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Filename : element_declarations.c
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/* Read an XML document from standard input and print
   element declarations (if any) to standard output.
   It must be used with Expat compiled for UTF-8 output.
                            __  __            _
                         ___\ \/ /_ __   __ _| |_
                        / _ \\  /| '_ \ / _` | __|
                       |  __//  \| |_) | (_| | |_
                        \___/_/\_\ .__/ \__,_|\__|
                                 |_| XML parser

   Copyright (c) 1997-2000 Thai Open Source Software Center Ltd
   Copyright (c) 2001-2003 Fred L. Drake, Jr. <fdrake@users.sourceforge.net>
   Copyright (c) 2004-2006 Karl Waclawek <karl@waclawek.net>
   Copyright (c) 2005-2007 Steven Solie <steven@solie.ca>
   Copyright (c) 2016-2024 Sebastian Pipping <sebastian@pipping.org>
   Copyright (c) 2017      Rhodri James <rhodri@wildebeest.org.uk>
   Copyright (c) 2019      Zhongyuan Zhou <zhouzhongyuan@huawei.com>
   Licensed under the MIT license:

   Permission is  hereby granted,  free of charge,  to any  person obtaining
   a  copy  of  this  software   and  associated  documentation  files  (the
   "Software"),  to  deal in  the  Software  without restriction,  including
   without  limitation the  rights  to use,  copy,  modify, merge,  publish,
   distribute, sublicense, and/or sell copies of the Software, and to permit
   persons  to whom  the Software  is  furnished to  do so,  subject to  the
   following conditions:

   The above copyright  notice and this permission notice  shall be included
   in all copies or substantial portions of the Software.

   THE  SOFTWARE  IS  PROVIDED  "AS  IS",  WITHOUT  WARRANTY  OF  ANY  KIND,
   EXPRESS  OR IMPLIED,  INCLUDING  BUT  NOT LIMITED  TO  THE WARRANTIES  OF
   MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
   NO EVENT SHALL THE AUTHORS OR  COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
   DAMAGES OR  OTHER LIABILITY, WHETHER  IN AN  ACTION OF CONTRACT,  TORT OR
   OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
   USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

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

#ifdef XML_LARGE_SIZE
#  define XML_FMT_INT_MOD "ll"
#else
#  define XML_FMT_INT_MOD "l"
#endif

#ifdef XML_UNICODE_WCHAR_T
#  define XML_FMT_STR "ls"
#else
#  define XML_FMT_STR "s"
#endif

// While traversing the XML_Content tree, we avoid recursion
// to not be vulnerable to a denial of service attack.
typedef struct StackStruct {
  const XML_Content *model;
  unsigned level;
  struct StackStruct *prev;
} Stack;

static Stack *
stackPushMalloc(Stack *stackTop, const XML_Content *model, unsigned level) {
  Stack *const newStackTop = malloc(sizeof(Stack));
  if (! newStackTop) {
    return NULL;
  }
  newStackTop->model = model;
  newStackTop->level = level;
  newStackTop->prev = stackTop;
  return newStackTop;
}

static Stack *
stackPopFree(Stack *stackTop) {
  Stack *const newStackTop = stackTop->prev;
  free(stackTop);
  return newStackTop;
}

static char *
contentTypeName(enum XML_Content_Type contentType) {
  switch (contentType) {
  case XML_CTYPE_EMPTY:
    return "EMPTY";
  case XML_CTYPE_ANY:
    return "ANY";
  case XML_CTYPE_MIXED:
    return "MIXED";
  case XML_CTYPE_NAME:
    return "NAME";
  case XML_CTYPE_CHOICE:
    return "CHOICE";
  case XML_CTYPE_SEQ:
    return "SEQ";
  default:
    return "???";
  }
}

static char *
contentQuantName(enum XML_Content_Quant contentQuant) {
  switch (contentQuant) {
  case XML_CQUANT_NONE:
    return "NONE";
  case XML_CQUANT_OPT:
    return "OPT";
  case XML_CQUANT_REP:
    return "REP";
  case XML_CQUANT_PLUS:
    return "PLUS";
  default:
    return "???";
  }
}

static void
dumpContentModelElement(const XML_Content *model, unsigned level,
                        const XML_Content *root) {
  // Indent
  unsigned u = 0;
  for (; u < level; u++) {
    printf("  ");
  }

  // Node
  printf("[%u] type=%s(%d), quant=%s(%d)", (unsigned)(model - root),
         contentTypeName(model->type), model->type,
         contentQuantName(model->quant), model->quant);
  if (model->name) {
    printf(", name=\"%" XML_FMT_STR "\"", model->name);
  } else {
    printf(", name=NULL");
  }
  printf(", numchildren=%d", model->numchildren);
  printf("\n");
}

static bool
dumpContentModel(const XML_Char *name, const XML_Content *root) {
  printf("Element \"%" XML_FMT_STR "\":\n", name);
  Stack *stackTop = stackPushMalloc(NULL, root, 1);
  if (! stackTop) {
    return false;
  }

  while (stackTop) {
    const XML_Content *const model = stackTop->model;
    const unsigned level = stackTop->level;

    dumpContentModelElement(model, level, root);

    stackTop = stackPopFree(stackTop);

    for (size_t u = model->numchildren; u >= 1; u--) {
      Stack *const newStackTop
          = stackPushMalloc(stackTop, model->children + (u - 1), level + 1);
      if (! newStackTop) {
        // We ran out of memory, so let's free all memory allocated
        // earlier in this function, to be leak-clean:
        while (stackTop != NULL) {
          stackTop = stackPopFree(stackTop);
        }
        return false;
      }
      stackTop = newStackTop;
    }
  }

  printf("\n");
  return true;
}

static void XMLCALL
handleElementDeclaration(void *userData, const XML_Char *name,
                         XML_Content *model) {
  XML_Parser parser = (XML_Parser)userData;
  const bool success = dumpContentModel(name, model);
  XML_FreeContentModel(parser, model);
  if (! success) {
    XML_StopParser(parser, /* resumable= */ XML_FALSE);
  }
}

int
main(void) {
  XML_Parser parser = XML_ParserCreate(NULL);
  int done;

  if (! parser) {
    fprintf(stderr, "Couldn't allocate memory for parser\n");
    return 1;
  }

  XML_SetUserData(parser, parser);
  XML_SetElementDeclHandler(parser, handleElementDeclaration);

  do {
    void *const buf = XML_GetBuffer(parser, BUFSIZ);
    if (! buf) {
      fprintf(stderr, "Couldn't allocate memory for buffer\n");
      XML_ParserFree(parser);
      return 1;
    }

    const size_t len = fread(buf, 1, BUFSIZ, stdin);

    if (ferror(stdin)) {
      fprintf(stderr, "Read error\n");
      XML_ParserFree(parser);
      return 1;
    }

    done = feof(stdin);

    if (XML_ParseBuffer(parser, (int)len, done) == XML_STATUS_ERROR) {
      enum XML_Error errorCode = XML_GetErrorCode(parser);
      if (errorCode == XML_ERROR_ABORTED) {
        errorCode = XML_ERROR_NO_MEMORY;
      }
      fprintf(stderr,
              "Parse error at line %" XML_FMT_INT_MOD "u:\n%" XML_FMT_STR "\n",
              XML_GetCurrentLineNumber(parser), XML_ErrorString(errorCode));
      XML_ParserFree(parser);
      return 1;
    }
  } while (! done);

  XML_ParserFree(parser);
  return 0;
}