cpython/Python/traceback.c

/* Traceback implementation */

#include "Python.h"

#include "code.h"
#include "frameobject.h"
#include "structmember.h"
#include "osdefs.h"
#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif

#define OFF(x) offsetof(PyTracebackObject, x)

#define PUTS(fd, str) write(fd, str, (int)strlen(str))
#define MAX_STRING_LENGTH 500
#define MAX_FRAME_DEPTH 100
#define MAX_NTHREADS 100

/* Function from Parser/tokenizer.c */
extern char * PyTokenizer_FindEncodingFilename(int, PyObject *);

static PyObject *
tb_dir(PyTracebackObject *self)
{
    return Py_BuildValue("[ssss]", "tb_frame", "tb_next",
                                   "tb_lasti", "tb_lineno");
}

static PyMethodDef tb_methods[] = {
   {"__dir__", (PyCFunction)tb_dir, METH_NOARGS},
   {NULL, NULL, 0, NULL},
};

static PyMemberDef tb_memberlist[] = {
    {"tb_next",         T_OBJECT,       OFF(tb_next),   READONLY},
    {"tb_frame",        T_OBJECT,       OFF(tb_frame),  READONLY},
    {"tb_lasti",        T_INT,          OFF(tb_lasti),  READONLY},
    {"tb_lineno",       T_INT,          OFF(tb_lineno), READONLY},
    {NULL}      /* Sentinel */
};

static void
tb_dealloc(PyTracebackObject *tb)
{
    PyObject_GC_UnTrack(tb);
    Py_TRASHCAN_SAFE_BEGIN(tb)
    Py_XDECREF(tb->tb_next);
    Py_XDECREF(tb->tb_frame);
    PyObject_GC_Del(tb);
    Py_TRASHCAN_SAFE_END(tb)
}

static int
tb_traverse(PyTracebackObject *tb, visitproc visit, void *arg)
{
    Py_VISIT(tb->tb_next);
    Py_VISIT(tb->tb_frame);
    return 0;
}

static void
tb_clear(PyTracebackObject *tb)
{
    Py_CLEAR(tb->tb_next);
    Py_CLEAR(tb->tb_frame);
}

PyTypeObject PyTraceBack_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "traceback",
    sizeof(PyTracebackObject),
    0,
    (destructor)tb_dealloc, /*tp_dealloc*/
    0,                  /*tp_print*/
    0,    /*tp_getattr*/
    0,                  /*tp_setattr*/
    0,                  /*tp_reserved*/
    0,                  /*tp_repr*/
    0,                  /*tp_as_number*/
    0,                  /*tp_as_sequence*/
    0,                  /*tp_as_mapping*/
    0,                  /* tp_hash */
    0,                  /* tp_call */
    0,                  /* tp_str */
    PyObject_GenericGetAttr,                    /* tp_getattro */
    0,                  /* tp_setattro */
    0,                                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,/* tp_flags */
    0,                                          /* tp_doc */
    (traverseproc)tb_traverse,                  /* tp_traverse */
    (inquiry)tb_clear,                          /* tp_clear */
    0,                                          /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    0,                                          /* tp_iter */
    0,                                          /* tp_iternext */
    tb_methods,         /* tp_methods */
    tb_memberlist,      /* tp_members */
    0,                                          /* tp_getset */
    0,                                          /* tp_base */
    0,                                          /* tp_dict */
};

static PyTracebackObject *
newtracebackobject(PyTracebackObject *next, PyFrameObject *frame)
{
    PyTracebackObject *tb;
    if ((next != NULL && !PyTraceBack_Check(next)) ||
                    frame == NULL || !PyFrame_Check(frame)) {
        PyErr_BadInternalCall();
        return NULL;
    }
    tb = PyObject_GC_New(PyTracebackObject, &PyTraceBack_Type);
    if (tb != NULL) {
        Py_XINCREF(next);
        tb->tb_next = next;
        Py_XINCREF(frame);
        tb->tb_frame = frame;
        tb->tb_lasti = frame->f_lasti;
        tb->tb_lineno = PyFrame_GetLineNumber(frame);
        PyObject_GC_Track(tb);
    }
    return tb;
}

int
PyTraceBack_Here(PyFrameObject *frame)
{
    PyThreadState *tstate = PyThreadState_GET();
    PyTracebackObject *oldtb = (PyTracebackObject *) tstate->curexc_traceback;
    PyTracebackObject *tb = newtracebackobject(oldtb, frame);
    if (tb == NULL)
        return -1;
    tstate->curexc_traceback = (PyObject *)tb;
    Py_XDECREF(oldtb);
    return 0;
}

static PyObject *
_Py_FindSourceFile(PyObject *filename, char* namebuf, size_t namelen, PyObject *io)
{
    Py_ssize_t i;
    PyObject *binary;
    PyObject *v;
    Py_ssize_t npath;
    size_t taillen;
    PyObject *syspath;
    PyObject *path;
    const char* tail;
    PyObject *filebytes;
    const char* filepath;
    Py_ssize_t len;
    PyObject* result;
    _Py_IDENTIFIER(open);

    filebytes = PyUnicode_EncodeFSDefault(filename);
    if (filebytes == NULL) {
        PyErr_Clear();
        return NULL;
    }
    filepath = PyBytes_AS_STRING(filebytes);

    /* Search tail of filename in sys.path before giving up */
    tail = strrchr(filepath, SEP);
    if (tail == NULL)
        tail = filepath;
    else
        tail++;
    taillen = strlen(tail);

    syspath = _PySys_GetObjectId(&_PyId_path);
    if (syspath == NULL || !PyList_Check(syspath))
        goto error;
    npath = PyList_Size(syspath);

    for (i = 0; i < npath; i++) {
        v = PyList_GetItem(syspath, i);
        if (v == NULL) {
            PyErr_Clear();
            break;
        }
        if (!PyUnicode_Check(v))
            continue;
        path = PyUnicode_EncodeFSDefault(v);
        if (path == NULL) {
            PyErr_Clear();
            continue;
        }
        len = PyBytes_GET_SIZE(path);
        if (len + 1 + (Py_ssize_t)taillen >= (Py_ssize_t)namelen - 1) {
            Py_DECREF(path);
            continue; /* Too long */
        }
        strcpy(namebuf, PyBytes_AS_STRING(path));
        Py_DECREF(path);
        if (strlen(namebuf) != len)
            continue; /* v contains '\0' */
        if (len > 0 && namebuf[len-1] != SEP)
            namebuf[len++] = SEP;
        strcpy(namebuf+len, tail);

        binary = _PyObject_CallMethodId(io, &PyId_open, "ss", namebuf, "rb");
        if (binary != NULL) {
            result = binary;
            goto finally;
        }
        PyErr_Clear();
    }
    goto error;

error:
    result = NULL;
finally:
    Py_DECREF(filebytes);
    return result;
}

int
_Py_DisplaySourceLine(PyObject *f, PyObject *filename, int lineno, int indent)
{
    int err = 0;
    int fd;
    int i;
    char *found_encoding;
    char *encoding;
    PyObject *io;
    PyObject *binary;
    PyObject *fob = NULL;
    PyObject *lineobj = NULL;
    PyObject *res;
    char buf[MAXPATHLEN+1];
    int kind;
    void *data;
    _Py_IDENTIFIER(close);
    _Py_IDENTIFIER(open);
    _Py_IDENTIFIER(TextIOWrapper);

    /* open the file */
    if (filename == NULL)
        return 0;

    io = PyImport_ImportModuleNoBlock("io");
    if (io == NULL)
        return -1;
    binary = _PyObject_CallMethodId(io, &PyId_open, "Os", filename, "rb");

    if (binary == NULL) {
        PyErr_Clear();

        binary = _Py_FindSourceFile(filename, buf, sizeof(buf), io);
        if (binary == NULL) {
            Py_DECREF(io);
            return -1;
        }
    }

    /* use the right encoding to decode the file as unicode */
    fd = PyObject_AsFileDescriptor(binary);
    if (fd < 0) {
        Py_DECREF(io);
        Py_DECREF(binary);
        return 0;
    }
    found_encoding = PyTokenizer_FindEncodingFilename(fd, filename);
    encoding = (found_encoding != NULL) ? found_encoding : "utf-8";
    /* Reset position */
    if (lseek(fd, 0, SEEK_SET) == (off_t)-1) {
        Py_DECREF(io);
        Py_DECREF(binary);
        PyMem_FREE(found_encoding);
        return 0;
    }
    fob = _PyObject_CallMethodId(io, &PyId_TextIOWrapper, "Os", binary, encoding);
    Py_DECREF(io);
    Py_DECREF(binary);
    PyMem_FREE(found_encoding);

    if (fob == NULL) {
        PyErr_Clear();
        return 0;
    }

    /* get the line number lineno */
    for (i = 0; i < lineno; i++) {
        Py_XDECREF(lineobj);
        lineobj = PyFile_GetLine(fob, -1);
        if (!lineobj) {
            err = -1;
            break;
        }
    }
    res = _PyObject_CallMethodId(fob, &PyId_close, "");
    if (res)
        Py_DECREF(res);
    else
        PyErr_Clear();
    Py_DECREF(fob);
    if (!lineobj || !PyUnicode_Check(lineobj)) {
        Py_XDECREF(lineobj);
        return err;
    }

    /* remove the indentation of the line */
    kind = PyUnicode_KIND(lineobj);
    data = PyUnicode_DATA(lineobj);
    for (i=0; i < PyUnicode_GET_LENGTH(lineobj); i++) {
        Py_UCS4 ch = PyUnicode_READ(kind, data, i);
        if (ch != ' ' && ch != '\t' && ch != '\014')
            break;
    }
    if (i) {
        PyObject *truncated;
        truncated = PyUnicode_Substring(lineobj, i, PyUnicode_GET_LENGTH(lineobj));
        if (truncated) {
            Py_DECREF(lineobj);
            lineobj = truncated;
        } else {
            PyErr_Clear();
        }
    }

    /* Write some spaces before the line */
    strcpy(buf, "          ");
    assert (strlen(buf) == 10);
    while (indent > 0) {
        if (indent < 10)
            buf[indent] = '\0';
        err = PyFile_WriteString(buf, f);
        if (err != 0)
            break;
        indent -= 10;
    }

    /* finally display the line */
    if (err == 0)
        err = PyFile_WriteObject(lineobj, f, Py_PRINT_RAW);
    Py_DECREF(lineobj);
    if  (err == 0)
        err = PyFile_WriteString("\n", f);
    return err;
}

static int
tb_displayline(PyObject *f, PyObject *filename, int lineno, PyObject *name)
{
    int err;
    PyObject *line;

    if (filename == NULL || name == NULL)
        return -1;
    line = PyUnicode_FromFormat("  File \"%U\", line %d, in %U\n",
                                filename, lineno, name);
    if (line == NULL)
        return -1;
    err = PyFile_WriteObject(line, f, Py_PRINT_RAW);
    Py_DECREF(line);
    if (err != 0)
        return err;
    /* ignore errors since we can't report them, can we? */
    if (_Py_DisplaySourceLine(f, filename, lineno, 4))
        PyErr_Clear();
    return err;
}

static int
tb_printinternal(PyTracebackObject *tb, PyObject *f, long limit)
{
    int err = 0;
    long depth = 0;
    PyTracebackObject *tb1 = tb;
    while (tb1 != NULL) {
        depth++;
        tb1 = tb1->tb_next;
    }
    while (tb != NULL && err == 0) {
        if (depth <= limit) {
            err = tb_displayline(f,
                                 tb->tb_frame->f_code->co_filename,
                                 tb->tb_lineno,
                                 tb->tb_frame->f_code->co_name);
        }
        depth--;
        tb = tb->tb_next;
        if (err == 0)
            err = PyErr_CheckSignals();
    }
    return err;
}

#define PyTraceBack_LIMIT 1000

int
PyTraceBack_Print(PyObject *v, PyObject *f)
{
    int err;
    PyObject *limitv;
    long limit = PyTraceBack_LIMIT;

    if (v == NULL)
        return 0;
    if (!PyTraceBack_Check(v)) {
        PyErr_BadInternalCall();
        return -1;
    }
    limitv = PySys_GetObject("tracebacklimit");
    if (limitv) {
        PyObject *exc_type, *exc_value, *exc_tb;

        PyErr_Fetch(&exc_type, &exc_value, &exc_tb);
        limit = PyLong_AsLong(limitv);
        if (limit == -1 && PyErr_Occurred()) {
            if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
                limit = PyTraceBack_LIMIT;
            }
            else {
                Py_XDECREF(exc_type);
                Py_XDECREF(exc_value);
                Py_XDECREF(exc_tb);
                return 0;
            }
        }
        else if (limit <= 0) {
            limit = PyTraceBack_LIMIT;
        }
        PyErr_Restore(exc_type, exc_value, exc_tb);
    }
    err = PyFile_WriteString("Traceback (most recent call last):\n", f);
    if (!err)
        err = tb_printinternal((PyTracebackObject *)v, f, limit);
    return err;
}

/* Reverse a string. For example, "abcd" becomes "dcba".

   This function is signal safe. */

static void
reverse_string(char *text, const size_t len)
{
    char tmp;
    size_t i, j;
    if (len == 0)
        return;
    for (i=0, j=len-1; i < j; i++, j--) {
        tmp = text[i];
        text[i] = text[j];
        text[j] = tmp;
    }
}

/* Format an integer in range [0; 999999] to decimal,
   and write it into the file fd.

   This function is signal safe. */

static void
dump_decimal(int fd, int value)
{
    char buffer[7];
    int len;
    if (value < 0 || 999999 < value)
        return;
    len = 0;
    do {
        buffer[len] = '0' + (value % 10);
        value /= 10;
        len++;
    } while (value);
    reverse_string(buffer, len);
    write(fd, buffer, len);
}

/* Format an integer in range [0; 0xffffffff] to hexadecimal of 'width' digits,
   and write it into the file fd.

   This function is signal safe. */

static void
dump_hexadecimal(int fd, unsigned long value, int width)
{
    int len;
    char buffer[sizeof(unsigned long) * 2 + 1];
    len = 0;
    do {
        buffer[len] = Py_hexdigits[value & 15];
        value >>= 4;
        len++;
    } while (len < width || value);
    reverse_string(buffer, len);
    write(fd, buffer, len);
}

/* Write an unicode object into the file fd using ascii+backslashreplace.

   This function is signal safe. */

static void
dump_ascii(int fd, PyObject *text)
{
    PyASCIIObject *ascii = (PyASCIIObject *)text;
    Py_ssize_t i, size;
    int truncated;
    int kind;
    void *data = NULL;
    wchar_t *wstr = NULL;
    Py_UCS4 ch;

    size = ascii->length;
    kind = ascii->state.kind;
    if (ascii->state.compact) {
        if (ascii->state.ascii)
            data = ((PyASCIIObject*)text) + 1;
        else
            data = ((PyCompactUnicodeObject*)text) + 1;
    }
    else if (kind != PyUnicode_WCHAR_KIND) {
        data = ((PyUnicodeObject *)text)->data.any;
        if (data == NULL)
            return;
    }
    else {
        wstr = ((PyASCIIObject *)text)->wstr;
        if (wstr == NULL)
            return;
        size = ((PyCompactUnicodeObject *)text)->wstr_length;
    }

    if (MAX_STRING_LENGTH < size) {
        size = MAX_STRING_LENGTH;
        truncated = 1;
    }
    else
        truncated = 0;

    for (i=0; i < size; i++) {
        if (kind != PyUnicode_WCHAR_KIND)
            ch = PyUnicode_READ(kind, data, i);
        else
            ch = wstr[i];
        if (ch < 128) {
            char c = (char)ch;
            write(fd, &c, 1);
        }
        else if (ch < 0xff) {
            PUTS(fd, "\\x");
            dump_hexadecimal(fd, ch, 2);
        }
        else if (ch < 0xffff) {
            PUTS(fd, "\\u");
            dump_hexadecimal(fd, ch, 4);
        }
        else {
            PUTS(fd, "\\U");
            dump_hexadecimal(fd, ch, 8);
        }
    }
    if (truncated)
        PUTS(fd, "...");
}

/* Write a frame into the file fd: "File "xxx", line xxx in xxx".

   This function is signal safe. */

static void
dump_frame(int fd, PyFrameObject *frame)
{
    PyCodeObject *code;
    int lineno;

    code = frame->f_code;
    PUTS(fd, "  File ");
    if (code != NULL && code->co_filename != NULL
        && PyUnicode_Check(code->co_filename))
    {
        write(fd, "\"", 1);
        dump_ascii(fd, code->co_filename);
        write(fd, "\"", 1);
    } else {
        PUTS(fd, "???");
    }

    /* PyFrame_GetLineNumber() was introduced in Python 2.7.0 and 3.2.0 */
    lineno = PyCode_Addr2Line(code, frame->f_lasti);
    PUTS(fd, ", line ");
    dump_decimal(fd, lineno);
    PUTS(fd, " in ");

    if (code != NULL && code->co_name != NULL
        && PyUnicode_Check(code->co_name))
        dump_ascii(fd, code->co_name);
    else
        PUTS(fd, "???");

    write(fd, "\n", 1);
}

static void
dump_traceback(int fd, PyThreadState *tstate, int write_header)
{
    PyFrameObject *frame;
    unsigned int depth;

    if (write_header)
        PUTS(fd, "Stack (most recent call first):\n");

    frame = _PyThreadState_GetFrame(tstate);
    if (frame == NULL)
        return;

    depth = 0;
    while (frame != NULL) {
        if (MAX_FRAME_DEPTH <= depth) {
            PUTS(fd, "  ...\n");
            break;
        }
        if (!PyFrame_Check(frame))
            break;
        dump_frame(fd, frame);
        frame = frame->f_back;
        depth++;
    }
}

void
_Py_DumpTraceback(int fd, PyThreadState *tstate)
{
    dump_traceback(fd, tstate, 1);
}

/* Write the thread identifier into the file 'fd': "Current thread 0xHHHH:\" if
   is_current is true, "Thread 0xHHHH:\n" otherwise.

   This function is signal safe. */

static void
write_thread_id(int fd, PyThreadState *tstate, int is_current)
{
    if (is_current)
        PUTS(fd, "Current thread 0x");
    else
        PUTS(fd, "Thread 0x");
    dump_hexadecimal(fd, (unsigned long)tstate->thread_id, sizeof(long)*2);
    PUTS(fd, " (most recent call first):\n");
}

const char*
_Py_DumpTracebackThreads(int fd, PyInterpreterState *interp,
                         PyThreadState *current_thread)
{
    PyThreadState *tstate;
    unsigned int nthreads;

    /* Get the current interpreter from the current thread */
    tstate = PyInterpreterState_ThreadHead(interp);
    if (tstate == NULL)
        return "unable to get the thread head state";

    /* Dump the traceback of each thread */
    tstate = PyInterpreterState_ThreadHead(interp);
    nthreads = 0;
    do
    {
        if (nthreads != 0)
            write(fd, "\n", 1);
        if (nthreads >= MAX_NTHREADS) {
            PUTS(fd, "...\n");
            break;
        }
        write_thread_id(fd, tstate, tstate == current_thread);
        dump_traceback(fd, tstate, 0);
        tstate = PyThreadState_Next(tstate);
        nthreads++;
    } while (tstate != NULL);

    return NULL;
}