implement REST client backend

Author: ThomasWaldmann

src/borgstore/backends/rest.py

@@ -0,0 +1,168 @@
+"""
+REST http client based backend implementation.
+
+Usage:
+
+b = get_rest_backend("https://username:password@username.repo.borgbase.com/restictest")
+b.open()
+b.create()
+b.store("config", b"foo")
+b.load("config")
+b.delete("config")
+b.store("config", b"bar")
+b.store("data/<sha256(value)>", value)
+b.list("data")
+b.load("data/<sha256>")
+b.close()
+"""
+import os
+import re
+import requests
+from typing import Iterator, Dict, Optional
+from urllib.parse import unquote
+
+from requests.auth import HTTPBasicAuth
+
+from ._base import BackendBase, ItemInfo, validate_name
+from .errors import ObjectNotFound
+
+
+def get_rest_backend(base_url: str):
+    # http(s)://username:password@hostname:port/path or http(s)://hostname:port/path + auth from env
+    http_regex = r"""
+        (?P<scheme>http|https)://
+        ((?P<username>[^:]+):(?P<password>[^@]+)@)?
+        (?P<host>[^:/]+)(:?(?P<port>\d+))?
+        (?P<path>(/.*))
+    """
+    m = re.match(http_regex, base_url, re.VERBOSE)
+    if m:
+        scheme = m.group("scheme")
+        host = m.group("host")
+        port = m.group("port")
+        path = m.group("path")
+
+        base_url = f"{scheme}://{host}{f':{port}' if port else ''}{path}"
+
+        username, password = m.group("username"), m.group("password")
+        if username and password:
+            username, password = unquote(username), unquote(password)
+        else:
+            username, password = os.environ.get("REST_BACKEND_USERNAME"), os.environ.get("REST_BACKEND_PASSWORD")
+
+        return RestClientBackend(base_url, username=username, password=password)
+
+
+class RestClientBackend(BackendBase):
+    def __init__(
+        self,
+        base_url: str,
+        username: Optional[str] = None,
+        password: Optional[str] = None,
+        headers: Optional[Dict[str, str]] = None,
+        timeout: Optional[int] = 30,
+    ):
+        self.base_url = base_url.rstrip("/")  # _url method adds slash
+        self.headers = headers or {}
+        self.headers["Accept"] = "application/vnd.x.restic.rest.v2"
+        self.timeout = timeout
+        self.auth = HTTPBasicAuth(username, password) if username and password else None
+        self.session = None
+
+    def _url(self, path: str) -> str:
+        return f"{self.base_url}/{path.lstrip('/')}"
+
+    def _request(self, method, url, *, headers=None, data=None, params=None):
+        if self.session is not None:  # between .open() and .close()
+            return self.session.request(method, url, params=params, data=data, headers=headers, timeout=self.timeout)
+        else:  # .create() and .destroy() are called when backend is not opened
+            assert headers is None
+            return requests.request(
+                method, url, auth=self.auth, params=params, data=data, headers=self.headers, timeout=self.timeout
+            )
+
+    def create(self) -> None:
+        # restic-server: repo creation creates all needed directories
+        response = self._request("post", self._url(""), params={"create": "true"})
+        if response.status_code != 200:
+            response.raise_for_status()
+
+    def destroy(self) -> None:
+        # XXX restic-server: repo deletion doesn't work on borgbase.com, 405 "Method not allowed"
+        response = self._request("delete", self._url(""))
+        if response.status_code != 200:
+            response.raise_for_status()
+
+    def open(self):
+        self.session = requests.Session()
+        self.session.auth = self.auth
+        self.session.headers.update(self.headers)
+
+    def close(self):
+        if self.session is not None:
+            self.session.close()
+            self.session = None
+
+    def mkdir(self, name: str) -> None:
+        pass
+
+    def rmdir(self, name: str) -> None:
+        pass
+
+    def info(self, name: str) -> ItemInfo:
+        # restic-server: only works on objects, not on directories
+        validate_name(name)
+        response = self._request("head", self._url(name))
+        if response.status_code != 200:
+            if response.status_code == 404:
+                raise ObjectNotFound(name)
+            else:
+                response.raise_for_status()
+        return ItemInfo(name=name, exists=True, size=int(response.headers["Content-Length"]), directory=False)
+
+    def load(self, name: str, *, size=None, offset=0) -> bytes:
+        validate_name(name)
+
+        r_hdr = (None if not offset else f"bytes={offset}-") if size is None else f"bytes={offset}-{offset + size - 1}"
+        headers = self.headers.copy()
+        if r_hdr:
+            headers["Range"] = r_hdr
+
+        response = self._request("get", self._url(name), headers=headers)
+        if response.status_code != 200:
+            if response.status_code == 404:
+                raise ObjectNotFound(name)
+            else:
+                response.raise_for_status()
+        return response.content
+
+    def store(self, name: str, value: bytes) -> None:
+        validate_name(name)
+        # restic-server only works with key == sha256(value) (verifies the hash while writing to disk)
+        # and it rejects overwriting existing objects.
+        response = self._request("post", self._url(name), data=value)
+        if response.status_code != 200:
+            response.raise_for_status()
+
+    def delete(self, name: str) -> None:
+        validate_name(name)
+        response = self._request("delete", self._url(name))
+        if response.status_code != 200:
+            if response.status_code == 404:
+                raise ObjectNotFound(name)
+            else:
+                response.raise_for_status()
+
+    def move(self, curr_name: str, new_name: str) -> None:
+        raise NotImplementedError
+
+    def list(self, name: str) -> Iterator[ItemInfo]:
+        validate_name(name)
+        response = self._request("get", self._url(name) + "/")  # trailing "/" needed to get list
+        if response.status_code != 200:
+            if response.status_code == 404:
+                raise ObjectNotFound(name)
+            else:
+                response.raise_for_status()
+        for entry in response.json():
+            yield ItemInfo(name=entry["name"], exists=True, size=entry["size"], directory=False)