Routing failure does not fall back to IPv4 from IPv6

[staticfloat]

Julia 1.5.3
HTTP.jl 0.9.1
MbedTLS.jl 1.0.3

I have an IPv6 address that is incorrect, so when I attempt to connect to a dual-stack host such as google.com, curl does the right thing:

$ curl -L -v -o /dev/null https://google.com
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
*   Trying 2607:f8b0:400a:803::200e:443...
* TCP_NODELAY set
* connect to 2607:f8b0:400a:803::200e port 443 failed: No route to host
*   Trying 172.217.14.206:443...
* TCP_NODELAY set
* Connected to google.com (172.217.14.206) port 443 (#0)
* ALPN, offering h2
* ALPN, offering http/1.1
* successfully set certificate verify locations:
*   CAfile: /etc/ssl/certs/ca-certificates.crt
  CApath: /etc/ssl/certs
} [5 bytes data]
* TLSv1.3 (OUT), TLS handshake, Client hello (1):
} [512 bytes data]
* TLSv1.3 (IN), TLS handshake, Server hello (2):
{ [122 bytes data]
...

However, HTTP.jl gets stuck after the IPv6 route fails to work:

julia> using HTTP
       HTTP.DEBUG_LEVEL[] = 3
3

julia> HTTP.get("https://google.com"; verbose=3)
ERROR: IOError(Base.IOError("connect: host is unreachable (EHOSTUNREACH)", -113) during request(https://google.com))

Stacktrace:
 [1] wait_connected(::Sockets.TCPSocket) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Sockets/src/Sockets.jl:525
 [2] connect at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Sockets/src/Sockets.jl:560 [inlined]
 [3] connect(::Sockets.IPv6, ::UInt64) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Sockets/src/Sockets.jl:546
 [4] getconnection(::Type{Sockets.TCPSocket}, ::SubString{String}, ::String; keepalive::Bool, connect_timeout::Int64, readtimeout::Int64, kw::Base.Iterators.Pairs{Symbol,Any,NTuple{4,Symbol},NamedTuple{(:require_ssl_verification, :iofunction, :reached_redirect_limit, :verbose),Tuple{Bool,Nothing,Bool,Int64}}}) at /home/sabae/.julia/packages/HTTP/1dCtY/src/ConnectionPool.jl:653
 [5] #getconnection#29 at /home/sabae/.julia/packages/HTTP/1dCtY/src/ConnectionPool.jl:705 [inlined]
 [6] newconnection(::HTTP.ConnectionPool.Pod, ::Type{T} where T, ::SubString{String}, ::SubString{String}, ::Int64, ::Bool, ::Int64; kw::Base.Iterators.Pairs{Symbol,Any,Tuple{Symbol,Symbol,Symbol},NamedTuple{(:iofunction, :reached_redirect_limit, :verbose),Tuple{Nothing,Bool,Int64}}}) at /home/sabae/.julia/packages/HTTP/1dCtY/src/ConnectionPool.jl:618
 [7] getconnection(::Type{HTTP.ConnectionPool.Transaction{MbedTLS.SSLContext}}, ::SubString{String}, ::SubString{String}; connection_limit::Int64, pipeline_limit::Int64, idle_timeout::Int64, reuse_limit::Int64, require_ssl_verification::Bool, kw::Base.Iterators.Pairs{Symbol,Any,Tuple{Symbol,Symbol,Symbol},NamedTuple{(:iofunction, :reached_redirect_limit, :verbose),Tuple{Nothing,Bool,Int64}}}) at /home/sabae/.julia/packages/HTTP/1dCtY/src/ConnectionPool.jl:562
 [8] request(::Type{ConnectionPoolLayer{DebugLayer{StreamLayer{Union{}}}}}, ::URIs.URI, ::HTTP.Messages.Request, ::Array{UInt8,1}; proxy::Nothing, socket_type::Type{T} where T, reuse_limit::Int64, kw::Base.Iterators.Pairs{Symbol,Any,Tuple{Symbol,Symbol,Symbol},NamedTuple{(:iofunction, :reached_redirect_limit, :verbose),Tuple{Nothing,Bool,Int64}}}) at /home/sabae/.julia/packages/HTTP/1dCtY/src/ConnectionRequest.jl:81
 [9] request(::Type{ExceptionLayer{ConnectionPoolLayer{DebugLayer{StreamLayer{Union{}}}}}}, ::URIs.URI, ::Vararg{Any,N} where N; kw::Base.Iterators.Pairs{Symbol,Any,Tuple{Symbol,Symbol,Symbol},NamedTuple{(:iofunction, :reached_redirect_limit, :verbose),Tuple{Nothing,Bool,Int64}}}) at /home/sabae/.julia/packages/HTTP/1dCtY/src/ExceptionRequest.jl:19
 [10] (::Base.var"#56#58"{Base.var"#56#57#59"{ExponentialBackOff,HTTP.RetryRequest.var"#2#3"{Bool,HTTP.Messages.Request},typeof(HTTP.request)}})(::Type{T} where T, ::Vararg{Any,N} where N; kwargs::Base.Iterators.Pairs{Symbol,Any,Tuple{Symbol,Symbol,Symbol},NamedTuple{(:iofunction, :reached_redirect_limit, :verbose),Tuple{Nothing,Bool,Int64}}}) at ./error.jl:301
 [11] #request#1 at /home/sabae/.julia/packages/HTTP/1dCtY/src/RetryRequest.jl:44 [inlined]
 [12] request(::Type{MessageLayer{RetryLayer{ExceptionLayer{ConnectionPoolLayer{DebugLayer{StreamLayer{Union{}}}}}}}}, ::String, ::URIs.URI, ::Array{Pair{SubString{String},SubString{String}},1}, ::Array{UInt8,1}; http_version::VersionNumber, target::String, parent::Nothing, iofunction::Nothing, kw::Base.Iterators.Pairs{Symbol,Integer,Tuple{Symbol,Symbol},NamedTuple{(:reached_redirect_limit, :verbose),Tuple{Bool,Int64}}}) at /home/sabae/.julia/packages/HTTP/1dCtY/src/MessageRequest.jl:58
 [13] request(::Type{BasicAuthLayer{MessageLayer{RetryLayer{ExceptionLayer{ConnectionPoolLayer{DebugLayer{StreamLayer{Union{}}}}}}}}}, ::String, ::URIs.URI, ::Array{Pair{SubString{String},SubString{String}},1}, ::Array{UInt8,1}; kw::Base.Iterators.Pairs{Symbol,Integer,Tuple{Symbol,Symbol},NamedTuple{(:reached_redirect_limit, :verbose),Tuple{Bool,Int64}}}) at /home/sabae/.julia/packages/HTTP/1dCtY/src/BasicAuthRequest.jl:28
 [14] request(::Type{RedirectLayer{BasicAuthLayer{MessageLayer{RetryLayer{ExceptionLayer{ConnectionPoolLayer{DebugLayer{StreamLayer{Union{}}}}}}}}}}, ::String, ::URIs.URI, ::Array{Pair{SubString{String},SubString{String}},1}, ::Array{UInt8,1}; redirect_limit::Int64, forwardheaders::Bool, kw::Base.Iterators.Pairs{Symbol,Int64,Tuple{Symbol},NamedTuple{(:verbose,),Tuple{Int64}}}) at /home/sabae/.julia/packages/HTTP/1dCtY/src/RedirectRequest.jl:24
 [15] request(::String, ::String, ::Array{Pair{SubString{String},SubString{String}},1}, ::Array{UInt8,1}; headers::Array{Pair{SubString{String},SubString{String}},1}, body::Array{UInt8,1}, query::
Nothing, kw::Base.Iterators.Pairs{Symbol,Int64,Tuple{Symbol},NamedTuple{(:verbose,),Tuple{Int64}}}) at /home/sabae/.julia/packages/HTTP/1dCtY/src/HTTP.jl:315
 [16] #get#13 at /home/sabae/.julia/packages/HTTP/1dCtY/src/HTTP.jl:392 [inlined]
 [17] top-level scope at REPL[3]:1

[fredrikekre]

Fixed by #675 ?