How the package_id
is computed¶
Let’s take some package and list its binaries, for example:
$ conan list "zlib/1.2.13:*" -r=conancenter
Local Cache
zlib
zlib/1.2.13
revisions
97d5730b529b4224045fe7090592d4c1 (2023-08-22 02:51:57 UTC)
packages
d62dff20d86436b9c58ddc0162499d197be9de1e # package_id
info
settings
arch: x86_64
build_type: Release
compiler: apple-clang
compiler.version: 13
os: Macos
options
fPIC: True
shared: False
abe5e2b04ea92ce2ee91bc9834317dbe66628206 # package_id
info
settings
arch: x86_64
build_type: Release
compiler: gcc
compiler.version: 11
os: Linux
options
shared: True
We can see several binaries for the latest recipe revision of zlib/1.2.13
. Every binary is identified by its own package_id
, and below it we can see some information for that binary under info
. This information is the one used to compute the package_id
. Every time something changes in this information, like the architecture, or being a static or a shared library, a new package_id
is computed because it represents a different binary.
The package_id
is computed as the sha1 hash of the conaninfo.txt
file, containing the info
displayed above. It is relatively easy to display such file:
$ conan install --requires=zlib/1.2.13 --build=missing
# Use the <package-id> listed in the install
$ conan cache path zlib/1.2.13:<package-id>
# cat the conaninfo.txt in the returned path
$ cat <path>/conaninfo.txt
[settings]
arch=x86_64
build_type=Release
compiler=msvc
compiler.runtime=dynamic
compiler.runtime_type=Release
compiler.version=193
os=Windows
[options]
shared=False
$ sha1sum <path>/conaninfo.txt
# Should be the "package_id"!
The package_id
is the sha1 checksum of the conaninfo.txt
file inside the package. You can validate it with the sha1sum
utility.
If now we have a look to the binaries of openssl
we can see something like:
$ conan list "openssl/3.1.2:*" -r=conancenter
conancenter
openssl
openssl/3.1.2
revisions
8879e931d726a8aad7f372e28470faa1 (2023-09-13 18:52:54 UTC)
packages
0348efdcd0e319fb58ea747bb94dbd88850d6dd1 # package_id
info
settings
arch: x86_64
build_type: Release
compiler: apple-clang
compiler.version: 13
os: Macos
options
386: False
...
shared: True
requires
zlib/1.3.Z
We see now that the conaninfo.txt
contains a new section the requires
section.
This happens because openssl
depends on zlib
, and due to the C and C++ compilation model, the dependencies can affect the binaries that use them. Some examples are when using inline or templates from #include
header files of the dependency.
Expanding the image above:
As it can be seen, even if the settings
and the options
are the same, different binaries will be obtained if the dependencies versions change.
In the next section how the versions affect the package_id is explained.