view contrib/python-zstandard/c-ext/decompressoriterator.c @ 30435:b86a448a2965

zstd: vendor python-zstandard 0.5.0

As the commit message for the previous changeset says, we wish
for zstd to be a 1st class citizen in Mercurial. To make that
happen, we need to enable Python to talk to the zstd C API. And
that requires bindings.

This commit vendors a copy of existing Python bindings. Why do we
need to vendor? As the commit message of the previous commit says,
relying on systems in the wild to have the bindings or zstd present
is a losing proposition. By distributing the zstd and bindings with
Mercurial, we significantly increase our chances that zstd will
work. Since zstd will deliver a better end-user experience by
achieving better performance, this benefits our users. Another
reason is that the Python bindings still aren't stable and the
API is somewhat fluid. While Mercurial could be coded to target
multiple versions of the Python bindings, it is safer to bundle
an explicit, known working version.

The added Python bindings are mostly a fully-featured interface
to the zstd C API. They allow one-shot operations, streaming,
reading and writing from objects implements the file object
protocol, dictionary compression, control over low-level compression
parameters, and more. The Python bindings work on Python 2.6,
2.7, and 3.3+ and have been tested on Linux and Windows. There are
CFFI bindings, but they are lacking compared to the C extension.
Upstream work will be needed before we can support zstd with PyPy.
But it will be possible.

The files added in this commit come from Git commit
e637c1b214d5f869cf8116c550dcae23ec13b677 from
https://github.com/indygreg/python-zstandard and are added without
modifications. Some files from the upstream repository have been
omitted, namely files related to continuous integration.

In the spirit of full disclosure, I'm the maintainer of the
"python-zstandard" project and have authored 100% of the code
added in this commit. Unfortunately, the Python bindings have
not been formally code reviewed by anyone. While I've tested
much of the code thoroughly (I even have tests that fuzz APIs),
there's a good chance there are bugs, memory leaks, not well
thought out APIs, etc. If someone wants to review the code and
send feedback to the GitHub project, it would be greatly
appreciated.

Despite my involvement with both projects, my opinions of code
style differ from Mercurial's. The code in this commit introduces
numerous code style violations in Mercurial's linters. So, the code
is excluded from most lints. However, some violations I agree with.
These have been added to the known violations ignore list for now.

/**
* Copyright (c) 2016-present, Gregory Szorc
* All rights reserved.
*
* This software may be modified and distributed under the terms
* of the BSD license. See the LICENSE file for details.
*/

#include "python-zstandard.h"

#define min(a, b) (((a) < (b)) ? (a) : (b))

extern PyObject* ZstdError;

PyDoc_STRVAR(ZstdDecompressorIterator__doc__,
"Represents an iterator of decompressed data.\n"
);

static void ZstdDecompressorIterator_dealloc(ZstdDecompressorIterator* self) {
	Py_XDECREF(self->decompressor);
	Py_XDECREF(self->reader);

	if (self->buffer) {
		PyBuffer_Release(self->buffer);
		PyMem_FREE(self->buffer);
		self->buffer = NULL;
	}

	if (self->dstream) {
		ZSTD_freeDStream(self->dstream);
		self->dstream = NULL;
	}

	if (self->input.src) {
		PyMem_Free((void*)self->input.src);
		self->input.src = NULL;
	}

	PyObject_Del(self);
}

static PyObject* ZstdDecompressorIterator_iter(PyObject* self) {
	Py_INCREF(self);
	return self;
}

static DecompressorIteratorResult read_decompressor_iterator(ZstdDecompressorIterator* self) {
	size_t zresult;
	PyObject* chunk;
	DecompressorIteratorResult result;
	size_t oldInputPos = self->input.pos;

	result.chunk = NULL;

	chunk = PyBytes_FromStringAndSize(NULL, self->outSize);
	if (!chunk) {
		result.errored = 1;
		return result;
	}

	self->output.dst = PyBytes_AsString(chunk);
	self->output.size = self->outSize;
	self->output.pos = 0;

	Py_BEGIN_ALLOW_THREADS
	zresult = ZSTD_decompressStream(self->dstream, &self->output, &self->input);
	Py_END_ALLOW_THREADS

	/* We're done with the pointer. Nullify to prevent anyone from getting a
	handle on a Python object. */
	self->output.dst = NULL;

	if (ZSTD_isError(zresult)) {
		Py_DECREF(chunk);
		PyErr_Format(ZstdError, "zstd decompress error: %s",
			ZSTD_getErrorName(zresult));
		result.errored = 1;
		return result;
	}

	self->readCount += self->input.pos - oldInputPos;

	/* Frame is fully decoded. Input exhausted and output sitting in buffer. */
	if (0 == zresult) {
		self->finishedInput = 1;
		self->finishedOutput = 1;
	}

	/* If it produced output data, return it. */
	if (self->output.pos) {
		if (self->output.pos < self->outSize) {
			if (_PyBytes_Resize(&chunk, self->output.pos)) {
				result.errored = 1;
				return result;
			}
		}
	}
	else {
		Py_DECREF(chunk);
		chunk = NULL;
	}

	result.errored = 0;
	result.chunk = chunk;

	return result;
}

static PyObject* ZstdDecompressorIterator_iternext(ZstdDecompressorIterator* self) {
	PyObject* readResult = NULL;
	char* readBuffer;
	Py_ssize_t readSize;
	Py_ssize_t bufferRemaining;
	DecompressorIteratorResult result;

	if (self->finishedOutput) {
		PyErr_SetString(PyExc_StopIteration, "output flushed");
		return NULL;
	}

	/* If we have data left in the input, consume it. */
	if (self->input.pos < self->input.size) {
		result = read_decompressor_iterator(self);
		if (result.chunk || result.errored) {
			return result.chunk;
		}

		/* Else fall through to get more data from input. */
	}

read_from_source:

	if (!self->finishedInput) {
		if (self->reader) {
			readResult = PyObject_CallMethod(self->reader, "read", "I", self->inSize);
			if (!readResult) {
				return NULL;
			}

			PyBytes_AsStringAndSize(readResult, &readBuffer, &readSize);
		}
		else {
			assert(self->buffer && self->buffer->buf);

			/* Only support contiguous C arrays for now */
			assert(self->buffer->strides == NULL && self->buffer->suboffsets == NULL);
			assert(self->buffer->itemsize == 1);

			/* TODO avoid memcpy() below */
			readBuffer = (char *)self->buffer->buf + self->bufferOffset;
			bufferRemaining = self->buffer->len - self->bufferOffset;
			readSize = min(bufferRemaining, (Py_ssize_t)self->inSize);
			self->bufferOffset += readSize;
		}

		if (readSize) {
			if (!self->readCount && self->skipBytes) {
				assert(self->skipBytes < self->inSize);
				if ((Py_ssize_t)self->skipBytes >= readSize) {
					PyErr_SetString(PyExc_ValueError,
						"skip_bytes larger than first input chunk; "
						"this scenario is currently unsupported");
					Py_DecRef(readResult);
					return NULL;
				}

				readBuffer = readBuffer + self->skipBytes;
				readSize -= self->skipBytes;
			}

			/* Copy input into previously allocated buffer because it can live longer
			than a single function call and we don't want to keep a ref to a Python
			object around. This could be changed... */
			memcpy((void*)self->input.src, readBuffer, readSize);
			self->input.size = readSize;
			self->input.pos = 0;
		}
		/* No bytes on first read must mean an empty input stream. */
		else if (!self->readCount) {
			self->finishedInput = 1;
			self->finishedOutput = 1;
			Py_DecRef(readResult);
			PyErr_SetString(PyExc_StopIteration, "empty input");
			return NULL;
		}
		else {
			self->finishedInput = 1;
		}

		/* We've copied the data managed by memory. Discard the Python object. */
		Py_DecRef(readResult);
	}

	result = read_decompressor_iterator(self);
	if (result.errored || result.chunk) {
		return result.chunk;
	}

	/* No new output data. Try again unless we know there is no more data. */
	if (!self->finishedInput) {
		goto read_from_source;
	}

	PyErr_SetString(PyExc_StopIteration, "input exhausted");
	return NULL;
}

PyTypeObject ZstdDecompressorIteratorType = {
	PyVarObject_HEAD_INIT(NULL, 0)
	"zstd.ZstdDecompressorIterator",   /* tp_name */
	sizeof(ZstdDecompressorIterator),  /* tp_basicsize */
	0,                                 /* tp_itemsize */
	(destructor)ZstdDecompressorIterator_dealloc, /* tp_dealloc */
	0,                                 /* tp_print */
	0,                                 /* tp_getattr */
	0,                                 /* tp_setattr */
	0,                                 /* tp_compare */
	0,                                 /* tp_repr */
	0,                                 /* tp_as_number */
	0,                                 /* tp_as_sequence */
	0,                                 /* tp_as_mapping */
	0,                                 /* tp_hash */
	0,                                 /* tp_call */
	0,                                 /* tp_str */
	0,                                 /* tp_getattro */
	0,                                 /* tp_setattro */
	0,                                 /* tp_as_buffer */
	Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /* tp_flags */
	ZstdDecompressorIterator__doc__,   /* tp_doc */
	0,                                 /* tp_traverse */
	0,                                 /* tp_clear */
	0,                                 /* tp_richcompare */
	0,                                 /* tp_weaklistoffset */
	ZstdDecompressorIterator_iter,     /* tp_iter */
	(iternextfunc)ZstdDecompressorIterator_iternext, /* tp_iternext */
	0,                                 /* tp_methods */
	0,                                 /* tp_members */
	0,                                 /* tp_getset */
	0,                                 /* tp_base */
	0,                                 /* tp_dict */
	0,                                 /* tp_descr_get */
	0,                                 /* tp_descr_set */
	0,                                 /* tp_dictoffset */
	0,                                 /* tp_init */
	0,                                 /* tp_alloc */
	PyType_GenericNew,                 /* tp_new */
};

void decompressoriterator_module_init(PyObject* mod) {
	Py_TYPE(&ZstdDecompressorIteratorType) = &PyType_Type;
	if (PyType_Ready(&ZstdDecompressorIteratorType) < 0) {
		return;
	}
}