CST-agent/src/attach.c

#ifndef _DEFAULT_SOURCE
#define _DEFAULT_SOURCE
#endif

#include "cJSON.h"
#include "cst_attach.h"
#include "cst_pdf.h"
#include "cst_util.h"
#include "os_compat.h"

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

/* --- base64 -------------------------------------------------------------- */

static const char B64[] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

char *cst_base64_encode(const void *data, size_t n) {
  const unsigned char *p = data;
  size_t olen = ((n + 2) / 3) * 4;
  char *out = malloc(olen + 1);
  if (!out)
    return NULL;
  size_t o = 0;
  for (size_t i = 0; i < n; i += 3) {
    unsigned v = (unsigned)p[i] << 16;
    if (i + 1 < n)
      v |= (unsigned)p[i + 1] << 8;
    if (i + 2 < n)
      v |= (unsigned)p[i + 2];
    out[o++] = B64[(v >> 18) & 63];
    out[o++] = B64[(v >> 12) & 63];
    out[o++] = i + 1 < n ? B64[(v >> 6) & 63] : '=';
    out[o++] = i + 2 < n ? B64[v & 63] : '=';
  }
  out[o] = 0;
  return out;
}

static int b64_val(unsigned char c) {
  if (c >= 'A' && c <= 'Z')
    return c - 'A';
  if (c >= 'a' && c <= 'z')
    return c - 'a' + 26;
  if (c >= '0' && c <= '9')
    return c - '0' + 52;
  if (c == '+' || c == '-')
    return 62;
  if (c == '/' || c == '_')
    return 63;
  return -1;
}

char *cst_base64_decode(const char *s, size_t n, size_t *out_len) {
  if (out_len)
    *out_len = 0;
  if (!s)
    return NULL;
  char *out = malloc(n / 4 * 3 + 4);
  if (!out)
    return NULL;
  size_t o = 0;
  unsigned acc = 0;
  int bits = 0;
  for (size_t i = 0; i < n; i++) {
    unsigned char c = (unsigned char)s[i];
    if (c == '=')
      break;
    if (c == ' ' || c == '\t' || c == '\r' || c == '\n')
      continue;
    int v = b64_val(c);
    if (v < 0) {
      free(out);
      return NULL;
    }
    acc = (acc << 6) | (unsigned)v;
    bits += 6;
    if (bits >= 8) {
      bits -= 8;
      out[o++] = (char)((acc >> bits) & 0xFF);
    }
  }
  if (out_len)
    *out_len = o;
  return out;
}

/* --- format sniffing ----------------------------------------------------- */

static int be32(const unsigned char *p) {
  return (p[0] << 24) | (p[1] << 16) | (p[2] << 8) | p[3];
}

static int le32(const unsigned char *p) {
  return (int)((unsigned)p[0] | ((unsigned)p[1] << 8) |
               ((unsigned)p[2] << 16) | ((unsigned)p[3] << 24));
}

static int le16(const unsigned char *p) {
  return (int)((unsigned)p[0] | ((unsigned)p[1] << 8));
}

static const char *mime_of_ext(const char *mime) {
  if (strcmp(mime, "application/pdf") == 0 ||
      strcmp(mime, "text/plain") == 0)
    return "txt"; /* a document is stored as the text it was reduced to */
  if (strcmp(mime, "image/png") == 0)
    return "png";
  if (strcmp(mime, "image/jpeg") == 0)
    return "jpg";
  if (strcmp(mime, "image/gif") == 0)
    return "gif";
  if (strcmp(mime, "image/webp") == 0)
    return "webp";
  if (strcmp(mime, "image/bmp") == 0)
    return "bmp";
  return "bin";
}

/* A JPEG SOF marker carries the frame size; skip it when scanning. */
static int jpeg_sof(int marker) {
  switch (marker) {
  case 0xC0:
  case 0xC1:
  case 0xC2:
  case 0xC3:
  case 0xC5:
  case 0xC6:
  case 0xC7:
  case 0xC9:
  case 0xCA:
  case 0xCB:
  case 0xCD:
  case 0xCE:
  case 0xCF:
    return 1;
  default:
    return 0;
  }
}

int cst_attach_sniff(const void *data, size_t n, char *mime, size_t mime_sz) {
  const unsigned char *p = data;
  const char *m = NULL;
  if (n >= 8 && memcmp(p, "\x89PNG\r\n\x1a\n", 8) == 0)
    m = "image/png";
  else if (n >= 3 && p[0] == 0xFF && p[1] == 0xD8 && p[2] == 0xFF)
    m = "image/jpeg";
  else if (n >= 6 && memcmp(p, "GIF87a", 6) == 0)
    m = "image/gif";
  else if (n >= 6 && memcmp(p, "GIF89a", 6) == 0)
    m = "image/gif";
  else if (n >= 12 && memcmp(p, "RIFF", 4) == 0 && memcmp(p + 8, "WEBP", 4) == 0)
    m = "image/webp";
  else if (n >= 2 && p[0] == 'B' && p[1] == 'M')
    m = "image/bmp";
  if (!m)
    return -1;
  snprintf(mime, mime_sz, "%s", m);
  return 0;
}

/* PNG / GIF / BMP are direct; JPEG needs a marker walk; WebP has three
 * container flavours. */
int cst_attach_dimensions(const void *data, size_t n, int *w, int *h) {
  const unsigned char *p = data;
  *w = *h = 0;
  char mime[32];
  if (cst_attach_sniff(data, n, mime, sizeof(mime)) != 0)
    return -1;

  if (strcmp(mime, "image/png") == 0) {
    /* 8 signature + 4 length + "IHDR" + w + h */
    if (n < 24 || memcmp(p + 12, "IHDR", 4) != 0)
      return -1;
    *w = be32(p + 16);
    *h = be32(p + 20);
    return 0;
  }
  if (strcmp(mime, "image/gif") == 0) {
    if (n < 10)
      return -1;
    *w = le16(p + 6);
    *h = le16(p + 8);
    return 0;
  }
  if (strcmp(mime, "image/bmp") == 0) {
    if (n < 26)
      return -1;
    int wi = le32(p + 18);
    int hi = le32(p + 22);
    if (wi < 0)
      wi = -wi; /* bottom-up rows are stored with a negative height */
    if (hi < 0)
      hi = -hi;
    *w = wi;
    *h = hi;
    return 0;
  }
  if (strcmp(mime, "image/webp") == 0) {
    if (n < 30)
      return -1;
    const unsigned char *c = p + 12;
    if (memcmp(c, "VP8 ", 4) == 0) {
      /* 4 tag + 3 start code, then 16-bit width / height (14 bits each) */
      if (n < 30 || !(c[7] == 0x9D && c[8] == 0x01 && c[9] == 0x2A))
        return -1;
      *w = le16(c + 10) & 0x3FFF;
      *h = le16(c + 12) & 0x3FFF;
      return 0;
    }
    if (memcmp(c, "VP8L", 4) == 0) {
      if (n < 25 || c[8] != 0x2F)
        return -1;
      unsigned b = (unsigned)c[9] | ((unsigned)c[10] << 8) |
                   ((unsigned)c[11] << 16) | ((unsigned)c[12] << 24);
      *w = (int)(b & 0x3FFF) + 1;
      *h = (int)((b >> 14) & 0x3FFF) + 1;
      return 0;
    }
    if (memcmp(c, "VP8X", 4) == 0) {
      if (n < 30)
        return -1;
      *w = (int)((unsigned)c[12] | ((unsigned)c[13] << 8) |
                 ((unsigned)c[14] << 16)) + 1;
      *h = (int)((unsigned)c[15] | ((unsigned)c[16] << 8) |
                 ((unsigned)c[17] << 16)) + 1;
      return 0;
    }
    return -1;
  }
  if (strcmp(mime, "image/jpeg") == 0) {
    size_t i = 2;
    while (i + 3 < n) {
      if (p[i] != 0xFF)
        return -1; /* lost sync */
      unsigned marker = p[i + 1];
      i += 2;
      if (marker == 0xD8 || (marker >= 0xD0 && marker <= 0xD7))
        continue; /* standalone markers: no payload */
      if (marker == 0xD9 || marker == 0x01)
        continue;
      if (i + 1 >= n)
        return -1;
      size_t seg = (size_t)((p[i] << 8) | p[i + 1]);
      if (seg < 2 || i + seg > n)
        return -1;
      if (jpeg_sof((int)marker) && seg >= 7) {
        *h = (p[i + 3] << 8) | p[i + 4];
        *w = (p[i + 5] << 8) | p[i + 6];
        return 0;
      }
      i += seg;
    }
  }
  return -1;
}

/* --- storage ------------------------------------------------------------- */

/* <session dir>/attachments/<session stem> — beside the JSONL so moving the
 * workspace keeps the two together. */
int cst_attach_dir(const char *session_path, char *out, size_t out_sz) {
  if (!session_path || !session_path[0])
    return -1;
  char dir[OS_PATH_MAX];
  snprintf(dir, sizeof(dir), "%s", session_path);
  char *slash = strrchr(dir, '/');
#ifdef _WIN32
  char *bslash = strrchr(dir, '\\');
  if (bslash && (!slash || bslash > slash))
    slash = bslash;
#endif
  char leaf[256];
  const char *base = slash ? slash + 1 : dir;
  size_t bl = strlen(base);
  if (bl >= sizeof(leaf))
    bl = sizeof(leaf) - 1;
  memcpy(leaf, base, bl);
  leaf[bl] = 0;
  if (slash)
    *(slash + 1) = 0;
  else {
    dir[0] = '.';
    dir[1] = 0;
  }
  char *dot = strstr(leaf, ".jsonl");
  if (dot)
    *dot = 0;
  char rel[320];
  snprintf(rel, sizeof(rel), "attachments/%s", leaf[0] ? leaf : "session");
  char full[OS_PATH_MAX];
  if (os_path_join(full, sizeof(full), dir, rel) != 0)
    return -1;
  if (os_mkdir_p(full, 0700) != 0)
    return -1;
  snprintf(out, out_sz, "%s", full);
  return 0;
}

/* Stored names are "<id>.<ext>" made by store(); anything else in a JSONL
 * (hand-edited or crafted) could point outside the attachment directory. */
int cst_attach_rel_ok(const char *rel) {
  if (!rel || !rel[0] || rel[0] == '.')
    return 0;
  for (const char *p = rel; *p; p++) {
    char c = *p;
    if (!((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') ||
          (c >= '0' && c <= '9') || c == '-' || c == '_' || c == '.'))
      return 0;
  }
  return strstr(rel, "..") == NULL;
}

int cst_attach_full_path(const char *session_path, const cst_attachment_t *a,
                         char *out, size_t out_sz) {
  if (!a || !cst_attach_rel_ok(a->rel))
    return -1;
  char dir[OS_PATH_MAX];
  if (cst_attach_dir(session_path, dir, sizeof(dir)) != 0)
    return -1;
  return os_path_join(out, out_sz, dir, a->rel);
}

static char *read_whole(const char *path, size_t *out_len, size_t max) {
  FILE *f = fopen(path, "rb");
  if (!f)
    return NULL;
  cst_buf_t b = {0};
  char chunk[16384];
  size_t n;
  while ((n = fread(chunk, 1, sizeof(chunk), f)) > 0) {
    if (b.len + n > max || cst_buf_append(&b, chunk, n) != 0) {
      cst_buf_free(&b);
      fclose(f);
      return NULL;
    }
  }
  fclose(f);
  *out_len = b.len;
  return cst_buf_steal(&b);
}

/* FNV over the bytes, the name and the clock: short, stable, unique enough
 * inside one session. */
static void make_id(const char *name, const char *data, size_t n, char *out,
                    size_t out_sz) {
  uint64_t h = cst_fnv1a64(CST_FNV_INIT, data, n > 4096 ? 4096 : n);
  h = cst_fnv1a64(h, name, strlen(name));
  h = cst_fnv1a64(h, &n, sizeof(n));
  double now = os_now_ms();
  h = cst_fnv1a64(h, &now, sizeof(now));
  h = cst_fnv1a64(h, &(int){os_getpid()}, sizeof(int));
  snprintf(out, out_sz, "img-%08x", (unsigned)(h & 0xFFFFFFFFu));
}

/* n bytes, NUL-terminated: a text payload is handed around as a C string. */
static char *memdup_z(const char *data, size_t n) {
  char *copy = malloc(n + 1);
  if (!copy)
    return NULL;
  memcpy(copy, data, n);
  copy[n] = 0;
  return copy;
}

/* What a picked file is, plus the payload to store for it: an image stays as
 * it is, a PDF is reduced to its text layer (the mime still says PDF, the
 * stored file holds text), anything else must be UTF-8 text. The caller frees
 * the result; *out_len is its length. */
static char *prepare(const char *data, size_t n, char *mime, size_t mime_sz,
                     int *pages, size_t *out_len, char *err, size_t err_sz) {
  *pages = 0;
  *out_len = n;
  if (cst_attach_sniff(data, n, mime, mime_sz) == 0) {
    if (n > CST_ATTACH_MAX_BYTES) {
      snprintf(err, err_sz, "image is %.1f MB; the limit is %d MB",
               (double)n / (1024 * 1024), (int)(CST_ATTACH_MAX_BYTES >> 20));
      return NULL;
    }
    char *copy = memdup_z(data, n);
    if (!copy)
      snprintf(err, err_sz, "out of memory");
    return copy;
  }
  if (n >= 4 && memcmp(data, "%PDF", 4) == 0) {
    int pg = 0;
    char perr[256];
    char *text = cst_pdf_text(data, n, &pg, perr, sizeof(perr));
    if (!text) {
      snprintf(err, err_sz, "cannot read the PDF: %.200s", perr);
      return NULL;
    }
    snprintf(mime, mime_sz, "application/pdf");
    *pages = pg;
    *out_len = strlen(text);
    return text;
  }
  if (n > CST_ATTACH_TEXT_MAX) {
    snprintf(err, err_sz, "text is %.1f MB; the limit is %d MB",
             (double)n / (1024 * 1024), (int)(CST_ATTACH_TEXT_MAX >> 20));
    return NULL;
  }
  if (memchr(data, 0, n) || !cst_utf8_valid(data, n)) {
    snprintf(err, err_sz,
             "not an image (PNG, JPEG, GIF, WebP or BMP), a PDF or UTF-8 "
             "text; the content decides, not the extension");
    return NULL;
  }
  snprintf(mime, mime_sz, "text/plain");
  char *copy = memdup_z(data, n);
  if (!copy)
    snprintf(err, err_sz, "out of memory");
  return copy;
}

/* Write one payload whose kind is already known. */
static cst_attachment_t *store(const char *session_path, const char *name,
                               const char *data, size_t n, const char *mime,
                               int pages, const char *origin, char *err,
                               size_t err_sz) {
  if (!name || !name[0])
    name = "image";
  char dir[OS_PATH_MAX];
  if (cst_attach_dir(session_path, dir, sizeof(dir)) != 0) {
    snprintf(err, err_sz, "cannot create the attachment directory");
    return NULL;
  }
  cst_attachment_t *a = calloc(1, sizeof(*a));
  if (!a) {
    snprintf(err, err_sz, "out of memory");
    return NULL;
  }
  make_id(name, data, n, a->id, sizeof(a->id));
  snprintf(a->rel, sizeof(a->rel), "%s.%s", a->id, mime_of_ext(mime));
  snprintf(a->name, sizeof(a->name), "%s", name && name[0] ? name : "image");
  snprintf(a->mime, sizeof(a->mime), "%s", mime);
  snprintf(a->origin, sizeof(a->origin), "%s", origin ? origin : "user");
  snprintf(a->detail, sizeof(a->detail), "auto");
  a->bytes = (long long)n;
  a->pages = pages;
  if (cst_attach_is_image(a))
    cst_attach_dimensions(data, n, &a->width, &a->height);

  char full[OS_PATH_MAX];
  if (cst_attach_full_path(session_path, a, full, sizeof(full)) != 0) {
    snprintf(err, err_sz, "attachment path is too long");
    free(a);
    return NULL;
  }
  FILE *f = fopen(full, "wb");
  if (!f) {
    snprintf(err, err_sz, "cannot write %.200s", full);
    free(a);
    return NULL;
  }
  size_t w = fwrite(data, 1, n, f);
  if (fclose(f) != 0 || w != n) {
    snprintf(err, err_sz, "cannot write %.200s", full);
    free(a);
    return NULL;
  }
  return a;
}

cst_attachment_t *cst_attach_import_bytes(const char *session_path,
                                          const char *name, const char *data,
                                          size_t n, char *err, size_t err_sz) {
  char dummy[8];
  if (!err || !err_sz) {
    err = dummy;
    err_sz = sizeof(dummy);
  }
  err[0] = 0;
  if (!session_path || !session_path[0]) {
    snprintf(err, err_sz, "no session to store the file in");
    return NULL;
  }
  if (!data || !n) {
    snprintf(err, err_sz, "the file is empty");
    return NULL;
  }
  char mime[32];
  if (cst_attach_sniff(data, n, mime, sizeof(mime)) != 0) {
    snprintf(err, err_sz,
             "not a supported image (PNG, JPEG, GIF, WebP or BMP; "
             "checked by content, not by extension)");
    return NULL;
  }
  if (n > CST_ATTACH_MAX_BYTES) {
    snprintf(err, err_sz, "image is %.1f MB; the limit is %d MB",
             (double)n / (1024 * 1024), (int)(CST_ATTACH_MAX_BYTES >> 20));
    return NULL;
  }
  return store(session_path, name, data, n, mime, 0, "user", err, err_sz);
}

cst_attachment_t *cst_attach_import_file(const char *session_path,
                                         const char *src_path, char *err,
                                         size_t err_sz) {
  char dummy[8];
  if (!err || !err_sz) {
    err = dummy;
    err_sz = sizeof(dummy);
  }
  err[0] = 0;
  size_t n = 0;
  char *data = read_whole(src_path, &n, CST_ATTACH_MAX_BYTES);
  if (!data) {
    snprintf(err, err_sz, "cannot read %.300s (or it is larger than %d MB)",
             src_path, (int)(CST_ATTACH_MAX_BYTES >> 20));
    return NULL;
  }
  const char *leaf = src_path;
  for (const char *p = src_path; *p; p++)
    if (*p == '/' || *p == '\\')
      leaf = p + 1;
  char mime[32];
  int pages = 0;
  size_t pn = 0;
  char *payload =
      prepare(data, n, mime, sizeof(mime), &pages, &pn, err, err_sz);
  free(data);
  if (!payload)
    return NULL;
  cst_attachment_t *a =
      store(session_path, leaf, payload, pn, mime, pages, "user", err, err_sz);
  free(payload);
  return a;
}

/* Images are opaque and travel as image parts; everything else is text the
 * store holds and the request inlines. */
int cst_attach_is_image(const cst_attachment_t *a) {
  return a && strncmp(a->mime, "image/", 6) == 0;
}

int cst_attach_is_text(const cst_attachment_t *a) {
  return a && !cst_attach_is_image(a);
}

char *cst_attach_read(const char *session_path, const cst_attachment_t *a,
                      size_t *out_len, char *err, size_t err_sz) {
  char dummy[8];
  if (!err || !err_sz) {
    err = dummy;
    err_sz = sizeof(dummy);
  }
  err[0] = 0;
  char full[OS_PATH_MAX];
  if (cst_attach_full_path(session_path, a, full, sizeof(full)) != 0) {
    snprintf(err, err_sz, "attachment has no stored file");
    return NULL;
  }
  char *data = read_whole(full, out_len, CST_ATTACH_MAX_BYTES);
  if (!data) {
    snprintf(err, err_sz,
             "%.200s is missing; it was deleted from the session store",
             a->name);
    return NULL;
  }
  if (!cst_attach_is_image(a)) /* a document is text, nothing to verify */
    return data;
  char mime[32];
  if (cst_attach_sniff(data, *out_len, mime, sizeof(mime)) != 0) {
    snprintf(err, err_sz, "%.200s in the session store is no longer an image",
             a->name);
    free(data);
    return NULL;
  }
  return data;
}

char *cst_attach_data_url(const char *session_path, const cst_attachment_t *a) {
  if (!cst_attach_is_image(a)) /* a document travels as text, not as a URL */
    return NULL;
  char err[256];
  size_t n = 0;
  char *data = cst_attach_read(session_path, a, &n, err, sizeof(err));
  if (!data)
    return NULL;
  char mime[32];
  cst_attach_sniff(data, n, mime, sizeof(mime)); /* the bytes decide */
  char *b64 = cst_base64_encode(data, n);
  free(data);
  if (!b64)
    return NULL;
  cst_buf_t b = {0};
  cst_buf_printf(&b, "data:%s;base64,", mime);
  cst_buf_puts(&b, b64);
  free(b64);
  return cst_buf_steal(&b);
}

void cst_attach_describe(const cst_attachment_t *a, char *out, size_t out_sz) {
  if (!a) {
    snprintf(out, out_sz, "(none)");
    return;
  }
  const char *kind = a->mime;
  char dim[32] = "";
  if (cst_attach_is_image(a)) {
    if (strncmp(a->mime, "image/", 6) == 0)
      kind = a->mime + 6;
    if (a->width > 0 && a->height > 0)
      snprintf(dim, sizeof(dim), "%dx%d ", a->width, a->height);
  } else if (strcmp(a->mime, "application/pdf") == 0) {
    kind = "pdf";
    if (a->pages > 0)
      snprintf(dim, sizeof(dim), "%d page%s ", a->pages,
               a->pages == 1 ? "" : "s");
  } else if (strcmp(a->mime, "text/plain") == 0 || !a->mime[0]) {
    kind = "text";
  }
  out[0] = 0;
  if (a->bytes >= 1024 * 1024)
    snprintf(out, out_sz, "%s%s %.1f MB", dim, kind,
             (double)a->bytes / (1024 * 1024));
  else if (a->bytes >= 1024)
    snprintf(out, out_sz, "%s%s %.1f KB", dim, kind, (double)a->bytes / 1024);
  else
    snprintf(out, out_sz, "%s%s %lld B", dim, kind, a->bytes);
}

/* --- lifetime ------------------------------------------------------------ */

void cst_attach_free(cst_attachment_t *a) { free(a); }

/* Entries always live in one array (a 1-element array for a single import),
 * so freeing the block releases them all. */
void cst_attachments_free(cst_attachment_t *list, int n) {
  (void)n;
  free(list);
}

cst_attachment_t *cst_attachments_dup(const cst_attachment_t *list, int n) {
  if (!list || n <= 0)
    return NULL;
  cst_attachment_t *out = calloc((size_t)n, sizeof(*out));
  if (!out)
    return NULL;
  for (int i = 0; i < n; i++)
    out[i] = list[i];
  return out;
}

int cst_attachments_push(cst_attachment_t **list, int *n, int *cap,
                         const cst_attachment_t *src) {
  if (!list || !n || !cap || !src)
    return -1;
  if (*n == *cap) {
    int nc = *cap ? *cap * 2 : 4;
    cst_attachment_t *nv = realloc(*list, (size_t)nc * sizeof(**list));
    if (!nv)
      return -1;
    *list = nv;
    *cap = nc;
  }
  (*list)[(*n)++] = *src;
  return 0;
}

/* --- JSONL --------------------------------------------------------------- */

char *cst_attachments_to_json(const cst_attachment_t *list, int n) {
  if (!list || n <= 0)
    return NULL;
  cJSON *arr = cJSON_CreateArray();
  if (!arr)
    return NULL;
  for (int i = 0; i < n; i++) {
    const cst_attachment_t *a = &list[i];
    cJSON *o = cJSON_CreateObject();
    cJSON_AddStringToObject(o, "id", a->id);
    cJSON_AddStringToObject(o, "name", a->name);
    cJSON_AddStringToObject(o, "mime", a->mime);
    cJSON_AddStringToObject(o, "rel", a->rel);
    cJSON_AddNumberToObject(o, "bytes", (double)a->bytes);
    if (a->width > 0 && a->height > 0) {
      cJSON_AddNumberToObject(o, "width", a->width);
      cJSON_AddNumberToObject(o, "height", a->height);
    }
    if (a->pages > 0)
      cJSON_AddNumberToObject(o, "pages", a->pages);
    if (a->detail[0] && strcmp(a->detail, "auto") != 0)
      cJSON_AddStringToObject(o, "detail", a->detail);
    if (a->origin[0])
      cJSON_AddStringToObject(o, "origin", a->origin);
    cJSON_AddItemToArray(arr, o);
  }
  char *s = cJSON_PrintUnformatted(arr);
  cJSON_Delete(arr);
  return s;
}

cst_attachment_t *cst_attachments_from_json(const void *array_json, int *n_out) {
  if (n_out)
    *n_out = 0;
  const cJSON *arr = array_json;
  if (!cJSON_IsArray(arr))
    return NULL;
  int n = cJSON_GetArraySize(arr);
  if (n <= 0)
    return NULL;
  cst_attachment_t *list = calloc((size_t)n, sizeof(*list));
  if (!list)
    return NULL;
  int k = 0;
  const cJSON *it = NULL;
  cJSON_ArrayForEach(it, arr) {
    if (!cJSON_IsObject(it))
      continue;
    const cJSON *jid = cJSON_GetObjectItemCaseSensitive(it, "id");
    const cJSON *jrel = cJSON_GetObjectItemCaseSensitive(it, "rel");
    if (!cJSON_IsString(jid) || !cJSON_IsString(jrel) ||
        !cst_attach_rel_ok(jrel->valuestring))
      continue;
    cst_attachment_t *a = &list[k];
    snprintf(a->id, sizeof(a->id), "%s", jid->valuestring);
    snprintf(a->rel, sizeof(a->rel), "%s", jrel->valuestring);
    const cJSON *v = cJSON_GetObjectItemCaseSensitive(it, "name");
    snprintf(a->name, sizeof(a->name), "%s",
             cJSON_IsString(v) ? v->valuestring : a->id);
    v = cJSON_GetObjectItemCaseSensitive(it, "mime");
    snprintf(a->mime, sizeof(a->mime), "%s",
             cJSON_IsString(v) ? v->valuestring : "image/*");
    v = cJSON_GetObjectItemCaseSensitive(it, "bytes");
    a->bytes = cJSON_IsNumber(v) ? (long long)v->valuedouble : 0;
    v = cJSON_GetObjectItemCaseSensitive(it, "width");
    a->width = cJSON_IsNumber(v) ? v->valueint : 0;
    v = cJSON_GetObjectItemCaseSensitive(it, "height");
    a->height = cJSON_IsNumber(v) ? v->valueint : 0;
    v = cJSON_GetObjectItemCaseSensitive(it, "pages");
    a->pages = cJSON_IsNumber(v) ? v->valueint : 0;
    v = cJSON_GetObjectItemCaseSensitive(it, "detail");
    snprintf(a->detail, sizeof(a->detail), "%s",
             cJSON_IsString(v) ? v->valuestring : "auto");
    v = cJSON_GetObjectItemCaseSensitive(it, "origin");
    snprintf(a->origin, sizeof(a->origin), "%s",
             cJSON_IsString(v) ? v->valuestring : "");
    k++;
  }
  if (k == 0) {
    free(list);
    return NULL;
  }
  if (n_out)
    *n_out = k;
  return list;
}