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How do you report on / bubble up what the precise nature of the problem was under this paradigm? E.g. Was it a network issue, content type issue, malformed JSO

How do you report on / bubble up what the precise nature of the problem was under this paradigm? E.g. Was it a network issue, content type issue, malformed JSON, unexpected JSON format, etc? I mostly enjoy Go, Python, and Java (in this order), but I must say the self-contained, self-dependency-installing script thing in TFA seems pretty appealing.

strken 3y ago
It's been a while since I've touched Phoenix, but from memory it uses separate process pools (meaning lightweight BEAM VM processes) for the http connection, application code, database connections, and probably any other external dependency. A crash in an application process is handled by the http process that sent the work to it. That being said, you return errors in a similar way to other languages if they're expected during the system's operation rather than crashes. Again it's been a while since I had to work with it.
sb8244 3y ago
People often take this paradigm too literally, especially if they have not programmed much in Elixir. It is most common to bubble up errors using error tuples, and exceptions are available. Fred Hebert's blog post called "it's about the guarantees" makes this more clear: https://ferd.ca/it-s-about-the-guarantees.html https://ferd.ca/it-s-about-the-guarantees.html
- throwawaymaths 3y ago
  It's actually a pet peeve of mine that people use error tuples so often in elixir. Honestly most of the time the correct thing is to raise. There really isn't anything you can do anyways, and avoiding the temptation to do something about it and make spaghetti out of the decision tree is worth it.
  - troupo 3y ago
    Many people don't write async code or use supervision trees for most tasks. A lot of code is straightforward synchronous code, so it makes sense not to throw. Once you run it in a task, then it makes less sense to do {:ok, something} on everything
    - throwawaymaths 3y ago
      In what situation are you not supervised? If you're in a phoenix controller, you're very much supervised (even if you didn't write that supervisor) What actually are you going to be doing with that error? Most of the time it gets raised at the end of the error chain resolution.
      - troupo 3y ago
        > If you're in a phoenix controller, you're very much supervised (even if you didn't write that supervisor) Yes, but do you want to kill your process and restart? I've been doing quite a bit of LiveView recently, and a thrown error will kill the process and reload the page. I... don't want to do that. > What actually are you going to be doing with that error? Depends on the error :) If it's "record not found", I redirect to a 404. If it's "can't resize image because file format is incorrect" I log it, and display an error message. And so on.
        throwawaymaths 3y ago
        > LiveView recently, and a thrown error will kill the process and reload the page. I... don't want to do that. Ok. That's 100% real and I've run into it myself and been annoyed by it. Probably liveview should do something about that because it's breaking BEAM idioms. > redirect to 404 Raise an error with plug_status set to 404. I believe there's a protocol way of doing it too if you dont own the exception and thus can't add plug_status as a field.
        troupo 3y ago
        > Probably liveview should do something about that because it's breaking BEAM idioms. It really doesn't. It's the `one_to_one` restart strategy for supervision. > Raise an error with plug_status set to 404. Honestly, first time I've heard about it :) It's somewhat well hidden in the docs I think. But 404 is just one of possible responses. I might want to redirect instead. Auth errors should be also handled by redirects. And so on. Not everything is an exception for the framework supervisor to handle through custom fields.
  - sph 3y ago
    > Honestly most of the time the correct thing is to raise. No that's just wrong. If you want to let it crash, just pattern match on the :ok tuple. You shouldn't have to write exception handler blocks to deal with functions that raise, instead of returning a tuple, that's bad Elixir style. All functions that can fail should return a tuple. For convenience, one might also add a ! version that raises.
    - throwawaymaths 3y ago
      No. This is exactly wrong. Pattern matching on ok tuple is awful because you will get a generic MatchError with an inscrutable message that requires reserialization of the exception struct and not a more useful Error where you can have an informative Exception.message protocol implementation. > All functions that can fail should return a tuple. For convenience, one might also add a ! version that raises. This is absolutely good advice for library writers. But if you're using a library, most of the time, use the raising version.
      - sph 3y ago
        You don't get an inscrutable message. An example from Elixir docs: iex> {a, b, c} = {:hello, "world"} * (MatchError) no match of right hand side value: {:hello, "world"} The MatchError shows you the part that was not matching. When pattern matching on {:ok, value}, on match error you'd be told it doesn't match, say {:error, %DatabaseError{reason: "Server has gone away."}} I always pair my production Elixir apps with Sentry, which gives me a backtrace, so I have everything needed to track down an error. > But if you're using a library, most of the time, use the raising version. I use the raising version to explicitly "I want this to crash." So this would happen only at the edges of the system. All internal code should operate on tuples. You don't want a core, internal function to raise and have to catch it on higher-level modules, because that's terrible form. In other words, feel free to raise, as long as there is no one that has to catch the exception. If you raise, the goal is to crash, not to leverage exceptions as control flow. This isn't Java. I've been using Elixir since 2016 and I don't think I have written more than a couple exception handlers since.
dbt00 3y ago
I'm not super familiar with Elixir, but Erlang uses both tuple error responses and panics, it's actually very similar to Go in that way. An erlang process (very similar to a goroutine) can subscribe to another process and will get a message if that process exits with a panic, and can choose what to do with that. The standard implementation is called supervisor, which you can read more about here, the Erlang documentation is very good: https://www.erlang.org/doc/design_principles/sup_princ https://www.erlang.org/doc/design_principles/sup_princ
- jolux 3y ago
  Elixir is much the same as Erlang in this regard.
throwawaymaths 3y ago
If you're in prod, You'll get that information bubbled up to you in sentry when the "process" (not os, green-thread) crashes. If you're in a script, it will come to you as red text (usually) that is generated by the error type. No big deal.

strken 3y ago

It's been a while since I've touched Phoenix, but from memory it uses separate process pools (meaning lightweight BEAM VM processes) for the http connection, application code, database connections, and probably any other external dependency. A crash in an application process is handled by the http process that sent the work to it. That being said, you return errors in a similar way to other languages if they're expected during the system's operation rather than crashes. Again it's been a while since I had to work with it.

sb8244 3y ago

People often take this paradigm too literally, especially if they have not programmed much in Elixir. It is most common to bubble up errors using error tuples, and exceptions are available. Fred Hebert's blog post called "it's about the guarantees" makes this more clear: https://ferd.ca/it-s-about-the-guarantees.html https://ferd.ca/it-s-about-the-guarantees.html

throwawaymaths 3y ago
It's actually a pet peeve of mine that people use error tuples so often in elixir. Honestly most of the time the correct thing is to raise. There really isn't anything you can do anyways, and avoiding the temptation to do something about it and make spaghetti out of the decision tree is worth it.
- troupo 3y ago
  Many people don't write async code or use supervision trees for most tasks. A lot of code is straightforward synchronous code, so it makes sense not to throw. Once you run it in a task, then it makes less sense to do {:ok, something} on everything
  - throwawaymaths 3y ago
    In what situation are you not supervised? If you're in a phoenix controller, you're very much supervised (even if you didn't write that supervisor) What actually are you going to be doing with that error? Most of the time it gets raised at the end of the error chain resolution.
    - troupo 3y ago
      > If you're in a phoenix controller, you're very much supervised (even if you didn't write that supervisor) Yes, but do you want to kill your process and restart? I've been doing quite a bit of LiveView recently, and a thrown error will kill the process and reload the page. I... don't want to do that. > What actually are you going to be doing with that error? Depends on the error :) If it's "record not found", I redirect to a 404. If it's "can't resize image because file format is incorrect" I log it, and display an error message. And so on.
      - throwawaymaths 3y ago
        > LiveView recently, and a thrown error will kill the process and reload the page. I... don't want to do that. Ok. That's 100% real and I've run into it myself and been annoyed by it. Probably liveview should do something about that because it's breaking BEAM idioms. > redirect to 404 Raise an error with plug_status set to 404. I believe there's a protocol way of doing it too if you dont own the exception and thus can't add plug_status as a field.
        troupo 3y ago
        > Probably liveview should do something about that because it's breaking BEAM idioms. It really doesn't. It's the `one_to_one` restart strategy for supervision. > Raise an error with plug_status set to 404. Honestly, first time I've heard about it :) It's somewhat well hidden in the docs I think. But 404 is just one of possible responses. I might want to redirect instead. Auth errors should be also handled by redirects. And so on. Not everything is an exception for the framework supervisor to handle through custom fields.
- sph 3y ago
  > Honestly most of the time the correct thing is to raise. No that's just wrong. If you want to let it crash, just pattern match on the :ok tuple. You shouldn't have to write exception handler blocks to deal with functions that raise, instead of returning a tuple, that's bad Elixir style. All functions that can fail should return a tuple. For convenience, one might also add a ! version that raises.
  - throwawaymaths 3y ago
    No. This is exactly wrong. Pattern matching on ok tuple is awful because you will get a generic MatchError with an inscrutable message that requires reserialization of the exception struct and not a more useful Error where you can have an informative Exception.message protocol implementation. > All functions that can fail should return a tuple. For convenience, one might also add a ! version that raises. This is absolutely good advice for library writers. But if you're using a library, most of the time, use the raising version.
    - sph 3y ago
      You don't get an inscrutable message. An example from Elixir docs: iex> {a, b, c} = {:hello, "world"} * (MatchError) no match of right hand side value: {:hello, "world"} The MatchError shows you the part that was not matching. When pattern matching on {:ok, value}, on match error you'd be told it doesn't match, say {:error, %DatabaseError{reason: "Server has gone away."}} I always pair my production Elixir apps with Sentry, which gives me a backtrace, so I have everything needed to track down an error. > But if you're using a library, most of the time, use the raising version. I use the raising version to explicitly "I want this to crash." So this would happen only at the edges of the system. All internal code should operate on tuples. You don't want a core, internal function to raise and have to catch it on higher-level modules, because that's terrible form. In other words, feel free to raise, as long as there is no one that has to catch the exception. If you raise, the goal is to crash, not to leverage exceptions as control flow. This isn't Java. I've been using Elixir since 2016 and I don't think I have written more than a couple exception handlers since.

dbt00 3y ago

I'm not super familiar with Elixir, but Erlang uses both tuple error responses and panics, it's actually very similar to Go in that way. An erlang process (very similar to a goroutine) can subscribe to another process and will get a message if that process exits with a panic, and can choose what to do with that. The standard implementation is called supervisor, which you can read more about here, the Erlang documentation is very good: https://www.erlang.org/doc/design_principles/sup_princ https://www.erlang.org/doc/design_principles/sup_princ

jolux 3y ago
Elixir is much the same as Erlang in this regard.

throwawaymaths 3y ago

If you're in prod, You'll get that information bubbled up to you in sentry when the "process" (not os, green-thread) crashes. If you're in a script, it will come to you as red text (usually) that is generated by the error type. No big deal.