# # This program is a stand-in for good intro docs. It just documents various # basics of using Mitogen. # from __future__ import absolute_import from __future__ import print_function import hashlib import io import os import spwd import mitogen.core import mitogen.master import mitogen.service import mitogen.utils def get_file_contents(path): """ Get the contents of a file. """ with open(path, 'rb') as fp: # mitogen.core.Blob() is a bytes subclass with a repr() that returns a # summary of the blob, rather than the raw blob data. This makes # logging output *much* nicer. Unlike most custom types, blobs can be # serialized. return mitogen.core.Blob(fp.read()) def put_file_contents(path, s): """ Write the contents of a file. """ with open(path, 'wb') as fp: fp.write(s) def streamy_download_file(context, path): """ Fetch a file from the FileService hosted by `context`. """ bio = io.BytesIO() # FileService.get() is not actually an exposed service method, it's just a # classmethod that wraps up the complicated dance of implementing the # transfer. ok, metadata = mitogen.service.FileService.get(context, path, bio) return { 'success': ok, 'metadata': metadata, 'size': len(bio.getvalue()), } def get_password_hash(username): """ Fetch a user's password hash. """ try: h = spwd.getspnam(username) except KeyError: return None # mitogen.core.Secret() is a Unicode subclass with a repr() that hides the # secret data. This keeps secret stuff out of logs. Like blobs, secrets can # also be serialized. return mitogen.core.Secret(h) def md5sum(path): """ Return the MD5 checksum for a file. """ return hashlib.md5(get_file_contents(path)).hexdigest() def work_on_machine(context): """ Do stuff to a remote context. """ print("Created context. Context ID is", context.context_id) # You don't need to understand any/all of this, but it's helpful to grok # the whole chain: # - Context.call() is a light wrapper around .call_async(), the wrapper # simply blocks the caller until a reply arrives. # - .call_async() serializes the call signature into a message and passes # it to .send_async() # - .send_async() creates a mitogen.core.Receiver() on the local router. # The receiver constructor uses Router.add_handle() to allocate a # 'reply_to' handle and install a callback function that wakes the # receiver when a reply message arrives. # - .send_async() puts the reply handle in Message.reply_to field and # passes it to .send() # - Context.send() stamps the destination context ID into the # Message.dst_id field and passes it to Router.route() # - Router.route() uses Broker.defer() to schedule _async_route(msg) # on the Broker thread. # [broker thread] # - The broker thread wakes and calls _async_route(msg) # - Router._async_route() notices 'dst_id' is for a remote context and # looks up the stream on which messages for dst_id should be sent (may be # direct connection or not), and calls Stream.send() # - Stream.send() packs the message into a bytestring, appends it to # Stream._output_buf, and calls Broker.start_transmit() # - Broker finishes work, reenters IO loop. IO loop wakes due to writeable # stream. # - Stream.on_transmit() writes the full/partial buffer to SSH, calls # stop_transmit() to mark the stream unwriteable once _output_buf is # empty. # - Broker IO loop sleeps, no readers/writers. # - Broker wakes due to SSH stream readable. # - Stream.on_receive() called, reads the reply message, converts it to a # Message and passes it to Router._async_route(). # - Router._async_route() notices message is for local context, looks up # target handle in the .add_handle() registry. # - Receiver._on_receive() called, appends message to receiver queue. # [main thread] # - Receiver.get() used to block the original Context.call() wakes and pops # the message from the queue. # - Message data (pickled return value) is deserialized and returned to the # caller. print("It's running on the local machine. Its PID is", context.call(os.getpid)) # Now let's call a function defined in this module. On receiving the # function call request, the child attempts to import __main__, which is # initially missing, causing the importer in the child to request it from # its parent. That causes _this script_ to be sent as the module source # over the wire. print("Calling md5sum(/etc/passwd) in the child:", context.call(md5sum, '/etc/passwd')) # Now let's "transfer" a file. The simplest way to do this is calling a # function that returns the file data, which is totally fine for small # files. print("Download /etc/passwd via function call: %d bytes" % ( len(context.call(get_file_contents, '/etc/passwd')) )) # And using function calls, in the other direction: print("Upload /tmp/blah via function call: %s" % ( context.call(put_file_contents, '/tmp/blah', b'blah!'), )) # Now lets transfer what might be a big files. The problem with big files # is that they may not fit in RAM. This uses mitogen.services.FileService # to implement streamy file transfer instead. The sender must have a # 'service pool' running that will host FileService. First let's do the # 'upload' direction, where the master hosts FileService. # Steals the 'Router' reference from the context object. In a real app the # pool would be constructed once at startup, this is just demo code. file_service = mitogen.service.FileService(context.router) # Start the pool. pool = mitogen.service.Pool(context.router, services=[file_service]) # Grant access to a file on the local disk from unprivileged contexts. # .register() is also exposed as a service method -- you can call it on a # child context from any more privileged context. file_service.register('/etc/passwd') # Now call our wrapper function that knows how to handle the transfer. In a # real app, this wrapper might also set ownership/modes or do any other # app-specific stuff relating to the file that was transferred. print("Streamy upload /etc/passwd: remote result: %s" % ( context.call( streamy_download_file, # To avoid hard-wiring streamy_download_file(), we want to pass it # a Context object that hosts the file service it should request # files from. Router.myself() returns a Context referring to this # process. context=router.myself(), path='/etc/passwd', ), )) # Shut down the pool now we're done with it, else app will hang at exit. # Once again, this should only happen once at app startup/exit, not for # every file transfer! pool.stop(join=True) # Now let's do the same thing but in reverse: we use FileService on the # remote download a file. This uses context.call_service(), which invokes a # special code path that causes auto-initialization of a thread pool in the # target, and auto-construction of the target service, but only if the # service call was made by a more privileged context. We could write a # helper function that runs in the remote to do all that by hand, but the # library handles it for us. # Make the file accessible. A future FileService could avoid the need for # this for privileged contexts. context.call_service( service_name=mitogen.service.FileService, method_name='register', path='/etc/passwd' ) # Now we can use our streamy_download_file() function in reverse -- running # it from this process and having it fetch from the remote process: print("Streamy download /etc/passwd: result: %s" % ( streamy_download_file(context, '/etc/passwd'), )) def main(): # Setup logging. Mitogen produces a LOT of logging. Over the course of the # stable series, Mitogen's loggers will be carved up so more selective / # user-friendly logging is possible. mitogen.log_to_file() just sets up # something basic, defaulting to INFO level, but you can override from the # command-line by passing MITOGEN_LOG_LEVEL=debug or MITOGEN_LOG_LEVEL=io. # IO logging is sometimes useful for hangs, but it is often creates more # confusion than it solves. mitogen.utils.log_to_file() # Construct the Broker thread. It manages an async IO loop listening for # reads from any active connection, or wakes from any non-Broker thread. # Because Mitogen uses a background worker thread, it is extremely # important to pay attention to the use of UNIX fork in your code -- # forking entails making a snapshot of the state of all locks in the # program, including those in the logging module, and thus can create code # that appears to work for a long time, before deadlocking randomly. # Forking in a Mitogen app requires significant upfront planning! broker = mitogen.master.Broker() # Construct a Router. This accepts messages (mitogen.core.Message) and # either dispatches locally addressed messages to local handlers (added via # Router.add_handle()) on the broker thread, or forwards the message # towards the target context. # The router also acts as an uglyish God object for creating new # connections. This was a design mistake, really those methods should be # directly imported from e.g. 'mitogen.ssh'. router = mitogen.master.Router(broker) # Router can act like a context manager. It simply ensures # Broker.shutdown() is called on exception / exit. That prevents the app # hanging due to a forgotten background thread. For throwaway scripts, # there are also decorator versions "@mitogen.main()" and # "@mitogen.utils.with_router" that do the same thing with less typing. with router: # Now let's construct a context. The '.local()' constructor just creates # the context as a subprocess, the simplest possible case. child = router.local() print("Created a context:", child) print() # This demonstrates the standard IO redirection. We call the print # function in the remote context, that should cause a log message to be # emitted. Any subprocesses started by the remote also get the same # treatment, so it's very easy to spot otherwise discarded errors/etc. # from remote tools. child.call(print, "Hello from child.") # Context objects make it semi-convenient to treat the local machine the # same as a remote machine. work_on_machine(child) # Now let's construct a proxied context. We'll simply use the .local() # constructor again, but construct it via 'child'. In effect we are # constructing a sub-sub-process. Instead of .local() here, we could # have used .sudo() or .ssh() or anything else. subchild = router.local(via=child) print() print() print() print("Created a context as a child of another context:", subchild) # Do everything again with the new child. work_on_machine(subchild) # We can selectively shut down individual children if we want: subchild.shutdown(wait=True) # Or we can simply fall off the end of the scope, effectively calling # Broker.shutdown(), which causes all children to die as part of # shutdown. # The child module importer detects the execution guard below and removes any # code appearing after it, and refuses to execute "__main__" if it is absent. # This is necessary to prevent a common problem where people try to call # functions defined in __main__ without first wrapping it up to be importable # as a module, which previously hung the target, or caused bizarre recursive # script runs. if __name__ == '__main__': main()