Example from "Client Tutorial" in README can't be build

[klartext]

As mentioned in the README, I used
ocamlbuild -pkg cohttp-lwt-unix client_example.native

And that's what I got:

ocamlopt.opt -I /home/oliver/.opam/default/lib/astring -I /home/oliver/.opam/default/lib/base -I /home/oliver/.opam/default/lib/base/base_internalhash_types -I /home/oliver/.opam/default/lib/base/caml -I /home/oliver/.opam/default/lib/base/shadow_stdlib -I /home/oliver/.opam/default/lib/base64 -I /home/oliver/.opam/default/lib/bytes -I /home/oliver/.opam/default/lib/cohttp -I /home/oliver/.opam/default/lib/cohttp-lwt -I /home/oliver/.opam/default/lib/cohttp-lwt-unix -I /home/oliver/.opam/default/lib/conduit -I /home/oliver/.opam/default/lib/conduit-lwt -I /home/oliver/.opam/default/lib/conduit-lwt-unix -I /home/oliver/.opam/default/lib/domain-name -I /home/oliver/.opam/default/lib/fieldslib -I /home/oliver/.opam/default/lib/fmt -I /home/oliver/.opam/default/lib/ipaddr -I /home/oliver/.opam/default/lib/ipaddr-sexp -I /home/oliver/.opam/default/lib/ipaddr/unix -I /home/oliver/.opam/default/lib/logs -I /home/oliver/.opam/default/lib/lwt -I /home/oliver/.opam/default/lib/lwt/unix -I /home/oliver/.opam/default/lib/macaddr -I /home/oliver/.opam/default/lib/magic-mime -I /home/oliver/.opam/default/lib/mmap -I /home/oliver/.opam/default/lib/ocplib-endian -I /home/oliver/.opam/default/lib/ocplib-endian/bigstring -I /home/oliver/.opam/default/lib/parsexp -I /home/oliver/.opam/default/lib/ppx_sexp_conv/runtime-lib -I /home/oliver/.opam/default/lib/re -I /home/oliver/.opam/default/lib/re/posix -I /home/oliver/.opam/default/lib/result -I /home/oliver/.opam/default/lib/seq -I /home/oliver/.opam/default/lib/sexplib -I /home/oliver/.opam/default/lib/sexplib0 -I /home/oliver/.opam/default/lib/stdlib-shims -I /home/oliver/.opam/default/lib/stringext -I /home/oliver/.opam/default/lib/uri -I /home/oliver/.opam/default/lib/uri-sexp -I /home/oliver/.opam/default/lib/uri/services -I /usr/lib/ocaml /home/oliver/.opam/default/lib/base64/base64.cmxa /home/oliver/.opam/default/lib/base/base_internalhash_types/base_internalhash_types.cmxa /home/oliver/.opam/default/lib/base/caml/caml.cmxa /home/oliver/.opam/default/lib/base/shadow_stdlib/shadow_stdlib.cmxa /home/oliver/.opam/default/lib/sexplib0/sexplib0.cmxa /home/oliver/.opam/default/lib/base/base.cmxa /home/oliver/.opam/default/lib/fieldslib/fieldslib.cmxa /home/oliver/.opam/default/lib/ppx_sexp_conv/runtime-lib/ppx_sexp_conv_lib.cmxa /home/oliver/.opam/default/lib/re/re.cmxa /home/oliver/.opam/default/lib/stdlib-shims/stdlib_shims.cmxa /home/oliver/.opam/default/lib/stringext/stringext.cmxa /home/oliver/.opam/default/lib/re/posix/re_posix.cmxa /home/oliver/.opam/default/lib/uri/uri.cmxa /home/oliver/.opam/default/lib/uri-sexp/uri_sexp.cmxa /home/oliver/.opam/default/lib/cohttp/cohttp.cmxa /home/oliver/.opam/default/lib/logs/logs.cmxa /home/oliver/.opam/default/lib/result/result.cmxa /home/oliver/.opam/default/lib/lwt/lwt.cmxa /home/oliver/.opam/default/lib/logs/logs_lwt.cmxa /home/oliver/.opam/default/lib/cohttp-lwt/cohttp_lwt.cmxa /home/oliver/.opam/default/lib/astring/astring.cmxa /home/oliver/.opam/default/lib/fmt/fmt.cmxa /home/oliver/.opam/default/lib/domain-name/domain_name.cmxa /home/oliver/.opam/default/lib/macaddr/macaddr.cmxa /home/oliver/.opam/default/lib/ipaddr/ipaddr.cmxa /home/oliver/.opam/default/lib/ipaddr-sexp/ipaddr_sexp.cmxa /usr/lib/ocaml/unix.cmxa /usr/lib/ocaml/bigarray.cmxa /home/oliver/.opam/default/lib/parsexp/parsexp.cmxa /home/oliver/.opam/default/lib/sexplib/sexplib.cmxa /home/oliver/.opam/default/lib/conduit/conduit.cmxa /home/oliver/.opam/default/lib/conduit-lwt/conduit_lwt.cmxa /home/oliver/.opam/default/lib/ipaddr/unix/ipaddr_unix.cmxa /home/oliver/.opam/default/lib/mmap/mmap.cmxa /home/oliver/.opam/default/lib/ocplib-endian/ocplib_endian.cmxa /home/oliver/.opam/default/lib/ocplib-endian/bigstring/ocplib_endian_bigstring.cmxa /home/oliver/.opam/default/lib/lwt/unix/lwt_unix.cmxa /home/oliver/.opam/default/lib/uri/services/uri_services.cmxa /home/oliver/.opam/default/lib/conduit-lwt-unix/conduit_lwt_unix.cmxa /home/oliver/.opam/default/lib/magic-mime/magic_mime_library.cmxa /home/oliver/.opam/default/lib/cohttp-lwt-unix/cohttp_lwt_unix.cmxa client_example.cmx -o client_example.native
+ ocamlopt.opt -I /home/oliver/.opam/default/lib/astring -I /home/oliver/.opam/default/lib/base -I /home/oliver/.opam/default/lib/base/base_internalhash_types -I /home/oliver/.opam/default/lib/base/caml -I /home/oliver/.opam/default/lib/base/shadow_stdlib -I /home/oliver/.opam/default/lib/base64 -I /home/oliver/.opam/default/lib/bytes -I /home/oliver/.opam/default/lib/cohttp -I /home/oliver/.opam/default/lib/cohttp-lwt -I /home/oliver/.opam/default/lib/cohttp-lwt-unix -I /home/oliver/.opam/default/lib/conduit -I /home/oliver/.opam/default/lib/conduit-lwt -I /home/oliver/.opam/default/lib/conduit-lwt-unix -I /home/oliver/.opam/default/lib/domain-name -I /home/oliver/.opam/default/lib/fieldslib -I /home/oliver/.opam/default/lib/fmt -I /home/oliver/.opam/default/lib/ipaddr -I /home/oliver/.opam/default/lib/ipaddr-sexp -I /home/oliver/.opam/default/lib/ipaddr/unix -I /home/oliver/.opam/default/lib/logs -I /home/oliver/.opam/default/lib/lwt -I /home/oliver/.opam/default/lib/lwt/unix -I /home/oliver/.opam/default/lib/macaddr -I /home/oliver/.opam/default/lib/magic-mime -I /home/oliver/.opam/default/lib/mmap -I /home/oliver/.opam/default/lib/ocplib-endian -I /home/oliver/.opam/default/lib/ocplib-endian/bigstring -I /home/oliver/.opam/default/lib/parsexp -I /home/oliver/.opam/default/lib/ppx_sexp_conv/runtime-lib -I /home/oliver/.opam/default/lib/re -I /home/oliver/.opam/default/lib/re/posix -I /home/oliver/.opam/default/lib/result -I /home/oliver/.opam/default/lib/seq -I /home/oliver/.opam/default/lib/sexplib -I /home/oliver/.opam/default/lib/sexplib0 -I /home/oliver/.opam/default/lib/stdlib-shims -I /home/oliver/.opam/default/lib/stringext -I /home/oliver/.opam/default/lib/uri -I /home/oliver/.opam/default/lib/uri-sexp -I /home/oliver/.opam/default/lib/uri/services -I /usr/lib/ocaml /home/oliver/.opam/default/lib/base64/base64.cmxa /home/oliver/.opam/default/lib/base/base_internalhash_types/base_internalhash_types.cmxa /home/oliver/.opam/default/lib/base/caml/caml.cmxa /home/oliver/.opam/default/lib/base/shadow_stdlib/shadow_stdlib.cmxa /home/oliver/.opam/default/lib/sexplib0/sexplib0.cmxa /home/oliver/.opam/default/lib/base/base.cmxa /home/oliver/.opam/default/lib/fieldslib/fieldslib.cmxa /home/oliver/.opam/default/lib/ppx_sexp_conv/runtime-lib/ppx_sexp_conv_lib.cmxa /home/oliver/.opam/default/lib/re/re.cmxa /home/oliver/.opam/default/lib/stdlib-shims/stdlib_shims.cmxa /home/oliver/.opam/default/lib/stringext/stringext.cmxa /home/oliver/.opam/default/lib/re/posix/re_posix.cmxa /home/oliver/.opam/default/lib/uri/uri.cmxa /home/oliver/.opam/default/lib/uri-sexp/uri_sexp.cmxa /home/oliver/.opam/default/lib/cohttp/cohttp.cmxa /home/oliver/.opam/default/lib/logs/logs.cmxa /home/oliver/.opam/default/lib/result/result.cmxa /home/oliver/.opam/default/lib/lwt/lwt.cmxa /home/oliver/.opam/default/lib/logs/logs_lwt.cmxa /home/oliver/.opam/default/lib/cohttp-lwt/cohttp_lwt.cmxa /home/oliver/.opam/default/lib/astring/astring.cmxa /home/oliver/.opam/default/lib/fmt/fmt.cmxa /home/oliver/.opam/default/lib/domain-name/domain_name.cmxa /home/oliver/.opam/default/lib/macaddr/macaddr.cmxa /home/oliver/.opam/default/lib/ipaddr/ipaddr.cmxa /home/oliver/.opam/default/lib/ipaddr-sexp/ipaddr_sexp.cmxa /usr/lib/ocaml/unix.cmxa /usr/lib/ocaml/bigarray.cmxa /home/oliver/.opam/default/lib/parsexp/parsexp.cmxa /home/oliver/.opam/default/lib/sexplib/sexplib.cmxa /home/oliver/.opam/default/lib/conduit/conduit.cmxa /home/oliver/.opam/default/lib/conduit-lwt/conduit_lwt.cmxa /home/oliver/.opam/default/lib/ipaddr/unix/ipaddr_unix.cmxa /home/oliver/.opam/default/lib/mmap/mmap.cmxa /home/oliver/.opam/default/lib/ocplib-endian/ocplib_endian.cmxa /home/oliver/.opam/default/lib/ocplib-endian/bigstring/ocplib_endian_bigstring.cmxa /home/oliver/.opam/default/lib/lwt/unix/lwt_unix.cmxa /home/oliver/.opam/default/lib/uri/services/uri_services.cmxa /home/oliver/.opam/default/lib/conduit-lwt-unix/conduit_lwt_unix.cmxa /home/oliver/.opam/default/lib/magic-mime/magic_mime_library.cmxa /home/oliver/.opam/default/lib/cohttp-lwt-unix/cohttp_lwt_unix.cmxa client_example.cmx -o client_example.native
File "_none_", line 1:
Error: No implementations provided for the following modules:
         Mutex referenced from /home/oliver/.opam/default/lib/lwt/unix/lwt_unix.cmxa(Lwt_main)
Command exited with code 2.
Hint: Recursive traversal of subdirectories was not enabled for this build,
  as the working directory does not look like an ocamlbuild project (no
  '_tags' or 'myocamlbuild.ml' file). If you have modules in subdirectories,
  you should add the option "-r" or create an empty '_tags' file.
  
  To enable recursive traversal for some subdirectories only, you can use the
  following '_tags' file:
  
      true: -traverse
      <dir1> or <dir2>: traverse

But
cohttp-lwt-unix is installed here.

[mseri]

That is surprising. The error points at an incorrect linking of lwt.unix maybe for a missing -threads, but all libraries in the invocation, including unix, seem correct. Does it work if you do

ocamlbuild -pkg cohttp-lwt-unix -pkg threads client_example.native

? (I cannot test the example in a fresh env at the moment)

[klartext]

That does also not work:

$ ocamlbuild -pkg cohttp-lwt-unix -pkg threads client_example.native
+ ocamlopt.opt -I /home/oliver/.opam/default/lib/astring -I /home/oliver/.opam/default/lib/base -I /home/oliver/.opam/default/lib/base/base_internalhash_types -I /home/oliver/.opam/default/lib/base/caml -I /home/oliver/.opam/default/lib/base/shadow_stdlib -I /home/oliver/.opam/default/lib/base64 -I /home/oliver/.opam/default/lib/bytes -I /home/oliver/.opam/default/lib/cohttp -I /home/oliver/.opam/default/lib/cohttp-lwt -I /home/oliver/.opam/default/lib/cohttp-lwt-unix -I /home/oliver/.opam/default/lib/conduit -I /home/oliver/.opam/default/lib/conduit-lwt -I /home/oliver/.opam/default/lib/conduit-lwt-unix -I /home/oliver/.opam/default/lib/domain-name -I /home/oliver/.opam/default/lib/fieldslib -I /home/oliver/.opam/default/lib/fmt -I /home/oliver/.opam/default/lib/ipaddr -I /home/oliver/.opam/default/lib/ipaddr-sexp -I /home/oliver/.opam/default/lib/ipaddr/unix -I /home/oliver/.opam/default/lib/logs -I /home/oliver/.opam/default/lib/lwt -I /home/oliver/.opam/default/lib/lwt/unix -I /home/oliver/.opam/default/lib/macaddr -I /home/oliver/.opam/default/lib/magic-mime -I /home/oliver/.opam/default/lib/mmap -I /home/oliver/.opam/default/lib/ocplib-endian -I /home/oliver/.opam/default/lib/ocplib-endian/bigstring -I /home/oliver/.opam/default/lib/parsexp -I /home/oliver/.opam/default/lib/ppx_sexp_conv/runtime-lib -I /home/oliver/.opam/default/lib/re -I /home/oliver/.opam/default/lib/re/posix -I /home/oliver/.opam/default/lib/result -I /home/oliver/.opam/default/lib/seq -I /home/oliver/.opam/default/lib/sexplib -I /home/oliver/.opam/default/lib/sexplib0 -I /home/oliver/.opam/default/lib/stdlib-shims -I /home/oliver/.opam/default/lib/stringext -I /home/oliver/.opam/default/lib/uri -I /home/oliver/.opam/default/lib/uri-sexp -I /home/oliver/.opam/default/lib/uri/services -I /usr/lib/ocaml /home/oliver/.opam/default/lib/base64/base64.cmxa /home/oliver/.opam/default/lib/base/base_internalhash_types/base_internalhash_types.cmxa /home/oliver/.opam/default/lib/base/caml/caml.cmxa /home/oliver/.opam/default/lib/base/shadow_stdlib/shadow_stdlib.cmxa /home/oliver/.opam/default/lib/sexplib0/sexplib0.cmxa /home/oliver/.opam/default/lib/base/base.cmxa /home/oliver/.opam/default/lib/fieldslib/fieldslib.cmxa /home/oliver/.opam/default/lib/ppx_sexp_conv/runtime-lib/ppx_sexp_conv_lib.cmxa /home/oliver/.opam/default/lib/re/re.cmxa /home/oliver/.opam/default/lib/stdlib-shims/stdlib_shims.cmxa /home/oliver/.opam/default/lib/stringext/stringext.cmxa /home/oliver/.opam/default/lib/re/posix/re_posix.cmxa /home/oliver/.opam/default/lib/uri/uri.cmxa /home/oliver/.opam/default/lib/uri-sexp/uri_sexp.cmxa /home/oliver/.opam/default/lib/cohttp/cohttp.cmxa /home/oliver/.opam/default/lib/logs/logs.cmxa /home/oliver/.opam/default/lib/result/result.cmxa /home/oliver/.opam/default/lib/lwt/lwt.cmxa /home/oliver/.opam/default/lib/logs/logs_lwt.cmxa /home/oliver/.opam/default/lib/cohttp-lwt/cohttp_lwt.cmxa /home/oliver/.opam/default/lib/astring/astring.cmxa /home/oliver/.opam/default/lib/fmt/fmt.cmxa /home/oliver/.opam/default/lib/domain-name/domain_name.cmxa /home/oliver/.opam/default/lib/macaddr/macaddr.cmxa /home/oliver/.opam/default/lib/ipaddr/ipaddr.cmxa /home/oliver/.opam/default/lib/ipaddr-sexp/ipaddr_sexp.cmxa /usr/lib/ocaml/unix.cmxa /usr/lib/ocaml/bigarray.cmxa /home/oliver/.opam/default/lib/parsexp/parsexp.cmxa /home/oliver/.opam/default/lib/sexplib/sexplib.cmxa /home/oliver/.opam/default/lib/conduit/conduit.cmxa /home/oliver/.opam/default/lib/conduit-lwt/conduit_lwt.cmxa /home/oliver/.opam/default/lib/ipaddr/unix/ipaddr_unix.cmxa /home/oliver/.opam/default/lib/mmap/mmap.cmxa /home/oliver/.opam/default/lib/ocplib-endian/ocplib_endian.cmxa /home/oliver/.opam/default/lib/ocplib-endian/bigstring/ocplib_endian_bigstring.cmxa /home/oliver/.opam/default/lib/lwt/unix/lwt_unix.cmxa /home/oliver/.opam/default/lib/uri/services/uri_services.cmxa /home/oliver/.opam/default/lib/conduit-lwt-unix/conduit_lwt_unix.cmxa /home/oliver/.opam/default/lib/magic-mime/magic_mime_library.cmxa /home/oliver/.opam/default/lib/cohttp-lwt-unix/cohttp_lwt_unix.cmxa client_example.cmx -o client_example.native
File "_none_", line 1:
Error: No implementations provided for the following modules:
         Mutex referenced from /home/oliver/.opam/default/lib/lwt/unix/lwt_unix.cmxa(Lwt_main)
Command exited with code 2.
Hint: Recursive traversal of subdirectories was not enabled for this build,
  as the working directory does not look like an ocamlbuild project (no
  '_tags' or 'myocamlbuild.ml' file). If you have modules in subdirectories,
  you should add the option "-r" or create an empty '_tags' file.
  
  To enable recursive traversal for some subdirectories only, you can use the
  following '_tags' file:
  
      true: -traverse
      <dir1> or <dir2>: traverse
      
Compilation unsuccessful after building 4 targets (3 cached) in 00:00:00.
$ 

[mseri]

I can reproduce the issue. The META file for lwt and lwt.unix seems correct, and it works using dune with the following dune file

(executable
    (name client_example)
    (libraries cohttp-lwt-unix)
    )

I don't know ocamlbuild well enough, @gasche since you are more knowledgeable, do you know by hearth what could be the reason of the failure?

[gasche]

I first checked with an old 4.05.0 switch which had cohttp-lwt-unix installed, and the instructions work fine. On a 4.10.0 switch, I can reproduce the failure, and I can fix it by adding the options -use-ocamlfind -tag thread. The error seems related to the order in which packages/flags are passed by the compiler (-use-ocamlfind invokes ocamlfind directly which uses a better order than ocamlbuild by default).

(If nobody is actively testing the ocamlbuild invocation in the README, maybe it is time to consider explaining the dune setup in the documentation?)

[mseri]

Thanks for looking into it. I will update the README adding both the new ocamlbuild invocation and the dune one.

To be honest, I was expecting ocamlbuild to be stable enough that we would not really need to test it and was quite surprised by the failure. Do you know why it changed between compiler (or tools) releases?

[klartext]

I can fix it by adding the options -use-ocamlfind -tag thread.

Yes, that works :-)

[klartext]

Thanks for looking into it. I will update the README adding both the new ocamlbuild invocation and the dune one.

To be honest, I was expecting ocamlbuild to be stable enough that we would not really need to test it and was quite surprised by the failure. Do you know why it changed between compiler (or tools) releases?

Compilation works, but error message is produced, when executing:

Fatal error: exception (Failure "No SSL or TLS support compiled into Conduit")

[mseri]

You need to have tls installed: opam install tls. I will add a remark about that as well, thanks
EDIT: it is already there, in a paragraph below the example

[gasche]

To be honest, I was expecting ocamlbuild to be stable enough that we would not really need to test it and was quite surprised by the failure.

Yes, me as well.

Do you know why it changed between compiler (or tools) releases?

No -- not yet. I have to investigate more, but given the low usage of ocamlbuild for new projects these days, and the existence of a reasonable workaround, I may prioritize other things.

[gasche]

P.S.: I forgot to mention explicitly that the ping and report was useful, thanks!

[mseri]

Fixed in current README update #720

[greenbagels]

Just encountered this issue today, and the -use-ocamlfind -tag thread solution worked for ocamlbuild, though README.md hasn't been updated to include that bit; is this due to the aforementioned lack of ocamlbuild users?

[mseri]

Thanks for the report, it should be fixed now