);
        return 1;
    }
    cJSON *json;
    cJSON *item;
    cJSON *id;
    cJSON *md5;
    cJSON *tag_string;
    cJSON *tag_count_general;
    char buffer[1024];
    fp = fopen("data.json", "r");
    fread(buffer, 1024, 1, fp);
    fclose(fp);
    json = cJSON_Parse(buffer);
    if (!json) {
        printf("Error before: [%s]\n", cJSON_GetErrorPtr());
        return 1;
    }
    cJSON_ArrayForEach(item, json) {
        id = cJSON_GetObjectItem(item, "id");
        md5 = cJSON_GetObjectItem(item, "md5");
        tag_string = cJSON_GetObjectItem(item, "tag_string");
        tag_count_general = cJSON_GetObjectItem(item, "tag_count_general");
        char insert_query[1024];
        sprintf(insert_query,
                "INSERT INTO data (id, md5, tag_string, tag_count_general) VALUES (%d,'%s','%s',%d);",
                id->valueint,
                md5->valuestring,
                tag_string->valuestring,
                tag_count_general->valueint
               );
        rc = sqlite3_exec(db, insert_query, callback, 0, &amp;err_msg);
        if (rc != SQLITE_OK) {
            fprintf(stderr, "SQL error: %s\n", err_msg);
            sqlite3_free(err_msg);
            sqlite3_close(db);
            return 1;
        }
    }
}

Compile: gcc cJSON.c file.c -lcurl -lsqlite3

Error: Error before: [tag_count_co]

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[–] Max_P@lemmy.max-p.me 9 points 1 year ago* (last edited 1 year ago) (7 children)
    fp = fopen("data.json", "r");
    fread(buffer, 1024, 1, fp);
    fclose(fp);

You're only reading the first 1024 bytes, that document is much larger than 1024 bytes. So the JSON library gets an incomplete JSON that ends unexpectedly. You need a much larger buffer than 1024 (ideally dynamically allocated to the right size or expandable). fread can also fail or read less than the specified amount of bytes. The correct way to use fread is to keep calling it until it returns <1 and feof returns true, and adjust the pointer in buffer to advance by whatever fread returns since you can't assume it will always return the full requested amount of data. If you have 256b of a file in memory and request to read 1024, it can return you the 256 immediately while it goes fetch the 768 others from disk. It usually doesn't, but it can:

RETURN VALUE
       On success, the number of bytes read is returned (zero indicates end of
       file),  and the file position is advanced by this number.  It is not an
       error if this number is smaller than the  number  of  bytes  requested;
       this  may happen for example because fewer bytes are actually available
       right now (maybe because we were close to end-of-file,  or  because  we
       are reading from a pipe, or from a terminal), or because read() was in‐
       terrupted by a signal.  See also NOTES.

Read man 3 fread and man 2 read for more details, or look it up online.

Any particular reason it has to be C? That would be much much easier in Python or JS since you don't have to worry about that kind of memory management. It's a good learning experience though, C is useful to know even if you never use it, since everything ends up in libc.

[–] Spider89@lemm.ee 1 points 1 year ago (4 children)

Really? That was the issue.

I wanted to learn C after having an Adruino (and making neat programs), but seeing what fread does, that is a nightmare.

Well, Python is my friend now.

Thanks.

[–] abhibeckert@lemmy.world 3 points 1 year ago* (last edited 1 year ago) (2 children)

Well, Python is my friend now.

The Python read() function, which is basically the same as fread() also accepts a length parameter and 1024 is a sensible number to give it.

You can read the entire file in python but you probably shouldn't do that. In the real world, your software will be given files larger than it can handle and it's important to have logic in place to process the file incrementally instead of all at once.

Honestly, it's what makes this particular problem so challenging... the proper way to parse a JSON file is as a "stream" and not by holding the entire string in memory at once unless you can guarantee it's very small.

It's definitely possible to write a C program that reads the entire file. You just won't find many examples of that because it's a bad idea. What if someone gives you a 30GB file?

You said you used an "AI to assist" but it failed? What were you using? I pasted it into ChatGPT 4 and it found eight problems - including this one. Some of the others are even worse... for example the CREATE TABLE query is literally never executed. Oops.

[–] farcaller@fstab.sh 2 points 1 year ago

Streaming JSON parsers are a thing, e.g. pdjson for C. It's, of course, a different approach and it's generally slightly trickier to work with those, but that's what you would use of you have unbound document size and you can process it in chunks.

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