/***************************************************************************
 * xml.cc -- Simple library to emit XML.                                   *
 ***********************IMPORTANT NMAP LICENSE TERMS************************
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/* $Id: xml.cc 15135 2009-08-19 21:05:21Z david $ */

/*
This is a simple library for writing XML. It handles two main things:
keeping track of the element stack, and escaping text where necessary.
If you wanted to write this XML:
  <?xml version="1.0" encoding="UTF-8"?>
  <!DOCTYPE elem>
  <elem name="&amp;10.5"></elem>
these are the functions you would call. Each one is followed by the text
it prints enclosed in ||.

xml_start_document("elem")             |<?xml version="1.0" encoding="UTF-8"?>\n<!DOCTYPE elem>|
xml_newline();                         |\n|
xml_open_start_tag("elem");            |<elem|
xml_attribute("name", "&%.1f", 10.5);  | name="&amp;10.5"|
xml_close_start_tag();                 |>|
xml_end_tag();                         |</elem>|

The typical use is to call xml_open_start_tag, then call xml_attribute a
number of times. That is followed by xml_close_empty_tag, or else
xml_close_start_tag followed by xml_end_tag later on. You can call
xml_start_tag if there are no attributes. Whenever a start tag is opened
with xml_open_start_tag or xml_start_tag, the element name is pushed on
the tag stack. xml_end_tag pops the element stack and closes the element
it finds.

Here is a summary of all the elementary writing functions. The functions
return 0 on success and -1 on error. The terms "start" and "end" refer
to start and end tags and the start and end of comments. The terms
"open" and "close" refer only to start tags and processing instructions.

xml_start_comment()           |<!--|
xml_end_comment()             |-->|
xml_open_pi("elem")           |<?elem|
xml_close_pi()                |?>|
xml_open_start_tag("elem")    |<elem|
xml_close_start_tag()         |>|
xml_close_empty_tag()         |/>|
xml_start_tag("elem")         |<elem>|
xml_end_tag()                 |</elem>|
xml_attribute("name", "val")  | name="val"|
xml_newline()                 |\n|

Additional functions are

xml_write_raw                 Raw unescaped output.
xml_write_escaped             XML-escaped output.
xml_write_escaped_v           XML-escaped output, with a va_list.
xml_start_document            Writes <?xml version="1.0" encoding="UTF-8"?>\n<!DOCTYPE elem>.
xml_depth                     Returns the size of the element stack.

The library makes it harder but not impossible to make non-well-formed
XML. For example, you can call xml_start_tag, xml_end_tag,
xml_start_tag, xml_end_tag to create a document with two root elements.
Things like element names aren't checked to be sure they're legal. Text
given to these functions should be ASCII or UTF-8.

All writing is done with log_write(LOG_XML), so if LOG_XML hasn't been
opened, calling these functions has no effect.
*/

#include "output.h"
#include "xml.h"
#include <nbase.h>

#include <assert.h>
#include <stdarg.h>
#include <stdio.h>
#include <list>

struct xml_writer {
  /* Sanity checking: Don't open a new tag while still defining
     attributes for another, like "<elem1<elem2". */
  bool tag_open;
  /* Has the root element been started yet? If so, and if
     element_stack.size() == 0, then the document is finished. */
  bool root_written;
  std::list<const char *> element_stack;
};

static struct xml_writer xml;

char *xml_unescape(const char *str) {
  size_t n = strlen(str) + 1;
  char *result = (char *) safe_malloc(n);
  size_t i = 0;

  for (const char *p = str; *p != '\0'; p++) {

    // Make sure there's enough space for 1 character. None of the replacements
    // here produce more than 1 character of unescaped output, so this function
    // should strictly return a string shorter than the original.
    assert(i < n - 1);

    // ordinary case: plain copy
    if (*p != '&') {
plain_copy:
      result[i++] = *p;
      continue;
    }

    // ampersand introduces entity
    const char *q = strchr(p + 1, ';');
    if (!q) {
      // unterminated entity
      goto plain_copy;
    }

    // decode the entity
    if (p[1] == '#') {
      // numeric entity
      long codepoint = 0;
      char *invalp = NULL;

      if (p[2] == 'x') {
        codepoint = strtol(p + 3, &invalp, 16);
      }
      else {
        codepoint = strtol(p + 2, &invalp, 10);
      }

      /* For now, we will not support unescape of code points greater than
       * 0xff. Anything higher requires choosing a multibyte encoding. */
      if (invalp != q || codepoint < 0 || codepoint > 0xff) {
        goto plain_copy;
      }
      result[i++] = (char) codepoint;
    }
    else if (strncmp(p, "lt;", 3) == 0) {
      result[i++] = '<';
    } else if (strncmp(p, "gt;", 3) == 0) {
      result[i++] = '>';
    } else if (strncmp(p, "amp;", 4) == 0) {
      result[i++] = '&';
    } else if (strncmp(p, "quot;", 5) == 0) {
      result[i++] = '"';
    } else if (strncmp(p, "apos;", 5) == 0) {
      result[i++] = '\'';
    } else {
      // unsupported entity
      goto plain_copy;
    }

    // jump to the ';' and let the loop move to the next character.
    p = q;
  }
  result[i] = '\0';

  return result;
}

/* Escape a string for inclusion in XML. This gets <>&, "' for attribute
   values, -- for inside comments, and characters with value > 0x7F. It
   also gets control characters with value < 0x20 to avoid parser
   normalization of \r\n\t in attribute values. If this is not desired
   in some cases, we'll have to add a parameter to control this. */
static char *escape(const char *str) {
  /* result is the result buffer; n + 1 is the allocated size. Double the
     allocation when space runs out. */
  size_t n = strlen(str);
  char *result = (char *) safe_malloc(n + 1);
  size_t len;
  const char *p;
  int i;

  i = 0;
  for (p = str; *p != '\0'; p++) {
    const char *repl;
    char buf[32];

    if (*p == '<')
      repl = "&lt;";
    else if (*p == '>')
      repl = "&gt;";
    else if (*p == '&')
      repl = "&amp;";
    else if (*p == '"')
      repl = "&quot;";
    else if (*p == '\'')
      repl = "&apos;";
    else if (*p == '-' && p > str && *(p - 1) == '-') {
      /* Escape -- for comments. */
      repl = "&#45;";
    } else if (*p < 0x20 || (unsigned char) *p > 0x7F) {
      /* Escape control characters and anything outside of ASCII. We have to
         emit UTF-8 and an easy way to do that is to emit ASCII. */
      Snprintf(buf, sizeof(buf), "&#x%x;", (unsigned char) *p);
      repl = buf;
    } else {
      /* Unescaped character. */
      buf[0] = *p;
      buf[1] = '\0';
      repl = buf;
    }

    len = strlen(repl);
    /* Double the size of the result buffer if necessary. */
    if (i == 0 || i + len > n) {
      n = (i + len) * 2;
      result = (char *) safe_realloc(result, n + 1);
    }
    memcpy(result + i, repl, len);
    i += len;
  }
  /* Trim to length. (Also does initial allocation when str is empty.) */
  result = (char *) safe_realloc(result, i + 1);
  result[i] = '\0';

  return result;
}

/* Write data directly to the XML file with no escaping. Make sure you
   know what you're doing. */
int xml_write_raw(const char *fmt, ...) {
  va_list va;
  char *s;

  va_start(va, fmt);
  alloc_vsprintf(&s, fmt, va);
  va_end(va);
  if (s == NULL)
    return -1;

  log_write(LOG_XML, "%s", s);
  free(s);

  return 0;
}

/* Write data directly to the XML file after escaping it. */
int xml_write_escaped(const char *fmt, ...) {
  va_list va;
  int n;

  va_start(va, fmt);
  n = xml_write_escaped_v(fmt, va);
  va_end(va);

  return n;
}

/* Write data directly to the XML file after escaping it. This version takes a
   va_list like vprintf. */
int xml_write_escaped_v(const char *fmt, va_list va) {
  char *s, *esc_s;

  alloc_vsprintf(&s, fmt, va);
  if (s == NULL)
    return -1;
  esc_s = escape(s);
  free(s);
  if (esc_s == NULL)
    return -1;

  log_write(LOG_XML, "%s", esc_s);
  free(esc_s);

  return 0;
}

/* Write the XML declaration: <?xml version="1.0" encoding="UTF-8"?>
 * and the DOCTYPE declaration: <!DOCTYPE rootnode>
 */
int xml_start_document(const char *rootnode) {
  if (xml_open_pi("xml") < 0)
    return -1;
  if (xml_attribute("version", "1.0") < 0)
    return -1;
  /* Practically, Nmap only uses ASCII, but UTF-8 encompasses ASCII and allows
   * for future expansion */
  if (xml_attribute("encoding", "UTF-8") < 0)
    return -1;
  if (xml_close_pi() < 0)
    return -1;
  if (xml_newline() < 0)
    return -1;

  log_write(LOG_XML, "<!DOCTYPE %s>\n", rootnode);

  return 0;
}

int xml_start_comment() {
  log_write(LOG_XML, "<!--");

  return 0;
}

int xml_end_comment() {
  log_write(LOG_XML, "-->");

  return 0;
}

int xml_open_pi(const char *name) {
  assert(!xml.tag_open);
  log_write(LOG_XML, "<?%s", name);
  xml.tag_open = true;

  return 0;
}

int xml_close_pi() {
  assert(xml.tag_open);
  log_write(LOG_XML, "?>");
  xml.tag_open = false;

  return 0;
}

/* Open a start tag, like "<name". The tag must be later closed with
   xml_close_start_tag or xml_close_empty_tag. Usually the tag is closed
   after writing some attributes. */
int xml_open_start_tag(const char *name, const bool write) {
  assert(!xml.tag_open);
  if (write)
    log_write(LOG_XML, "<%s", name);
  xml.element_stack.push_back(name);
  xml.tag_open = true;
  xml.root_written = true;

  return 0;
}

int xml_close_start_tag(const bool write) {
  assert(xml.tag_open);
  if(write)
    log_write(LOG_XML, ">");
  xml.tag_open = false;

  return 0;
}

/* Close an empty-element tag. It should have been opened with
   xml_open_start_tag. */
int xml_close_empty_tag() {
  assert(xml.tag_open);
  assert(!xml.element_stack.empty());
  xml.element_stack.pop_back();
  log_write(LOG_XML, "/>");
  xml.tag_open = false;

  return 0;
}

int xml_start_tag(const char *name, const bool write) {
  if (xml_open_start_tag(name, write) < 0)
    return -1;
  if (xml_close_start_tag(write) < 0)
    return -1;

  return 0;
}

/* Write an end tag for the element at the top of the element stack. */
int xml_end_tag() {
  const char *name;

  assert(!xml.tag_open);
  assert(!xml.element_stack.empty());
  name = xml.element_stack.back();
  xml.element_stack.pop_back();

  log_write(LOG_XML, "</%s>", name);

  return 0;
}

/* Write an attribute. The only place this makes sense is between
   xml_open_start_tag and either xml_close_start_tag or
   xml_close_empty_tag. */
int xml_attribute(const char *name, const char *fmt, ...) {
  va_list va;
  char *val, *esc_val;

  assert(xml.tag_open);

  va_start(va, fmt);
  alloc_vsprintf(&val, fmt, va);
  va_end(va);
  if (val == NULL)
    return -1;
  esc_val = escape(val);
  free(val);
  if (esc_val == NULL)
    return -1;

  log_write(LOG_XML, " %s=\"%s\"", name, esc_val);
  free(esc_val);

  return 0;
}

int xml_newline() {
  log_write(LOG_XML, "\n");

  return 0;
}

/* Return the size of the element stack. */
int xml_depth() {
  return xml.element_stack.size();
}

/* Return true iff a root element has been started. */
bool xml_tag_open() {
  return xml.tag_open;
}

/* Return true iff a root element has been started. */
bool xml_root_written() {
  return xml.root_written;
}
