cargo can't fetch crates when the SOCKS5 server is in an IPv4-only network

[Lanius-collaris]

Problem

cargo can't fetch crates when the SOCKS5 server is in an IPv4-only network. ( index.crates.io is dual-stack )

~/hello $ export https_proxy=socks5://192.168.1.1:1080
~/hello $ cargo add libc
    Updating crates.io index
error: download of config.json failed

Caused by:
  failed to download from `https://index.crates.io/config.json`

Caused by:
  [97] proxy handshake error (cannot complete SOCKS5 connection to index.crates.io. (3))

Reply field = 3 means "network unreachable".
https://www.rfc-editor.org/rfc/rfc1928#section-6

Steps

1. delete the IPv6 default route on a SOCKS5 server
   ip route del ::/0
2. tell cargo to fetch something via this SOCKS5 server

Possible Solution(s)

retry with other IP addresses anyway or use "socks5h://"

Notes

No response

Version

cargo 1.85.1 (d73d2caf9 2024-12-31)
release: 1.85.1
commit-hash: d73d2caf9e41a39daf2a8d6ce60ec80bf354d2a7
commit-date: 2024-12-31
host: x86_64-unknown-linux-musl
libgit2: 1.8.1 (sys:0.19.0 vendored)
libcurl: 8.9.0-DEV (sys:0.4.74+curl-8.9.0 vendored ssl:OpenSSL/1.1.1w)
ssl: OpenSSL 1.1.1w  11 Sep 2023

[weihanglo]

Can you still reach index.crates.io with the same proxy configuration with curl?

[weihanglo]

Also, would you mind attaching the log output of running CARGO_HTTP_DEBUG=true CARGO_LOG=network=debug cargo fetch?

[Lanius-collaris]

Can you still reach index.crates.io with the same proxy configuration with curl?

The output of curl:

~/hello $ curl -x socks5://192.168.1.1:1080 -v -I https://index.crates.io/config.json
*   Trying 192.168.1.1:1080...
* Connected to 192.168.1.1 (192.168.1.1) port 1080
* Host index.crates.io:443 was resolved.
* IPv6: 2600:9000:21d3:2e00:1f:a9f5:69c0:93a1, 2600:9000:21d3:5200:1f:a9f5:69c0:93a1, 2600:9000:21d3:6200:1f:a9f5:69c0:93a1, 2600:9000:21d3:e800:1f:a9f5:69c0:93a1, 2600:9000:21d3:9600:1f:a9f5:69c0:93a1, 2600:9000:21d3:9a00:1f:a9f5:69c0:93a1, 2600:9000:21d3:f800:1f:a9f5:69c0:93a1, 2600:9000:21d3:d000:1f:a9f5:69c0:93a1
* IPv4: 13.225.117.120, 13.225.117.106, 13.225.117.79, 13.225.117.5
* SOCKS5 connect to [2600:9000:21d3:2e00:1f:a9f5:69c0:93a1]:443 (locally resolved)
* cannot complete SOCKS5 connection to index.crates.io. (3)
* closing connection #0
curl: (97) cannot complete SOCKS5 connection to index.crates.io. (3)

Also, would you mind attaching the log output of running CARGO_HTTP_DEBUG=true CARGO_LOG=network=debug cargo fetch?

The output of cargo:

~/hello $ CARGO_HTTP_DEBUG=true CARGO_LOG=network=debug https_proxy=socks5://192.168.1.1:1080 cargo add libc
   0.007052993s DEBUG network: Version {
    version: "8.12.0-DEV",
    rust_crate_version: "0.4.47",
    rust_sys_crate_version: "0.4.79+curl-8.12.0",
    vendored: true,
    host: "unknown",
    feature_ipv6: true,
    feature_ssl: true,
    feature_libz: true,
    feature_ntlm: false,
    feature_gss_negotiate: false,
    feature_debug: false,
    feature_spnego: false,
    feature_largefile: false,
    feature_idn: false,
    feature_sspi: false,
    feature_async_dns: true,
    feature_conv: false,
    feature_tlsauth_srp: false,
    feature_ntlm_wb: false,
    feature_unix_domain_socket: true,
    feature_https_proxy: true,
    feature_altsvc: true,
    feature_zstd: false,
    feature_unicode: false,
    feature_http3: false,
    feature_http2: true,
    feature_gsasl: false,
    feature_brotli: false,
    ssl_version: "OpenSSL/1.1.1w",
    libz_version: "1.3.1",
    iconv_version_num: "0",
    brotli_version_num: "0",
    nghttp2_version_num: "14000",
    nghttp2_version: "1.64.0",
    zstd_ver_num: "0",
    protocols: [
        "file",
        "http",
        "https",
        "mqtt",
        "ws",
        "wss",
    ],
}
    Updating crates.io index
   0.007631006s DEBUG network: Version {
    version: "8.12.0-DEV",
    rust_crate_version: "0.4.47",
    rust_sys_crate_version: "0.4.79+curl-8.12.0",
    vendored: true,
    host: "unknown",
    feature_ipv6: true,
    feature_ssl: true,
    feature_libz: true,
    feature_ntlm: false,
    feature_gss_negotiate: false,
    feature_debug: false,
    feature_spnego: false,
    feature_largefile: false,
    feature_idn: false,
    feature_sspi: false,
    feature_async_dns: true,
    feature_conv: false,
    feature_tlsauth_srp: false,
    feature_ntlm_wb: false,
    feature_unix_domain_socket: true,
    feature_https_proxy: true,
    feature_altsvc: true,
    feature_zstd: false,
    feature_unicode: false,
    feature_http3: false,
    feature_http2: true,
    feature_gsasl: false,
    feature_brotli: false,
    ssl_version: "OpenSSL/1.1.1w",
    libz_version: "1.3.1",
    iconv_version_num: "0",
    brotli_version_num: "0",
    nghttp2_version_num: "14000",
    nghttp2_version: "1.64.0",
    zstd_ver_num: "0",
    protocols: [
        "file",
        "http",
        "https",
        "mqtt",
        "ws",
        "wss",
    ],
}
   0.007668845s DEBUG network: fetch https://index.crates.io/config.json
   0.007677497s DEBUG network: downloading config.json as 0
   0.007709167s DEBUG network: http-debug: * Uses proxy env variable https_proxy == 'socks5://192.168.1.1:1080'
   0.007781784s DEBUG network: http-debug: *   Trying 192.168.1.1:1080...
   0.516884445s DEBUG network: http-debug: * Host index.crates.io:443 was resolved.
   0.517154996s DEBUG network: http-debug: * IPv6: 2600:9000:21d3:2e00:1f:a9f5:69c0:93a1, 2600:9000:21d3:5200:1f:a9f5:69c0:93a1, 2600:9000:21d3:6200:1f:a9f5:69c0:93a1, 2600:9000:21d3:e800:1f:a9f5:69c0:93a1, 2600:9000:21d3:9600:1f:a9f5:69c0:93a1, 2600:9000:21d3:9a00:1f:a9f5:69c0:93a1, 2600:9000:21d3:f800:1f:a9f5:69c0:93a1, 2600:9000:21d3:d000:1f:a9f5:69c0:93a1
   0.517173686s DEBUG network: http-debug: * IPv4: 13.225.117.120, 13.225.117.106, 13.225.117.79, 13.225.117.5
   0.517190750s DEBUG network: http-debug: * SOCKS5 connect to [2600:9000:21d3:2e00:1f:a9f5:69c0:93a1]:443 (locally resolved)
   0.519363174s DEBUG network: http-debug: * cannot complete SOCKS5 connection to index.crates.io. (3)
   0.519448447s DEBUG network: http-debug: * closing connection #0
error: download of config.json failed
Caused by:

failed to download from https://index.crates.io/config.json
Caused by:

[97] proxy handshake error (cannot complete SOCKS5 connection to index.crates.io. (3))

[weihanglo]

Thanks for help debugging!

Looks like curl with the same setting also failed. Since Cargo under the hood uses libcurl to do networking stuff, I am not sure if there is anything Cargo can do.

…or use "socks5h://"

If skipping curl's local name resolution works for both curl CLI and Cargo, then it is probably the workaround here. (The curl book also recommends that).