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ikreymer bufferedwriter close fix: (#36)
* bufferedwriter close fix:
- add close_stream option (defaulting to true) to indicate if underlying stream should be closed to match pre-1.5.2 behavior
- archiveiterator does not close underlying stream, as before, only the decompressor. Fixes #35
- tests: add tests for close_stream true/false
- bump version to 1.5.3, update changelist

* bufferedreader: an even simpler fix, remove close_stream option, just add separate close_decompressor()
to close decompressor only, called from ArchiveIterator
BufferedReader.close() also closes decompressor

* update CHANGELIST.rst
Latest commit 95d5dcd Jun 1, 2018


WARCIO: WARC (and ARC) Streaming Library


This library provides a fast, standalone way to read and write WARC Format commonly used in web archives. Supports Python 2.7+ and Python 3.3+ (using six, the only external dependency)

Install with: pip install warcio

This library is a spin-off of the WARC reading and writing component of the pywb high-fidelity replay library, a key component of Webrecorder

The library is designed for fast, low-level access to web archival content, oriented around a stream of WARC records rather than files.

Reading WARC Records

A key feature of the library is to be able to iterate over a stream of WARC records using the ArchiveIterator

It includes the following features: - Reading a WARC/ARC stream - On the fly ARC to WARC record conversion - Decompressing and de-chunking HTTP payload content stored in WARC/ARC files.

For example, the following prints the the url for each WARC response record:

from warcio.archiveiterator import ArchiveIterator

with open('path/to/file', 'rb') as stream:
    for record in ArchiveIterator(stream):
        if record.rec_type == 'response':

The stream object could be a file on disk or a remote network stream. The ArchiveIterator reads the WARC content in a single pass. The record is represented by an ArcWarcRecord object which contains the format (ARC or WARC), record type, the record headers, http headers (if any), and raw stream for reading the payload.

class ArcWarcRecord(object):
    def __init__(self, *args):
        (self.format, self.rec_type, self.rec_headers, self.raw_stream,
         self.http_headers, self.content_type, self.length) = args

Reading WARC Content

The raw_stream can be used to read the rest of the payload directly. A special ArcWarcRecord.content_stream() function provides a stream that automatically decompresses and de-chunks the HTTP payload, if it is compressed and/or transfer-encoding chunked.

ARC Files

The library provides support for reading (but not writing ARC) files. The ARC format is legacy but is important to support in a consistent matter. The ArchiveIterator can equally iterate over ARC and WARC files to emit ArcWarcRecord objects. The special arc2warc option converts ARC records to WARCs on the fly, allowing for them to be accessed using the same API.

(Special WARCIterator and ARCIterator subclasses of ArchiveIterator are also available to read only WARC or only ARC files).

WARC and ARC Streaming

For example, here is a snippet for reading an ARC and a WARC using the same API.

The example streams a WARC and ARC file over HTTP using requests, printing the warcinfo record (or ARC header) and any response records (or all ARC records) that contain HTML:

import requests
from warcio.archiveiterator import ArchiveIterator

def print_records(url):
    resp = requests.get(url, stream=True)

    for record in ArchiveIterator(resp.raw, arc2warc=True):
        if record.rec_type == 'warcinfo':

        elif record.rec_type == 'response':
            if record.http_headers.get_header('Content-Type') == 'text/html':


# ARC with arc2warc

Writing WARC Records

The library provides a simple and extensible interface for writing WARC records conformant to WARC 1.0 ISO standard (see draft)

The library comes with a basic WARCWriter class for writing to a single WARC file and BufferWARCWriter for writing to an in-memory buffer. The BaseWARCWriter can be extended to support more complex operations.

(There is no support for writing legacy ARC files)

The following example loads, creates a WARC response record, and writes it, gzip compressed, to example.warc.gz The block and payload digests are computed automatically.

from warcio.warcwriter import WARCWriter
from warcio.statusandheaders import StatusAndHeaders

import requests

with open('example.warc.gz', 'wb') as output:
    writer = WARCWriter(output, gzip=True)

    resp = requests.get('',
                        headers={'Accept-Encoding': 'identity'},

    # get raw headers from urllib3
    headers_list = resp.raw.headers.items()

    http_headers = StatusAndHeaders('200 OK', headers_list, protocol='HTTP/1.0')

    record = writer.create_warc_record('', 'response',


The library also includes additional semantics for: - Creating warcinfo and revisit records - Writing response and request records together - Writing custom WARC records - Reading a full WARC record from a stream

Please refer to and test/ for additional examples.

WARCIO CLI: Indexing and Recompression

The library currently ships with two simple command line tools.


The warcio index cmd will print a simple index of the records in the warc file as newline delimited JSON lines (NDJSON).

WARC header fields to include in the index can be specified via the -f flag, and are included in the JSON block (in order, for convenience).

warcio index ./test/data/ -f warc-type,warc-target-uri,content-length
{"warc-type": "warcinfo", "content-length": "137"}
{"warc-type": "response", "warc-target-uri": "", "content-length": "7566"}
{"warc-type": "request", "warc-target-uri": "", "content-length": "76"}

HTTP header fields can be included by prefixing them with the prefix http:. The special field offset refers to the record offset within the warc file.

warcio index ./test/data/ -f offset,content-type,http:content-type,warc-target-uri
{"offset": "0", "content-type": "application/warc-fields"}
{"offset": "405", "content-type": "application/http;msgtype=response", "http:content-type": "text/html; charset=UTF-8", "warc-target-uri": ""}
{"offset": "8379", "content-type": "application/http;msgtype=request", "warc-target-uri": ""}

(Note: this library does not produce CDX or CDXJ format indexes often associated with web archives. To create these indexes, please see the cdxj-indexer tool which extends warcio indexing to provide this functionality)


The recompress command allows for re-compressing or normalizing WARC (or ARC) files to a record-compressed, gzipped WARC file.

Each WARC record is compressed individually and concatenated. This is the 'canonical' WARC storage format used by Webrecorder and other web archiving institutions, and usually stored with a .warc.gz extension.

It can be used to: - Compress an uncompressed WARC - Convert any ARC file to a compressed WARC - Fix an improperly compressed WARC file (eg. a WARC compressed entirely instead of by record)

warcio recompress ./input.arc.gz ./output.warc.gz


warcio is licensed under the Apache 2.0 License and is part of the Webrecorder project.

See NOTICE and LICENSE for details.