Cargo Can't update crates.io Index

[Tloru]

Cargo's worked for me in the past, but for some reason it stopped working today. I haven't done anything recently (that I can see) that would cause this behaviour, so I'm fairly puzzled. Here's the minimum required to encounter this error on my machine:

Start a new project, and add a dependency to cargo.toml:

# ...
[dependencies]
rand = "0.7.2"

(The package doesn't matter, the error is the same no matter what.)

upon running $ cargo run (or any command that requires crates to be fetched), I encounter the following error:

Updating crates.io index
error: failed to load source for a dependency on `rand`

Caused by:
  Unable to update registry `https:/rust-lang/crates.io-index`

Caused by:
  failed to fetch `https:/rust-lang/crates.io-index`

Caused by:
  error inflating zlib stream; class=Zlib (5)

At first, I thought I might have a problem with zlib, but this doesn't seem to be the case.
I updated Rust & Cargo, but nothing changed.

(I'm running cargo 1.39.0 (1c6ec66d5 2019-09-30) on MacOS Catalina 10.15)

If you have any idea as to what's going on (is it my machine?, a cargo bug? zlib?) please don't hesitate to leave a comment 😄.

[alexcrichton]

Thanks for the report!

Do you have a firewall, proxy, or any other sort of network configuration setting in effect?

[ehuss]

You can also try setting the environment variables CARGO_HTTP_DEBUG=true and CARGO_LOG=cargo::ops::registry=debug to see if it shows anything interesting.

[Tloru]

@alexcrichton - My organization does install Umbrella Roaming Client on all our laptops, however, github is not blocked, the settings have remained the same, cargo's worked without error with it in the past. I checked, and I'm able to clone the repo, curl it, or visit it online. Strange.

@ehuss - I set both of those variables and tried a few commands, but the output remained the same.

I'm starting to suspect the zlib might be the issue after all. If that's the case, is there anyway to update it, or check that it's fully functional?

[Tloru]

Looking through cargo's code, I found a few potential causes for this error.

in cargo/src/cargo/sources/registry/remote.rs line 222, the code that produces the error message failed to fetch `https:/rust-lang/crates.io-index` is found. I'm pretty certain that this is the only place where this exact error message is produced. This error is thrown as a result of git::fetch failing.

git::fetch is defined in cargo/src/cargo/sources/git/utils.rson line 665. My suspicion is that cargo itself is working fine - the error message error inflating zlib stream; class=Zlib (5) is produced by a library cargo depends upon. So, what library throws this error?

Unfortunately, I wasn't able to find the exact cause of this error - I suspect it has to do with the flate2 or git2 library. While searching through cargo for the source of this error, I came across issue #5101, which suggested clearing the git cache. I ended up clearing the entirety of ~/.cargo/registry/*which fixed the issue. In the future, it might help to give a more specific error message to guide others in the right direction (e.x. something along the lines of: git fetch failed, try clearing your cargo git cache).

TL;DR: Issue was resolved by clearing the contents of the cargo registry folder (& the cargo git cache). See #5101.