c10e382d2a flatfile: check whether the file has been closed successfully (Vasil Dimov)
4bb5dd78ea util: check that a file has been closed before ~AutoFile() is called (Vasil Dimov)
8bb34f07df Explicitly close all AutoFiles that have been written (Vasil Dimov)
a69c4098b2 rpc: take ownership of the file by WriteUTXOSnapshot() (Hodlinator)
Pull request description:
`fclose(3)` may fail to flush the previously written data to disk, thus a failing `fclose(3)` is as serious as a failing `fwrite(3)`.
Previously the code ignored `fclose(3)` failures. This PR improves that by changing all users of `AutoFile` that use it to write data to explicitly close the file and handle a possible error.
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Other alternatives are:
1. `fflush(3)` after each write to the file (and throw if it fails from the `AutoFile::write()` method) and hope that `fclose(3)` will then always succeed. Assert that it succeeds from the destructor 🙄. Will hurt performance.
2. Throw nevertheless from the destructor. Exception within the exception in C++ I think results in terminating the program without a useful message.
3. (this is implemented in the latest incarnation of this PR) Redesign `AutoFile` so that its destructor cannot fail. Adjust _all_ its users 😭. For example, if the file has been written to, then require the callers to explicitly call the `AutoFile::fclose()` method before the object goes out of scope. In the destructor, as a sanity check, assume/assert that this is indeed the case. Defeats the purpose of a RAII wrapper for `FILE*` which automatically closes the file when it goes out of scope and there are a lot of users of `AutoFile`.
4. Pass a new callback function to the `AutoFile` constructor which will be called from the destructor to handle `fclose()` errors, as described in https://github.com/bitcoin/bitcoin/pull/29307#issuecomment-2243842400. My thinking is that if that callback is going to only log a message, then we can log the message directly from the destructor without needing a callback. If the callback is going to do more complicated error handling then it is easier to do that at the call site by directly calling `AutoFile::fclose()` instead of getting the `AutoFile` object out of scope (so that its destructor is called) and inspecting for side effects done by the callback (e.g. set a variable to indicate a failed `fclose()`).
ACKs for top commit:
l0rinc:
ACK c10e382d2a
achow101:
ACK c10e382d2a
hodlinator:
re-ACK c10e382d2a
Tree-SHA512: 3994ca57e5b2b649fc84f24dad144173b7500fc0e914e06291d5c32fbbf8d2b1f8eae0040abd7a5f16095ddf4e11fe1636c6092f49058cda34f3eb2ee536d7ba
ea4285775e